As the electrocardiogram detects the electrical activity of the patient's heart, so the EEG electroencephalogram traces that of the brain.

Studying brain activity serves, for example, to identify and then solve the most common sleep disorders (apnea, epilepsy, insomnia or narcolepsy) but also sleepwalking, bruxism, nocturnal incontinence and pavor nocturnus (nocturnal terror) that generally affect children, as well as some adults.