Distribution of vigilance states. Typically for a nocturnal rodent, wakefulness was strongly reduced during the light period (ZT0-ZT12), compared to the dark period (ZT12-ZT22). Inversed patterns were obtained for NREM sleep and REM sleep with significant differences between baseline and treatment recordings only for REM sleep (asterisks). Data points represent two hour means ± SEM. Gray background indicates the dark period.