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nREM Sleep—stages 1 – 4

By Darien Simon

nREM, or non-Rapid Eye Movement sleep, includes the first four stages of the normal sleep cycle sequence. In sleep stage 1, closed-eye drowsiness, the level of activity detected via polysomnography [LINK: TBW] is about 50% less than that of people who are wide awake. Sleep state 1 is so light, people who are awakened from it are often confused about whether they have actually been asleep or not. This stage usually lasts a few minutes only, with 5 – 10 minutes being the most common duration. Stage 2 sleep is considered light sleep, but is a deeper form than stage 1 sleep. In this nREM stage of sleep, polysomnography shows a characteristic set of peak and valley readings corresponding to alternating muscle tone and relaxation. Also in this stage of sleep, heart rates decrease, as does body temperature. Both nREM stages 3 and 4 are considered deep sleep, and both show delta brain waves in polysomnographic recordings. These two sleep stages differ mostly by the intensity or depth of sleep, with stage 4 being deeper and more intense than stage 3. During a normal, good night’s sleep, you pass through all four stages, plus REM sleep [LINK: REM Sleep—Stage 5]. The first four stages, nREM sleep, last about 90 – 120 minutes in the first cycle through the sleep stages, each stage lasting approximately 5 – 15 minutes, after which there is a brief period of REM sleep. However, it has been suggested that the first four stages of sleep do not occur in sequence immediately followed by REM sleep. Instead, you may progress through stages 1 – 4, then revert to stage 3, followed by stage 2, and then REM sleep. This sequence of sleep stages repeats in cycles throughout the night, but with changes in the duration of some stages as you progress through each cycle. In general, deep sleep, stages 3 and 4, decreases in length, while REM sleep increases. During a single night’s sleep, you may go through the cycle of sleep stages 4 – 5 times. At present, it is thought that nREM sleep may be necessary for physical recovery from daily activity, repair of normal wear and tear, and to reset biochemical systems of brain and body to full normal sensitivity for the new day. Whether or not this is the reason for nREM sleep, sleep deprivation [LINK: Sleep debt: overdrawn at the energy bank], has been shown to adversely impact both physical and mental health, but sleep quantity and quality may be enhanced by certain herbs and nutrients, such as those found in DreamBoost