delta rhythm

WordReference Random House Unabridged Dictionary of American English © 2025

del′ta rhythm′, [Physiol.]

1. Physiology a pattern of slow brain waves, having a frequency of less than 6 cycles per second as recorded by an electroencephalograph, associated with deep sleep.

• 1935–40

Collins Concise English Dictionary © HarperCollins Publishers::

delta rhythm, delta wave noun

1. the normal electrical activity of the cerebral cortex during deep sleep, occurring at a frequency of 1 to 4 hertz and detectable with an electroencephalograph
   See also brain wave