Social context and dominance status contribute to sleep patterns and quality in groups of freely-moving mice

In many socially-living species, sleep patterns are subject to group influences, as individuals adjust to the presence, daily rhythms, and social pressures inherent to cohabitation. Disturbances in social functioning are comorbid with sleep problems in many prevalent psychiatric disorders, most notably, autism-spectrum, mood, and anxiety disorders (e.g., [1-3]). Our understanding of the common causality and the interplay between sleep impairment and psychiatric symptomatology could greatly benefit from experimental paradigms that allow simultaneous assessment of both domains of functioning. In laboratory mice, much is known about the sensitivity of sleep quality to a variety of experimental manipulations. Due to existing methodological restrictions, however, sleep studies are typically conducted in single-housed mice, thereby neglecting the influence of social dynamics and group-derived individual differences (however, see [4,5]). Here, we investigated sleep in a semi-naturalistic environment with freely-moving socially-housed groups of male mice using wireless electroencephalographic (EEG) monitoring devices and automated video tracking. In addition to multiple days of continuous behavioral data, we collected over fifty hours of EEG signal per mouse, recording simultaneously from all individuals in a group. We found evidence of in-group synchrony of sleep state patterns. Moreover, social status was a powerful predictor of sleep quality, such that sleep fragmentation, slow-wave sleep power, and rapid eye movement (REM) episode duration differed as a function of dominance status in the group. Finally, acute stress exposure had differential effects on REM sleep during recovery in dominant versus subordinate individuals. These findings highlight the importance of exploring sleep in a social context and are a step toward more informative research on the interplay between social functioning and sleep.