[77] Herbert Wright, who finds that in children night-terrors are apt to be associated with somnambulism, points out that when the somnambulism replaces the night-terrors it leaves no memory behind (British Medical Journal, 19th August 1899, p. 465). An interesting study of movement in normal and morbid sleep has been contributed by Segre ('Contributo alla Conoscenza dei Movimenti del Sonno,' Archivio di Psichiatria, 1907, fasc. 1.).
[78] This question is, for instance, asked by F. H. Bradley ('On the Failure of Movement in Dreams,' Mind, 1894, p. 373). The explanation he prefers is that the dream vision is out of relation to the very dimly conscious actual position of the body, so that the information necessary to complete the idea of the movement is wanting. Only as regards the less complicated movements of lips, tongue, or finger, when the motor idea is in harmony with the actual position of the body movements, does movement take place. We have no means of distinguishing the real world from the world of our vision; 'our images thus move naturally to realise themselves in the world of our real limbs. But the world and its arrangement is for the moment out of connection with our ideas, and hence the attempt at motion for the most part must fail.' It is quite true that this conflict is an important factor in dreaming, but it fails to apply to the large number of movements which we dream of actually doing.
[79] The action of some drugs produces a state in this respect resembling that which prevails in dreams. 'Under the influence of a large dose of haschisch,' Professor Stout remarks (Analytic Psychology, vol. i. p. 14), 'I found myself totally unable to distinguish between what I actually did and saw, and what I merely thought about.' Not only are the motor and sensory activities relatively dormant, but the central activity is perfectly able, and content, to dispense with their services. 'Thought,' as Jastrow says (Fact and Fable in Psychology, p. 386), 'is but more or less successfully suppressed action.'
[80] This seems to me to be the answer to the question, asked by Freud, (Die Traumdeutung, p. 227), why we do not always dream of inhibited movement. Freud considers that the idea of inhibited movement, when it occurs in dreams, has no relation to the actual condition of the dreamer's nervous system, but is simply an ideatory symbol of an erotic wish that is no longer capable of fulfilment. But it is certain that sleep is not always at the same depth and that the various nervous groups are not always equally asleep. A dream arising on the basis of partial and imperfect sleep can scarcely fail to lead to the attempt at actual movement and the more or less complete inhibition of that movement, presenting a struggle which is often visible to the onlooker, and is not purely ideatory.
[81] This explanation, based on the depth and kind of the sleep, is entirely distinct from the theory of Aliotta (Il Pensiero e la Personalità nei Sogni, 1905), who believes that dreamers differ according to their nervous type, the person of visual type assisting passively at the spectacle of his dreams, while the person of motor type takes actual part in them. I have no evidence of this, though I believe that dreams differ in accordance with the dreamer's personal type.
[82] Dugald Stewart argued that there is loss of control over the muscular system during sleep, and the body, therefore, is not subject to our command; volition is present but it cannot influence the limbs. Hammond argued, on the contrary, that Stewart was quite wrong; the reason why voluntary movements are not performed during sleep is, he said, that volition is suspended. 'We do not will our actions when we are asleep. We imagine that we do, and that is all' (Treatise on Insanity, p. 205). Dugald Stewart and Hammond, though their phraseology may have been too metaphysical, were, from the standpoint I have adopted, both maintaining tenable positions. In one type of dream, we imagine we easily achieve all sorts of difficult and complicated actions, but in reality we make no movement; the ease and rapidity with which the mental machine moves is due to the fact that it is ungeared, and is effecting no work at all. In the other type of dream we make violent but inadequate efforts at movement and only partially succeed; the machine is partially geared, in a state intermediate between deep sleep and the waking condition.
[83] Jacques le Lorrain, Revue Philosophique, July 1895.
[84] The systematic megalomania of insanity can, however, have its rise in dreams; Régis and Lalanne (International Medical Congress, 1900; Proceedings, Section de Psychiatrie, p. 227) met within a short period with four cases in which this had taken place.
[85] This indeed seems to have been recognised by Wundt, who regards a 'functional rest of the sensory centres and of the apperception centre,' resulting in heightened latent energy which lends unusual strength to excitations, as a secondary condition of the dream state. Külpe (Outline of Psychology, p. 212) argues that the existence of vivid dreams shows that fatigue with its diminished associability fails to affect the central sensations themselves; this increased excitability resulting from dissociation may itself, however, be regarded as a symptom of fatigue; hyperaesthesia and anaesthesia are alike signs of exhaustion.
[86] The exhaustion sometimes felt on awaking from a dream perhaps testifies to its emotional potency. Delboeuf states that a friend of his experienced a dream so terrible in its emotional strain that on awaking his black hair was found to have turned completely white.