Delta waves are high amplitude, low frequency brain waves that occur during stage three sleep. They are important for physiological function and can be identified on an EEG. Delta waves are not seen in an awake brain, but can occur in intoxicated or delirious individuals and those with certain mental illnesses or dementia. A sleep study can help diagnose sleep problems by monitoring brain activity and other physiological processes.
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 thought to be important for physiological function. Studies have shown, for example, that after sleep deprivation, people experience more stage three sleep, as if their brain is trying to make up for the period of deprivation. People also tend to be extremely confused when awakened from this stage of sleep, indicating that consciousness was far removed from the waking world.
Like other brain waves, the delta wave can be identified on an EEG, where electrical activity in the brain is recorded with sensors on the scalp. Delta waves are characterized by their high amplitude and low frequency, resulting in a markedly different appearance from other brain waves such as gamma waves. A delta wave has an amplitude of one to four Hertz and a frequency that occurs about six times per second.
In healthy people, delta waves are not seen in an awake brain. However, people intoxicated with certain substances or in a state of delirium can have delta wave activity even when awake, and some types of mental illness are also characterized by the presence of delta waves in the waking brain. Adults with dementia can demonstrate delta wave activity even during waking hours, as has been shown in brain studies of these individuals.
During sleep, 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 their brain activity is made up of delta waves. While in this state, the level of sensory input required to awaken the sleeper is very high. Light touch or soft noises may fail to wake someone up, with people generally needing loud noises, bright lights, or firm touch such as shaking. Once awakened, the sleeper often appears groggy and disoriented.
People who have trouble sleeping may be told to participate in a sleep study, in which brain activity and other physiological processes are monitored overnight in a sleep laboratory. During the study, the patient wears equipment that records physiological processes and transmits the results to a monitoring station. By looking at things like brain activity, breathing rate, and heart rate, a doctor can explore why a patient is having trouble sleeping and make recommendations to help them sleep better.
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