During Zen meditation (Zazen), slow alpha brain waves appeared in most subjects regardless of meditation experience, but theta waves appeared only in monks (priests and disciples), predominantly in the frontal region. The frequency of theta waves increased with more years of Zen training. In experienced monks, theta 2–3 (6.0–8.0 Hz) waves increased while the increase in alpha 2 (9.0–10.0 Hz) waves was attenuated over the course of meditation. These EEG changes may reflect a mental state of relaxation combined with heightened consciousness induced by Zazen.
During Zen meditation, brainwave activity shifts toward increased fast theta and slow alpha power in the frontal area, while heart rate variability indicates greater parasympathetic and reduced sympathetic activity. These changes correlate with specific personality traits: increased slow alpha power, reflecting internalized attention, is linked to higher novelty seeking scores and reduced sympathetic indices; increased fast theta power, reflecting mindfulness, is linked to higher harm avoidance scores and greater parasympathetic activity. The findings suggest that internalized attention and mindfulness during meditation involve distinct psychophysiological and personality profiles.