Copyright © 1977 by J. Allan Hobson and Hoffman-La Roche Inc.

Selections from the "Black Catalog":

Dreaming is a universal human experience that occurs regularly every night during sleep.

The brain operates differently during the waking state than it does during the sleeping state. The instrument that best reveals these differences, the electroencephalograph, detects, amplifies and records electrical signals given off by the brain through electrodes placed on the scalp. A record of these signals, or brain waves, is referred to as an EEG (electroencephalogram).

In the early 1950's, a discovery was made that significantly changed the course of sleep and dream research. The discovery was that at regular intervals during sleep, the eyes of a person move rapidly back and forth beneath the eyelids. Brain electrical activity associated with these rapid eye movements was strikingly similar to that of an awake EEG; yet, the subjects in whom this phenomenon was observed were clearly asleep.

Subsequently, it was learned that if a subject was awakened during one of these periods of rapid eye movements, or REM episodes, he frequently reported he had been dreaming. Often he would give long, clear, detailed accounts of his dream.

Thus, the discovery of REM revealed that there were two kinds of sleep that alternate rhythmically with each other throughout the night. One kind of sleep, now referred to as REM, is the sleep during which most dreaming takes place.

The other kind of sleep that alternates with REM is called nonREM or NREM. It is distinctly different from REM sleep and is usually described in terms of its four stages defined by specific EEG characteristics.

The cyclic nature of sleep, as revealed by the human EEG, strongly suggests that it may be under the control of a master biologic clock that governs the 24-hour alternation between waking and sleeping characteristic of all mammals. REM sleep, then, may be regarded as a mini-rhythm within the 24-hour circadian cycle. Behavioral studies in which sleeping subjects were photographed at fixed intervals throughout the night support this notion. Body movements are not seen in the photographs that correspond to Stages III and IV of NREM sleep. A major postural change may occur, however, during the transition to REM and again at the termination of REM, when the NREM phase of the sleep cycle is resumed.

Today there is abundant evidence pointing to a group of giant cells in the pontine reticular formation of the brainstem as the neurons most likely to be responsible for the generation of REM sleep. Immediately prior to and during each REM episode, the neural activity of these giant cells greatly increases.

Dreams occur as a result of periodic brain activation during sleep; they are an integral part of a built-in physiologic process. The nature of dreams is determined by the nature of brain activation: neural activity generated in one part of the brain (the giant pontine cells) is transmitted to another part of the brain (the cerebral cortex). The cerebral cortex contains memories of events perceived during consciousness; as these memories are randomly evoked by neural activity coming from the giant pontine cells, a dream is composed. Thus, the strangeness of dreams may simply be a reflection of the cerebral cortex putting together the most coherent story possible from a series of evoked, but not necessarily related, memories.