48-hour sleep-wake cycles in manic-depressive illness: naturalistic observations and sleep deprivation experiments.

Wrist motor activity and sleep were monitored longitudinally in 15 rapidly cycling and 52 nonrapidly cycling manic-depressive patients. The majority of patients experienced one or more consecutive 48-hour sleep-wake cycles (alternate nights with no sleep) when they switched out of depression into mania of hypomania. During a depressive phase, nine rapidly cycling patients were asked to simulate a 48-hour sleep-wake cycle by remaining awake for 40 hours (one night's total sleep deprivation). Eight switched out of depression, and seven were rated as manic or hypomanic; indicating that sleep loss (such as occurs with spontaneous 48-hour sleep-wake cycles) may help to trigger switches from depression to mania. The 48-hour sleep-wake cycles in patients may depend on a mechanism that is normally present in all humans, since normal persons also spontaneously experience near-48 hour sleep-wake cycles in certain experimental conditions.