Stages of sleep

Although the shape of the EEG tracing changes gradually, minute by minute, during the first hour after sleep, researchers have divided the sequence into four stages.

Stage 1 is considered a transition from wakefulness into sleep.



Stage 2 is marked by the appearance of brief bursts of rapid brain activity (called sleep spindles) in the midst of the overall slowing of the EEG waves. At this point the person is truly asleep.