In polysomnography, what does high theta activity on EEG indicate?

High theta activity on EEG is associated with lighter stages of sleep, particularly during NREM sleep stages 1 and 2, as well as periods of drowsiness. Theta waves have a frequency range of about 4 to 7 Hz and are prominent during the transition from wakefulness to sleep, indicating a relaxed yet alert state. In these lighter sleep stages, the brain is not in a deep sleep pattern, and theta activity is more common than in deeper sleep stages where delta waves become more prominent.

Theta waves also appear in REM sleep, but their presence alone is not indicative of this stage since it is characterized primarily by low muscle tone and distinct sleep patterns. Thus, high theta activity is most accurately reflective of lighter sleep or drowsiness rather than deep sleep or full wakefulness.