Somnambulism
3 of the 6 encyclopedias on this shelf carry an entry for Somnambulism. All 3 are reproduced below, so you can see where they agree and where they differ.
An Encyclopaedia of Occultism (1920)
(Latin, somnus, sleep, and ambulare, to walk.) The condition in which walking, talking, and actions of a more complicated character are performed during sleep, without the agent's consciousness or after recollection. The somnambulist may have his eyes closed, and ears deaf to auditory impressions or sense impressions, without waking in him any gleam of consciousness. This may have some effect in rousing new trains of association. and suggesting a new line of action. It is suggested that the sleep-walker may see only a mental picture of what he is doing that is, a dream-and not the objective reality, and certain experimental tests have proved that this occurs in some cases at least. Somnambulism admits of many varying degrees. Its mildest form is typified in the inarticulate murmurings or vague gestures of a dreaming child, while in the most extreme cases where all the senses are active, and the actions apparently as purposive as in the normal waking state, it borders on the condition of spontaneous hypnotism. Indeed its affinity with hypnosis was early recognised, when the hypnotic subjects of the magnetists were designated somnambules. It is remarkable that somnambulists may walk in dangerous paths with perfect safety, but if they are suddenly awakened they are liable to fall. Spontaneous somnambulism generally indicates some morbid tendency of the nervous system, since, as a rule, only in some abnormal state could the dream ideas exercise so exciting an influence on the brain as to rouse to activity centres normally controlling voluntary movements.
Collier's New Encyclopedia (1921)
literally, the act or practice of walking in sleep; but, in a wider and more usual sense, that state of sleep or unconsciousness in which the mind retains its power over the limbs, but has no influence over its own thoughts.
Aiton's Encyclopedia (1910)
walking while asleep. See Sleep
What Has Changed in the Last Century
The 1920 Encyclopaedia of Occultism guessed that the sleep-walker acts out "a mental picture of what he is doing" — a dream — and that the habit "generally indicates some morbid tendency of the nervous system." Both points fell away once brain waves could be recorded: after the identification of REM sleep by Aserinsky and Kleitman in 1953, EEG studies showed that sleepwalking arises out of deep non-REM slow-wave sleep, usually in the first hours of the night, when vivid dreaming is not occurring. It is now classed as a parasomnia, a disorder of partial arousal rather than of dreaming, and is regarded as common and largely benign — affecting a large minority of children, most of whom grow out of it — with a strong hereditary component. The old link to hypnotism, which had the magnetists calling their subjects "somnambules," is gone entirely; a modern curiosity instead is the handful of criminal trials in which sleepwalking has been offered as a defence.
Written for this edition, 2026.