REM Sleep


 * See related article: Sleep

REM Sleep is a type of sleep characterized by greater cortical activity.

Frequency
REM Sleep is much less frequent than non-REM Sleep, consisting of about 25% of all sleep compared to non-REM sleep, which accounts for 75% of all sleep. It typically occurs in the later stages of sleep, compared to non-REM sleep, which is greater in earlier stages of sleep.

Induction
REM Sleep is induced by the rise of acetylcholine levels, specifically, the activation of cholingeric neurons in the pons. This is believed to be the causative effect of REM Sleep, although it is not definitively known.

Introduction
Cortical activity during REM Sleep is highly elevated, even comparable to that of consciousness or intense mental activity during consciousness, as REM Sleep is predominated by beta waves compared to the theta waves of early sleep and delta waves of deep sleep.

REM sleep is characterized by:


 * Electrical Activity: Asyncrhonous, high frequency, approaching that of conscious patterns
 * Sensation: Active and vivid, internal sensation (external stimuli not percieved)
 * Thought: Illogical, bizzare, repetitive
 * Movement: Upper motor system active
 * Children: descending information sometimes blocked, therefore some children can sleepwalk
 * Adults: descending information blocked, paralysis, inability to move in REM sleep

Dreaming
In non-REM sleep, cortical activity is suppressed because of the results of Stage Two sleep and associated non-REM sleep patterns. However, in REM sleep, the activation of the cholinergic pons is believed to stimulate cortical activity. The major cortices of the brain are activated during REM sleep, including the somatosensory and motor cortices. However, receptacle organs for external stimuli and their connections to the appropriate processing cortices are blocked: the brain is nonresponsive to the external environment, but because the cortices are active, the brain can feel somatosensation, but not ones derived from the external environment, instead those that are often copies of the brain's somatosensory state immediately before sleep. These waves are repetitive, and therefore the brain repetitively feels these sensory cues.

This is the progenitor to dreams: there is vivid cortical activity, but it is completely disassociated with the external environment. Furthermore, the motor cortex is also active. In dreams, one may be executing movements, and therefore, the motor cortex is prerequisite to those kinds of thoughts. However, descending information from upper motor neurons is blocked: the brain is commanding skeletal muscles to move, but neuromodulation by the diffuse neuromodulatory system prevents the muscles from moving. The proprioceptors also register that there is no movement, which is why there is considerable stress in nightmares where one is trying to move but can not.

Furthermore, the sympathetic nervous system is active in REM Sleep, and persons in REM Sleep exhibit elevated heart and respiratory rates.