What is a Sleep EEG?

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  • Written By: Susan Grindstaff
  • Edited By: Heather Bailey
  • Last Modified Date: 08 October 2019
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A sleep electroencephalogram (EEG) is used to study sleep patterns. Excluding pain, sleeping problems are believed to be the second most common symptom of illness, and a sleep EEG is normally used to determine if a patient is going through all five levels of sleep. An EEG machine detects and measures brain activity, which exhibits different patterns during different levels of sleep.

The human brain consists of cells that must be able to transfer information. They do this by using faint electrical pulses, which an EEG is able to detect and evaluate. When a person is undergoing a sleep EEG, small electrodes are attached to his scalp. The electrodes transfer the activity of the electrical pulses to the EEG machine, which then presents the information, usually in the form of a graph.

Sleep cycles are usually characterized by rapid eye movement (REM) and non-REM, which normally corresponds to EEG activity. Stage 1 sleep is a non-REM cycle that typically lasts for only a short while, and is sometimes referred to as dozing. During stage 1 sleep, people are usually very easy to wake. The electrical activity of the brain during this stage is usually quite low.

When sleep transitions from stage 1 to stage 2, a sleep EEG begins to show much larger brain waves. Stage 2 sleep comprises about 45 percent of the total time spent in non-REM sleep. Most sleep studies show that eye movement has greatly diminished during this sleep level.


Stage 3 sleep is usually an introduction to deep sleep. During this period, this test typically shows brain wave activity with very large waves, interrupted occasionally by small spikes that are referred to as “delta” waves. During this level of sleep, it is often more difficult to bring sleepers into wakefulness.

By the time a person finally reaches stage 4 sleep, he is normally sleeping very deeply. Sleepers awakened during this level may take several minutes to become oriented to their surroundings. They will commonly be quite groggy and confused. During this level, a sleep EEG is mainly showing only delta waves.

Level 5 sleep occurs when a sleeper finally reaches sleep that is producing REM, and during this level, dreams are usually taking place. Sleepers will sometimes exhibit changes in breathing, blood pressure, and heart rate. During this level, a sleep EEG often shows a great variety of wave patterns. Most physicians believe that overall health may be linked to the amount of time an individual spends in level 5.


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