Sleep-wake cycles in rhesus monkeys during Spacelab flight simulations

Neurophysiological data has been obtained in orbital flight from various non-human Primates. Aboard Russian satellites during both Bion and Biocosmos missions, impairments in duration and organization of the states of vigilance were observed in rhesus monkeys during flight: increase in nocturnal awakening, decrease of Rapid Eye Movements-sleep (REM-sleep). It was assumed that weightlessness played a role in these changes. The former "Rhesus Project", a joint program between CNES and NASA, was devoted to physiological studies using the rhesus monkey as a human model aboard Spacelab, during 14 to 16 day orbital flights. In the first stage of this project, we investigated the effect of experimental conditions as well as specific restraint and confinement on the circadian sleep-wake rhythm in a group of rhesus monkeys. Prior to flight, our aim was to determine quantitatively and qualitatively sleep-wake cycles. These control data would thus be compared with inflight data in order to assess the influence of weightlessness.