by Tony Robinson
There are four distinct stages to the sleep cycle, and every human goes through several such sleep cycles in a typical night. The average full sleep cycle lasts from 90-120 minutes, so an average eight hour night of sleep could contain four or more separate sleep cycles.
Dreams may occur at any of the four stages of sleep, but the most vivid dreams, and the ones most likely to be remembered in the morning, occur during the REM stage of sleep. This sleep stage is generally referred to as REM (rapid eye movement) sleep. The name comes from the eye movements that are observed during this stage of sleep.
Since the entire sleep cycle repeats at least four and sometimes as many as seven, times per night, it is therefore possible and even likely that the same person will experience several different dreams every night. In most cases, however, the only dreams that are remembered are those that take place closest to waking. Not remembering dreams, however, does not mean they have not occurred.
Let us begin our look at the four stages of sleep.
Stage 1 During the first stage of sleep, the sleeper’s eyes move back and forth in an erratic fashion. For this reason, this stage of sleep is referred to as REM, or rapid eye movement, sleep. This stage generally occurs from 90-100 minutes after the initial onset of sleep. During this period of sleep, the blood pressure rises and the heart rate and respiration speeds up and may become erratic as well. During this stage of sleep, the voluntary muscles become paralyzed. This stage of sleep is the one in which the majority of dreaming occurs.
Stage 2 Stage two is a light sleep, and it is characterized by non rapid eye movements. During this stage of sleep the muscles are relaxed that the heart rate is slowed. This stage of sleep prepares the body for deeper sleep.
Stage 3 and 4 Stages three and four also feature non rapid eye movements. During stages three and four of the sleep cycle, the body enters into a deep sleep. You are completely asleep during both stages, but stage four is more intense than stage three.
All four stages of sleep repeat themselves throughout the sleep period, generally occurring from four to seven times. Each time the sleeper enters REM sleep, dreaming occurs. Sometimes dreamers remember dreams from earlier in the night, but in most cases the dreams that are remembered are those that occur closest to waking.
Researchers know, however, that dreaming occurs during all four to seven sessions of REM sleep. They know this through their work with volunteers who agree to be awakened during REM sleep. Those awakened during REM sleep generally provide very vivid descriptions of those dreams, as do those who awaken naturally during a particularly vivid, intense or frightening dream.