ABSTRACT: This pilot study investigates EEG correlates of successive stages of concentration meditation. During the course of a 30 minute meditation session, an experienced meditator subjectively observed stages of meditative depth, and reported the presence of a particular stage of meditation using simple finger positions. Meanwhile, EEG data were measured at 19 locations on the scalp. The EEG data collected during each reported stage of meditation were independently analyzed. A comparison of the frequency spectra at successive stages of the meditation session show positive correlation between subjectively reported meditative depth and the strength of 7-8 Hz theta peaks at all locations, with the strongest signals present in the central locations. Only in the deepest stages do these peaks emerge in the frontal locations.
Lindsley’s work, however, did not account for differences between EEG measurements at various locations on the scalp. Jasper (1958) introduced the standardized system for electrode placement in EEG research that is still in use today. There are seven frontal positions (FP1, FP2, F3, F4, F7, F8, Fz), three central positions (C3, C4, Cz), four temporal positions (T3, T4, T5, T6), three parietal positions (P3, P4, Pz), and two occipital positions (O1, O2). There are also two ear-lobe positions (A1, A2) used as electrical references for the other electrodes. Even-numbered positions correspond to the right side of the head, odd-numbered positions correspond to the left side of the head, and positions on the left-right plane of symmetry are denoted by the letter “z”. (This system is illustrated in each of the various figures shown later in this article.)
The relationship between EEG measurements and meditation was first investigated in the 1950s and 1960s. Although the differences between various meditative practices must be taken into account, these studies generally suggest that increased alpha and theta activity is strongly correlated with most meditative states of mind. Of particular relevance to the present paper is the study of advanced zazen meditators by Hirai (1974). Four EEG stages were identified in meditation sessions: (1) initial appearance of alpha, (2) increased alpha, (3) decrease in alpha, (4) increased rhythmical theta (bursts of 6-7 Hz primarily in central locations). The presence of these distinct phases of the objective EEG data suggest that there may be distinct subjective states that correspond to these phases during the meditation session. It is the purpose of this pilot study to experimentally explore this question.
The experiment also requires a technique that allows the subject to communicate introspective data during the meditation without interfering significantly with the qualities of mind being reported. After experimenting with various communication schemes, it was found that the subjective experience of mental disruptions were minimized by using a simple communication technique that keeps physical movements to a minimum. The technique used for the present study uses the fingers of one hand to indicate a successive stage in the meditation session. A sequence of identifiable subjective stages were identified and practiced during a meditation session every day for several weeks prior to the experiment. For example, the meditation session begins with no fingers extended; after “settling” the mind and body and resting the mind on an object of meditation the next phase of the meditation is indicated by extending one finger (which remains extended). When a deeper sense of mental and physical relaxation and stability is experienced, an additional finger is extended. During practice, typically three to four fingers were extended by the end of a 30 minute session. The experiment was performed in the morning of Wednesday 15 March, 2000 in a small room containing research-grade EEG equipment. An EEG cap was placed on my head, and 19 electrodes were all connected. They all had impedances below 5 kilo-Ohms with reference to my ear lobes. As is usual in my morning meditation practice, I sat in a half-lotus on my zafu pillow. An experimental assistant (David) was present in the room to operate and monitor the EEG equipment. He also had the task of recording my finger signals during the experiment, as well as their corresponding EEG epoch numbers.
For a three minute period just prior to the formal meditation session, a “baseline” measurement was made. In order to avoid artifacts due to eye movements, it was necessary for me to hold the gaze of my eyes fixed as much as possible. This had the undesired effect of beginning to induce a slight meditative state of mind. This draws attention to the fact that even a “normal” state of mind is in some sense conditioned by various factors. In any case, the “baseline” at least provided a measurement of a state of mind prior to an extended period of meditation.
The meditation session proper then started as I started my digital watch timer for 30 minutes and rang my gong. In the preliminary phase (phase “zero”), my attention was intentionally scanned throughout my entire body, and any tensions were released. I also took two or three deep breaths. After about a minute or two of these standard preliminaries, I then began the initial phase of the concentration meditation, which was indicated by moving my right forefinger from the curled position to the extended position. In this initial phase my practice was to place the attention on the breath and continue to relax the mind and body. After a few minutes, there was a sense of slight deepening of relaxation of mind and body, and my middle finger on my right hand was also extended to signal phase two. The fingers remained in an extended position as long as I sensed that the degree of depth in the meditation was at a certain subjective level. After a few more minutes, the meditation deepened slightly more and I extended my ring finger to signal phase three. Most of the remaining meditation session was experienced in phase three.
It should be noted that there were loud sounds of a jackhammer and other construction sounds during the meditation session (the experimental room was located on the 6th floor of a building in downtown San Francisco). These distracted the attention from the breath. Rather than resisting these distractions, however, my attitude was to be open to them and accept them into awareness. Nevertheless, these sounds did tend to keep the mind and body at a certain level of stimulation and seemed to prevent relaxation from progressing beyond a certain point, as compared to other meditations in other more quiet circumstances. It should also be noted that, near the end of phase three, physical discomforts due to minor back strain and the pressure of the EEG cap on the head were distractions from the breath. As with the jackhammer, my attitude toward these was to open up to them with acceptance rather than resistance. Near the end of the 30 minute session, my state of consciousness shifted for a minute or two into a significantly deeper level that was accompanied by an enhanced sense of stillness of both mind and body, and an increased subtlety of awareness. At this point, the physical discomforts seemed to pale in comparison to the increased intensity of awareness. There was also an increased sense of disengagement with the visual field for a few moments. This state then seemed to gradually shift back toward phase three, but the meditation session then came to a close as the watch timer rang. Other than the discomfort near the end of phase three, the cap was not experienced as interfering with the meditation.
Regarding the finger signals, because I had practiced these signals every day or two for two weeks prior to the experiment, and since they required little effort or involvement, they did not seem to interfere much at all with the meditation.
This technique involves an interplay between laxity and excitement. This suggests another possibility, which would be to use a two-dimensional map rather than a linear map of the subjective states. Fingers of the right hand could be used to indicate degrees of excitement, while fingers of the left hand could be used to indicate degrees of laxity. For an expert meditator, introspecting and reporting these two qualities of mind should be feasible without interfering with the meditation. For example, the laxity and excitement could be independently reported, each with three degrees. There are a total of six fingers are used (e.g., three fingers 1R, 2R, 3R on the right hand and three fingers 1L, 2L, 3L on the left hand), providing a map of nine states of mind, as shown in the table below.
Vivid Mind vs. Dull Mind (Clarity vs. Laxity)
Vivid and Engaged
Dull and Disengaged
Jasper, H. H. (1958), The ten-twenty electrode system of the International Federation. Electroencephalography and Clinical Neurophysiology, 10, 371-375.
Lindsley, D. B. (1952), Psychological phenomena and the electroencephalogram. EEG and Clinical Neurophysiology, 4, 442-456.