REM sleep

Rapid Eye Movement (REM) sleep is a stage of sleep that is characterized by intense brain activity, high levels of metabolic activity, and vivid dreaming. It is during REM sleep that the brain processes emotions and learns or unlearns certain information. The stage is associated with the ability to uncouple emotions from experiences, acting as a sort of self-induced therapy, which is similar to certain trauma therapies like Eye Movement Desensitization and Reprocessing (EMDR) and Ketamine therapy. It is also when spatial information and associated neuronal firing patterns from the day are replayed and consolidated in memory.

REM sleep involves the eponymous rapid eye movements as well as atonia, or paralysis of the muscles, which prevents physical acting out of dreams. Interestingly, the neurotransmitters serotonin and norepinephrine are absent during REM sleep, with epinephrine (involved in stress responses) also being at low levels. This absence of chemicals normally involved in stress and alertness allows replay and processing of emotional content without the somatic experience of fear or anxiety. As such, REM sleep is critical for emotional stability and the consolidation of spatial information. However, disturbance or deprivation of REM can lead to hallucinations and an increase in emotional reactivity 1 2 3 4 5 6.

Deprivation or disruption of REM sleep is related to increased associating of unrelated events, hallucinations, and heightened sensitivity to emotional disturbances. The sleep cycle typically incorporates more slow-wave sleep early in the night and more REM sleep towards the morning, with sleep consistency playing an important role in cognitive and emotional stability 6.