REM-SLEEP TIMING IS CONTROLLED HOMEOSTATICALLY BY ACCUMULATION OF REM-SLEEP PROPENSITY IN NON-REM SLEEP

Sleep structure in the rat was characterized during uninterrupted full -day recordings using an analytic procedure that identifies rapid eye movement (REM) sleep episodes based on REM-sleep-onset electroencephal ograph phenomena, hence independently of REM-sleep duration. The data were used to determine whether REM-sleep timing is controlled homeosta tically or by an oscillatory mechanism. The findings and conclusions a re that 1) non-REM (NREM) sleep episode duration is positively correla ted with prior REM-sleep episode duration, suggesting that REM-sleep e xpression is permissive of NREM sleep; 2) mean NREM-sleep episode dura tion decreases after repeated brief REM-sleep episodes (<30 s), also s uggesting that discharge of REM-sleep propensity is essential for NREM -sleep expression; 3) REM-sleep episode duration is independent of pri or sleep history, suggesting that REM-sleep maintenance is controlled by factors other than accumulated REM-sleep propensity; 4) brief REM-s leep episodes occur progressively more frequently over the course of t he NREM-sleep interval between sustained REM-sleep episodes (> 30 s), suggesting that REM-sleep propensity increases progressively within ep isodes of NREM sleep; and 5) the diurnal cycle of REM-sleep expression primarily reflects modulation in the efficiency of REM-sleep maintena nce. These findings support the hypothesis that REM-sleep timing is co ntrolled by accumulation of REM-sleep propensity during NREM sleep.