THE MATERIAL MECHANISM OF DREAM.
It is difficult to describe, without the use of technical terms, the
structure of the mechanism by which Dream is produced. But as these
are at once unintelligible and repulsive to the non-scientific reader,
indulgence is entreated for an endeavour to present the subject in shape
and language that may be understood by everybody.
It must be premised that this description is partly derived from the
recent treatise of Professor FERRIER on “The Functions of the Brain,”[1]
in which he details the experiments that have thrown so much light alike
upon physiology and psychology.
The spinal cord expands at its upper end into a ganglion or cluster of
nerves called the _medulla oblongata_.
At this point the brain is said to cease and the nerve system to begin.
But there is no perceptible beginning nor ending either of the brain or
of the nerves. The entire nerve system is, in fact, only an extension
of the brain. When a nerve is irritated at the point of the finger the
brain as well as the nerve is affected. The nerve transmits the sensation
and the brain feels it. Psychologists would venture a step further, and
say, “It is not the brain that feels, but the intelligent individual
entity, the living soul or self, of whom the brain is only the material
transmitting organ.”
It is at the extremity of this ganglion that the cords wrapped within
that great bundle of nerve cords which constitutes the spinal cord cross
each other and pass into opposite sides of the brain and of the body.
The nerves that control the left side of the body pass into the right
side of the brain, and those that control the right side of the body pass
into the left side of the brain. As the consequence of this exchange, the
right side of the brain controls and directs the left side of the body,
and the left side of the brain the right side of the body.
Above this basal ganglion, but connected with it, is a ganglion which
anatomists have divided into two parts, but which for the present purpose
it will be convenient to recognize as one whole lying at the base of the
brain and crowned and inclosed by the cerebral hemispheres. From this
great basal ganglion small white threads radiate into the two cerebral
hemispheres in the form of a hollow cone.
Above the basal ganglion lies another great ganglion (the _cerebellum_),
also divided into lobes, and which is connected with the basal ganglion
by two bands (or peduncles). It is connected also with the two cerebral
hemispheres by two bands. It is connected with the central ganglion by a
thin lamina, which stretches to the other ganglia, thus connecting all
the ganglia with the centres of the senses and the centres of motion—that
is to say, with the centre that receives the messages of the senses and
with the centre that conveys the commands of the Will to the body.
Above and extending in front of these are the _cerebrum_, the organ of
the intelligence, composed of two hemispheres, which crown, inclose, and
overlap the ganglia at the base of the brain.
These two great hemispheres are distinct bodies, each complete in itself
but united by fibres that pass from one hemisphere to the other and thus
secure their united action. These fibres are observed to connect together
corresponding regions of the two hemispheres.
At their bases the two hemispheres are in direct contact with the
ganglion above described as the central ganglion, but which has been
anatomically subdivided into two pairs of ganglia. For the purposes of
this treatise, however, minute divisions are not necessary.
This ganglion is the centre upon which all the nerves of the senses
converge and each division of it is supposed to be appropriated to a
distinct sense. But even if each part has its own work to do, it is not
less a whole than is the cerebral hemisphere, which is now proved to have
various parts devoted to various mental operations.
The cerebral hemispheres are formed of great bundles of fibres, in the
shape of rolls, plainly visible on the outside, but which baffle the
attempts of the most dexterous anatomist to sever them below the surface.
And the whole brain is covered with an extremely delicate and highly
sensitive membrane, which is now conjectured to be the medium by means of
which all the parts of the brain are brought into communication, and the
co-ordination and unity of action of the entire organ preserved.
The substance of the brain itself is insensible, although it is the
recipient and supposed seat of the pains and pleasures of the body—or
rather of the nerves, for what we call the body is only the insensible
clothing of the nerves. The nerves feel; the flesh and bones do not feel.
Is not this fact another powerful argument _against_ the doctrine of the
Materialists that consciousness and mind are only states of brain or
conditions of matter? If the brain is not conscious of injuries done to
itself, if it is insensible even to its own destruction, how can it be
the “_Conscious_ Self?”
But the enveloping membrane of the brain is exquisitely sensitive. It
is the seat of headache, of _delirium tremens_, of brain fever, of
hydrocephalus, and probably of many more diseases which we are wont to
refer to the substance of the brain.
_We_ refer—_Who_ refers? _What_ refers? The brain to the brain? Or one
part of the brain to another part of the brain? Will the Materialists
explain?
It is probable that this envelope of nerves unites all the parts of the
brain and by transmitting to each part the condition of all the other
parts produces co-ordination of the parts and unity of action. But this
membrane of nerve cannot surely be deemed by the most bigoted Materialist
to constitute the Conscious Self.
Professor FERRIER has proved, by a multitude of minutely detailed
experiments, that not only has each ganglion its function, but that each
part of each ganglion is devoted to some special duty, thus completely
shattering the theory that holds every mental operation to be an act
of the whole brain. He establishes at least the grand basis of modern
mental Science, the assumption that the brain is the material organ of
the mind; that distinct parts of the brain are devoted to distinct mental
operations; that not the whole brain, but only parts of it, are employed
in any mental operation. The question is still open for observation and
experiment to ascertain what are the parts of the brain so appropriated
and what are the precise functions of each part.
Professor FERRIER has made considerable advances towards the
determination of this question. His experiments have demonstrated what
are the functions of the ganglia at the base of the brain, not being
the seat of the Intelligence. His experiments were attended with more
cruelty than I could excuse even for the important accessions they have
brought to our knowledge. But they are not therefore the less valuable as
contributions to Physiology and Psychology. I can but briefly describe
the results of such of them as bear immediately upon the subject here
treated of.
Let me, however, first confirm, by the authority of Professor FERRIER,
the proposition I have ventured to advance as to the various functions of
various parts of the brain.
“That the brain is the organ of the mind,” he says, “and that mental
operations are possible only in and through the brain, is now so
thoroughly well established and recognized that we may, without further
question, start from this as an ultimate fact.” He proceeds:
The physiological activity of the brain is not, however,
altogether co-extensive with its psychological functions. The
brain as an organ of motion and sensation, or presentative
consciousness, is a single organ composed of two halves;
the brain as an organ of ideation, or re-presentative
consciousness, is a dual organ, each hemisphere complete
in itself. When one hemisphere is removed or destroyed by
disease, motion and sensation are abolished unilaterally, but
mental operations are still capable of being carried on in
their completeness through the agency of the one hemisphere.
The individual who is paralysed as to sensation and motion by
disease of the opposite side of the brain (say the right),
is not paralysed mentally, for he can still feel and will and
think, and intelligently comprehend with the one hemisphere.
If these functions are not carried on with the same vigour as
before, they at least do not appear to suffer in respect of
completeness.
As the object of this treatise is not anatomy but psychology, it will be
unnecessary to describe minutely the entire of the brain structure. It
will suffice for the present purpose to view the brain, above roughly
sketched, as having three well marked divisions, each with definite and
distinct functions.
The ganglia at the base of the brain govern the actions of the body. The
ganglia in the centre of the brain are the recipients of the impressions
made upon the senses and thus connect us with the external world. The two
hemispheres at the summit of the brain are the organs of the Intelligence.
Professor FERRIER’S experiments were made with a view to ascertain
whether the theory of Dr. CARPENTER is true, that the whole brain works
in each mental action, or if the phrenological doctrine be the true one,
that the several parts of the brain have several and distinct functions.
Dr. CARPENTER had prematurely boasted that he had killed Phrenology.
The boast would have been justified if his assertion (for it was merely
a dogma, not a proved fact) had been found to be true. But Professor
FERRIER’S experiments have decisively _disproved_ the boast of Dr.
CARPENTER and killed his theory of mental unity.
The experiments were conducted chiefly with monkeys and dogs. The former
were the most valuable, because the brain structure of the monkey is
almost identical with that of man. The experiments were certainly cruel
and I should object to procure even such valuable knowledge at such a
price. But, as it is obtained, we may use it.
The experiments were performed by making the animal insensible by
chloroform and then extracting in mass certain portions of the brain,
or destroying parts of the brain by the actual cautery. Electrodes were
applied to the various parts of the brain to which access had been thus
obtained and their effects upon the actions of the animal were carefully
observed.
I will not attempt to detail these experiments—but merely state some of
the results. For the many important facts that were discovered by them
reference must be made to the valuable volume in which they are reported.
He found the entire brain to be connected with the nerve system by the
process of interlacing. Excitation of the right brain was shown by the
left side of the body; of the left brain by the right side. So it was
with the nerves of the senses. Whether the like structure exists in the
duplex organ of the intelligence he could not trace, because the mental
results were incapable of being expressed by experiment upon animals,
who cannot tell us what are their emotions. But he entertains no doubt
that the same structural scheme is observed in the action of the two
hemispheres also.
The great ganglia at the base of the brain, whether excited by
electricity or destroyed by cautery, yielded the same result. They proved
beyond doubt that _their_ function is to direct the actions of the body
under the peculiar conditions of its duplex structure—that is to say, a
formation by two distinct and not wholly similar halves joined together
and requiring community of action. This process of separate action for
each part combined with motion in _co-ordination_—that is to say, the
regulation of the motions of the limbs, so that the two halves of which
the body is builded may act in definite relationship—was found to be the
special business of those basal ganglia, any disturbance in those ganglia
being attended with imperfect movements of the body, even to the extent
of causing the animal to walk in a circle, having lost entirely the
power to “walk straight.” The results of this ingenious experiment are
extremely curious and throw great light on the physiology of locomotion.
The second division of the brain, lying in its centre, overlapped behind
by the cerebrum, resting on the centres that direct bodily actions and
dominated by the hemispheres that are the organs of the intelligence,
is shown by these experiments to be the centre upon which the senses
converge. To this common centre the impressions made upon the senses by
the external world are conveyed. The experiments seem to indicate that
a distinct ganglion is devoted to each sense, although all are united
in one mass for the common purpose of reception of the information they
bring. The destruction of different parts of this brain centre is found
to be followed by the loss or impairment of different senses. It was
found, also, that this part of the brain was duplex, like the other
parts, for destruction of the right side of the ganglion caused paralysis
of the senses on the left side of the body and _vice versâ_.
A question of much interest arises here. What is the precise function
of this sense-receiving portion of the brain? Is _itself_ perceptive
of the sense-impressions brought to it, or is it merely the medium
for transmitting those impressions to the hemispheres above? That in
health it does communicate to the intelligence the same impressions that
it receives there can be no doubt, for we take cognisance of them in
almost every mental act. We know also that when the brain is diseased
false impressions are conveyed to the Intelligence. But in exploring
the psychology of Sleep and Dream, it would be of great advantage to
ascertain if the same receiving portion of the brain is an active or
merely a passive agent.
The experiments of Professor FERRIER are almost conclusive upon this most
important point. He removed the two brain hemispheres of a monkey and
of a dog. The animals lived and appeared to enjoy health, but _they had
lost intelligence_. They had not, however, lost the use of the _senses_
and they were manifestly conscious of the impressions brought by the
nerves of sense. The external world continued to exist for them and was
perceived by them as before the organs of the intelligence were removed.
But when this central division of the brain was taken away and nothing
left but the lower lobes that govern muscular motion, all the senses
ceased to act, or consciousness of action had ceased. Nevertheless the
power of locomotion and the co-ordinate action of the limbs was preserved
with very little loss of power.
Above the central sense-organ tower two hemispheres—_two_ brains, each
distinct and complete in itself and each capable to act without the
other. The function of these hemispheres is that we term _mental_. They
are the organs of the intellect and of the sentiments. Through them we
think, reason and feel. Injury to parts of these injures more or less,
_not_ the _whole_ mind, but _parts of the mind_—certain mental faculties
only. Destruction of the entire of these hemispheres is not death but
idiotcy.
Let it then be clear in the mind of the reader, when surveying the
phenomena of sleep and dream and inquiring into their causes, that for
the purpose of such an outline of the Physiology of the Mind as this,
the brain is to be viewed by him as having _three_ marked divisions—the
organ of the _intelligence_ at the summit, of the _senses_ in the centre,
of _bodily motion_ at the base.
There are many sub-divisions of the brain known to anatomists and
necessary to be known by the Student of Physiology. But these will
suffice for the Student of Psychology. They are easily understood and
readily remembered.
In the waking and normal state, the whole brain is awake, all its parts
acting in concert and preserving strict co-ordination. The reasoning
faculties correct the senses; the senses correct the imagination; the
intelligence controls the emotions; the emotions give vigour to the Will;
the Will commands the entire mechanism of the body and expresses upon the
external world the results of that combination of intelligent actions and
emotions which we term “_the mind_.”
In sleep this relationship is changed. The reasoning faculties cease to
correct the senses; the senses no longer correct the imagination; the
emotions are unable to influence the Will; the Will loses its command of
body and mind alike.
However it may be in dreamless sleep, in the condition of dream the
entire mechanism certainly does not sleep. Some part of it is awake and
active. What is that waking part?
It is undoubted that the cerebral hemispheres are wholly or partially
awake in the process of dream. In deep sleep the sense-ganglia are
wholly asleep. In all sleep the senses sleep, only sometimes not so
profoundly as completely to exclude cognizance, by the Conscious Self, of
the sense-borne impressions. Sleep affects also the ganglia at the base
of the brain that control the actions of the body. This, indeed, would
appear to be the primary purpose of sleep. Sleep is obviously designed
to give rest to the _material structure_—time for growth and renovation.
It is for this reason that the Will, which in the waking state directs
the motions of the structure, ceases to control it during sleep. The
Will itself wakes—for we are self-conscious in dream—but in sleep the
material mechanism does not obey the command of the Will, because itself
is sleeping.
The central and basal portions of the brain are, therefore, the seat of
sleep. Unless they sleep we do not sleep. If they sleep we sleep, even
although both brain hemispheres are at the same time wide awake.
And this raises the question, so important in the Psychology of Dream;
do the brain hemispheres, that duplex organ of the intelligence,
sleep wholly or partially, or do they continue to be awake while the
sense-brain and the body-moving brain are sleeping?
This problem can be solved only by careful examination of the phenomena
of dream. Suppose that Professor FERRIER could do with us as he did
with the monkeys and dogs—take out a portion of the brain—and it were
possible to remove altogether the middle and basal sections, leaving
the hemispheres alone in the skull, would they sleep wholly or in part
or, if awake, would they exhibit the phenomena of dream as they are now
experienced?
Contemplate, then, if you can, a duplex intelligent brain, in a state
of activity, but cut off from all communication with the external world
through the media of the senses and from all control over the body;—in
fact, an isolated, self-acting, self-contained mechanism, the organ of
intelligence and emotion.
How would it work?
First, it must be set in motion. Thus we are brought directly to the
problem “What moves the mind?” Why does _this_ particular thought or
feeling come into the mind at this moment rather than some other?
The solution commonly accepted is that ideas come by _suggestion_. This
means that ideas are, as it were, linked together and consequently that
when one idea comes it is followed by certain other ideas which at some
former time were connected with it. Probably the greater portion of the
ideas that come to us apparently without such association are suggested
by some impression brought by the senses, but received by the sensorium
unconsciously to ourselves and that thus the “train of thought” is
started.
If it be so in one waking time, when the mind is busy with a multitude of
impressions flowing in upon it from every sense—much more is it likely so
to be when the impressions made by the senses are few, as is proved by
the experience of every reader. In sleep, a slight sound falling upon the
ear will suggest a dream of roaring cannon or rattling thunder.
But the idea, once suggested, draws after it whole trains of associated
ideas, and these ideas excite the _emotions_ precisely as they would have
done had they been brought by the senses in the waking state. Thus far,
then, we learn that the faculties which produce what we call ideas and
sentiments and passions are not asleep. Some, if not all, of them are
certainly awake and as active as in waking life.
The Will, too, is not asleep, although powerless to command. In dream we
_will_ to speak and do, but the body does not obey the Will. The efforts
of the Will to command the limbs to move—as to escape from dreamed-of
danger—and the failure of the limbs to obey, are often attended with
consciousness of painful efforts made in vain.
So far the phenomena of dream are consistent with the entire of the
duplex brain organ of the intelligence being awake while the lower
portion of the brain is sleeping. Certainly it is difficult to conceive
of parts of such an organ as the two hemispheres sleeping, relaxed, and
insensible, while other parts of it are awake and active.
For, if Professor FERRIER is right, and distinct functions belong, not
only to each ganglion but to various parts of each ganglion, the brain
hemispheres, which are the material mechanism of the intelligence, must
consist of many parts having different duties. We know that anatomically
these parts, if they exist, are in intimate connection, lying closely
packed together if not actually interlacing, and it is difficult to
suppose that one part can be sleeping while its neighbour is awake,
especially as sleep is attended, if not caused, by a depletion of blood
from the fibres of the brain, retreating from the entire hemisphere and
not from parts of it.
Nevertheless, there are characteristics of Dream which appear to indicate
a suspension of activity in some parts of the intellectual mechanism.
Although perfectly conscious of the presence of the dream, we are unable
to discover that it is not real; we cannot discern incongruities, nor
recognize impossibilities. The dead of long ago come to us and we are not
amazed. We walk the waters and float in the air and are not astonished.
Nothing is too impossible to be done and nothing too monstrous to be
implicitly believed. We are, in fact, insane in dream.
What is the solution of this problem? Some faculty that corrects the
action of the mind when we are awake is certainly absent or paralysed
during dream. Something must come to us from without or operate upon the
mind within that restores us to sanity when we wake, enabling us then
to discern the false from the true, the shadow from the substance, the
impossible from the possible.
What is this absent faculty?
The solution most favoured by psychologists is that in sleep we lack the
correcting influence of the senses. The mind, they say, having nothing
wherewith to compare its own creations, necessarily accepts them as
realities; it puts implicit faith in them, however monstrous, simply
because they are presented to it as facts and in the same manner as facts
are presented when it is awake.
I confess to great doubt if this explanation be adequate. True, that we
believe the impossibilities of our dreams _to be_ because they appear
to the mind to be. But that does not explain the strange absence of
perplexity and wonder when we witness (as we then verily believe) the
dead alive, the distant near, and impossible things performed with ease.
In our waking state, if the like dreams come into the mind at some moment
of idleness, they are never mistaken for realities. Reason rejects them,
and if entertained for awhile it is only as a pleasant vision. Nor is
the problem solved by the suggested slumber of the reasoning faculties.
These are not always asleep in dream, for often we dream that we are
exercising them readily and effectively. The power of reasoning employed
in dream is, however, very limited. It can exercise itself on the subject
of the dream, but not upon its surroundings. It is not uncommon for the
sleeper to dream that he is making a speech or preaching a sermon. The
discourse is argumentative and logical. It is not merely that he dreams
he is logical; he is so in fact, for the dream is often remembered after
waking and no flaw is found in the argument. Nevertheless, at the moment
that our reasoning faculties are constructing a strictly logical and
perfectly rational discourse, they are unable to inform us—as when we are
awake they would have done—that the place where we suppose the speech to
be spoken, the occurrence and the occasion, are not merely fictitious but
attended with the most palpable absurdities.
Looking, then, at one hemisphere only of the brain, it is difficult to
infer that one or more parts of it are sleeping while the other parts
are awake. May the solution of the problem be found in the fact that
we have _two_ brains? Can it be that in the condition of dream one
hemisphere—that is, one mind—is awake while the other is asleep?
To answer this it is necessary to inquire what is the action of _two_
brains working, like the two eyes, together or separately?
For the common purposes of life the two brains act in complete accord.
Like the two nerves of vision, they co-ordinate. Either can act alone
for the ordinary uses of existence, just as one eye will do the usual
work of sight. But as we see more perfectly, extensively, and roundly
with two eyes than with one—so it may be reasonably concluded that we
think more truly and clearly, and feel more strongly, when the two brains
act together than when one is working alone. The faculty of _comparison_
is one of the most important of the mental powers, for it is the basis of
accurate knowledge. But it is doubtful if this faculty can do its work in
one brain unless co-ordinated with the same faculty in the other brain.
Unlike the other mental faculties, “comparison” can exercise itself
only upon _two_ ideas. Its very purpose is to make us conscious of the
resemblances and differences between any two ideas presented to it. All
mental processes are successive—that is to say, no two mental actions
are performed by the same mental faculty at the same instant of time.
Consequently, the faculty of comparison cannot exercise itself without
having before it _two_ ideas to contrast. As one brain can present only
one idea at any one moment, one brain cannot provide the materials
wherewith comparison can work. The process of comparison cannot therefore
be effected without the aid of the other brain. This, in healthy waking
life, is done instantly, perfectly and unconsciously, by means of the
power of co-ordination possessed by the two hemispheres.
Such being the action of the waking brain, does sleep present any
conditions that might be explained in like manner? Suppose the state of
dream to be the slumber of one hemisphere only, the other being awake.
May not this solve the problem?
In dream we believe shadows to be substances, ideas to be things,
incongruities to be natural, and impossibilities to be realities; and so
believing, we have no sense of surprise and reason is not shocked.
Nothing of these results presents itself when we are awake. Why?
Waking, the faculty of _Comparison_ is enabled to do its work. It
compares the idea with the reality, the shadow with the substance, the
dream within with the impression without, the present picture of the
mind with the stored knowledge of the past. The differences being thus
discovered, the mind dismisses them as being the mere visions that they
are.
The mental operation is performed somewhat in this manner. Two ideas are
present in the mind, which compares them and traces their resemblances
and differences. The sense-borne idea being thus brought face to face, as
it were, with the brain-born idea, the distinction is discovered, and the
latter is relegated to the limbo of visions, the former is accepted as a
reality and made the basis of action.
But inasmuch as two ideas cannot be presented at the same instant of
time by one brain hemisphere, the presence of the two ideas requisite
to the process of comparison can be had only by the combined action of
both hemispheres. Hence the usual inability of persons afflicted with
hemiplegia to compare or reason accurately.
If the action of the faculty of comparison were paralysed, we should
dream when awake. The suspension of the action of this faculty in dream
would suffice to account for the accepted incongruities of dream, without
assuming the sleep of the entire hemisphere.
But, as observed above, it is difficult to assume the slumber of one
mental faculty alone, packed as all are among many with which they are
intimately united. It is more probable that in dream the entire of one
hemisphere sleeps. The facts are in accordance with such a suggestion.
But, however this may be, it does not disturb the conclusion, that the
seat of sleep is in the ganglia at the base of the brain. That portion
of the brain which directs the motions of the body sleeps always. Sleep
reigns more or less perfectly in the portions of the brain that receive
the impressions of the senses. Sleep is very partial in the cerebrum, the
duplex organ of the intelligence, and probably—(for it is as yet only
conjectural)—partial sleep prevails there, if at all, by the contrivance
of slumber by one hemisphere while the other is awake.
Such being the _Physiology_ of Dream—so far as science has yet succeeded
in tracing it—we proceed now to investigate its _Psychology_.
[1] _The Functions of the Brain._ By DAVID FERRIER, M.D., F.R.S. London:
Smith, Elder, & Co., 1876.