Delta Rhythms: Models and Physiology
A high amplitude brain rhythm with frequency between 1 and 4 Hz.
The term “delta” was first introduced by Walter in 1936 to describe frequencies below the alpha (9–11 Hz) band while attempting to diagnose tumors using EEG signatures (Walter 1936). He subsequently, with Berger, subdivided this band to include theta rhythms (between 4 and 8 Hz). Since then the presentation of delta rhythms has been shown to be variable in frequency and amplitude during sleep (Church 1975), and some observers subdivide delta further into delta1 (1–2 Hz) and delta2 (3–4 Hz); this may have some mechanistic validity given the different potential origins of the rhythm (see below, Weiss and Rappelsberger 2000).
Association with Brain State
Delta rhythms (1–4 Hz) are predominantly associated with deep sleep (stage N3). These sleep stages are manifest most strongly during the first few hours of sleep in humans,...
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