Abstract
Sleep is indispensable for humans to maintain normal life activities. Sex and individual differences in sleep patterns and quality of sleep cannot be ignored. Nevertheless, the overall population generalities and sex- or individual- differences in cerebral cortical functional connectivity (FC) during sleep have not been well described. Here, we evaluated the characteristic patterns of FC based on whole-night sleep electroencephalography (EEG) recordings. An improved weighted phase lag index (WPLI) algorithm was applied to obtain the FC in delta (0.5-4Hz), theta (4-8Hz), alpha (8-12Hz) and beta band (12-32Hz). FC strength, short-term stability and inter-regional imbalance of FC were studied. We found that the variations in FC-related parameters among sleep stages had overall population commonalities, and these parameters also showed stage- and frequency band-dependent sex differences. With the deepening of no-rapid eye movement (NREM), increased delta and beta FC strength were observed. Rapid eye movement (REM) showed weaker FC strength, higher FC stability, and higher anterior-posterior FC anisotropy than NREM in beta band. Meanwhile, females exhibited higher sleep EEG synchronization and higher delta FC stability in deep NREM sleep than males. Moreover, the dominant hemisphere in terms of FC did not show group generality or stage- and frequency-dependence. Our results add to the understanding of sleep staging function and may provide clues to sex differences in sleep patterns and quality as well as the prevalence and clinical manifestations of sleep-related illness. Short-term stability offers a new perspective in analyzing FC, which cannot be ignored.
Highlights
Sleep is one of the most widespread biological processes, occupying one-third of our life [1]
Our study found that, in beta band, the Functional connectivity (FC) strength hemispheric lateralization was higher in Rapid eye movement (REM) than in N2 and N3 sleep stages
We found that average FC strengths were higher in females in all sleep stages and frequency bands
Summary
Sleep is one of the most widespread biological processes, occupying one-third of our life [1]. Using tracing by electroencephalography (EEG) during sleep, it has been observed that a healthy individual will experience rapid eye movement (REM, R) and no-REM (NREM) sleep, with occasional transitions to wakefulness (WAKE, W) [2]. Further divided into N1, N2, and N3 stages [2]. Despite the relatively good understanding of sleep behavior and mechanism, the exact functional significance of sleep remains enigmatic. Sleep plays a key role in psychiatric comorbidity processes [3], and the degree of sleep disturbance in patients with certain psychiatric disorders can predict future treatment outcomes to some extent [4]. Basic research on different stages of normal sleep is important for understanding sleep function and how sleep affects mental states.
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