Local aspects of sleep and wakefulness

Abstract

Slow waves, the hallmark of NREM (Non Rapid Eye Movement) sleep, are not uniformly distributed across the cortical surface, but can occur locally and asynchronously across brain regions. Their regional distribution and amplitude is affected by brain maturation and by time spent awake, mediated in part by experience-dependent changes in synaptic strength. Recent studies have shown that local low-frequency oscillations (<10Hz) can also occur in REM sleep and during wakefulness, leading to region-specific cognitive errors. Local decreases and increases of slow wave activity in posterior brain regions have been linked to the occurrence of dreaming and to unconscious sleep, respectively. Finally, the coexistence of local sleep-like and wake-like patterns in different brain areas is characteristic of several sleep disorders and may offer insights into these conditions.

Figure 1

Local aspects of sleep. (a) Example of local sleep slow waves in human NREM sleep occurring at different times in left and right posterior cingulate cortices, where 100% of units are locked to slow waves. Rows (top to bottom) depict activity in scalp EEG (Cz, red), left posterior cingulate, and right posterior cingulate. Blue, depth EEG; green, MUA; black lines, single-unit spikes. White shadings mark local OFF periods (reproduced, with permission, from Ref. [11]). (b) Laminar recordings revealing slow waves in layer 3 and 4 of mouse primary cortex in REM sleep (reproduced, with permission, from Ref. [14^••]). (c) Representative examples of local theta waves (boxed) occurring in left frontal derivations (top panel) after prolonged audio-book (AB) listening and in parietal derivations after playing with a driving simulator game for extended periods of time. Red circles indicate the negative peaks of theta waves detected in each EEG trace (reproduced, with permission, from Ref. [19^•]).