<P> Most of the eye movements in "rapid eye movement" sleep are in fact less rapid than those normally exhibited by waking humans . They are also shorter in duration and more likely to loop back to their starting point . About seven of such loops take place over one minute of REM sleep . In slow - wave sleep the eyes can drift apart; however, the eyes of the paradoxical sleeper move in tandem . These eye movements follow the ponto - geniculo - occipital waves originating in the brain stem . The eye movements themselves may relate to the sense of vision experienced in the dream, but a direct relationship remains to be clearly established . Congenitally blind people, who do not typically have visual imagery in their dreams, still move their eyes in REM sleep . An alternative explanation suggests that the functional purpose of REM sleep is for procedural memory processing, and the rapid eye movement is only a side effect of the brain processing the eye - related procedural memory . </P> <P> Generally speaking, the body suspends homeostasis during paradoxical sleep . Heart rate, cardiac pressure, cardiac output, arterial pressure, and breathing rate quickly become irregular when the body moves into REM sleep . In general, respiratory reflexes such as response to hypoxia diminish . Overall, the brain exerts less control over breathing; electrical stimulation of respiration - linked brain areas does not influence the lungs, as it does during non-REM sleep and in waking . The fluctuations of heart rate and arterial pressure tend to coincide with PGO waves and rapid eye movements, twitches, or sudden changes in breathing . </P> <P> Erections of the penis (nocturnal penile tumescence or NPT) normally accompany REM sleep in rats and humans . If a male has erectile dysfunction (ED) while awake, but has NPT episodes during REM, it would suggest that the ED is from a psychological rather than a physiological cause . In females, erection of the clitoris (nocturnal clitoral tumescence or NCT) causes enlargement, with accompanying vaginal blood flow and transudation (i.e. lubrication). During a normal night of sleep the penis and clitoris may be erect for a total time of from one hour to as long as three and a half hours during REM . </P> <P> Body temperature is not well regulated during REM sleep, and thus organisms become more sensitive to temperatures outside their thermoneutral zone . Cats and other small furry mammals will shiver and breathe faster to regulate temperature during NREMS but not during REMS . With the loss of muscle tone, animals lose the ability to regulate temperature through body movement . (However, even cats with pontine lesions preventing muscle atonia during REM did not regulate their temperature by shivering .) Neurons which typically activate in response to cold temperatures--triggers for neural thermoregulation--simply do not fire during REM sleep, as they do in NREM sleep and waking . </P>

Rapid eye movement (rem) sleep and dreaming occur mostly in