<prompt> Theta waves are seen inStage 1 sleepStage 2 sleepStage 3 sleepStage 4 sleep  <response>: The first stage of sleep is characterized by theta waves, which are even slower in frequency and greater in amplitude than alpha waves. The difference between relaxation and stage 1 sleep is gradual and subtle. A person falling asleep first enters stage 1, the EEG begins to show a low-voltage, mixed-frequency pattern. A theta rhythm 4-7 Hz can be seen at this early stage of slow-wave sleep. Theta and delta rhythms are normal during sleep, their appearance during wakefulness is a sign of brain dysfunction.Ref: Ganongs Review of Medical Physiology, Twenty-Third Edition 