High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! A delta wave is a high amplitude brain wave with a frequency of 1 4 hertz which can be recorded with an electroencephalogram (EEG) and is usually associated with slow-wave sleep (SWS). Delta wave activity occurs most frequently during stage N3 slow-wave sleep, accounting for 20% or more of the EEG record during this stage. These waves are believed to originate in the thalamus in coordination with the reticular formation.