On the psychophysiology of dreaming: a sensory image--free association hypothesis of the dream process.

A psychophysiological hypothesis of the dream process during REM sleep called "a sensory image-free association hypothesis" is proposed. It is assumed that a state with a sustained EEG pattern of drowsiness (non-REM stage-1) and muscle atonia produces a stream of disorganized and vague thinking as a background mentation during the REM sleep. The phasic excitation of the brain occurring concurrently with the burst of rapid eye movements (REMs) activates the hippocampal-neocortical memory system and draws out sensory images from the memory reservoir of the brain. The dreamer makes a freely organized association about the successive sensory images and makes up a dream story. This hypothesis is compatible not only with the recent neurophysiological findings but also with traditional psychological interpretation of the dream content.