the physiology of dreams. A brief reference to the definition of sleep
must suffice to indicate what is signified by the process. Sleep does
not wholly arrest the functions of the brain. A certain amount of
projection into the field of consciousness seems to continue even
during the most perfect repose, and the ideas thus aroused form the
material of our dreams. Our waking hours are occupied with the ideas
and with the associated trains of thought that are presented in
consciousness through the action of our several senses. As a
consequence of the harmonious function of these senses, correcting and
supplementing each other, a continuous process of logical thought is
maintained. But along with the procession of ideas which are
distinctly conceived by the mind, the field of consciousness is also
invaded by a cloud of half-formed perceptions that are too imperfect
and too fleeting to occupy the attention. As in the act of sight,
though the periphery of the visual field is clouded with a whole world
of objects dimly perceived without arresting particular attention, the
centre of that field alone presents a clear image before the brain, so
the eye of the mind perceives clearly only a few of the impressions
which enter the sphere of consciousness. These neglected perceptions,
however, are none the less the result of abiding impressions graven in
the substance of the brain, from which, through the action of memory,
they may at any favorable opportunity re-enter consciousness. It is
well known that a suspension of the functions of any portion of the
nervous apparatus tends to increase the energy of the remaining
organs; consequently, it becomes highly probable that with the arrest
of external perception in sleep the activity of certain portions of
the brain must be considerably exalted, so that the impressions which
they have previously registered may now more clearly reach the seat of
consciousness. The probability of this hypothesis is greatly
strengthened by numerous facts that lie open to observation. During
the first moments that succeed the closing of the eyes mental activity
and the power of attention are not diminished, but are rather
increased. As the controlling influence of the cerebrum is withdrawn
the reflex energy of the spinal cord becomes temporarily exalted.
Witness the paroxysms of cough that sometimes harass a sleeping child
who has scarcely coughed at all during his waking hours. Witness the
voiding of urine in the bed by nervous children during the early hours
of sleep. Witness the phenomena of night-terrors, which always occur
at the time of night when sleep should be most tranquil.
It appears, therefore, that the harmonious activity of all parts of
the nervous system is indispensable to the highest exercise of the
conscious mind. Healthy intellectual life is the perfectly-balanced
outcome of the complex polygon of forces which has its seat within the
brain. But the suppression of certain lines of this polygon does not
suppress life, nor does it necessarily destroy consciousness. It only
occasions a redistribution of force and a proportionate narrowing of
the stream of related {370} ideas. Since the suppression just
mentioned is not an absolute quantity, but a variable factor, the
polygon of forces in the brain and the corresponding succession of
ideas in consciousness must necessarily be in a state of continual
change. Accordingly, our dreams are as variable as the clouds that
drift upon the currents of the air. As on a hot day in summer, when
the steady equatorial draught has ceased to guide the wind, we may
observe all manner of local tides in the masses of vapor which arise
from the earth, so in sleep, when the guiding influence of the senses
is withdrawn from the brain, the ideas that still arise are chiefly
dependent upon its automatic and reflex action for their origin and
association. Undisturbed by impulses from the external world, the
brain seems then more sensitive to impressions that originate within
the body. An overloaded stomach, an enfeebled heart, a turgid sexual
apparatus, or an irritable nervous ganglion may become the source of
irregular and uncompensated movements which may invade the cerebral
cortex, and may there set in motion a whole battery of mechanisms
whose influence upon consciousness would be quite unnoticed were the
external senses in full operation.
Night-Terrors.
The preceding argument will render it easy to comprehend the phenomena
of night-terrors. These are commonly observed in young children of a
highly nervous temperament before the conclusion of their second
dentition. The subjects of the disorder are generally of neurotic
descent. Insanity, hysteria, neurasthenia, epilepsy, chorea, and
nervous dyspepsia are often discovered among their near relatives. Not
infrequently they have been or will become themselves choreic.
The attack is often preceded by symptoms of indigestion, but it may
result simply from the commotion of a brain wearied by the excitement
and effort of the previous day. The little patient starts up out of an
apparently sound sleep crying with alarm, calling for his mother, and
staring wildly with every possible expression of terror. Sometimes he
springs from his couch and runs headlong into a corner or seeks to
hide under the bed, as if escaping from some frightful object. The
eyes are open, tears flow, perspiration covers the skin, there is the
greatest excitement, and the little one, convulsively clinging to its
parent, will not be quieted. Only after fifteen or twenty minutes, as
tranquillity gradually returns, does the child seem to recover the
power of recognizing his friends. Presently, however, he lies down and
falls quickly asleep, waking in the morning without the slightest
recollection of the unpleasant event.
Such paroxysms occur during the early part of the night, one or two
hours after the child has been put to bed, just at the time when,
according to the previously-quoted experiments of Kohlschütter, sleep
is passing from its maximum intensity to a lesser degree of depth.
This, then, is the time when the controlling power of the sensory
apparatus over other portions of the nervous system has already
reached its minimum. The spinal centres and those intracranial ganglia
which do not share in the full measure of this repose are therefore in
a condition of relative {371} exaltation. Disturbances of internal
organs consequently produce inordinate excitement of these waking
portions of the nervous apparatus. The morbid quality of this
excitement is attested both by the history of the patient and by the
fact that it does not arouse the whole brain. The distribution of
motion in the cerebrum is impeded, so that certain portions of the
organ remain asleep while other regions are thrown into a state of
tumultuous uproar. Disconnection of these different organs of the
nervous system, by withdrawing particular portions from the inhibitory
influence of the remaining parts, gives opportunity for violent
explosions of nervous force analogous to the convulsions of a headless
fowl or to the course of an epileptic paroxysm. Now, in sleep, in
somnambulism, in hypnotism, in delirium, in certain stages of
intoxication with alcohol or with narcotics, such ungearing of the
different nervous ganglia is more or less completely effected. In
narcotic and anæsthetic sleep besides the disassociation of ganglia
there is paresis of the nervous molecules; hence the phenomena soon
merge into insensibility and coma. But in natural sleep, in
somnambulism, or in hypnotism there is no toxic paresis; hence the
dissociated portions of the brain and nervous system, if aroused, are
in a physiological condition to dispense great stores of force. Hence
the vividness of certain dreams and the astonishing vigor of
particular nervous functions in somnambulism and hypnotism.
Somnambulism.
The phenomena of night-terrors constitute merely a special form of
somnambulism, a condition of which the mechanism, so far as the
present state of cerebral physiology will permit, has been already
suggested. The affection should not be ranked by itself as a
particular variety of disease, but should rather be considered a
violent perturbation in the cerebral organs of a neurotic subject
during the period of sleep. In ordinary dreaming the muscular
apparatus usually remains passive, even though the dream be a
nightmare or an incubus of the most terrifying character. But when the
desires and the emotions are powerfully addressed by the dream, a
certain amount of muscular movement may ensue, as when a dog barks in
his sleep, or when a child laughs upon his nurse's lap, or when a
weary soldier marches on though overpowered by sleep. One night, when
parched with thirst during a voyage at sea,[9] I saw in sleep a
sparkling fountain, by the side of which appeared a young girl holding
out a cup of cold water. Awakened by the excitement, I found myself
sitting up in bed with my right arm extended in the direction of the
tantalizing vision: my dream had merged itself in action. In like
manner, the victim of night-terrors not only moves his body, but gives
vocal expression of his feeling of apprehension and alarm. In like
manner, projecting his dream into action, a sleep-walker may arise
from his bed; he climbs out of the window and descends to the ground,
executing all manner of complicated and dangerous movements; he walks
long distances, and finally returns to his couch without waking. In
the morning no recollection of the event of the night survives. Again,
the movement {372} may be less locomotive in its character. The
intellectual faculties chiefly may be aroused, and then only such
movements are executed as may be necessary to give expression to the
mental process.
[Footnote 9: A proclivity to dreaming has often been remarked among
the consequences of partial starvation.]
Such, then, are the principal characteristics of somnambulism, a state
in which dreams are supplemented by more or less complete and
appropriate action, ordinarily without subsequent recollection of
either dream or action.
The somnambulistic dream generally occurs during or soon after the
period of deepest sleep, when the influences of the external world are
largely suppressed. Released from the control of its sensory portion,
the remainder of the brain awakes and becomes aroused to a condition
of functional exaltation. No longer distracted by the recollection of
the special senses, the attention is concentrated upon the
hallucinations which constitute the dream. In the simpler forms of
noctambulism only the automatic locomotive apparatus is awakened, and
the sleeper moves in accordance with the impressions derived from
habit aided by exaltation of the muscular sense. But in some of the
more complicated cases a certain amount of special sensibility seems
to exist. The patient is capable of exercising just that amount of
sensation which is necessary to accomplish his purpose, though blind
and deaf and insensible to every other impression. The more complete
the waking of the organs of sense, the closer the resemblance to the
condition of ecstasy in which cerebral exaltation is the prominent
feature. Accordingly, it sometimes happens that the somnambulist can
recall the events of his paroxysm.[10] In such cases the power of
recollection is due to the same conditions that control the
recollection of our ordinary dreams. We remember very imperfectly, if
at all, the dreams that occur during sound sleep, but the visions with
which sleep sometimes commences (hypnagogic hallucinations) and those
that occupy the period of morning slumber are very easily reviewed in
memory, because they are associated with impressions directly derived
from the partially-waking organs of sense. Such dreams are therefore
chiefly recalled through their association with the train of our
waking thoughts. But the dreams of somnambulism and the dreams of
night-terrors, and all other visions during profound sleep, are as
completely as possible cut off from all connection with the mental
activities which arise directly from the action of the senses. By
reason of such isolation the ordinary association of ideas affords no
help to the memory, and the dream remains in the limbo of oblivion.
[Footnote 10: A. Bertrand, _Traité du Somnambulisme_, p. 80.]
Alfred Maury expresses the opinion[11] that the principal cause of
forgetfulness of the events of somnambulism consists in the exhaustion
of the cerebral elements through the intensity of the excitement to
which they are subjected during the paroxysm. Doubtless this in
certain cases may contribute to the loss of memory, but it should be
remembered that the excitement may be relative rather than absolute.
Certain elements wake while others are asleep, and the waking cells
may be aroused to a degree far in excess of what is usual during the
sleep of the brain without attaining to the level of their diurnal
activity. The mind, undisturbed by external impressions, gives its
attention to the activity of these waking organs, and a dream with all
its consequences, somnambulic or otherwise, is the result. In other
words, the plane of consciousness, so to speak, is lowered {373}
during sleep to the level of these molecular vibrations. But when the
whole brain is again awakened after sleep the residual vibrations of
those elements which yielded the physical basis of the dream, and
which, had they occurred during the waking state, might have persisted
with energy sufficient to furnish a groundwork for recollection of the
ideas which they had originally suggested, are no longer sufficiently
energetic to be felt in consciousness. Recollection of mental states
thus generated must necessarily be impossible so long as the mind is
dependent upon the brain as its register of events. Sometimes,
however, the somnambulist, who while awake had forgotten all the
incidents of his somnambulic experience, can remember in a subsequent
paroxysm all that occurred during the preceding attack. Facts of this
kind have been observed in the waking life of certain hysterical
persons,[12] but the apparent interruptions of their personality
attach to the waking state, while in ordinary somnambulism it is only
in sleep that the alternations of memory and forgetfulness occur. A
similar recollection of previous visions is sometimes experienced in
dreams, showing the close relation that subsists between the dreams of
sleep and of somnambulism. The bond of association between these
events thus isolated in time must be sought in a renewal of like
conditions of the brain during the successive periods of somnambulic
exaltation. We must suppose that the molecules which were in a state
of functional excitement during the first paroxysm are again aroused
in like manner after a period of waking quiescence. If, during sleep,
their movements, though of an exalted character, have only just
sufficed to arouse consciousness in the form of a dream, it would not
be probable that during the phase of comparative inactivity which
supervenes when the whole brain is awake their residual motion could
disturb the sphere of consciousness. Hence the time occupied by their
somnambulic vigor must remain a blank in memory during the waking
state. But when the original state of exaltation has been reproduced
by a second period of disorder, if the same molecular movements be in
any way renewed, the conditions of memory are fulfilled; consciousness
is once more aroused as before, and the patient remembers the dream or
the events of the previous attack.
[Footnote 11: _Le Sommeil et les Rêves_, p. 226.]
[Footnote 12: _Annales Medico-psychologiques_, 5e Série, t. xvi. p. 5,
1876.]
Artificial Somnambulism, or Hypnotism.
The phenomena which have now been passed in review are of apparently
spontaneous origin during the ordinary period of sleep. But from the
remotest antiquity it has been known that certain persons may be
thrown into an artificial sleep which closely resembles the condition
of the somnambulist. During the persistence of this state certain
portions of the nervous system become utterly insensible to external
impressions, while other portions acquire an exalted degree of
sensibility. The subject of the experiment can then by special methods
be placed in such relations with other waking individuals that his
surviving sensations, mental processes, and physical actions shall be
no longer regulated by his own volition, but by the will of another.
Such susceptibility is not common to all persons. About 20 per cent.
of the ordinary population is, by some observers, considered capable
of experiencing this condition. {374} Heidenhain,[13] experimenting
upon a class of medical students, found only one in twelve who was
thus susceptible. Charcot, whose field of observation covers the
inmates of the Salpêtrière Hospital, finds the best exemplars of the
hypnotic state among the hystero-epileptic females in that asylum. To
these experimenters we are largely indebted for the most extended
scientific observation of the phenomena of hypnotism, giving precision
and publicity to the knowledge of facts which, though equally well
known within a narrow circle of investigation[14] during the earlier
decades of the present century, have been compelled to await the
development of cerebral physiology before their full significance
could become apparent to the mass of the medical profession.
[Footnote 13: _Animal Magnetism: Physiological Observations_, by
Rudolph Heidenhain.]
[Footnote 14: Braid, _Neuro-hypnology considered in Relation with
Animal Magnetism_, London, 1843.]
The antecedent condition most favorable to the production of the
hypnotic state is a highly unstable constitution of the nervous
system. For this reason the larger number of qualified subjects is
furnished by the female sex, especially by those who possess the
hysterical temperament. Frequent repetition of hypnotic exercises
renders the subject still more susceptible. Heidenhain was at first
inclined to believe that such experiences were not prejudicial to the
health of the subject, but the observation of Harting in the
University of Utrecht, and of Milne-Edwards in Paris,[15] have
demonstrated danger to the health of animals subjected to similar
experiments. It is easy to discover, in the various clinical
narratives published by Charcot and his pupils,[16] evidence that
hysterical patients often manifest considerable exhaustion after
hypnotic exhibitions; consequently, it cannot be admitted that the
practice is devoid of risk to the health of the individual.
[Footnote 15: _Lancet_, July 29, 1882, p. 164.]
[Footnote 16: Paul Richer, _L'hystéro-Epilepsie_, Paris, 1881; _Le
Progrès médical_, 1881-82.]
Numerous methods of inducing the hypnotic state have been employed by
different experimenters. The greater number consist in modifications
of the sensory impulses derived from the periphery of the body. Gentle
pressure upon the closed eyelids; convergence of the axes of the
eyeballs upon some object nearer than the proper focal distance of the
eyes; fatigue of the retina by gazing upon any brilliant or luminous
object; monotonous excitation or sudden surprise of the auditory
nerve; various impressions through gentle friction or pressure upon
different regions of the body,—all these are capable of inducing
hypnotic sleep. An appeal to the imagination, or even the mere attempt
to abnegate the possibility of vigorous thought by confining the
attention to the most trivial of things, sometimes suffices to produce
the desired phenomenon. Thus, Heidenhain put one of his students to
sleep at a distance by merely informing him beforehand that at a
certain hour he would hypnotize him in his absence. The state of
ecstatic meditation into which the monks of Mount Athos plunged
themselves by the practice of omphaloscopy affords an illustration of
the hypnotic effects of concentrated attention.
The duration of hypnotic sleep is exceedingly variable, but if left to
himself the patient usually wakes spontaneously, without recollection
of anything that has happened. If it be desirable to awaken him before
the natural termination of the paroxysm, consciousness can be restored
by almost any sudden and energetic appeal to the senses, such as an
{375} electric shock, a sudden illumination of the eye with vivid
light, or a sharp puff of air upon the face.
According to Charcot,[17] three principal types may be remarked among
the hysterical subjects upon whom he experimented: (1) the cataleptic,
(2) the lethargic, and (3) the somnambulic. Of these, the first may be
developed primarily by any abrupt and powerful impression upon an
organ of sense, as a bright light or a loud noise (gong). Fixing the
eyes upon some object may produce the same result. Dumontpallier, for
example, has reported the case of a young woman[18] who accidentally
hypnotized herself by gazing at her own image in the mirror before
which she was dressing her hair. The cataleptic state may also be
secondarily induced by merely opening the eyes of a patient in whom a
condition of hypnotic lethargy has been previously developed. If only
one eye is thus opened, the corresponding side of the body alone
becomes cataleptic. Closing the eyes causes the disappearance of this
symptom, with complete restoration of the purely lethargic state.
During the cataleptic condition the several tendinous reflexes
disappear, neuro-muscular hyperexcitability ceases; the skin becomes
insensible, but the special senses, particularly those of sight and
hearing, maintain a partial activity. In this state the senses may
become avenues of suggestion for the production of muscular movements,
but if left to themselves the limbs remain motionless.
[Footnote 17: _Le Progrès médical_, Feb. 18, 1882, p. 124.]
[Footnote 18: _Ibid._, March 25, 1882, p. 223.]
The lethargic state may be induced by simply closing the eyes of the
patient or by causing him to fix his gaze upon some definite object.
The paroxysm begins with a deep inspiration causing a peculiar
laryngeal sound, followed by the appearance of a little foam on the
lips. The eyelids are either wholly or partially closed, and are in a
state of continual tremulous motion. The eyeballs are generally turned
upward and inward. The muscles are completely relaxed. The tendinous
reflexes are exaggerated; pressure over a muscle or upon a nerve
arouses a peculiar contraction of synergic muscles and of groups of
muscles which are supplied by the excited nerve-trunk. The facial
muscles, however, do not thus become contractured: they merely
contract during the application of the stimulus. If the lethargic
patient be rendered cataleptic by opening the eyes, these contractions
persist even after awaking, and they can only be dispelled by renewing
the lethargic state before resorting to pressure upon the antagonistic
muscles—a process by which the contractures peculiar to this species
of lethargy may always be annulled. By the approach of a magnet to a
contractured limb the phenomenon may be completely transferred to the
corresponding muscles upon the opposite side of the body. If upon a
limb of a lethargic patient who has been rendered cataleptic by
opening the eyes an Esmarch's band be applied, pressure over the
bloodless muscles excites no contracture until the band is removed. A
contracture is then developed, and it may even be transferred to the
opposite limb by the approach of a magnet. To this phenomenon has been
applied the term latent contracture.
The extraordinary muscular excitability manifested by these hysterical
hypnotics is further illustrated by an observation recorded by
Dumontpallier.[19] If one end of a caoutchouc tube one centimeter in
diameter and {376} five or six meters in length be applied over a
muscle in the leg, and if the other end be in like manner connected
with a watch, every movement of the second hand will be followed by a
slight contraction in the muscle. The same result follows connection
with the wire of a telephone, and if a microphone be introduced into
the circuit the incidence of a ray of artificial light upon the
instrument, or even its glancing reflection from the eye, will arouse
a responsive muscular contraction. Charcot has sometimes observed
muscular contractions upon the opposite side of the body when a mild
galvanic current was applied to the parietal surface of the head.
During the manifestation of muscular hyperexcitability there is
complete analgesia, but the senses of sight and hearing seem to
preserve some degree of activity. The patient, however, does not
manifest any susceptibility to influence by suggestion.
[Footnote 19: _Ibid._, Jan. 14, 1882, p. 25.]