DISRUPTION OF SLEEP RECOVERY AFTER 36 HOURS OF EXPOSURE TO MODERATELYBRIGHT LIGHT

Eight young adults were exposed to either 36 hours of moderate bright light (BL; 1,000-2,000 lux) or a light/dark cycle (L/D <50 lux) during constant routine. Sleep was recorded on the two subsequent recovery s leeps (R1 and R2) and compared to baseline. After the BL exposure, the rebound of stage 4 sleep and slow wave activity (SWA) were split over R1 and R2, whereas after the L/D cycle, the stage 4 sleep debt was al most completely compensated for during R1. During R1, stage 2 sleep an d wakefulness accumulated faster in the BL condition than in the L/D c ondition. An elevation of the temperature level was also found during R1 of the BL condition. No differences between light conditions were f ound in urinary levels of melatonin or cortisol secreted during R1 or R2. Homeostasic process does not appear to be affected by the BL condi tion. A modification in the sleep-wake balance and a change in the tem poral relationship between the circadian system and the sleep-wake cyc le are discussed.