Delta wave

A delta wave is a high amplitude brain wave with a frequency of oscillation between 0.5–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram (EEG) and are usually associated with the deep stage 3 of NREM sleep, also known as slow-wave sleep (SWS), and aid in characterizing the depth of sleep.

"Delta waves" were first described in the 1930s by W. Grey Walter, who improved upon Dr. Hans Berger's electroencephalograph machine (EEG) to detect alpha and delta waves. Delta waves can be quantified using Quantitative electroencephalography (qEEG) using freely available toolboxes, such as, EEGLAB or the Neurophysiological Biomarker Toolbox (NBT).

Delta waves, like all brain waves, can be detected by electroencephalography (EEG). Delta waves were originally defined as having a frequency between 1-4 Hz, although more recent classifications put the boundaries at between 0.5 and 2 Hz. They are the slowest and highest amplitude classically described brainwaves, although recent studies have described slower (<0.1 Hz) oscillations Delta waves begin to appear in stage 3 sleep, but by stage 4 nearly all spectral activity is dominated by delta waves. Stage 3 sleep is defined as having less than 50% delta wave activity, while stage 4 sleep has more than 50% delta wave activity. These stages have recently been combined and are now collectively referred to as stage N3 slow-wave sleep. During N3 SWS, delta waves account for 20% or more of the EEG record during this stage. Delta waves occur in all mammals, and potentially all animals as well.

Delta waves are often associated with another EEG phenomenon, the K-complex. K-Complexes have been shown to immediately precede delta waves in slow wave sleep.

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