Rapid eye movement sleep resemblance to waking life), and incorporation of instinctual themes. Sometimes they include elements of the dreamer's recent experience taken directly from episodic memory. By one estimate, 80% of dreams occur during REM. Hobson and McCarley proposed that the PGO waves characteristic of “phasic” REM might supply the visual cortex and forebrain with electrical excitement which amplifies the hallucinatory aspects of dreaming. However, people woken up during sleep do not report significantly more bizarre dreams during phasic REMS, compared to tonic REMS. Another possible relationship between the two phenomena could be that the higher threshold for sensory interruption during REM sleep
Rapid eye movement sleep sleep due to a shrapnel injury to the brainstem did not find the individual's memory to be impaired. Antidepressants, which suppress REM sleep, show no evidence of impairing memory and may improve it. Graeme Mitchison and Francis Crick proposed in 1983 that by virtue of its inherent spontaneous activity, the function of REM sleep "is to remove certain undesirable modes of interaction in networks of cells in the cerebral cortex", which process they characterize as "unlearning". As a result, those memories which are relevant (whose underlying neuronal substrate is strong enough to withstand such spontaneous, chaotic activation) are further strengthened,