Abstract

Theta oscillations (4-8 Hz) are a prominent electrophysiological feature of rapid-eye move- ment (REM) sleep. Theta activity during REM sleep has been linked to memory consolidation; however, the role of cortical theta oscillations in this process remains unclear. Interestingly, theta rhythms are not exclusive to REM sleep but also appear in frontal regions during resting wakefulness and working memory tasks. To advance our understanding of human REM sleep and the mechanisms that support memory processing, a spatially resolved, whole-brain char- acterisation of REM oscillatory activity is essential. Magnetoencephalography (MEG) offers high temporal and spatial resolution, making it ideal for examining the topographic distribu- tion of theta oscillations in REM sleep. In this study, we recorded electroencephalography (EEG)/MEG data during overnight sleep in 10 healthy subjects. We also analysed a separate MEG/EEG data of 17 healthy subjects who performed a working memory task. Our aims were to characterise the spatio-temporal patterns of theta-band activity during REM sleep by 1) dis- tinguishing theta from the overlapping alpha (8-12 Hz) network, 2) comparing REM and non- rapid-eye movement (NREM) sleep oscillatory activity, and 3) evaluating similarities between REM and working memory task theta patterns. Our results show theta activity in frontal mid- line regions is best observed within a focused 5-7 Hz range, separating it from occipital alpha activity. Theta-band activity was greater in REM sleep compared to NREM in frontal-central, parietal, temporal, and subcortical regions. Theta topographies during the working memory task correlated positively with phasic REM sleep. These results enhance our understanding of REM sleep physiology and suggest future research targets for learning and memory roles.