Cat sleep: a unique first night effect.

Longitudinal sleep studies in chronically implanted cats revealed a unique first night effect. Unlike other species, during the first 24 hr of sleep recording, the electroencephalogram and reticular formation multiple unit activity revealed more rapid eye movement sleep occurred than during subsequent 24 hr recording sessions. In addition, higher rapid eye movement to slow wave sleep ratios were observed for the first 24 hr as compared to the following days. An increase in wakefulness and decrease in slow wave sleep occurred on the third recording day as compared to the initial 24 hr period. These data have important implications for studies of variables on the sleep pattern of animals.