Although sleepwalking (somnambulism) affects up to 4% of adults, its pathophysiology remains poorly understood. Sleepwalking can be preceded by fluctuations in slow-wave sleep EEG signals, but the significance of these pre-episode changes remains unknown and methods based on EEG functional connectivity have yet to be used to better comprehend the disorder.
We investigated the sleep EEG of 27 adult sleepwalkers (mean age: 29 ± 7.6 years) who experienced a somnambulistic episode during slow-wave sleep. The 20-sec segment of sleep EEG immediately preceding each patient’s episode was compared with the 20-sec segment occurring two minutes prior to episode onset.
Results from spectral analyses revealed increased delta and theta spectral power in the 20 sec preceding the episodes’ onset as compared to the 20 sec occurring 2 minutes before the episodes. The imaginary part of the coherence immediately prior to episode onset revealed (i) decreased delta EEG functional connectivity in parietal and occipital regions, (ii) increased alpha connectivity over a fronto-parietal network, and (iii) increased beta connectivity involving symmetric inter-hemispheric networks implicating frontotemporal, parietal and occipital areas.
Taken together, these modifications in EEG functional connectivity suggest that somnambulistic episodes are preceded by brain processes characterized by the co-existence of arousal and deep sleep.