Ultradian circa 112 hours rhythms: A multioscillatory system

Recent research has demonstrated rhythms in physiologic, behavioral, and endocrine processes with periodicity similar to that of the sleep REM-NONREM cycles. These findings confirm that part of Kleitman's Basic Rest-Activity (BRAC) hypothesis which predicted about $\text{1}\text{1}\text{2}\text{hour}$ cycles in waking levels of arousal. In contrast, however, with the BRAC model, which viewed the waking rhythms as fragments of the same oscillatory system controlling the REM-NONREM cycles, the accumulated data suggest that ultradian 90–100 min rhythms are generated by a multi-oscillatory system. It is hypothesized that the diverse ultradian variations in behavioral, physiologic and endocrine subsystems may play a role in the adaptation of group living animals to their environment.