During Zen meditation, EEG recordings from 48 Zen priests and disciples showed a consistent pattern of brainwave changes: alpha waves appeared within 50 seconds of starting meditation, their amplitude increased, and their frequency decreased over time. In some priests, rhythmic theta trains emerged. These four EEG stages corresponded to the disciples' mental states, as evaluated by a Zen master, and to their years of training. Unlike drowsiness or hypnotic sleep, the meditation EEG pattern was more persistent and did not shift into deeper sleep. Alpha blocking in response to repeated click stimuli showed no habituation during meditation, whereas control subjects habituated quickly. These findings indicate a specific change of consciousness during Zen meditation.
During well-achieved Zen meditation, the brain's alpha rhythm shows reduced habituation to sensory stimuli compared to the ordinary waking state, indicating a unique state of consciousness characterized by calm, pure, and serene concentration without tension. This subjective experience, achieved through strict adherence to Zen training rules, contrasts with hypnotic trance, though both alter consciousness. The electroencephalogram serves as a useful neurophysiological method for detecting disturbances of consciousness in clinical practice, and the authors detail electrographic characteristics reflecting the mental state during Zen-sitting.