Stages of Sleep

To many of us, sleep seems like a very passive experience for our bodies. The truth is that sleep is a very active state. Our bodies move during the night and our brain activity is more varied than during the waking state. While we’re awake, our brain waves patterns are called alpha and beta. The alpha waves correspond to states of relaxation, peacefulness and meditation, and the beta waves are associated with wakefulness.


Alpha, Theta, Delta and REM Sleep

As we’re drifting asleep we’re in the alpha stage. Our brain waves are relaxed and the transition to sleep is subtle. Once asleep, our brain waves move into the theta pattern. The theta portion of our cycle of rest is often referred to as stages 1 and 2 of sleep. This is characterized by light sleep. If one were to be awakened during stages 1 or 2 of sleep, they might not even recognize they were asleep at all.

In stages 3 and 4 of sleep, we are in the delta brain wave patterns. Both these stages are nearly identical, except that in stage 3 less than half the brain waves are delta, and in stage 4, delta is the majority. During delta sleep, we experience our deepest sleep. Awakening someone during delta sleep is difficult, and once awakened, the person may appear disoriented. Intriguingly, although we’re deep in sleep, this stage is the one in which we’re most likely to sleepwalk and sleeptalk.

The next phase is called rapid eye movement (REM) sleep. Sometimes it’s referred to as the fifth stage of sleep. The body experiences a sudden and marked loss of muscle tone. The musculoskeletal system becomes basically paralyzed. Our brain waves during REM sleep closely resemble the patterns of wakefulness: alpha, beta and desynchronous waves. This is the phase of the sleep cycle where dreams take place. In sleep studies, when a patient is found to be in REM sleep and awakened, they report powerful, story-like dreaming in great detail. In other phases of sleep, dreaming is usually not reported.

As you sleep your body cycles through each of the 4 stages of sleep. After reaching stage 4, REM sleep replaces stage 1, and the cycle repeats. The initial cycle from stage 1 to REM takes about 90 minutes. After that, the REM periods lengthen as the delta stage decreases until there’s none at all.