Women's vaginal responses during REM Sleep.

Eight female subjects underwent vaginal photoplethysmographic recordings while asleep. Results demonstrated consistent findings of decreases in relative blood volume and increases in relative pulse pressure within the vagina during REM periods. Thes vascular changes indicate that females undergo phasic shifts in vascular blood flow in the vagina during REM sleep, similar to the phasic shifts of blood flow in the male's penis during REM sleep.