Individual variation in sleep and motor activity in rats

We examined individual differences in sleep and motor activity across 2 consecutive days in rats. EEG and motor activity were recorded via telemetry in Wistar rats (n = 29) for 48 h under well-habituated conditions. Rats were grouped based on sleep amounts and stability across days (short [SS, n = 7], intermediate [IS, n = 15] and long [LS, n = 7] sleep) and comparisons were conducted to determine group differences for measures of sleep and motor activity. We found that correlations across recording days were significant for all selected sleep measures and motor activity counts. Rankings for 24 h total sleep time and non-rapid eye movement sleep (NREM) were SS < IS < LS rats whereas amounts of rapid eye movement sleep did not differ among groups. Further analyses of NREM episode parameters found significant differences in mean episode length (SS < IS < LS) but not in the number of episodes. Total and average motor activity counts (per waking min) were greater (32-38%) in SS compared to LS rats on both recording days. The results indicate that individual differences in sleep and motor activity in Wistar rats are stable across days. Differences between SS and LS rats have parallels to those reported for short and long sleep humans. (c) 2007 Elsevier B.V. All rights reserved.