8 . Hypnosis is the name applied to certain states related to sleep and dreams and produced by means of certain definite psychical agencies. Consciousness is here generally in a condition halfway between waking and sleeping. The main cause of hypnosis is suggestion, that is, the communi- [p. 273] cation of an idea strong in affective tone. This generally comes in the form of a command from some other person (outward suggestion), but may sometimes be produced by the subject himself, when it is called autosuggestion. The command or resolution to sleep, to make certain movements, to see objects not present or not to see objects that are present, etc., -- these are the most frequent suggestions. Monotonous stimuli, especially tactual stimuli are helpful auxiliaries. Then, too, there is a certain disposition of the nervous system of still unknown character, which is necessary for the rise of the hypnotic state and is increased when the state is repeatedly produced.
The first symptom of hypnosis is the more or less complete inhibition of volition, connected with a concentration of the attention on one thing, generally the commands of the hypnotizer (automatism). The subject not only sleeps at command, but retains in this state any position that is given him, however unnatural (hypnotic catalepsy).
If the sleep becomes still deeper the subject carries out movements as directed, to all appearances automatically, and shows that ideas suggested to him appear like real objects (somnambulism). In this last state it is possible to give either motor or sensory suggestions to go into effect when the subject awakes, or even at some later time (terminal suggestions).
The phenomena that accompany such "posthypnotic effects" render it probable that the latter are due either to a partial persistence of the hypnosis or (in the case of terminal suggestions) to a renewal of the hypnotic state.
9. It appears from all these phenomena that sleep and hypnosis are related states, differing only in that their mode of origin is different. They have as common characteristics the inhibition of volition, which permits only passive apperception, and a disposition toward aroused excitability in [p. 274] the sensory centres that brings about an assimilation of the sense-impressions which results in hallucinations.
The characteristics that distinguish them are the complete inhibition of volition in sleep, especially of the motor functions, and the concentration in hypnosis of the passive attention on one thing. This concentration is conditioned by suggestion and is at the same time favorable to the reception of further suggestions. Still, these differences are not absolute, for in sleep-walking the will is not completely inhibited, while on the other hand it is inhibited in the first lethargic stages of hypnosis just as in ordinary sleep.
Sleep, dreams, and hypnosis are, accordingly, in all probability, essentially the same in their psychophysical conditions.
These conditions are specially modified dispositions to sensational and volitional reactions, and can therefore, like all such dispositions, be explained on their physiological side only by assuming changes in the activity of certain central regions. These changes have not yet been investigation directly. Still, we may assume from the psychological symptoms that they consist in the inhibition of the activity in the regions connected with processes of volition and attention, and in the increase in the excitability of sensory centres.
9a. It is then, strictly speaking, a physiological problem to formulate a theory of sleep, dreams, and hypnosis. Apart from the general assumption based on psychological symptoms, of an inhibition of activity in certain parts of the cerebral cortex, and increase in the activity of other parts, we can apply only .one general neurological principle with any degree of probability. That is the principle of compensation of functions, according to which the inhibition of the activity of one region is always connected with an increase in the activity of the others interrelated with it. This interrelation may be either direct, neurodynamic, or indirect, vasomotoric . The first is probably due to the fact that energy which accumulates in one region as the [p. 275] result of inhibition, is discharged through the connecting fibres into other central regions.
The second is due to contraction of the capillaries as a result of inhibition and a compensating dilation of the blood-vessels in other regions. The increased blood supply due to this dilation is in turn attended by an increase in the activity of the region in question.
Dreams and hypnosis are often made the subjects of mystical and fanciful hypotheses, in some cases even by psychologists.
We hear of increased mental activity in dreams and of influence of mind on minds at a distance in dreams and hypnosis. Especially hypnotism has been used in modern times, in this way, to support superstitious spiritualistic ideas. In connection with "animal magnetism", which may be completely explained by the theory of hypnosis and suggestion, and in connection with "somnambulism", there are a great many cases of self-deception and intentional humbug.
In reality all that can stand the light of thorough examination in these phenomena is in general readily explicable on psychological and physiological grounds; what is not explicable in this way has always proved on closer examination to be superstitious self-deception or intentional fraud.
[ 1] The expression "illusions of fancy" is used when this class of illusions is to be distinguished from the sense-illusions that appear in the normal state of consciousness, as, for example, the radiating for in of the stars, which is due to the refraction of light in the crystalline lens, or the varying apparent size of the sun or moon at the horizon and at the zenith.