EEG alpha activity and hallucinatory experience during sensory deprivation.

The relationship between hallucinatory experiences under sensory deprivation and EEG alpha activities was studied. Each of seven male students lived alone in an air conditioned, soundproof dark room for 72 hours. When hallucinatory experiences occurred, the students pressed a button at once. If they could not press the button during the experience, they were required to press it two times when the hallucinatory experience was finished. Spectral analysis was performed on the consecutive EEG samples from just before button-presses to 10 min. before them, and the average alpha band amplitudes were obtained for the four epochs (0-.5, .5-2, 2-5, 5-10 min.). For the single button-presses, the amplitude of alpha band increased 2 min. before the button-presses. Right-hemisphere EEG activation was observed in the occipital area for the double button-presses. The results suggest an association between the hallucinatory experiences under sensory deprivation and the amount of EEG alpha activity.