Sleep begins with non-rapid eye movement (NREM) phases, and after 60 to 90 min, the first rapid eye movement (REM) period starts; thereafter, REM sleep occurs cyclically at about 90-min intervals. After infancy, the percentage of REM sleep remains relatively stable through life, while total sleep and stage 4 sleep decrease progressively with increasing age. Dream recall is most frequent if subjects are awakened from REM sleep but may also occur after awakening from NREM sleep. During REM sleep, neuronal and metabolic activity and antonomic functions such as heart rate, respirations, and blood pressure are at increased levels, often comparable to those of the waking state.
Sleepwalking and bedwetting occur predominantly during stages 3 and 4, while seizure discharge rates are higher during these sleep stages than in REM sleep. The sleep of narcoleptics with cataplexy is characterized by REM sleep at sleep onset, while coronary artery and duodenal ulcer patients experience angina and increased gastric acid secretion, respectively, during REM sleep. Nocturnal asthmatic episodes occur out of all sleep stages proportionally to the time in each stage. (See summarized findings in Table 6.)
Selective deprivation of REM or stage 4 sleep is followed by compensatory increases in the deprived stage on recovery nights. Total sleep deprivation in man produces on recovery nights an initial increase in stage 4 sleep over base-line levels, followed by increases in REM sleep. Behavioral changes are frequent after prolonged sleep deprivation, while behavioral changes associated with REM deprivation have been varied and subtle.
Sleep alterations are induced by most psychotropic drugs; REM sleep is generally suppressed during drug administration and increased after drug withdrawal. Withdrawal of patients addicted to sedatives and antidepressants has produced marked rebound increases in the percentage of REM sleep. These REM sleep changes, together with the observations of nightmares and insomnia after withdrawal, may be significant in the development of dependence to these compounds.