Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds characterized by random rapid movement of the eyes accompanied by low muscle tone throughout the body and the propensity of the sleeper to dream vividly. The REM phase is also known as paradoxical sleep (PS) and sometimes desynchronized sleep or dreamy sleep because of physiological similarities to waking states including rapid low-voltage desynchronized brain waves. Electrical and chemical activity regulating this phase seem to originate in the brain stem and is characterized most notably by an abundance of the neurotransmitter acetylcholine combined with a nearly complete absence of monoamine neurotransmitters histamine serotonin and norepinephrine. Experiences of REM sleep are not transferred to permanent memory due to absence of norepinephrine.