WHEN THE HUMAN CIRCADIAN SYSTEM IS CAUGHT NAPPING - EVIDENCE FOR ENDOGENOUS RHYTHMS CLOSE TO 24 HOURS

It is now well acknowledged that napping constitutes an inherent compo nent of the human circadian system. To date, however, few studies have examined the effects of spontaneous napping on human free-running rhy thms. This study investigated the free-running circadian periods of re st/activity and body core temperature in a group of young subjects who were permitted to nap during their time in isolation. Based on the fr equency of self-reported sleep bouts, subjects were classified as Napp ers or Nonnappers. Nappers exhibited free-running rhythms in both rest /activity and body core temperature that were not significantly differ ent from 24 hours. Nappers showed a tendency for shorter free-running periods in both variables, when compared with Nonnappers. These findin gs emphasize the need for careful reassessment of data obtained from t raditional free-run protocols.