When awake, two typical patterns of brain activity are shown. When a person is relaxed, brain activity shows waves that are smooth and regular, called alpha waves. However, when a person is alert, the waves become faster and irregular, called beta waves.
Different brain activity is shown when someone is asleep. There are 4 stages of sleep. The first stage is a transition from wakefulness to sleep. In the second stage, there are brief bursts of rapid brain activity, called sleep spindles, in the middle of slow waves. This is when the person is truly asleep. Stages 3 and 4 are deep sleep. Stage 3 has some low frequency, high amplitude waves called delta waves. Stage 4, the deepest sleep, has almost only delta waves. After staying in Stage 4 for a short time, the person moves back through the stages in reverse order. After repassing Stage 2, the EEG tracings are fast and irregular, which is the stage of REM sleep, which stands for rapid eye movement sleep. There is almost complete muscle relaxation except the eye muscles.
STAGES OF SLEEP