Dreams Three different, but not mutually exclusive states exist with humans and many mammals. Channels one and two depict central EEG, the middle channel reflects EMG and the last two channels of each fragment demonstrate eye movement activities. The sleep processes are active, with many changes occurring throughout the course of the sleep episode. It is now understood that we pass through several sleep cycles alternating between NREM and REM sleep in 60 to 90 minute increments.
Age affects sleep too.
As we enter our 60's and beyond, we may exhibit a lack of stages 3 and 4 sleep, spend more time in bed without sleeping and awaken a little more frequently during the sleep period. Circadian Rhythms Sleep and wakefulness are examples of biologic rhythms. One's internal temperature rhythm usually remains synchronized with the sleep-wake cycle. Neurophysiology Advances in brain research and sleep-wake mechanisms have emerged. We now know that several regions are implicated in generating and maintaining NREM and REM sleep cycles.