CHAPTER XVI.

MEMORY

Primary memory. Analysis of the phenomenon of memory.

Retention and reproduction are both caused by paths of association

in the brain. The conditions of goodness in memory. Native

retentiveness is unchangeable. All improvement of memory consists

in better _thinking_. Other conditions of good memory.

Recognition, or the sense of familiarity. Exact measurements of

memory. Forgetting. Pathological cases. Professor Ladd

criticised.

INDEX.

PSYCHOLOGY.

CHAPTER I.

THE SCOPE OF PSYCHOLOGY.

Psychology is the Science of Mental Life, both of its phenomena

and of their conditions. The phenomena are such things as we call

feelings, desires, cognitions, reasonings, decisions, and the like;

and, superficially considered, their variety and complexity is such as

to leave a chaotic impression on the observer. The most natural and

consequently the earliest way of unifying the material was, first,

to classify it as well as might be, and, secondly, to affiliate the

diverse mental modes thus found, upon a simple entity, the personal

Soul, of which they are taken to be so many facultative manifestations.

Now, for instance, the Soul manifests its faculty of Memory, now of

Reasoning, now of Volition, or again its Imagination or its Appetite.

This is the orthodox 'spiritualistic' theory of scholasticism and of

common-sense. Another and a less obvious way of unifying the chaos is

to seek common elements in the divers mental facts rather than a common

agent behind them, and to explain them constructively by the various

forms of arrangement of these elements, as one explains houses by

stones and bricks. The 'associationist' schools of Herbart in Germany,

and of Hume the Mills and Bain in Britain have thus constructed a

_psychology without a soul_ by taking discrete 'ideas,' faint or

vivid, and showing how, by their cohesions, repulsions, and forms

of succession, such things as reminiscences, perceptions, emotions,

volitions, passions, theories, and all the other furnishings of an

individual's mind may be engendered. The very Self or _ego_ of the

individual comes in this way to be viewed no longer as the pre-existing

source of the representations, but rather as their last and most

complicated fruit.

Now, if we strive rigorously to simplify the phenomena in either of

these ways, we soon become aware of inadequacies in our method. Any

particular cognition, for example, or recollection, is accounted for

on the soul-theory by being referred to the spiritual faculties of

Cognition or of Memory. These faculties themselves are thought of as

absolute properties of the soul; that is, to take the case of memory,

no reason is given why we should remember a fact as it happened, except

that so to remember it constitutes the essence of our Recollective

Power. We may, as spiritualists, try to explain our memory's failures

and blunders by secondary causes. But its _successes_ can invoke no

factors save the existence of certain objective things to be remembered

on the one hand, and of our faculty of memory on the other. When,

for instance, I recall my graduation-day, and drag all its incidents

and emotions up from death's dateless night, no mechanical cause can

explain this process, nor can any analysis reduce it to lower terms or

make its nature seem other than an ultimate _datum_, which, whether we

rebel or not at its mysteriousness, must simply be taken for granted if

we are to psychologize at all. However the associationist may represent

the present ideas as thronging and arranging themselves, still, the

spiritualist insists, he has in the end to admit that _something_,

be it brain, be it 'ideas,' be it 'association,' _knows_ past time

_as_ past, and fills it out with this or that event. And when the

spiritualist calls memory an 'irreducible faculty,' he says no more

than this admission of the associationist already grants.

And yet the admission is far from being a satisfactory simplification

of the concrete facts. For why should this absolute god-given Faculty

retain so much better the events of yesterday than those of last

year, and, best of all, those of an hour ago? Why, again, in old

age should its grasp of childhood's events seem firmest? Why should

illness and exhaustion enfeeble it? Why should repeating an experience

strengthen our recollection of it? Why should drugs, fevers, asphyxia,

and excitement resuscitate things long since forgotten? If we content

ourselves with merely affirming that the faculty of memory is so

peculiarly constituted by nature as to exhibit just these oddities,

we seem little the better for having invoked it, for our explanation

becomes as complicated as that of the crude facts with which we

started. Moreover there is something grotesque and irrational in the

supposition that the soul is equipped with elementary powers of such an

ingeniously intricate sort. Why _should_ our memory cling more easily

to the near than the remote? Why should it lose its grasp of proper

sooner than of abstract names? Such peculiarities seem quite fantastic;

and might, for aught we can see _a priori_, be the precise opposites of

what they are. Evidently, then, _the faculty does not exist absolutely,

but works under conditions_; and _the quest of the conditions_ becomes

the psychologist's most interesting task.

However firmly he may hold to the soul and her remembering faculty, he

must acknowledge that she never exerts the latter without a _cue_, and

that something must always precede and _remind_ us of whatever we are

to recollect. "An _idea_," says the associationist, "an idea associated

with the remembered thing; and this explains also why things repeatedly

met with are more easily recollected, for their associates on the

various occasions furnish so many distinct avenues of recall." But this

does not explain the effects of fever, exhaustion, hypnotism, old age,

and the like. And in general, the pure associationist's account of our

mental life is almost as bewildering as that of the pure spiritualist.

This multitude of ideas, existing absolutely, yet clinging together,

and weaving an endless carpet of themselves, like dominoes in ceaseless

change, or the bits of glass in a kaleidoscope,--whence do they get

their fantastic laws of clinging, and why do they cling in just the

shapes they do?

For this the associationist must introduce the order of experience in

the outer world. The dance of the ideas is a copy, somewhat mutilated

and altered, of the order of phenomena. But the slightest reflection

shows that phenomena have absolutely no power to influence our ideas

until they have first impressed our senses and our brain. The bare

existence of a past fact is no ground for our remembering it. Unless

we have seen it, or somehow _undergone_ it, we shall never know of its

having been. The expediences of the body are thus one of the conditions

of the faculty of memory being what it is. And a very small amount

of reflection on facts shows that one part of the body, namely, the

brain, is the part whose experiences are directly concerned. If the

nervous communication be cut off between the brain and other parts,

the experiences of those other parts are non-existent for the mind.

The eye is blind, the ear deaf, the hand insensible and motionless.

And conversely, if the brain be injured, consciousness is abolished or

altered, even although every other organ in the body be ready to play

its normal part. A blow on the head, a sudden subtraction of blood, the

pressure of an apoplectic hemorrhage, may have the first effect; whilst

a very few ounces of alcohol or grains of opium or hasheesh, or a whiff

of chloroform or nitrous oxide gas, are sure to have the second. The

delirium of fever, the altered self of insanity, are all due to foreign

matters circulating through the brain, or to pathological changes in

that organ's substance. The fact that the brain is the one immediate

bodily condition of the mental operations is indeed so universally

admitted nowadays that I need spend no more time in illustrating it,

but will simply postulate it and pass on. The whole remainder of the

book will be more or less of a proof that the postulate was correct.

Bodily experiences, therefore, and more particularly brain-experiences,

must take a place amongst those conditions of the mental life of which

Psychology need take account. _The spiritualist and the associationist

must both be 'cerebralists'_, to the extent at least of admitting that

certain peculiarities in the way of working of their own favorite

principles are explicable only by the fact that the brain laws are a

codeterminant of the result. Our first conclusion, then, is that a

certain amount of brain-physiology must be presupposed or included in

Psychology.[1]

* * * * *

In still another way the psychologist is forced to be something of a

nerve-physiologist. Mental phenomena are not only conditioned _a parte

ante_ by bodily processes; but they lead to them _a parte post_. That

they lead to _acts_ is of course the most familiar of truths, but I do

not merely mean acts in the sense of voluntary and deliberate muscular

performances. Mental states occasion also changes in the calibre of

blood-vessels, or alteration in the heart-beats, or processes more

subtle still, in glands and viscera. If these are taken into account,

as well as acts which follow at some _remote period_ because the mental

state was once there, it will be safe to lay down the general law

that _no mental modification ever occurs which is not accompanied or

followed by a bodily change_. The ideas and feelings, _e.g_., which

these present printed characters excite in the reader's mind not only

occasion movements of his eyes and nascent movements of articulation in

him, but will some day make him speak, or take sides in a discussion,

or give advice, or choose a book to read, differently from what would

have been the case had they never impressed his retina. Our psychology

must therefore take account not only of the conditions antecedent to

mental states, but of their resultant consequences as well.

* * * * *

But actions originally prompted by conscious intelligence may grow

so automatic by dint of habit as to be apparently unconsciously

performed. Standing, walking, buttoning and unbuttoning, piano-playing,

talking, even saying one's prayers, may be done when the mind is

absorbed in other things. The performances of animal _instinct_ seem

semi-automatic, and the _reflex acts_ of self-preservation certainly

are so. Yet they resemble intelligent acts in bringing about the

_same ends_ at which the animals' consciousness, on other occasions,

deliberately aims. Shall the study of such machine-like yet purposive

acts as these be included in Psychology?

The boundary-line of the mental is certainly vague. It is better not

to be pedantic, but to let the science be as vague as its subject,

and include such phenomena as these if by so doing we can throw any

light on the main business in hand. It will ere long be seen, I trust,

that we can; and that we gain much more by a broad than by a narrow

conception of our subject. At a certain stage in the development

of every science a degree of vagueness is what best consists with

fertility. On the whole, few recent formulas have done more real

service of a rough sort in psychology than the Spencerian one that

the essence of mental life and of bodily life are one, namely, 'the

adjustment of inner to outer relations.' Such a formula is vagueness

incarnate; but because it takes into account the fact that minds

inhabit environments which act on them and on which they in turn

react; because, in short, it takes mind in the midst of all its

concrete relations, it is immensely more fertile than the old-fashioned

'rational psychology,' which treated the soul as a detached existent,

sufficient unto itself, and assumed to consider only its nature and

properties. I shall therefore feel free to make any sallies into

zoology or into pure nerve-physiology which may seem instructive

for our purposes, but otherwise shall leave those sciences to the

physiologists.

* * * * *

Can we state more distinctly still the manner in which the mental life

seems to intervene between impressions made from without upon the body,

and reactions of the body upon the outer world again? Let us look at a

few facts.

If some iron filings be sprinkled on a table and a magnet brought near

them, they will fly through the air for a certain distance and stick

to its surface. A savage seeing the phenomenon explains it as the

result of an attraction or love between the magnet and the filings.

But let a card cover the poles of the magnet, and the filings will

press forever against its surface without its ever occurring to them

to pass around its sides and thus come into more direct contact with

the object of their love. Blow bubbles through a tube into the bottom

of a pail of water, they will rise to the surface and mingle with the

air. Their action may again be poetically interpreted as due to a

longing to recombine with the mother-atmosphere above the surface. But

if you invert a jar full of water over the pail, they will rise and

remain lodged beneath its bottom, shut in from the outer air, although

a slight deflection from their course at the outset, or a re-descent

towards the rim of the jar when they found their upward course impeded,

would easily have set them free.

If now we pass from such actions as these to those of living things,

we notice a striking difference. Romeo wants Juliet as the filings

want the magnet; and if no obstacles intervene he moves towards her by

as straight a line as they. But Romeo and Juliet, if a wall be built

between them, do not remain idiotically pressing their faces against

its opposite sides like the magnet and the filings with the card. Romeo

soon finds a circuitous way, by scaling the wall or otherwise, of

touching Juliet's lips directly. With the filings the path is fixed;

whether it reaches the end depends on accidents. With the lover it is

the end which is fixed, the path may be modified indefinitely.

Suppose a living frog in the position in which we placed our bubbles

of air, namely, at the bottom of a jar of water. The want of breath

will soon make him also long to rejoin the mother-atmosphere, and he

will take the shortest path to his end by swimming straight upwards.

But if a jar full of water be inverted over him, he will not, like the

bubbles, perpetually press his nose against its unyielding roof, but

will restlessly explore the neighborhood until by re-descending again

he has discovered a path round its brim to the goal of his desires.

Again the fixed end, the varying means!

Such contrasts between living and inanimate performances end by leading

men to deny that in the physical world final purposes exist at all.

Loves and desires are to-day no longer imputed to particles of iron or

of air. No one supposes now that the end of any activity which they

may display is an ideal purpose presiding over the activity from its

outset and soliciting or drawing it into being by a sort of _vis a

fronte_. The end, on the contrary, is deemed a mere passive result,

pushed into being _a tergo_, having had, so to speak, no voice in its

own production. Alter the pre-existing conditions, and with inorganic

materials you bring forth each time a different apparent end. But

with intelligent agents, altering the conditions changes the activity

displayed, but not the end reached; for here the idea of the yet

unrealized end co-operates with the conditions to determine what the

activities shall be.

* * * * *

_The pursuance of future ends and the choice of means for their

attainment are thus the mark and criterion of the presence of

mentality_ in a phenomenon. We all use this test to discriminate

between an intelligent and a mechanical performance. We impute no

mentality to sticks and stones, because they never seem to move for

_the sake of_ anything, but always when pushed, and then indifferently

and with no sign of choice. So we unhesitatingly call them senseless.

Just so we form our decision upon the deepest of all philosophic

problems: Is the Kosmos an expression of intelligence rational in its

inward nature, or a brute external fact pure and simple? If we find

ourselves, in contemplating it, unable to banish the impression that it

is a realm of final purposes, that it exists for the sake of something,

we place intelligence at the heart of it and have a religion. If,

on the contrary, in surveying its irremediable flux, we can think

of the present only as so much mere mechanical sprouting from the

past, occurring with no reference to the future, we are atheists and

materialists.

In the lengthy discussions which psychologists have carried on about

the amount of intelligence displayed by lower mammals, or the amount

of consciousness involved in the functions of the nerve-centres of

reptiles, the same test has always been applied: Is the character of

the actions such that we must believe them to be performed _for the

sake_ of their result? The result in question, as we shall hereafter

abundantly see, is as a rule a useful one,--the animal is, on the

whole, safer under the circumstances for bringing it forth. So far

the action has a teleological character; but such mere outward

teleology as this might still be the blind result of _vis a tergo_.

The growth and movements of plants, the processes of development,

digestion, secretion, etc., in animals, supply innumerable instances

of performances useful to the individual which may nevertheless be,

and by most of us are supposed to be, produced by automatic mechanism.

The physiologist does not confidently assert conscious intelligence

in the frog's spinal cord until he has shown that the useful result

which the nervous machinery brings forth under a given irritation

_remains the same when the machinery is altered_. If, to take the stock

instance, the right knee of a headless frog be irritated with acid, the

right foot will wipe it off. When, however, this foot is amputated,

the animal will often raise the _left_ foot to the spot and wipe the

offending material away.

Pflüger and Lewes reason from such facts in the following way: If the

first reaction were the result of mere machinery, they say; if that

irritated portion of the skin discharged the right leg as a trigger

discharges its own barrel of a shot-gun; then amputating the right

foot would indeed frustrate the wiping, but would not make the _left_

leg move. It would simply result in the right stump moving through

the empty air (which is in fact the phenomenon sometimes observed).

The right trigger makes no effort to discharge the left barrel if the

right one be unloaded; nor does an electrical machine ever get restless

because it can only emit sparks, and not hem pillow-cases like a

sewing-machine.

If, on the contrary, the right leg originally moved for the _purpose_

of wiping the acid, then nothing is more natural than that, when the

easiest means of effecting that purpose prove fruitless, other means

should be tried. Every failure must keep the animal in a state of

disappointment which will lead to all sorts of new trials and devices;

and tranquillity will not ensue till one of these, by a happy stroke,

achieves the wished-for end.

In a similar way Goltz ascribes intelligence to the frog's optic

lobes and cerebellum. We alluded above to the manner in which a sound

frog imprisoned in water will discover an outlet to the atmosphere.

Goltz found that frogs deprived of their cerebral hemispheres would

often exhibit a like ingenuity. Such a frog, after rising from the

bottom and finding his farther upward progress checked by the glass

bell which has been inverted over him, will not persist in butting

his nose against the obstacle until dead of suffocation, but will

often re-descend and emerge from under its rim as if, not a definite

mechanical propulsion upwards, but rather a conscious desire to reach

the air by hook or crook were the main-spring of his activity. Goltz

concluded from this that the hemispheres are not the sole seal of

intellect in frogs. He made the same inference from observing that a

brainless frog will turn over from his back to his belly when one of

his legs is sewed up, although the movements required are then very

different from those excited under normal circumstances by the same

annoying position. They seem determined, consequently, not merely by

the antecedent irritant, but by the final end,--though the irritant of

course is what makes the end desired.

Another brilliant German author, Liebmann,[2] argues against the

brain's mechanism accounting for mental action, by very similar

considerations. A machine as such, he says, will bring forth right

results when it is in good order, and wrong results if out of repair.

But both kinds of result flow with equally fatal necessity from their

conditions. We cannot suppose the clock-work whose structure fatally

determines it to a certain rate of speed, noticing that this speed is

too slow or too fast and vainly trying to correct it. Its conscience,

if it have any, should be as good as that of the best chronometer, for

both alike obey equally well the same eternal mechanical laws--laws

from behind. But if the _brain_ be out of order and the man says "Twice

four are two," instead of "Twice four are eight," or else "I must go to

the coal to buy the wharf," instead of "I must go to the wharf to buy

the coal," instantly there arises a consciousness of error. The wrong

performance, though it obey the same mechanical law as the right, is

nevertheless condemned,--condemned as contradicting the inner law--the

law from in front, the purpose or ideal for which the brain _should_

act, whether it do so or not.

We need not discuss here whether these writers in drawing their

conclusion have done justice to all the premises I involved in the

cases they treat of. We quote their arguments only to show how they

appeal to the principle that _no actions but such as are done for an

end, and show a choice of means, can be called indubitable expressions

of Mind_.

I shall then adopt this as the criterion by which to circumscribe the

subject-matter of this work so far as action enters into it. Many

nervous performances will therefore be unmentioned, as being purely

physiological. Nor will the anatomy of the nervous system and organs of

sense be described anew. The reader will find in H. N. Martin's 'Human

Body,' in G. T. Ladd's 'Physiological Psychology,' and in all the other

standard Anatomies and Physiologies, a mass of information which we

must regard as preliminary and take for granted in the present work.[3]

Of the functions of the cerebral hemispheres, however, since they

directly subserve consciousness, it will be well to give some little

account.

FOOTNOTES:

[1] _Cf._ Geo. T. Ladd: Elements of Physiological Psychology (1887),

pt. iii, chap. iii, §§ 9, 12.

[2] Zur Analysis der Wirklichkeit, p. 489.

[3] Nothing is easier than to familiarize one's self with the mammalian

brain. Get a sheep's head, a small saw, chisel, scalpel and forceps

(all three can best be had from a surgical-instrument maker), and

unravel its parts either by the aid of a human dissecting book, such as

Holden's 'Manual of Anatomy,' or by the specific directions _ad hoc_

given in such books as Foster and Langley's 'Practical Physiology'

(Macmillan) or Morrell's 'Comparative Anatomy and Dissection of

Mammalia' (Longmans).

CHAPTER II.

THE FUNCTIONS OF THE BRAIN.

If I begin chopping the foot of a tree, its branches are unmoved by my

act, and its leaves murmur as peacefully as ever in the wind. If, on

the contrary, I do violence to the foot of a fellow-man, the rest of

his body instantly responds to the aggression by movements of alarm or

defence. The reason of this difference is that the man has a nervous

system whilst the tree has none; and the function of the nervous system

is to bring each part into harmonious co-operation with every other.

The afferent nerves, when excited by some physical irritant, be this

as gross in its mode of operation as a chopping axe or as subtle as

the waves of light, conveys the excitement to the nervous centres. The

commotion set up in the centres does not stop there, but discharges

itself, if at all strong, through the efferent nerves into muscles

and glands, exciting movements of the limbs and viscera, or acts of

secretion, which vary with the animal, and with the irritant applied.

These acts of response have usually the common character of being of

service. They ward off the noxious stimulus and support the beneficial

one; whilst if, in itself indifferent, the stimulus be a sign of some

distant circumstance of practical importance, the animal's acts are

addressed to this circumstance so as to avoid its perils or secure its

benefits, as the case may be. To take a common example, if I hear the

conductor calling 'All aboard!' as I enter the depot, my heart first

stops, then palpitates, and my legs respond to the air-waves falling

on my tympanum by quickening their movements. If I stumble as I run,

the sensation of falling provokes a movement of the hands towards the

direction of the fall, the effect of which is to shield the body from

too sudden a shock. If a cinder enter my eye, its lids close forcibly

and a copious flow of tears tends to wash it out.

These three responses to a sensational stimulus differ, however, in

many respects. The closure of the eye and the lachrymation are quite

involuntary, and so is the disturbance of the heart. Such involuntary

responses we know as 'reflex' acts. The motion of the arms to break the

shock of falling may also be called reflex, since it occurs too quickly

to be deliberately intended. Whether it be instinctive or whether it

result from the pedestrian education of childhood may be doubtful; it

is, at any rate, less automatic than the previous acts, for a man might

by conscious effort learn to perform it more skilfully, or even to

suppress it altogether. Actions of this kind, into which instinct and

volition enter upon equal terms, have been called 'semi-reflex.' The

act of running towards the train, on the other hand, has no instinctive

element about it. It is purely the result of education, and is preceded

by a consciousness of the purpose to be attained and a distinct mandate

of the will. It is a 'voluntary act.' Thus the animal's reflex and

voluntary performances shade into each other gradually, being connected

by acts which may often occur automatically, but may also be modified

by conscious intelligence.

An outside observer, unable to perceive the accompanying consciousness,

might be wholly at a loss to discriminate between the automatic acts

and those which volition escorted. But if the criterion of mind's

existence be the choice of the proper means for the attainment of a

supposed end, all the acts seem to be inspired by intelligence, for

_appropriateness_ characterizes them all alike. This fact, now, has led

to two quite opposite theories about the relation to consciousness of

the nervous functions. Some authors, finding that the higher voluntary

ones seem to require the guidance of feeling, conclude that over the

lowest reflexes some such feeling also presides, though it may be a

feeling of which _we_ remain unconscious. Others, finding that reflex

and semi-automatic acts may, notwithstanding their appropriateness,

take place with an unconsciousness apparently complete, fly to the

opposite extreme and maintain that the appropriateness even of

voluntary actions owes nothing to the fact that consciousness attends

them. They are, according to these writers, results of physiological

mechanism pure and simple. In a near chapter we shall return to this

controversy again. Let us now look a little more closely at the brain

and at the ways in which its states may be supposed to condition those

of the mind.

THE FROG'S NERVE-CENTRES.

Both the minute anatomy and the detailed physiology of the brain are

achievements of the present generation, or rather we may say (beginning

with Meynert) of the past twenty years. Many points are still obscure

and subject to controversy; but a general way of conceiving the organ

has been reached on all hands which in its main feature seems not

unlikely to stand, and which even gives a most plausible scheme of the

way in which cerebral and mental operations go hand in hand.

[Illustration: FIG. 1.--_C H_, cerebral Hemispheres; _O Th_, Optic

Thalami; _O L_, Optic Lobes; _Cb_, Cerebellum; _M O_, Medulla

Oblongata; _S C_, Spinal cord.]

The best way to enter the subject will be to take a lower creature,

like a frog, and study by the vivisectional method the functions of

his different nerve-centres. The frog's nerve-centres are figured

in the accompanying diagram, which needs no further explanation. I

will first proceed to state what happens when various amounts of the

anterior parts are removed, in different frogs, in the way in which an

ordinary student removes them; that is, with no extreme precautions

as to the purity of the operation. We shall in this way reach a very

simple conception of the functions of the various centres, involving

the strongest possible contrast between the cerebral hemispheres and

the lower lobes. This sharp conception will have didactic advantages,

for it is often very instructive to start with too simple a formula

and correct it later on. Our first formula, as we shall later see,

will have to be softened down somewhat by the results of more careful

experimentation both on frogs and birds, and by those of the most

recent observations on dogs, monkeys, and man. But it will put us,

from the outset, in clear possession of some fundamental notions and

distinctions which we could otherwise not gain so well, and none of

which the later more completed view will overturn.

If, then, we reduce the frog's nervous system to the spinal cord

alone, by making a section behind the base of the skull, between the

spinal cord and the medulla oblongata, thereby cutting off the brain

from all connection with the rest of the body, the frog will still

continue to live, but with a very peculiarly modified activity. It

ceases to breathe or swallow; it lies flat on its belly, and does not,

like a normal frog, sit up on its fore paws, though its hind legs

are kept, as usual, folded against its body and immediately resume

this position if drawn out. If thrown on its back, it lies there

quietly, without turning over like a normal frog. Locomotion and voice

seem entirely abolished. If we suspend it by the nose, and irritate

different portions of its skin by acid, it performs a set of remarkable

'defensive' movements calculated to wipe away the irritant. Thus, if

the breast be touched, both fore paws will rub it vigorously; if we

touch the outer side of the elbow, the hind foot of the same side

will rise directly to the spot and wipe it. The back of the foot will

rub the knee if that be attacked, whilst if the foot be cut away, the

stump will make ineffectual movements, and then, in many frogs, a pause

will come, as if for deliberation, succeeded by a rapid passage of the

opposite unmutilated foot to the acidulated spot.

The most striking character of all these movements, after their

teleological appropriateness, is their precision. They vary, in

sensitive frogs and with a proper amount of irritation, so little as

almost to resemble in their machine-like regularity the performances of

a jumping-jack, whose legs must twitch whenever you pull the string.

The spinal cord of the frog thus contains arrangements of cells and

fibres fitted to convert skin irritations into movements of defence. We

may call it the _centre for defensive movements_ in this animal. We may

indeed go farther than this, and by cutting the spinal cord in various

places find that its separate segments are independent mechanisms,

for appropriate activities of the head and of the arms and legs

respectively. The segment governing the arms is especially active,

in male frogs, in the breeding season; and these members alone with

the breast and back appertaining to them, everything else being cut

away, will then actively grasp a finger placed between them and remain

hanging to it for a considerable time.

The spinal cord in other animals has analogous powers. Even in man

it makes movements of defence. Paraplegics draw up their legs when

tickled; and Robin, on tickling the breast of a criminal an hour after

decapitation, saw the arm and hand move towards the spot. Of the lower

functions of the mammalian cord, studied so ably by Goltz and others,

this is not the place to speak.

If, in a second animal, the cut be made just behind the optic lobes so

that the cerebellum and medulla oblongata remain attached to the cord,

then swallowing, breathing, crawling, and a rather enfeebled jumping

and swimming are added to the movements previously observed.[4] There

are other reflexes too. The animal, thrown on his back, immediately

turns over to his belly. Placed in a shallow bowl, which is floated on

water and made to rotate, he responds to the rotation by first turning

his head and then waltzing around with his entire body, in the opposite

direction to the whirling of the bowl. If his support be tilted so that

his head points downwards, he points it up; he points it down if it be

pointed upwards, to the right if it be pointed to the left, etc. But

his reactions do not go farther than these movements of the head. He

will not, like frogs whose thalami are preserved, climb up a board if

the latter be tilted, but will slide off it to the ground.

If the cut be made on another frog between the thalami and the optic

lobes, the locomotion both on land and water becomes quite normal, and,

in addition to the reflexes already shown by the lower centres, he

croaks regularly whenever he is pinched under the arms. He compensates

rotations, etc., by movements of the head, and turns over from his

back; but still drops off his tilted board. As his optic nerves are

destroyed by the usual operation, it is impossible to say whether he

will avoid obstacles placed in his path.

When, finally, a frog's cerebral hemispheres alone are cut off by a

section between them and the thalami which preserves the latter, an

unpractised observer would not at first suspect anything abnormal

about the animal. Not only is he capable, on proper instigation, of

all the acts already described, but he guides himself by sight, so

that if an obstacle be set up between him and the light, and he be

forced to move forward, he either jumps over it or swerves to one

side. He manifests sexual passion at the proper season, and, unlike an

altogether brainless frog, which embraces anything placed between his

arms, postpones this reflex act until a female of his own species is

provided. Thus far, as aforesaid, a person unfamiliar with frogs might

not suspect a mutilation; but even such a person would soon remark the

almost entire absence of spontaneous motion--that is, motion unprovoked

by any _present_ incitation of sense. The continued movements of

swimming, performed by the creature in the water, seem to be the fatal

result of the contact of that fluid with its skin. They cease when a

stick, for example, touches his hands. This is a sensible irritant

towards which the feet are automatically drawn by reflex action, and

on which the animal remains sitting. He manifests no hunger, and will

suffer a fly to crawl over his nose unsnapped at. Fear, too, seems

to have deserted him. In a word, he is an extremely complex machine

whose actions, so far as they go, tend to self-preservation; but still

a _machine_, in this sense--that it seems to contain no incalculable

element. By applying the right sensory stimulus to him we are almost

as certain of getting a fixed response as an organist is of hearing a

certain tone when he pulls out a certain stop.

But now if to the lower centres we add the cerebral hemispheres,

or if, in other words, we make an intact animal the subject of our

observations, all this is changed. In addition to the previous

responses to present incitements of sense, our frog now goes through

long and complex acts of locomotion _spontaneously_, or as if moved by

what in ourselves we should call an idea. His reactions to outward

stimuli vary their form, too. Instead of making simple defensive

movements with his hind legs like a headless frog if touched, or of

giving one or two leaps and then sitting still like a hemisphereless

one, he makes persistent and varied efforts at escape, as if, not the

mere contact of the physiologist's hand, but the notion of danger

suggested by it were now his spur. Led by the feeling of hunger, too,

he goes in search of insects, fish, or smaller frogs, and varies his

procedure with each species of victim. The physiologist cannot by

manipulating him elicit croaking, crawling up a board, swimming or

stopping, at will. His conduct has become incalculable. We can no

longer foretell it exactly. Effort to escape is his dominant reaction,

but he _may_ do anything else, even swell up and become perfectly

passive in our hands.

* * * * *

Such are the phenomena commonly observed, and such the impressions

which one naturally receives. Certain general conclusions follow

irresistibly. First of all the following:

_The acts of all the centres involve the use of the same muscles._ When

a headless frog's hind leg wipes the acid, he calls into play all the

leg-muscles which a frog with his full medulla oblongata and cerebellum

uses when he turns from his back to his belly. Their contractions are,

however, _combined_ differently in the two cases, so that the results

vary widely. We must consequently conclude that specific arrangements

of cells and fibres exist in the cord for wiping, in the medulla for

turning over, etc. Similarly they exist in the thalami for jumping

over seen obstacles and for balancing the moved body; in the optic

lobes for creeping backwards, or what not. But in the hemispheres,

since the presence of these organs _brings no new elementary form of

movement_ with it, but only _determines differently the occasions_

on which the movements shall occur, making the usual stimuli less

fatal and machine-like; we need suppose no such machinery _directly_

co-ordinative of muscular contractions to exist. We may rather

assume, when the mandate for a wiping-movement is sent forth by the

hemispheres, that a current goes straight to the wiping-arrangement in

the spinal cord, exciting this arrangement as a whole. Similarly, if an

intact frog wishes to jump over a stone which he sees, all he need do

is to excite from the hemispheres the jumping-centre in the thalami or

wherever it may be, and the latter will provide for the details of the

execution. It is like a general ordering a colonel to make a certain

movement, but not telling him how it shall be done.[5]

_The same muscle, then, is repeatedly represented at different

heights;_ and at each it enters into a different combination with other

muscles to co-operate in some special form of concerted movement.

_At each height the movement is discharged by some particular form

of sensorial stimulus._ Thus in the cord, the skin alone occasions

movements; in the upper part of the optic lobes, the eyes are added;

in the thalami, the semi-circular canals would seem to play a part;

whilst the stimuli which discharge the hemispheres would seem not so

much to be elementary sorts of sensation, as groups of sensations

forming determinate _objects_ or _things. Prey_ is not pursued nor are

_enemies_ shunned by ordinary hemisphereless frogs. Those reactions

upon complex circumstances which we call instinctive rather than

reflex, are already in this animal dependent on the brain's highest

lobes, and still more is this the case with animals higher in the

zoological scale.

The results are just the same if, instead of a frog, we take a pigeon,

and cut out his hemispheres as they are ordinarily cut out for a

lecture-room demonstration. There is not a movement natural to him

which this brainless bird cannot perform if expressly excited thereto;

only the inner promptings seem deficient, and when left to himself

he spends most of his time crouched on the ground with his head sunk

between his shoulders as if asleep.

GENERAL NOTION OF HEMISPHERES.

All these facts lead us, when we think about them, to some such

explanatory conception as this: _The lower centres act from present

sensational stimuli alone; the hemispheres act from perceptions and

considerations,_ the sensations which they may receive serving only as

suggesters of these. But what are perceptions but sensations grouped

together? and what are considerations but expectations, in the fancy,

of sensations which will be felt one way or another according as action

takes this course or that? If I step aside on seeing a rattlesnake,

from considering how dangerous an animal he is, the mental materials

which constitute my prudential reflection are images more or less vivid

of the movement of his head, of a sudden pain in my leg, of a state of

terror, a swelling of the limb, a chill, delirium, unconsciousness,

etc., etc., and the ruin of my hopes. But all these images are

constructed out of my past experiences. They are _reproductions_ of

what I have felt or witnessed. They are, in short, _remote_ sensations;

and the _difference between the hemisphereless animal and the whole

one_ may be concisely expressed by saying that the _one obeys absent,

the other only present, objects._

The hemispheres would then seem to be _the seat of memory_. Vestiges

of past experience must in some way be stored up in them, and must,

when aroused by present stimuli, first appear as representations of

distant goods and evils; and then must discharge into the appropriate

motor channels for warding off the evil and securing the benefits of

the good. If we liken the nervous currents to electric currents, we

can compare the nervous system, _C_, below the hemispheres to a direct

circuit from sense-organ to muscle along the line _S ... C ... M_ of

Fig. 2. The hemisphere, _H_, adds the long circuit or loop-line through

which the current may pass when for any reason the direct line is not

used.

Thus, a tired wayfarer on a hot day throws himself on the damp earth

beneath a maple-tree. The sensations of delicious rest and coolness

pouring themselves through the direct line would naturally discharge

into the muscles of complete extension: he would abandon himself

to the dangerous repose. But the loop-line being open, part of the

current is drafted along it, and awakens rheumatic or catarrhal

reminiscences, which prevail over the instigations of sense, and

make the man arise and pursue his way to where he may enjoy his rest

more safely. Presently we shall examine the manner in which the

hemispheric loop-line may be supposed to serve as a reservoir for such

reminiscences as these. Meanwhile I will ask the reader to notice some

corollaries of its being such a reservoir.

[Illustration: FIG. 2.]

First, no animal without it can deliberate, pause, postpone, nicely

weigh one motive against another, or compare. Prudence, in a word,

is for such a creature an impossible virtue. Accordingly we see that

nature removes those functions in the exercise of which prudence is

a virtue from the lower centres and hands them over to the cerebrum.

Wherever a creature has to deal with complex features of the

environment, prudence is a virtue. The higher animals have so to deal;

and the more complex the features, the higher we call the animals. The

fewer of his acts, then, can _such_ an animal perform without the help

of the organs in question. In the frog many acts devolve wholly on the

lower centres; in the bird fewer; in the rodent fewer still; in the dog

very few indeed; and in apes and men hardly any at all.

The advantages of this are obvious. Take the prehension of food as an

example and suppose it to be a reflex performance of the lower centres.

The animal will be condemned fatally and irresistibly to snap at it

whenever presented, no matter what the circumstances may be; he can no

more disobey this prompting than water can refuse to boil when a fire

is kindled under the pot. His life will again and again pay the forfeit

of his gluttony. Exposure to retaliation, to other enemies, to traps,

to poisons, to the dangers of repletion, must be regular parts of his

existence. His lack of all thought by which to weigh the danger against

the attractiveness of the bait, and of all volition to remain hungry

a little while longer, is the direct measure of his lowness in the

mental scale. And those fishes which, like our cunners and sculpins,

are no sooner thrown back from the hook into the water, than they

automatically seize the hook again, would soon expiate the degradation

of their intelligence by the extinction of their type, did not their

exaggerated fecundity atone for their imprudence. Appetite and the acts

it prompts have consequently become in all higher vertebrates functions

of the cerebrum. They disappear when the physiologist's knife has left

the subordinate centres alone in place. The brainless pigeon will

starve though left on a corn-heap.

Take again the sexual function. In birds this devolves exclusively

upon the hemispheres. When these are shorn away the pigeon pays no

attention to the billings and cooings of its mate. And Goltz found that

a bitch in heat would excite no emotion in male dogs who had suffered

large loss of cerebral tissue. Those who have read Darwin's 'Descent of

Man' know what immense importance in the amelioration of the breed in

birds this author ascribes to the mere fact of sexual selection. The

sexual act is not performed until every condition of circumstance and

sentiment is fulfilled, until time, place, and partner all are fit. But

in frogs and toads this passion devolves on the lower centres. They

show consequently a machine-like obedience to the present incitement of

sense, and an almost total exclusion of the power of choice. Copulation

occurs _per fas aut nefas_, occasionally between males, often with dead

females, in puddles exposed on the highway, and the male may be cut in

two without letting go his hold. Every spring an immense sacrifice of

batrachian life takes place from these causes alone.

No one need be told how dependent all human social elevation is upon

the prevalence of chastity. Hardly any factor measures more than this

the difference between civilisation and barbarism. Physiologically

interpreted, chastity means nothing more than the fact that present

solicitations of sense are overpowered by suggestions of æsthetic and

moral fitness which the circumstances awaken in the cerebrum; and that

upon the inhibitory or permissive influence of these alone action

directly depends.

Within the psychic life due to the cerebrum itself the same general

distinction obtains, between considerations of the more immediate

and considerations of the more remote. In all ages the man whose

determinations are swayed by reference to the most distant ends has

been held to possess the highest intelligence. The tramp who lives

from hour to hour; the bohemian whose engagements are from day to day;

the bachelor who builds but for a single life; the father who acts

for another generation; the patriot who thinks of a whole community

and many generations; and finally, the philosopher and saint whose

cares are for humanity and for eternity,--these range themselves in

an unbroken hierarchy, wherein each successive grade results from an

increased manifestation of the special form of action by which the

cerebral centres are distinguished from all below them.

In the 'loop-line' along which the memories and ideas of the distant

are supposed to lie, the action, so far as it is a physical process,

must be interpreted after the type of the action in the lower centres.

If regarded here as a reflex process, it must be reflex there as

well. The current in both places runs out into the muscles only after

it has first run in; but whilst the path by which it runs out is

determined in the lower centres by reflections few and fixed amongst

the cell-arrangements, in the hemispheres the reflections are many and

instable. This, it will be seen, is only a difference of degree and not

of kind, and does not change the reflex type. The conception of _all_

action as conforming to this type is the fundamental conception of

modern nerve-physiology. So much for our general preliminary conception

of the nerve-centres! Let us define it more distinctly before we see

how well physiological observation will bear it out in detail.

THE EDUCATION OF THE HEMISPHERES.

Nerve-currents run in through sense-organs, and whilst provoking reflex

acts in the lower centres, they arouse ideas in the hemispheres, which

either permit the reflexes in question, check them, or substitute

others for them. All ideas being in the last resort reminiscences,

the question to answer is: _How can processes become organized in the

hemispheres which correspond to reminiscences in the mind?_[6]

Nothing is easier than to conceive a _possible_ way in which this might

be done, provided four assumptions be granted. These assumptions (which

after all are inevitable in any event) are:

1) The same cerebral process which, when aroused from without by a

sense-organ, gives the perception of an object, will give an _idea_ of

the same object when aroused by other cerebral processes from within.

2) If processes 1, 2, 3, 4 have once been aroused together or in

immediate succession, any subsequent arousal of any one of them

(whether from without or within) will tend to arouse the others in the

original order. [This is the so-called law of association.]

3) Every sensorial excitement propagated to a lower centre tends to

spread upwards and arouse an idea.

4) Every idea tends ultimately either to produce a movement or to check

one which otherwise would be produced.

[Illustration: FIG. 3.]

Suppose now (these assumptions being granted) that we have a baby

before us who sees a candle-flame for the first time, and, by virtue

of a reflex tendency common in babies of a certain age, extends his

hand to grasp it, so that his fingers get burned. So far we have two

reflex currents in play: first, from the eye to the extension movement,

along the line 1--1--1--1 of Fig. 3; and second, from the finger to the

movement of drawing back the hand, along the line 2--2--2--2. If this

were the baby's whole nervous system, and if the reflexes were once for

all organic, we should have no alteration in his behavior, no matter

how often the experience recurred. The retinal image of the flame would

always make the arm shoot forward, the burning of the finger would

always send it back. But we know that 'the burnt child dreads the

fire,' and that one experience usually protects the fingers forever.

The point is to see how the hemispheres may bring this result to pass.

[Illustration: FIG. 4.--The dotted lines stand for afferent paths,

the broken lines for paths between the centres; the entire lines for

efferent paths.]

We must complicate our diagram (see Fig. 4). Let the current 1--1,

from the eye, discharge upward as well as downward when it reaches the

lower centre for vision, and arouse the perceptional process _s^1_ in

the hemispheres; let the feeling of the arm's extension also send up

a current which leaves a trace of itself, _m^1_; let the burnt finger

leave an analogous trace, _s^2_; and let the movement of retraction

leave _m^2_. These four processes will now, by virtue of assumption

2), be associated together by the path _s^1--m^1--s^2--m^2_, running

from the first to the last, so that if anything touches off _s^1_,

ideas of the extension, of the burnt finger, and of the retraction will

pass in rapid succession through the mind. The effect on the child's

conduct when the candle-flame is next presented is easy to imagine.

Of course the sight of it arouses the grasping reflex; but it arouses

simultaneously the idea thereof, together with that of the consequent

pain, and of the final retraction of the hand; and if these cerebral

processes prevail in strength over the immediate sensation in the

centres below, the last idea will be the cue by which the final action

is discharged. The grasping will be arrested in mid-career, the hand

drawn back, and the child's fingers saved.

In all this we assume that the hemispheres do not _natively_ couple

any particular sense-impression with any special motor discharge. They

only register, and preserve traces of, such couplings as are already

organized in the reflex centres below. But this brings it inevitably

about that, when a chain of experiences has been already registered and

the first link is impressed once again from without, the last link will

often be awakened in _idea_ long before it can exist in _fact_. And

if this last link were previously coupled with a motion, that motion

may now come from the mere ideal suggestion without waiting for the

actual impression to arise. Thus an animal with hemispheres acts in

_anticipation_ of future things; or, to use our previous formula, he

acts from considerations of distant good and ill. If we give the name

of _partners_ to the original couplings of impressions with motions

in a reflex way, then we may say that the function of the hemispheres

is simply to bring about _exchanges among the partners_. Movement

_m^n_, which natively is sensation _s^n_'s partner, becomes through

the hemispheres the partner of sensation _s^1, s^2_, or _s^3_. It is

like the great commutating switch-board at a central telephone station.

No new elementary process is involved; no impression nor any motion

peculiar to the hemispheres; but any number of combinations impossible

to the lower machinery taken alone, and an endless consequent increase

in the possibilities of behavior on the creature's part.

All this, as a mere scheme,[7] is so clear and so concordant with the

general look of the facts as almost to impose itself on our belief;

but it is anything but clear in detail. The brain-physiology of late

years has with great effort sought to work out the paths by which

these couplings of sensations with movements take place, both in the

hemispheres and in the centres below.

So we must next test our scheme by the facts discovered m this

direction. We shall conclude, I think, after taking them all into

account, that the scheme probably makes the lower centres too

machine-like and the hemispheres not quite machine-like enough, and

must consequently be softened down a little. So much I may say in

advance. Meanwhile, before plunging into the details which await us, it

will somewhat clear our ideas if we contrast the modern way of looking

at the matter with the _phrenological_ conception which but lately

preceded it.

THE PHRENOLOGICAL CONCEPTION.

In a certain sense Gall was the first to seek to explain in detail

how the brain could subserve our mental operations. His way of

proceeding was only too simple. He took the faculty-psychology as his

ultimatum on the mental side, and he made no farther psychological

analysis. Wherever he found an individual with some strongly-marked

trait of character he examined his head; and if he found the latter

prominent in a certain region, he said without more ado that that

region was the 'organ' of the trait or faculty in question. The traits

were of very diverse constitution, some being simple sensibilities

like 'weight' or 'color;' some being instinctive tendencies like

'alimentiveness' or 'amativeness;' and others, again, being complex

resultants like 'conscientiousness,' 'individuality.' Phrenology fell

promptly into disrepute among scientific men because observation

seemed to show that large faculties and large 'bumps' might fail to

coexist; because the scheme of Gall was so vast as hardly to admit

of accurate determination at all--who of us can say even of his own

brothers whether their perceptions of _weight_ and of _time_ are well

developed or not?--because the followers of Gall and Spurzheim were

unable to reform these errors in any appreciable degree; and, finally,

because the whole analysis of faculties was vague and erroneous from

a psychologic point of view. Popular professors of the lore have

nevertheless continued to command the admiration of popular audiences;

and there seems no doubt that Phrenology, however little it satisfy

our scientific curiosity about the functions of different portions of

the brain, may still be, in the hands of intelligent practitioners, a

useful help in the art of reading character. A hooked nose and a firm

jaw are usually signs of practical energy; soft, delicate hands are

signs of refined sensibility. Even so may a prominent eye be a sign

of power over language, and a bull-neck a sign of sensuality. But

the brain behind the eye and neck need no more be the _organ_ of the

signified faculty than the jaw is the organ of the will or the hand

the organ of refinement. These correlations between mind and body are,

however, so frequent that the 'characters' given by phrenologists are

often remarkable for knowingness and insight.

Phrenology hardly does more than restate the problem. To answer the

question, "Why do I like children?" by saying, "Because you have a

large organ of philoprogenitiveness," but renames the phenomenon

to be explained. What _is_ my philoprogenitiveness? Of what mental

elements does it consist? And how _can_ a part of the brain be its

organ? A science of the mind must reduce such complex manifestations

as 'philoprogenitiveness' to their _elements_. A science of the brain

must point out the functions of _its_ elements. A science of the

relations of mind and brain must show how the elementary ingredients

of the former correspond to the elementary functions of the latter.

But phrenology, except by occasional coincidence, takes no account of

elements at all. Its 'faculties,' as a rule, are fully equipped persons

in a particular mental attitude. Take, for example, the 'faculty' of

language. It involves in reality a host of distinct powers. We must

first have images of concrete things and ideas of abstract qualities

and relations; we must next have the memory of words and then the

capacity so to associate each idea or image with a particular word

that, when the word is heard, the idea shall forthwith enter our mind.

We must conversely, as soon as the idea arises in our mind, associate

with it a mental image of the word, and by means of this image we must

innervate our articulatory apparatus so as to reproduce the word as

physical sound. To read or to write a language other elements still

must be introduced. But it is plain that the faculty of spoken language

alone is so complicated as to call into play almost all the elementary

powers which the mind possesses, memory, imagination, association,

judgment, and volition. A portion of the brain competent to be the

adequate seat of such a faculty would needs be an entire brain in

miniature,--just as the faculty itself is really a specification of the

entire man, a sort of homunculus.

Yet just such homunculi are for the most part the phrenological organs.

As Lange says:

"We have a parliament of little men together, each one of whom, as

happens also in a real parliament, possesses but a single idea which

he ceaselessly strives to make prevail"--benevolence, firmness, hope,

and the rest. "Instead of one soul, phrenology gives us forty, each

alone as enigmatic as the full aggregate psychic life can be. Instead

of dividing the latter into effective elements, she divides it into

personal beings of peculiar character.... 'Herr Pastor, sure there be

a horse inside,' called out the peasants to X after their spiritual

shepherd had spent hours in explaining to them the construction of the

locomotive. With a horse inside truly everything becomes clear, even

though it be a queer enough sort of horse--the horse itself calls for

no explanation! Phrenology takes a start to get beyond the point of

view of the ghost-like soul entity, but she ends by populating the

whole skull with ghosts of the same order."[8]

Modern Science conceives of the matter in a very different way. _Brain

and mind alike consist of simple elements, sensory and motor_. "All

nervous centres," says Dr. Hughlings Jackson,[9] "from the lowest to

the very highest (the substrata of consciousness), are made up of

nothing else than nervous arrangements, representing impressions and

movements.... I do not see of what other materials the brain _can_ be

made." Meynert represents the matter similarly when he calls the cortex

of the hemispheres the surface of projection for every muscle and every

sensitive point of the body. The muscles and the sensitive points are

_represented_ each by a cortical point, and the brain is nothing but

the sum of all these cortical points, to which, on the mental side, as

many _ideas_ correspond. _Ideas of sensation, ideas of motion_ are,

on the other hand, _the elementary factors out of which the mind is

built up by the associationists in psychology_. There is a complete

parallelism between the two analyses, the same diagram of little dots,

circles, or triangles joined by lines symbolizes equally well the

cerebral and mental processes: the dots stand for cells or ideas, the

lines for fibres or associations. We shall have later to criticise

this analysis so far as it relates to the mind; but there is no doubt

that it is a most convenient, and has been a most useful, hypothesis,

formulating the facts in an extremely natural way.

If, then, we grant that motor and sensory ideas variously associated

are the materials of the mind, all we need do to get a complete diagram

of the mind's and the brain's relations should be to ascertain which

sensory idea corresponds to which sensational surface of projection,

and which motor idea to which muscular surface of projection. The

associations would then correspond to the fibrous connections between

the various surfaces. This distinct _cerebral localization_ of the

various elementary sorts of idea has been treated as a 'postulate' by

many physiologists (e.g. Munk); and the most stirring controversy in

nerve-physiology which the present generation has seen has been the

_localization-question_.

THE LOCALIZATION OF FUNCTIONS IN THE HEMISPHERES.

Up to 1870, the opinion which prevailed was that which the experiments

of Flourens on pigeons' brains had made plausible, namely, that the

different functions of the hemispheres were not locally separated,

but carried on each by the aid of the whole organ. Hitzig in 1870

showed, however, that in a dog's brain highly specialized movements

could be produced by electric irritation of determinate regions of

the cortex; and Ferrier and Munk, half a dozen years later, seemed to

prove, either by irritations or excisions or both, that there were

equally determinate regions connected with the senses of sight, touch,

hearing, and smell. Munk's special sensorial localizations, however,

disagreed with Ferrier's; and Goltz, from his extirpation-experiments,

came to a conclusion adverse to strict localization of any kind. The

controversy is not yet over. I will not pretend to say anything more

of it historically, but give a brief account of the condition in which

matters at present stand.

The one thing which is _perfectly_ well established is this, that the

'central' convolutions, on either side of the fissure of Rolando, and

(at least in the monkey) the calloso-marginal convolution (which is

continuous with them on the mesial surface where one hemisphere is

applied against the other), form the region by which all the motor

incitations which leave the cortex pass out, on their way to those

executive centres in the region of the pons, medulla, and spinal cord

from which the muscular contractions are discharged in the last resort.

The existence of this so-called 'motor zone' is established by the

lines of evidence successively given below:

(1) _Cortical Irritations._ Electrical currents of small intensity

applied to the surface of the said convolutions in dogs, monkeys, and

other animals, produce well-defined movements in face, fore-limb,

hind-limb, tail, or trunk, according as one point or another of the

surface is irritated. These movements affect almost invariably the

side opposite to the brain irritations: If the left hemisphere be

excited, the movement is of the right leg, side of face, etc. All the

objections at first raised against the validity of these experiments

have been overcome. The movements are certainly not due to irritations

of the base of the brain by the downward spread of the current, for:

_a_) mechanical irritations will produce them, though less easily than

electrical; _b_) shifting the electrodes to a point close by on the

surface changes the movement in ways quite inexplicable by changed

physical conduction of the current; _c_) if the cortical 'centre'

for a certain movement be cut under with a sharp knife but left _in

situ_, although the electric conductivity is physically unaltered by

the operation, the physiological conductivity is gone and currents

of the same strength no longer produce the movements which they

did; _d_) the time-interval between the application of the electric

stimulus to the cortex and the resultant movement is what it would

be if the cortex acted physiologically and not merely physically in

transmitting the irritation. It is namely a well-known fact that when a

nerve-current has to pass through the spinal cord to excite a muscle by

reflex action, the time is longer than if it passes directly down the

motor nerve: the cells of the cord take a certain time to discharge.

Similarly, when a stimulus is applied directly to the cortex the muscle

contracts two or three hundredths of a second later than it does when

the place on the cortex is cut away and the electrodes are applied to

the white fibres below.[10]

(2) _Cortical Ablations._ When the cortical spot which is found to

produce a movement of the fore-leg, in a dog, is excised (see spot 5

in Fig. 5), the leg in question becomes peculiarly affected. At first

it seems paralyzed. Soon, however, it is used with the other legs, but

badly. The animal does not bear his weight on it, allows it to rest on

its dorsal surface, stands with it crossing the other leg, does not

remove it if it hangs over the edge of a table, can no longer 'give the

paw' at word of command if able to do so before the operation, does

not use it for scratching the ground, or holding a bone as formerly,

lets it slip out when running on a smooth surface or when shaking

himself, etc., etc. Sensibility of all kinds seems diminished as well

as motility, but of this I shall speak later on. Moreover the dog tends

in voluntary movements to swerve towards the side of the brain-lesion

instead of going straight forward. All these symptoms gradually

decrease, so that even with a very severe brain-lesion the dog may be

outwardly indistinguishable from a well dog after eight or ten weeks.

Still, a slight chloroformization will reproduce the disturbances, even

then. There is a certain appearance of ataxic in-coordination in the

movements--the dog lifts his fore-feet high and brings them down with

more strength than usual, and yet the trouble is not ordinary lack of

co-ordination. Neither is there paralysis. The strength of whatever

movements are made is as great as ever--dogs with extensive destruction

of the motor zone can jump as high and bite as hard as ever they did,

but they seem _less easily moved_ to do _anything_ with the affected

parts. Dr. Loeb, who has studied the motor disturbances of dogs more

carefully than any one, conceives of them _en masse_ as effects of an

increased inertia in all the processes of innervation towards the side

opposed to the lesion. All such movements require an unwonted effort

for their execution; and when only the normally usual effort is made

they fall behind in effectiveness.[11]

[Illustration: FIG. 5.--Left Hemisphere of Dog's Brain, after Ferrier.

_A_, the fissure of Sylvius. _B_, the crucial sulcus. _O_, the

olfactory bulb. _I, II, III, IV,_ indicate the first, second, third,

and fourth external convolutions respectively. (1), (4), and (5) are on

the _sigmoid_ gyrus.]

[Illustration: FIG. 6.--Left Hemisphere of Monkey's Brain. Outer

Surface.]

Even when the entire motor zone of a dog is removed, there is no

permanent paralysis of any part, but only this curious sort of relative

inertia when the two sides of the body are compared; and this itself

becomes hardly noticeable after a number of weeks have elapsed. Prof.

Goltz has described a dog whose entire left hemisphere was destroyed,

and who retained only a slight motor inertia on the right half of

the body. In particular he could use his right paw for holding a

bone whilst gnawing it, or for reaching after a piece of meat. Had

he been taught to give his paw Before the operations, it would have

been curious to see whether that faculty also came back. His tactile

sensibility was permanently diminished on the right side.[12] In

_monkeys_ a genuine paralysis follows upon ablations of the cortex

in the motor region. This paralysis affects parts of the body which

vary with the brain-parts removed. The monkey's opposite arm or leg

hangs flaccid, or at most takes a small part in associated movements.

When the entire region is removed there is a genuine and permanent

hemiplegia in which the arm is more affected than the leg; and this

is followed months later by contracture of the muscles, as in man

after inveterate hemiplegia.[13] According to Schaefer and Horsley, the

trunk-muscles also become paralyzed after destruction of the _marginal_

convolution on _both_ sides (see Fig. 7). These differences between

dogs and monkeys show the danger of drawing general conclusions from

experiments done on any one sort of animal. I subjoin the figures

given by the last-named authors of the motor regions in the monkey's

brain.[14]

[Illustration: FIG. 7.--Left Hemisphere of Monkey's Brain. Mesial

Surface.]

_In man_ we are necessarily reduced to the observation _post-mortem_ of

cortical ablations produced by accident or disease (tumor, hemorrhage,

softening, etc.). What results during life from such conditions is

either localized spasm, or palsy of certain muscles of the opposite

side. The cortical regions which invariably produce these results are

homologous with those which we have just been studying in the dog,

cat, ape, etc. Figs. 8 and 9 show the result of 169 cases carefully

studied by Exner. The parts shaded are regions where lesions produced

_no_ motor disturbance. Those left white were, on the contrary, never

injured without motor disturbances of some sort. Where the injury to

the cortical substance is profound in man, the paralysis is permanent

and is succeeded by muscular rigidity in the paralyzed parts, just as

it may be in the monkey.

[Illustration: FIG. 8.--Right Hemisphere of Human Brain. Lateral

Surface.]

[Illustration: FIG. 9.--Right Hemisphere of Human Brain. Mesial

Surface.]

(3) _Descending degenerations_ show the intimate connection of the

rolandic regions of the cortex with the motor tracts of the cord. When,

either in man or in the lower animals, these regions are destroyed, a

peculiar degenerative change known as secondary sclerosis is found to

extend downwards through the white fibrous substance of the brain in

a perfectly definite manner, affecting certain distinct strands which

pass through the inner capsule, crura, and pons, into the anterior

pyramids of the medulla oblongata, and from thence (partly crossing

to the other side) downwards into the anterior (direct) and lateral

(crossed) columns of the spinal cord.

(4) _Anatomical proof_ of the continuity of the rolandic regions with

these motor columns of the cord is also clearly given. Flechsig's

'Pyramidenbahn' forms an uninterrupted strand (distinctly traceable in

human embryos, before its fibres have acquired their white 'medullary

sheath') passing upwards from the pyramids of the medulla, and

traversing the internal capsule and corona radiata to the convolutions

in question (Fig. 10). None of the inferior gray matter of the brain

seems to have any connection with this important fibrous strand. It

passes directly from the cortex to the motor arrangements in the cord,

depending for its proper nutrition (as the facts of degeneration show)

on the influence of the cortical cells, just as motor nerves depend for

their nutrition on that of the cells of the spinal cord. Electrical

stimulation of this motor strand in any accessible part of its course

has been shown in dogs to produce movements analogous to those which

excitement of the cortical surface calls forth.

[Illustration: FIG. 10.--Schematic Transverse Section of Brain showing

Motor Strand.--After Edinger.]

One of the most instructive proofs of motor localization in the

cortex is that furnished by the disease now called aphemia, or _motor

Aphasia_. Motor aphasia is neither loss of voice nor paralysis of the

tongue or lips. The patient's voice is as strong as ever, and all

the innervations of his hypoglossal and facial nerves, except those

necessary for speaking, may go on perfectly well. He can laugh and

cry, and even sing; but he either is unable to utter any words at

all; or a few meaningless stock phrases form his only speech; or else

he speaks incoherently and confusedly, mispronouncing, misplacing,

and misusing his words in various degrees. Sometimes his speech is

a mere broth of unintelligible syllables. In cases of pure motor

aphasia the patient recognizes his mistakes and suffers acutely from

them. Now whenever a patient dies in such a condition as this, and an

examination of his brain is permitted, it is found that the lowest

frontal gyrus (see Fig. 11) is the seat of injury. Broca first noticed

this fact in 1861, and since then the gyrus has gone by the name of

Broca's convolution. The injury in right-handed people is found on the

left hemisphere, and in left-handed people on the right hemisphere.

Most people, in fact, are left-brained, that is, all their delicate

and specialized movements are handed over to the charge of the left

hemisphere. The ordinary right-handedness for such movements is only

a consequence of that fact, a consequence which shows outwardly on

account of that extensive decussation of the fibres whereby most of

those from the left hemisphere pass to the right half of the body only.

But the left-brainedness might exist in equal measure and not show

outwardly. This would happen wherever organs on _both_ sides of the

body could be governed by the left hemisphere; and just such a case

seems offered by the vocal organs, in that highly delicate and special

motor service which we call speech. Either hemisphere _can_ innervate

them bilaterally, just as either seems able to innervate bilaterally

the muscles of the trunk, ribs, and diaphragm. Of the special movements

of speech, however, it would appear (from the facts of aphasia) that

the left hemisphere in most persons habitually takes exclusive charge.

With that hemisphere thrown out of gear, speech is undone; even though

the opposite hemisphere still be there for the performance of less

specialized acts, such as the various movements required in eating.

[Illustration: FIG. 11.--Schematic Profile of Left Hemisphere, with

the parts shaded whose destruction causes motor ('Broca') and sensory

('Wernicke') Aphasia.]

It will be noticed that Broca's region is homologous with the parts

ascertained to produce movements of the lips, tongue, and larynx when

excited by electric currents in apes (cf. Fig. 6). The evidence is

therefore as complete as it well can be that the motor incitations to

these organs leave the brain by the lower frontal region.

Victims of motor aphasia generally have other disorders. One which

interests us in this connection has been called _agraphia_: they have

lost the power to _write_. They can read writing and understand it;

but either cannot use the pen at all or make egregious mistakes with

it. The seat of the lesion here is less well determined, owing to an

insufficient number of good cases to conclude from.[15] There is no

doubt, however, that it is (in right-handed people) on the left side,

and little doubt that it consists of elements of the hand-and-arm

region specialized for that service, The symptom may exist when there

is little or no disability in the hand for other uses. If it does not

get well, the patient usually educates his right hemisphere, i.e.

learns to write with his left hand. In other cases of which we shall

say more a few pages later on, the patient can write both spontaneously

and at dictation, but cannot _read_ even what he has himself written!

All these phenomena are now quite clearly explained by separate

brain-centres for the various feelings and movements and tracts for

associating these together. But their minute discussion belongs to

medicine rather than to general psychology, and I can only use them

here to illustrate the principles of motor localization.[16] Under the

heads of sight and hearing I shall have a little more to say.

The different lines of proof which I have taken up establish

conclusively the proposition that _all the motor impulses which leave

the cortex pass out_, in healthy animals, _from the convolutions about

the fissure of Rolando_.

When, however, it comes to defining precisely what is involved in

a motor impulse leaving the cortex, things grow more obscure. Does

the impulse start independently from the convolutions in question,

or does it start elsewhere and merely flow through? And to what

particular phase of psychic activity does the activity of these

centres correspond? Opinions and authorities here divide; but it will

be better, before entering into these deeper aspects of the problem,

to cast a glance at the facts which have been made out concerning the

relations of the cortex to sight, hearing, and smell.

_Sight._

Ferrier was the first in the field here. He found, when the _angular_

convolution (that lying between the 'intra parietal' and 'external

occipital' fissures, and bending round the top of the fissure of

Sylvius, in Fig. 6) was excited in the monkey, that movements of

the eyes and head as if for vision occurred; and that when it was

extirpated, what he supposed to be total and permanent blindness of

the opposite eye followed. Munk almost immediately declared total and

permanent blindness to follow from destruction of the _occipital lobe_

in monkeys as well as dogs, and said that the angular gyrus had nothing

to do with sight, but was only the centre for tactile sensibility

of the eyeball. Hunk's absolute tone about his observations and his

theoretic arrogance have led to his ruin as an authority. But he did

two things of permanent value. He was the first to distinguish in these

vivisections between sensorial and _psychic_ blindness, and to describe

the phenomenon of _restitution_ of the visual function after its first

impairment by an operation; and the first to notice the _hemiopic_

character of the visual disturbances which result when only one

hemisphere is injured. Sensorial blindness is absolute insensibility

to light; psychic blindness is inability to recognize the _meaning_ of

the optical impressions, as when we see a page of Chinese print but

it suggests nothing to us. A hemiopic disturbance of vision is one in

which neither retina is affected in its totality, but in which, for

example, the left portion of _each_ retina is blind, so that the animal

sees nothing situated in space towards its right. Later observations

have corroborated this hemiopic character of all the disturbances of

sight from injury to a single hemisphere in the higher animals; and the

question whether an animal's apparent blindness is sensorial or only

psychic has, since Munk's first publications, been the most urgent one

to answer, in all observations relative to the function of sight.

Goltz almost simultaneously with Ferrier and Munk reported experiments

which led him to deny that the visual function was essentially bound

up with any one localized portion of the hemispheres. Other divergent

results soon came in from many quarters, so that, without going into

the history of the matter any more, I may report the existing state of

the case as follows:[17]

In _fishes, frogs_, and _lizards_ vision persists when the hemispheres

are entirely removed. This is admitted for frogs and fishes even by

Munk, who denies it for birds.

All of Munk's _birds_ seemed totally blind (blind sensorially) after

removal of the hemispheres by his operation. The following of a candle

by the head and winking at a threatened blow, which are ordinarily held

to prove the retention of crude optical sensations by the lower centres

in supposed hemisphereless pigeons, are by Munk ascribed to vestiges

of the visual sphere of the cortex left behind by the imperfection of

the operation. But Schrader, who operated after Munk and with every

apparent guarantee of completeness, found that all his pigeons saw

after two or three weeks had elapsed, and the inhibitions resulting

from the wound had passed away. They invariably avoided even the

slightest obstacles, flew very regularly towards certain perches, etc.,

differing _toto cœlo_ in these respects with certain simply _blinded_

pigeons who were kept with them for comparison. They did not pick up

food strewn on the ground, however. Schrader found that they would do

this if even a small part of the frontal region of the hemispheres

was left, and ascribes their non-self-feeding when deprived of their

occipital cerebrum not to a visual, but to a motor, defect, a sort of

alimentary aphasia.[18]

In presence of such discord as that between Munk and his opponents

one must carefully note how differently significant is _loss_, from

_preservation_, of a function after an operation on the brain. The

_loss_ of the function does not necessarily show that it _is_ dependent

on the part cut out; but its _preservation_ does show that it is

_not_ dependent: and this is true though the loss should be observed

ninety-nine times and the preservation only once in a hundred similar

excisions. That birds and mammals _can_ be blinded by cortical ablation

is undoubted; the only question is, _must_ they be so? Only then can

the cortex be certainly called the 'seat of sight.' The blindness may

always be due to one of those remote effects of the wound on distant

parts, inhibitions, extensions of inflammation,--interferences, in

a word,--upon which Brown-Séquard and Goltz have rightly insisted,

and the importance of which becomes more manifest every day. Such

effects are transient; whereas the _symptoms of deprivation_

(_Ausfallserscheinungen_, as Goltz calls them) which come from the

actual loss of the cut-out region must from the nature of the case

be permanent. Blindness in the pigeons, _so far as it passes away_,

cannot possibly be charged to their seat of vision being lost, but only

to some influence which temporarily depresses the activity of that

seat. The same is true _mutatis mutandis_ of all the other effects

of operations, and as we pass to mammals we shall see still more the

importance of the remark.

_In rabbits_ loss of the entire cortex seems compatible with the

preservation of enough sight to guide the poor animals' movements,

and enable them to avoid obstacles. Christiani's observations and

discussions seem conclusively to have established this, although Munk

found that all _his_ animals were made totally blind.[19]

_In dogs_ also Munk found absolute stone-blindness after ablation

of the occipital lobes. He went farther and mapped out determinate

portions of the cortex thereupon, which he considered correlated with

definite segments of the two retinæ, so that destruction of given

portions of the cortex produces blindness of the retinal centre, top,

bottom, or right or left side, of the same or opposite eye. There

seems little doubt that this definite correlation is mythological.

Other observers, Hitzig, Goltz, Luciani, Loeb, Exner, etc., find,

whatever part of the cortex may be ablated on one side, that there

usually results a _hemiopic_ disturbance of _both_ eyes, slight and

transient when the anterior lobes are the parts attacked, grave when an

occipital lobe is the seat of injury, and lasting in proportion to the

latter's extent. According to Loeb, the defect is a dimness of vision

('hemiamblyopia') in which (however severe) the centres remain the

best seeing portions of the retina, just as they are in normal dogs.

The lateral or temporal part of each retina seems to be in exclusive

connection with the cortex of its own side. The centre and nasal part

of each seems, on the contrary, to be connected with the cortex of

the opposite hemispheres. Loeb, who takes broader views than any one,

conceives the hemiamblyopia as he conceives the motor disturbances,

namely, as the expression of an increased inertia in the whole optical

machinery, of which the result is to make the animal respond with

greater effort to impressions coming from the half of space opposed to

the side of the lesion. If a dog has right hemiamblyopia, say, and two

pieces of meat are hung before him at once, he invariably turns first

to the one on his left. But if the lesion be a slight one, _shaking_

slightly the piece of meat on his right (this makes of it a stronger

stimulus) makes him seize upon it first. If only one piece of meat be

offered, he takes it, on whichever side it be.

[Illustration: FIGS. 12 and 13. The Dog's visual centre according to

Munk, the entire striated region, _A, A_, being the exclusive seat of

vision, and the dark central circle, _A^1_, being correlated with the

retinal centre of the opposite eye.]

When both occipital lobes are extensively destroyed total blindness

may result. Munk maps out his 'Sehsphäre' definitely, and says that

blindness _must_ result when the entire shaded part, marked _A, A,_ in

Figs. 12 and 13, is involved in the lesion. Discrepant reports of other

observations he explains as due to incomplete ablation. Luciani, Goltz,

and Lannegrace, however, contend that they have made complete bilateral

extirpations of Munk's Sehsphäre more than once, and found a sort of

crude indiscriminating sight of objects to return in a few weeks.[20]

The question whether a dog is blind or not is harder to solve than

would at first appear; for simply blinded dogs, in places to which they

are accustomed, show little of their loss and avoid all obstacles;

whilst dogs whose occipital lobes are gone may run against things

frequently and yet see notwithstanding. The best proof that they may

see is that which Goltz's dogs furnished: they carefully avoided, as it

seemed, strips of sunshine or paper on the floor, as if they were solid

obstacles. This no really blind dog would do. Luciani tested his dogs

when hungry (a condition which sharpens their attention) by strewing

pieces of meat and pieces of cork before them. If they went straight

at them, they _saw_; and if they chose the meat and left the cork,

they _saw discriminatingly_. The quarrel is very acrimonious; indeed

the subject of localization of functions in the brain seems to have a

peculiar effect on the temper of those who cultivate it experimentally.

The amount of preserved vision which Goltz and Luciani report seems

hardly to be worth considering, on the one hand; and on the other, Munk

admits in his penultimate paper that out of 85 dogs he only 'succeeded'

4 times in his operation of producing complete blindness by complete

extirpation of his 'Sehsphäre.'[21] The safe conclusion for _us_ is

that Luciani's diagram, Fig. 14, represents something like the truth.

The occipital lobes are far more important for vision than any other

part of the cortex, so that their complete destruction makes the animal

almost blind. As for the crude sensibility to light which _may_ then

remain, nothing exact is known either about its nature or its seat.

[Illustration: FIG. 14.--Distribution of the Visual Function in the

Cortex, according to Luciani.]

_In the monkey_, doctors also disagree. The truth seems, however, to be

that the _occipital lobes_ in this animal also are the part connected

most intimately with the visual function. The function would seem to

go on when very small portions of them are left, for Ferrier found no

'appreciable impairment' of it after almost complete destruction of

them on both sides. On the other hand, he found complete and permanent

blindness to ensue when they and the _angular gyri_ in addition were

destroyed on both sides. Munk, as well as Brown and Schaefer, found no

disturbance of sight from destroying the _angular gyri_ alone, although

Ferrier found blindness to ensue. This blindness was probably due to

inhibitions exerted _in distans_, or to cutting of the white optical

fibres passing under the angular gyri on their way to the occipital

lobes. Brown and Schaefer got complete and permanent blindness in

one monkey from total destruction of both occipital lobes. Luciani

and Seppili, performing this operation on two monkeys, found that

the animals were only mentally, not sensorially, blind. After some

weeks they saw their food, but could not distinguish by sight between

figs and pieces of cork. Luciani and Seppili seem, however, not to

have extirpated the entire lobes. When one lobe only is injured the

affection of sight is hemiopic in monkeys: in this all observers agree.

On the whole, then, Munk's original location of vision in the occipital

lobes is confirmed by the later evidence.[22]

_In man_ we have more exact results, since we are not driven to

interpret the vision from the outward conduct. On the other hand,

however, we cannot vivisect, but must wait for pathological lesions

to turn up. The pathologists who have discussed these (the literature

is tedious _ad libitum_) conclude that the occipital lobes are the

indispensable part for vision in man. Hemiopic disturbance in both eyes

comes from lesion of either one of them, and total blindness, sensorial

as well as psychic, from destruction of both.

Hemiopia may also result from lesion in other parts, especially the

neighboring angular and supra-marginal gyri, and it may accompany

extensive injury in the motor region of the cortex. In these cases

it seems probable that it is due to an _actio in distans_, probably

to the interruption of fibres proceeding from the occipital lobe.

There seem to be a few cases on record where there was injury to the

occipital lobes without visual defect. Ferrier has collected as many

as possible to prove his localization in the angular gyrus.[23] A

strict application of logical principles would make one of these cases

outweigh one hundred contrary ones. And yet, remembering how imperfect

observations may be, and how individual brains may vary, it would

certainly be rash for their sake to throw away the enormous amount

of positive evidence for the occipital lobes. Individual variability

is always a _possible_ explanation of an anomalous case. There is no

more prominent anatomical fact than that of the 'decussation of the

pyramids,' nor any more usual pathological fact than its consequence,

that left-handed hemorrhages into the motor region produce right-handed

paralyses. And yet the decussation is variable in amount, and seems

sometimes to be absent altogether.[24] If, in such a case as this last,

the left brain were to become the seat of apoplexy, the left and not

the right half of the body would be the one to suffer paralysis.

The _schema_ below [Fig. 15], copied from Dr. Seguin, expresses, on

the whole, the probable truth about the regions concerned in vision.

Not the entire occipital lobes, but the so-called cunei, and the

first convolutions, are the cortical parts most intimately concerned.

Nothnagel agrees with Seguin in this limitation of the essential

tracts.[25]

[Illustration: FIG. 15.--Scheme of the mechanism of vision, after

Seguin. The _cuneus_ convolution (_Cu_) of the right occipital lobe is

supposed to be injured, and all the parts which lead to it are darkly

shaded to show that they fail to exert their function. _F. O._ are the

intra-hemispheric optical fibres. _P. O. C._ is the region of the lower

optic centres (corpora geniculata and quadrigemina). _T. O. D._ is the

right optic tract; _C_, the chiasma; _F. L. D._ are the fibres going

to the lateral or temporal half _T_ of the right retina; and _F. C. S._

are those going to the central or nasal half of the left retina. _O.

D._ is the right, and _O. S._ the left eyeball. The rightward half of

each is therefore blind: in other words, the right nasal field, _R. N.

F._, and the left temporal field _L. T. F._, have become invisible to

the subject with the lesion at _Cu_.]

* * * * *

A most interesting effect of cortical disorder is _mental blindness_.

This consists not so much in insensibility to optical impressions, as

in _inability to understand them_. Psychologically it is interpretable

as _loss of associations_ between optical sensations and what they

signify; and any interruption of the paths between the optic centres

and the centres for other ideas ought to bring it about. Thus, printed

letters of the alphabet, or words, signify certain sounds and certain

articulatory movements. If the connection between the articulating or

auditory centres, on the one hand, and the visual centres on the other,

be ruptured we ought _a priori_ to expect that the sight of words would

fail to awaken the idea of their sound, or the movement for pronouncing

them. We ought, in short, to have _alexia_, or inability to read:

and this is just what we do have in many cases of extensive injury

about the fronto-temporal regions, as a complication of _aphasic_

disease. Nothnagel suggests that whilst the _cuneus_ is the seat of

optical _sensations_, the other parts of the occipital lobe may be the

field of optical _memories and ideas_, from the loss of which mental

blindness should ensue. In fact, all the medical authors speak of

mental blindness as if it must consist in the loss of visual images

from the memory. It seems to me, however, that this is a psychological

misapprehension. A man whose power of visual imagination has decayed

(no unusual phenomenon in its lighter grades) is not mentally blind

in the least, for he recognizes perfectly all that he sees. On the

other hand, he _may_ be mentally blind, with his optical imagination

well preserved; as in the interesting case published by Wilbrand in

1887.[26] In the still more interesting case of mental blindness

recently published by Lissauer,[27] though the patient made the most

ludicrous mistakes, calling for instance a clothes-brush a pair of

spectacles, an umbrella a plant with flowers, an apple a portrait of

a lady, etc. etc., he seemed, according to the reporter, to have his

mental images fairly well preserved. It is in fact the momentary loss

of our _non_-optical images which makes us mentally blind, just as it

is that of our _non_-auditory images which makes us mentally deaf. I

am mentally deaf if, _hearing_ a bell, I can't recall how it _looks_;

and mentally blind if, _seeing_ it, I can't recall its _sound or its

name_. As a matter of fact, I should have to be not merely mentally

blind, but stone-blind, if all my visual images were lost. For although

I am blind to the right half of the field of view if my left occipital

region is injured, and to the left half if my right region is injured,

such hemianopsia does not deprive me of visual _images_, experience

seeming to show that the unaffected hemisphere is always sufficient

for production of these. To abolish them entirely I should have to be

deprived of both occipital lobes, and that would deprive me not only

of my inward images of sight, but of my sight altogether.[28] Recent

pathological annals seem to offer a few such cases.[29] Meanwhile there

are a number of cases of mental blindness, especially for written

language, coupled with hemianopsia, usually of the rightward field of

view. These are all explicable by the breaking down, through disease,

of the _connecting tracts_ between the occipital lobes and other parts

of the brain, especially those which go to the centres for speech in

the frontal and temporal regions of the left hemisphere. They are to

be classed among disturbances of _conduction_ or of _association_;

and nowhere can I find any fact which should force us to believe that

optical images need[30] be lost in mental blindness, or that the

cerebral centres for such images are locally distinct from those for

direct sensations from the eyes.[31]

Where an object fails to be recognized by sight, it often happens

that the patient will recognize and name it as soon as he touches it

with his hand. This shows in an interesting way how numerous the

associative paths are which all end by running out of the brain through

the channel of speech. The hand-path is open, though the eye-path be

closed. When mental blindness is most complete, neither sight, touch,

nor sound avails to steer the patient, and a sort of dementia which

has been called _asymbolia_ or _apraxia_ is the result. The commonest

articles are not understood. The patient will put his breeches on one

shoulder and his hat upon the other, will bite into the soap and lay

his shoes on the table, or take his food into his hand and throw it

down again, not knowing what to do with it, etc. Such disorder can only

come from extensive brain-injury.[32]

The _method of degeneration_ corroborates the other evidence localizing

the tracts of vision. In young animals one gets secondary degeneration

of the occipital regions from destroying an eyeball, and, _vice versâ_,

degeneration of the optic nerves from destroying the occipital regions.

The corpora geniculata, thalami, and subcortical fibres leading to the

occipital lobes are also found atrophied in these cases. The phenomena

are not uniform, but are indisputable;[33] so that, taking all lines of

evidence together, the special connection of vision with the occipital

lobes is perfectly made out. It should be added, that the occipital

lobes have frequently been found shrunken in cases of inveterate

blindness in man.

_Hearing._

Hearing is hardly as definitely localized as sight. _In the dog_,

Luciani's diagram will show the regions which directly or indirectly

affect it for the worse when injured. As with sight, one-sided lesions

produce symptoms on both sides. The mixture of black dots and gray dots

in the diagram is meant to represent this mixture of 'crossed' and

'uncrossed' connections, though of course no topographical exactitude

is aimed at. Of all the region, the temporal lobe is the most important

part; yet permanent absolute deafness did not result in a dog of

Luciani's, even from bilateral destruction of both temporal lobes in

their entirety.[34]

[Illustration: FIG. 16.--Luciani's Hearing Region.]

_In the monkey_, Ferrier and Yeo once found permanent deafness to

follow destruction of the upper temporal convolution (the one just

below the fissure of Sylvius in Fig. 6) on both sides. Brown and

Schaefer found, on the contrary, that in several monkeys this operation

failed to noticeably affect the hearing. In one animal, indeed, both

entire temporal lobes were destroyed. After a week or two of depression

of the mental faculties this beast recovered and became one of the

brightest monkeys possible, domineering over all his mates, and

admitted by all who saw him to have all his senses, including hearing,

'perfectly acute.'[35] Terrible recriminations have, as usual, ensued

between the investigators, Ferrier denying that Brown and Schaefer's

ablations were complete,[36] Schaefer that Ferrier's monkey was really

deaf.[37] In this unsatisfactory condition the subject must be left,

although there seems no reason to doubt that Brown and Schaefer's

observation is the more important of the two.

_In man_ the temporal lobe is unquestionably the seat of the hearing

function, and the superior convolution adjacent to the sylvian fissure

is its most important part. The phenomena of aphasia show this. We

studied motor aphasia a few pages back; we must now consider _sensory

aphasia_. Our knowledge of this disease has had three stages: we may

talk of the period of Broca, the period of Wernicke, and the period

of Charcot. What Broca's discovery was we have seen. Wernicke was the

first to discriminate those cases in which the patient can _not even

understand_ speech from those in which he can understand, only not

talk; and to ascribe the former condition to lesion of the temporal

lobe.[38] The condition in question is _word-deafness_, and the disease

is _auditory aphasia_. The latest statistical survey of the subject is

that by Dr. Allen Starr.[39] In the seven cases of _pure_ word-deafness

which he has collected, cases in which the patient could read, talk,

and write, but not understand what was said to him, the lesion was

limited to the first and second temporal convolutions in their

posterior two thirds. The lesion (in right-handed, i.e. left-brained,

persons) is always on the left side, like the lesion in motor aphasia.

Crude hearing would not be abolished, even were the left centre for it

utterly destroyed; the right centre would still provide for that. But

the _linguistic use_ of hearing appears bound up with the integrity of

the left centre more or less exclusively. Here it must be that words

heard enter into association with the things which they represent, on

the one hand, and with the movements necessary for pronouncing them, on

the other. In a large majority of Dr. Starr's fifty cases, the power

either to name objects or to talk coherently was impaired. This shows

that in most of us (as Wernicke said) speech must go on from auditory

cues; that is, it must be that our ideas do not innervate our motor

centres directly, but only after first arousing the mental sound of

the words. This is the immediate stimulus to articulation; and where

the possibility of this is abolished by the destruction of its usual

channel in the left temporal lobe, the articulation must suffer. In

the few cases in which the channel is abolished with no bad effect on

speech we must suppose an idiosyncrasy. The patient must innervate

his speech-organs either from the corresponding portion of the other

hemisphere or directly from the centres of ideation, those, namely,

of vision, touch, etc., without leaning on the auditory region. It

is the minuter analysis of the facts in the light of such individual

differences as these which constitutes Charcot's contribution towards

clearing up the subject.

Every nameable thing, act, or relation has numerous properties,

qualities, or aspects. In our minds the properties of each thing,

together with its name, form an associated group. If different parts

of the brain are severally concerned with the several properties, and

a farther part with the hearing, and still another with the uttering,

of the name, there must inevitably be brought about (through the law

of association which we shall later study) such a dynamic connection

amongst all these brain-parts that the activity of any one of them will

be likely to awaken the activity of all the rest. When we are talking

as we think, the _ultimate_ process is that of utterance. If the

brain-part for _that_ be injured, speech is impossible or disorderly,

even though all the other brain-parts be intact: and this is just the

condition of things which, on page 37, we found to be brought about

by limited lesion of the left inferior frontal convolution. But back

of that last act various orders of succession are possible in the

associations of a talking man's ideas. The more usual order seems

to be from the tactile, visual, or other properties of the things

thought-about to the sound of their names, and then to the latter's

utterance. But if in a certain individual the thought of the _look_ of

an object or of the _look_ of its printed name be the process which

habitually precedes articulation, then the loss of the _hearing_ centre

will _pro tanto_ not affect that individual's speech. He will be

mentally deaf, i.e. his _understanding_ of speech will suffer, but he

will not be aphasic. In this way it is possible to explain the seven

cases of _pure_ word-deafness which figure in Dr. Starr's table.

If this order of association be ingrained and habitual in that

individual, injury to his _visual_ centres will make him not only

word-blind, but aphasic as well. His speech will become confused in

consequence of an occipital lesion. Naunyn, consequently, plotting

out on a diagram of the hemisphere the 71 irreproachably reported

cases of aphasia which he was able to collect, finds that the lesions

concentrate themselves in three places: first, on Broca's centre;

second, on Wernicke's; third, on the supra-marginal and angular gyri

under which those fibres pass which connect the visual centres with

the rest of the brain[40] (see Fig. 17). With this result Dr. Starr's

analysis of purely sensory cases agrees.

[Illustration: FIG. 17.]

In a later chapter we shall again return to these differences in

the effectiveness of the sensory spheres in different individuals.

Meanwhile few things show more beautifully than the history of our

knowledge of aphasia how the sagacity and patience of many banded

workers are in time certain to analyze the darkest confusion into an

orderly display.[41] There is no 'centre of Speech' in the brain any

more than there is a faculty of Speech in the mind. The entire brain,

more or less, is at work in a man who uses language. The subjoined

diagram, from Boss, shows the four parts most critically concerned,

and, in the light of our text, needs no farther explanation (see Fig.

18).

[Illustration: FIG. 18.]

_Smell._

Everything conspires to point to the median descending part of the

temporal lobes as being the organs of smell. Even Ferrier and Munk

agree on the hippocampal gyrus, though Ferrier restricts olfaction, as

Munk does not, to the lobule or uncinate process of the convolution,

reserving the rest of it for touch. Anatomy and pathology also point to

the hippocampal gyrus; but as the matter is less interesting from the

point of view of human psychology than were sight and hearing, I will

say no more, but simply add Luciani and Seppili's diagram of the dog's

smell-centre.[42] Of

_Taste_

we know little that is definite. What little there is points to the

lower temporal regions again. Consult Ferrier as below.

[Illustration: FIG. 19.--Luciani's Olfactory Region in the Dog.]

_Touch._

Interesting problems arise with regard to the seat of tactile and

muscular sensibility. Hitzig, whose experiments on _dogs' brains_

fifteen years ago opened the entire subject which we are discussing,

ascribed the disorders of motility observed after ablations of the

motor region to a loss of what he called muscular consciousness.

The animals do not notice eccentric positions of their limbs, will

stand with their legs crossed, with the affected paw resting on its

back or hanging over a table's edge, etc.; and do not resist our

bending and stretching of it as they resist with the unaffected paw.

Goltz, Munk, Schiff, Herzen, and others promptly ascertained an equal

defect of cutaneous sensibility to pain, touch, and cold. The paw

is not withdrawn when pinched, remains standing in cold water, etc.

Ferrier meanwhile denied that there was any true anæsthesia produced

by ablations in the motor zone, and explains the appearance of it as

an effect of the sluggish motor responses of the affected side.[43]

Munk[44] and Schiff[45], on the contrary, conceive of the 'motor

zone' as essentially sensory, and in different ways explain the motor

disorders as secondary results of the anæsthesia which is always there,

Munk calls the motor zone the Fühlsphäre of the animal's limbs, etc.,

and makes it coördinate with the Sehsphäre, the Hörsphäre, etc., the

entire cortex being, according to him, nothing but a projection-surface

for sensations, with no exclusively or essentially motor part. Such a

view would be important if true, through its bearings on the psychology

of volition. What is the truth? As regards the fact of cutaneous

anæsthesia from motor-zone ablations, all other observers are against

Ferrier, so that he is probably wrong in denying it. On the other hand,

Munk and Schiff are wrong in making the motor symptoms _depend_ on

the anæsthesia, for in certain rare cases they have been observed to

exist not only without insensibility, but with actual hyperæsthesia of

the parts.[46] The motor and sensory symptoms seem, therefore, to be

independent variables.

_In monkeys_ the latest experiments are those of Horsley and

Schaefer,[47] whose results Ferrier accepts. They find that excision

of the hippocampal convolution produces transient insensibility of

the opposite side of the body, and that permanent insensibility is

produced by destruction of its continuation upwards above the corpus

callosum, the so-called _gyrus fornicatus_ (the part just below

the 'calloso-marginal fissure' in Fig. 7). The insensibility is at

its maximum when the entire tract comprising both convolutions is

destroyed. Ferrier says that the sensibility of monkeys is 'entirely

unaffected' by ablations of the motor zone,[48] and Horsley and

Schaefer consider it by no means necessarily abolished.[49] Luciani

found it diminished in his three experiments on apes.[50]

[Illustration: FIG. 20.--Luciani's Tactile Region in the Dog.]

_In man_ we have the fact that one-sided paralysis from disease of the

opposite motor zone may or may not be accompanied with anæsthesia of

the parts. Luciani, who believes that the motor zone is also sensory,

tries to minimize the value of this evidence by pointing to the

insufficiency with which patients are examined. He himself believes

that in dogs the tactile sphere extends backwards and forwards of the

directly excitable region, into the frontal and parietal lobes (see

Fig. 20). Nothnagel considers that pathological evidence points in the

same direction;[51] and Dr. Mills, carefully reviewing the evidence,

adds the gyri fornicatus and hippocampi to the cutaneo-muscular

region in man.[52] If one compare Luciani's diagrams together (Figs.

14, 16, 19, 20) one will see that the entire parietal region of the

dog's skull is common to the four senses of sight, hearing, smell,

and touch, including muscular feeling. The corresponding region in

the human brain (upper parietal and supra-marginal gyri--see Fig. 17)

seems to be a somewhat similar place of conflux. Optical aphasias and

motor and tactile disturbances all result from its injury, especially

when that is on the left side.[53] The lower we go in the animal scale

the less differentiated the functions of the several brain-parts seem

to be.[54] It may be that the region in question still represents

in ourselves something like this primitive condition, and that the

surrounding parts, in adapting themselves more and more to specialized

and narrow functions, have left it as a sort of _carrefour_ through

which they send currents and converse. That it should be connected

with musculo-cutaneous feeling is, however, no reason why the motor

zone proper should not be so connected too. And the cases of paralysis

from the motor zone with no accompanying anæsthesia may be explicable

without denying all sensory function to that region. For, as my

colleague Dr. James Putnam informs me, sensibility is always harder to

kill than motility, even where we know for a certainty that the lesion

affects tracts that are both sensory and motor. Persons whose hand is

paralyzed in its movements from compression of arm-nerves during sleep,

still feel with their fingers; and they may still feel in their feet

when their legs are paralyzed by bruising of the spinal cord. In a

similar way, the motor cortex might be sensitive as well as motor, and

yet by this greater subtlety (or whatever the peculiarity may be) in

the sensory currents, the sensibility might survive an amount of injury

there by which the motility was destroyed. Nothnagel considers that

there are grounds for supposing the _muscular_ sense to be exclusively

connected with the parietal lobe and not with the motor zone. "Disease

of this lobe gives pure ataxy without palsy, and of the motor zone

pure palsy without loss of muscular sense."[55] He fails, however,

to convince more competent critics than the present writer,[56] so I

conclude with them that as yet we have no decisive grounds for locating

muscular and cutaneous feeling apart. Much still remains to be learned

about the relations between musculo-cutaneous sensibility and the

cortex, but one thing is certain: that neither the occipital, the

forward frontal, nor the temporal lobes seem to have anything essential

to do with it in man. It is knit up with the performances of the

_motor zone and of the convolutions backwards and midwards of them_.

The reader must remember this conclusion when we come to the chapter on

the Will.

* * * * *

I must add a word about the connection of aphasia with the tactile

sense. On p. 40 I spoke of those cases in which the patient can write

but not read his own writing. He cannot read by his eyes; but he can

read by the feeling in his fingers, if he retrace the letters in the

air. It is convenient for such a patient to have a pen in hand whilst

reading in this way, in order to make the usual feeling of writing more

complete.[57] In such a case we must suppose that the path between the

optical and the graphic centres remains open, whilst that between the

optical and the auditory and articulatory centres is closed. Only thus

can we understand how the look of the writing should fail to suggest

the sound of the words to the patient's mind, whilst it still suggests

the proper movements of graphic imitation. These movements in their

turn must of course be felt, and the feeling of them must be associated

with the centres for hearing and pronouncing the words. The injury in

cases like this where very special combinations fail, whilst others go

on as usual, must always be supposed to be of the nature of increased

resistance to the passage of certain currents of association. If any of

the _elements_ of mental function were destroyed the incapacity would

necessarily be much more formidable. A patient who can both read and

write with his fingers most likely uses an identical 'graphic' centre,

at once sensory and motor, for both operations.

* * * * *

I have now given, as far as the nature of this book will allow, a

complete account of the present state of the localization-question.

In its main outlines it stands firm, though much has still to be

discovered. The anterior frontal lobes, for example, so far as is yet

known, have no definite functions. Goltz finds that dogs bereft of them

both are incessantly in motion, and excitable by every small stimulus.

They are irascible and amative in an extraordinary degree, and their

sides grow bare with perpetual reflex scratching; but they show no

_local_ troubles of either motion or sensibility. In monkeys not even

this lack of inhibitory ability is shown, and neither stimulation nor

excision of the prefrontal lobes produces any symptoms whatever. One

monkey of Horsley and Schaefer's was as tame, and did certain tricks as

well, after as before the operation.[58] It is probable that we have

about reached the limits of what can be learned about brain-functions

from vivisecting inferior animals, and that we must hereafter look more

exclusively to human pathology for light. The existence of separate

speech and writing centres in the left hemisphere in man; the fact

that palsy from cortical injury is so much more complete and enduring

in man and the monkey than in dogs; and the farther fact that it seems

more difficult to get complete sensorial blindness from cortical

ablations in the lower animals than in man, all show that functions get

more specially localized as evolution goes on. In birds localization

seems hardly to exist, and in rodents it is much less conspicuous than

in carnivora. Even for man, however, Munk's way of mapping out the

cortex into absolute areas within which only one movement or sensation

is represented is surely false. The truth seems to be rather that,

although there is a correspondence of certain regions of the brain to

certain regions of the body, yet the several _parts_ within each bodily

region are represented throughout the _whole_ of the corresponding

brain-region like pepper and salt sprinkled from the same caster. This,

however, does not prevent each 'part' from having its _focus_ at one

spot within the brain-region. The various brain-regions merge into each

other in the same mixed way. As Mr. Horsley says: "There are border

centres, and the area of representation of the face merges into that

for the representation of the upper limb. If there was a focal lesion

at that point, you would have the movements of these two parts starting

together."[59] The accompanying figure from Paneth shows just how the

matter stands in the dog.[60]

[Illustration: FIG. 21.--Dog's motor centres, right hemisphere,

according to Paneth.--The points of the motor region are correlated as

follows with muscles: the _loops_ with the _orbicularis palpebrarum_;

the _plain crosses_ with the _flexor_, the _crosses inscribed in

circles_ with the _extensor, digitorum communis_ of the fore-paw;

the _plain circles_ with the _abductor pollicis longus_; the _double

crosses_ with the _extensor communis_ of the hind-limb.]