Delta wave

A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 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. Background and history "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.