Theta waves normally are seen in sleep at any age. In awake adults, these waves are abnormal if they occur in excess. Theta and delta waves are known collectively as slow waves. These slow waves have a frequency of 3 Hz or less. They normally are seen in deep sleep in adults as well as in infants and children.
Delta waves are abnormal in the awake adult.
Often, they have the largest amplitude of all waves. These waves are recognized by their shape and form and secondarily by their frequency. K complex waves are large-amplitude delta frequency waves, sometimes with a sharp apex. They can occur throughout the brain and usually are higher in amplitude and more prominent in the bifrontal regions. Usually symmetric, they occur each time the patient is aroused partially from sleep.