Dream recall after awakening is linked to specific brain oscillations that differ between REM and NREM sleep. After REM sleep, higher frontal theta activity (5-7 Hz) predicts successful dream recall, mirroring the brain activity seen when encoding episodic memories while awake. After stage 2 NREM sleep, lower alpha activity (8-12 Hz) in the right temporal area predicts successful recall. These findings suggest that the neurophysiological mechanisms for encoding and recalling episodic memories may be consistent across different states of consciousness.
After 40 hours of prolonged wakefulness, a recovery night of sleep almost completely abolished dream recall, reducing it by about 75% compared to adaptation and baseline nights. The number of dreams recalled by those who did remember dreams did not differ significantly between nights, and gender or sleep stage at awakening did not affect recall. The drastic impairment of dream recall was associated with a larger increase in slow-wave sleep and shorter REM sleep duration. The authors suggest dream recall may be impaired due to fewer spontaneous awakenings, less dreamlike mental experiences during SWS, and poorer consolidation of dream content as episodic memory during recovery sleep.