EEG signatures for Zazen

I recently obtained and read Zen Meditation and Psychotherapy by Tomio Hirai (1989).  It reports some of the early scientific studies of Zen meditation. Dr. Hira, a Japanese psychiatrist, studied the practice of Zazen by seasoned priest practitioners and controls using EEG and various physiological measures. He found that there were four distinct phases in the meditation of the experienced priests:  Stage I-- appearance of alpha waves, Stage II-- increasing alpha amplitude, Stage III-- decreasing alpha frequency, and Stage IV-- appearance of rhythmical theta trains.  He introduced various sounds, clicks and names, to see what happened to the brain waves of the meditators and controls.  While both the experienced meditators and the controls initially reacted to these stimuli by blocking the then dominant rhythm, the meditators' blocking time was a matter of a few seconds and the controls much longer.  However, whereas the controls habituated to the sounds very quickly, the experienced meditators did not.  This indicated that the controls got caught up by the stimuli with associations, but eventually ignored the stimuli, whereas the experienced meditation quickly let go of whatever associations that may have occurred to them and remained open to new stimuli.

Dr. Hirai discussed EEG biofeedback and the potential to bring brainwaves under conscious control.  However, he did not speculate on the possibility of using this technology to assist individuals in developing meditation skills.