Changes of individual sleep pattern to group-level sleep pattern in freely-moving mice group

Abstract

As a social animal, mice naturally show huddling behavior during sleep and influence each other conspecifics' sleep patterns. Accordingly, group-level sleep pattern is observed in group hosing; however, it remains to be investigated how individual sleep patterns change and what factors influence the formation of group-level sleep patterns. Due to the limitation of the experimental setup, sleep studies were mainly conducted in individual mice. Also, it requires a lot of labor to compare video and sleep states in a group of mice. Here, we developed the algorithm of CBRAIN (Collective Brain Research Aided by Illuminating Neural activity) system for wireless real-time sleep monitoring. Briefly, EEG and EMG signals were acquired at 256 Hz, and real-time analysis of the 2-s signals was performed in every 10 sample updates for wake / NREM sleep / REM sleep classification by a microprocessor. The classified sleep and wake states were indicated by the color of the LED attached in CBRAIN. Using this system, we measured sleep patterns in a small group of mice (n=4) and measured them again individually. We found that Group-level sleep patterns are adjusted to those of individuals who slept shorter. During group sleep, the overall sleep time tends to decrease, and the subjects with longer sleep times decrease to the amount of those with shorter sleep durations. Also, the sleep states were more synchronized, and REM sleep was rich when mice huddled together. These results showed that the amount of individual sleep could be maintained internally as well as flexibly changed according to the group sleep pattern under the naturalistic environment.