Sleep is essential to maintain good health. While the CDC recommends that adults get seven to nine hours of sleep a night, the type of sleep is also important, meaning that the sleep cycle enters all the four stages NREM sleep and REM sleep. This image shows what this looks like.
Stage One: Drowsiness
Joanna Saisan MSW, Tina de Benedictis, Ph.D., Suzanne Barston, and Robert Segal, M.A., authors of the article “Understanding Sleep: Deep Sleep, REM Sleep, Cycles, Stages, and Needs,” state that the first stage of sleep, or drowsiness, lasts between five and ten minutes. During stage one, the person can be awakened without much effort; it becomes more difficult in the later stages of sleep. Eye movement is minimal, as there is less muscle activity. The University of Washington adds that the EEG rate for stage one sleep is 6-8 Hz, which is a low amplitude; in comparison, the EEG rate for the waking stage is 8-25 Hz, which also has a low amplitude. Stage one is the first stage of NREM sleep, or non-rapid eye movement sleep.
Stage Two: Light Sleep
In stage two, sleep is “beginning,” as the person has entered a light sleep. Saisan, de Benedictis, Barston, and Segal note that during stage two sleep, “eye movements stop, heart rate slows and body temperature decreases.” The EEG rate for stage two is 4-7 Hz, which is a medium amplitude, according to the University of Washington.
Stage Three and Four: Deep Sleep
During deep sleep, waking the person is not easy; if it does occur, the person does not “adjust immediately and often feel groggy and disoriented for several minutes,” according to Saisan, de Benedictis, Barston, and Segal. The authors note that during these stages, “blood flow decreases to the brain in this stage, and redirects itself towards the muscles, restoring physical energy. Research also shows that immune functions increase during deep sleep.”
Stage three and four are also known as “slow wave sleep,” due to their smaller EEG frequency. The University of Washington stages that the EEG frequency for stage three is 1-3 Hz (a high amplitude), and the EEG frequency for stage four is less that 2 Hz (also a high amplitude).
REM Sleep
The last stage of sleep is REM sleep, or rapid eye movement sleep. During this stage, the person dreams: Saisan, de Benedictis, Barston, and Segal state that the person is “processing emotions, retaining memories and relieving stress.” The body is also more active during REM sleep, with increased breathing and heart rate. The University of Washington adds that the EEG frequency for REM sleep is more than 10 Hz, which is a low frequency.
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Elizabeth Stannard Gromisch received her bachelor’s of science degree in neuroscience from Trinity College in Hartford, CT in May 2009. She is the Hartford Women's Health Examiner and she writes about abuse on Suite 101.