Sleep in young and old rats.

Five young rats, age 152--175 days, and six old rats, age 782--801 days, all of the F-344 strain, were compared by electronic methods for amplitude of slow wave activity during sleep and for other sleep parameters. Unlike humans, who show a pronounced loss of slow wave activity with advanced age, no significant difference in delta activity could be detected between young and old rats. Several hypotheses about the species difference were reviewed. Young and old rats, however, did show several differences in other sleep parameters which parallel those observed in humans. These age-related changes were a moderate decrease in the percent of total sleep time spent in paradoxical sleep, a decrease in the length of sleep bouts, an increase in the number of sleep bouts, and a decrease in the amplitude of the diurnal rhythm of sleep.