Changes in REM sleep occurrence due to rhythmical auditory stimulation in the rat

The effects of the rhythmical delivery of an auditory stimulus (1000 Hz, fr om 50 to 100 dB, 20 ms, every 20 s) on the pattern of rapid eye movement (R EM) sleep occurrence was studied in the rat. The stimulation was simultaneo usly carried out on pairs of rats over 5 consecutive days (10-h recording s essions), during which a tone of increasing intensity (50, 63, 75, 88, 100 dB) was used. In each experimental session, auditory stimulation was trigge red by the REM sleep occurrence of one rat (REMS-selective stimulation) whi lst the other rat simultaneously received the same stimuli, but during any stage of the wake-sleep cycle (REMS-unselective stimulation). The results s howed that the total amount of REM sleep in the 10-h recording session was increased over the 5 days of stimulation in the REMS-unselective group. Thi s effect was due to an increase in the mean duration of REM sleep episodes. However, no significant changes were observed in animals under REMS-select ive stimulation, nor in a third group of animals in which the spontaneous e volution of REM sleep occurrence (REMS-spontaneous) was studied. Since 86% of the stimuli under the REMS-unselective auditory stimulation fell outside REM sleep, the result would suggest that REM sleep occurrence is affected when the stimuli are delivered during a time period (i.e. during wakefulnes s or non-REM sleep) in which it is well known that physiological regulation s are fully operant. (C) 2000 Elsevier Science B.V. All rights reserved.