The sleep is structured in cycles. The number and length of the cycles vary by age and individuals but on average for an adult the cycle lasts 90 minutes and about 4-6 cycles occur per night. Each cycle is divided into two parts: the non REM (non-rapid eye movement) and the REM (rapid eye movement) sleep. Dr. Michel Jouvet discovered the phase called "REM sleep." In the late 1950s, he made experiments on cats and noted a phase of rapid cortical activity identical to the waking phase. In 1962, Jouvet presented the necessary arguments to validate his theory on sleep, theory that states two dependent states of different structures and mechanisms.
Sleep phase is structured as follows: for each cycle occurs first the non-REM sleep, and then towards the end begins REM sleep. Non-REM sleep represents 75 to 80% of sleep. REM sleep represents 20 to 25% of sleep. During the period of REM sleep, brain activity becomes intense. This is a fairly close period of awakening. It was noted that during this period that the individual experiences very fast eyes movements, jerking but the muscles remain inert. This would be the time when we dream the most.
REM sleep mechanisms are well known. It is believed that REM has physiological and psychological functions. Michel Jouvet proposed a biological hypothesis in which REM sleep serve to relay neurogenesis ensuring the genetic programming of the individual to maintain functional synaptic circuits responsible for the psychological heredity (personal temperament). Certain assumptions argue that learning occurs during REM sleep period and if we disturb REM sleep of an individual it will be more difficult to learn certain things. It seems that REM sleep is important for learning motor and visual capabilities.
Parasomnia that is to say, movements, emotions unusual dreams can disrupt REM sleep period. The disorder of REM sleep behavior (RBD) is a parasomnia characterized by abnormal muscle tone recovery during REM sleep, which can create surprising involuntary behaviors that are sometimes violent (which may be in line with the content of the dream). People affected by this disorder are often men over 50 years. This is characterized in patients with sudden, brutal and noisy movements. At the origin of this disorder would be a sleep deficit. To diagnose a patient with this disorder different criteria must be taken in account such as research for excessive daytime sleepiness and make a recording of sleep. This recording will then show an abnormal loss of sluggishness and excessive motor activity. In 60% of cases RBD has no known cause, but it may be associated with other neuro degenerative diseases as a form of dementia or Parkinsonism. It is therefore necessary to monitor the evolution of the RBD.
Other sleep disorders such as narcolepsy may affect REM sleep. Narcolepsy can cause a lack of REM sleep and is characterized by attacks of cataplexy, daytime sleep attacks, hypnagogic hallucinations and sleep paralysis. Depression causes a significant decrease in REM sleep. Anxiety can also disrupted REM sleep. If depression is treated, this disorder disappears. It is the same for anxiety.
Sources :
http://www.millenaire3.com/uploads/tx_ressm3/Michel_Jouvet_synthese.pdf
http://lecerveau.mcgill.ca/flash/capsules/outil_bleu23.html
https://sommeil.univ-lyon1.fr/articles/savenir/troubles/troubles.php
http://www.hopital.fr/Vos-dossiers-sante/Sommeil
http://www.sommeil-mg.net/spip/Troubles-du-Comportement-en
