EEG oscillations during sleep and dream recall: state- or trait-like individual differences?

Dream recall is predicted by theta (5-8 Hz) EEG oscillations over frontal regions just before awakening, paralleling the role of theta activity in successful episodic memory retrieval during wakefulness. This continuity suggests shared neurophysiological mechanisms between encoding and retrieval of episodic memories across sleep and wakefulness. REM sleep shows limbic activation and prefrontal deactivation, which may explain emotional dream content. Amygdala and hippocampus morphoanatomical measures predict dream bizarreness, vividness, and emotional load. Existing evidence cannot definitively determine whether this theta-dream recall relation reflects state- or trait-like differences.

Study at a glance

Abstract

Dreaming represents a peculiar form of cognitive activity during sleep. On the basis of the well-known relationship between sleep and memory, there has been a growing interest in the predictive role of human brain activity during sleep on dream recall. Neuroimaging studies indicate that rapid eye movement (REM) sleep is characterized by limbic activation and prefrontal cortex deactivation. This pattern could explain the presence of emotional contents in dream reports. Furthermore, the morphoanatomical measures of amygdala and hippocampus predict some features of dream contents (bizarreness, vividness, and emotional load). More relevant for a general view of dreaming mechanisms, empirical data from neuropsychological and electroencephalographic (EEG) studies support the hypothesis that there is a sort of continuity between the neurophysiological mechanisms of encoding and retrieval of episodic memories across sleep and wakefulness. A notable overlap between the electrophysiological mechanisms underlying emotional memory formation and some peculiar EEG features of REM sleep has been suggested. In particular, theta (5-8 Hz) EEG oscillations on frontal regions in the pre-awakening sleep are predictive of dream recall, which parallels the predictive relation during wakefulness between theta activity and successful retrieval of episodic memory. Although some observations support an interpretation more in terms of an intraindividual than interindividual mechanism, the existing empirical evidence still precludes from definitely disentangling if this relation is explained by state- or trait-like differences.