What is a Delta Wave?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 21 October 2019
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A delta wave is a type of brain wave seen during Stage Three sleep, also known as slow wave sleep or deep sleep. This stage of sleep is believed to be important for physiological function. Studies have shown, for example, that after sleep deprivation, people experience more Stage Three sleep, as though their brains are trying to make up for the period of deprivation. People also tend to be extremely confused when they are woken from this stage of sleep, indicating that the consciousness was very far away from the waking world.

Like other brain waves, the delta wave can be identified on an electroencephalogram, in which electrical activity in the brain is recorded with sensors on the scalp. Delta waves are characterized by their high amplitude and low frequency, looking markedly different from other brain waves such as gamma waves. A delta wave has an amplitude of one to four Hertz, and a frequency which occurs about six times a second.

In healthy people, delta waves are not observed in an awake brain. However, people intoxicated by certain substances or in a state of delerium may have delta wave activity even though they are awake, and some types of mental illness are characterized by the presence of delta waves in the waking brain, as well. Adults with dementia may demonstrate delta wave activity during their waking hours too, as has been demonstrated in brain studies on these individuals.


While sleeping, delta wave activity occurs during non-rapid eye movement (REM) sleep. People are said to be in deep or slow wave sleep when at least 20% of the brain activity consists of delta waves. While in this state, the level of sensory input needed to arouse the sleeper is very high. Light touch or soft noises may not succeed in waking someone up, with people generally needing loud noises, bright lights, or firm touch such as shaking. Once aroused, the sleeper often appears groggy and disoriented.

People who experience sleep problems may be told to participate in a sleep study, in which brain activity and other physiological processes are monitored overnight in a sleep lab. During the study, the patient wears gear which records physiological processes and transmits the results to a monitoring station. By looking at things like brain activity, respiration rate, and heart rate, a doctor can explore why the patient is experiencing sleep difficulties, and make recommendations to help the patient sleep better.


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