Effects of group huddling on individual sleep dynamics and neural activity in mice

Abstract

Huddling, or sleeping together in physical contact, is a thermoregulatory behavior observed in social animals. Mice, known as social animals, also exhibit group sleeping behavior. While individual sleep patterns have traditionally been the focus, recent studies have highlighted synchronization in sleep initiation and waking times during group sleep. However, the effects of group sleep on neural activities remain less understood. This study aimed to investigate changes in sleep patterns when mice huddle in groups compared to when they sleep alone. We conducted 12-hour recordings using wireless neurophysiological devices and video monitoring. Each experimental group consisted of four male mice, with recordings of each mouse alone on one day and all four mice together on the next day. We collected electroencephalogram (EEG) from the frontal and parietal cortex, along with electromyography (EMG) signals from neck muscles using CBRAIN (Kim et al., Sci Adv, 2023). Our findings revealed that group sleep reduced the duration of both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep phases. As overall wakefulness increased, the REM to NREM ratio decreased. Despite the stable power across different frequencies in both sleep conditions in each sleep state, we noted a peak frequency shift in the theta band (5 - 10 Hz) during REM sleep for huddled mice. Furthermore, phase synchrony in the theta band during REM sleep increased among the huddling mice, indicating enhanced inter-brain synchrony. These results highlight the significant influence of huddling on neural activity during sleep in mice as showing theta coherence during REM sleep, indicating potential mutual modulation of neural activity in social sleep dynamics.