Mind, Brain, Consciousness
An EEG Study of Samatha meditation
An electroencephalogram or EEG is a recording of the brain’s electrical activity using sensors placed across the head. It is a non-invasive procedure, completely safe and painless. Most modern studies use specially designed headcaps, reasonably comfortable to wear, that automatically position electrodes according to internationally agreed positions (below left) so that different studies can be compared consistently. For many years EEG recordings have been widely used to study epilepsy and other neurological disorders, but more recently they are also being increasingly used to study the mind-brain interface, and consciousness itself. In this section, some early results from a pilot study of Samatha meditators that began in July 2010 are described.
A typical recording using 19 electrodes is shown below right. Each horizontal trace is the electrical signal from a single position on the head, compared to a reference point, either A1 or A2 (usually the earlobes, or the mastoid bone below each ear). The labels identify the position on the head, where F, P, C, O and T denote the frontal, parietal, central, occipital and temporal lobes of the brain. For example, the T5-A1 trace is the electrical signal from the posterior left temporal region, compared to the left mastoid reference. At a quick glance, the recording below shows enhanced activity at the left-frontal sites Fp1 and F3, and also (4th trace up) at the right posterior temporal site T6
The raw electrical signals are analysed to find the intensities of different frequency bands across the head. This particular recording is of a meditator practicing rūpa jhāna, and the 2-dimensional plots shown below the raw electrical traces show the electrical intensity maps looking down on the head, and from the side. The two left-hand maps show the slowest Delta wave band (1.0–4.0 Hz), and the two right-hand maps show the Theta wave band (4.0–8.0 Hz).
One of the most striking observations from this study, even for relatively inexperienced meditators, has been to find enhanced low-frequency Delta and Theta EEG activity during Samatha meditation. Compared to a typical waking state, the higher frequency Alpha and Beta bands (8–30Hz) that are normally dominant in the waking state are effectively suppressed compared to the lower Delta and Theta frequencies in deep meditation. Alpha and Beta plots are therefore not shown here in these pilot results.
For this meditator, the most intense electrical activity is focused in the left-of-centre frontal cortex, in the Theta band (4.0–8.0 Hz). There is also a second significant, though less intense, area around the right posterior temporal region (T6) again in the Theta band, but also extending (weakly) into the even slower Delta band. Delta and Theta slow waves are known to be associated with deep relaxation. Theta activity normally tends to develop at the borders of sleep, and Delta activity in deep sleep. However, in Samatha meditation these slow waves develop as part of a highly alert state. One of the benefits of this type of study is that the meditator is able to give detailed subjective feedback immediately after the recording, and in this case, the meditator was giving attention to a strong visual nimitta.
When this same meditator then changed to develop arūpa jhāna, the recordings, shown below, changed dramatically. As the meditator let go of attending to the nimitta, electrical brain activity shifted to the right posterior temporal lobe (particularly around the site T6 in the raw electrical signals below), which, among other functions, is known to be involved in integrating spatial representations.
The corresponding 2-dimensional plots, below left, show that this intense posterior temporal lobe energisation has now spread into the low-frequency (1.0–4 Hz) Delta band, as well as the Theta band. Delta activity is normally mostly found in deep dreamless sleep, but, as already noted, in Samatha meditation it can occur as part of the highly aware meditative state.
Interestingly, this meditator acknowledged being at a fairly early stage in developing arūpa jhāna, and was very encouraged to see the dramatic change in moving from rūpa jhāna to arūpa jhāna practice, i.e., that their subjective willed experience was actually reflected in profound changes in their brain’s activity.
This highlights another important finding, which is that there appears to be a process of development of jhāna, and the degree of absorption, rather than an on/off transition into a clearly delineated state. It seems that at an early stage, the jhāna may only be momentary, and the meditator may not be fully aware of what has been experienced, perhaps because the perception is more subtle than the normal sensory processes and their familiar continuity of experience.. For this reason, “recollection” immediately after practice of what has been experienced is very important in Samatha traditions, and is part of the development of mastery of jhāna ̶ of entering jhāna, of duration of the jhāna , and of emerging from the jhāna.
From the limited sample of meditators so far (~12), it also appears that individual meditators may have their own “signature” to their brain activity in jhāna. Thus, rūpa jhāna for one meditator may look slightly different in terms of brainwaves to the experience of another meditator. There may also be gender and age differences in meditators’ brain activity, which will require further study.
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The next example below shows the arūpa jhāna practice of a very experienced meditator. The raw electrical signals on the left show highly synchronised activity (top to bottom traces) across large areas of the brain.
The 2-dimensional plots on the right confirm this, and show extensive areas of the brain across frontal, parietal and rear occipital areas to be highly energised. The frequency range is strongest in the Theta band, but the lower frequency Delta band is also strongly energised. These two arūpa jhāna examples suggest Delta-band very deep “relaxation” – or in our terminology “absorption” – develops in an active form in arūpa jhāna, unlike its more normal “unconscious” occurrence in deep sleep.
Many meditators, as their concentration develops, at some stage experience states of energisation that can cause bodily vibration or shaking of various degrees. This is related to Pīti, one of the five jhāna factors, that becomes fully developed in the 2nd rūpa jhāna, and which is usually translated as “joyful interest”, or “rapture”. In the Abhidhamma it is not, however, classified as part of the feeling group, and is more a sign of a deepening connection with the meditation object at the level of both body and mind. In the progression of the jhānas, pīti is superceded by the deeper happiness of sukha in the 3rd jhāna, while In the Bojjangas, or Factors of Enlightenment, pīti arises in connection with, or follows, viriya, usually translated as “effort” or “energy”, and which leads to passaddhi, “tranquillity”.
The energisation of pīti in the normal development of the jhānas may be quite gentle, such as a tingling of the hairs on the body, but it is possible to deliberately focus on the developing energisation to arouse intense effects such as shaking or even jumping of the body. For some meditators this is an interesting exercise in becoming more familiar with the nervous and muscular systems of the body, even though it is not a main purpose of developing meditation.
Below is an historic picture – the first EEG recording (July 2010) of the electrical brain activity of an experienced Samatha meditator demonstrating the deliberate arousing of the highly energised state alluded to above. The recording shows intriguing similarity to EEG recordings of some epileptic seizures, but in this case the meditator arouses the state and then calms it down at will, and with no discomfort.
The thought naturally arises, that if an experienced Samatha meditator is able to control his/her brain’s electrical activity to this degree, what lessons might be transferred to help epilepsy sufferers better manage their symptoms?
This is a particularly dramatic recording, and a big problem in analysing a recording such as this is in knowing how to separate movement or muscle artifacts from the actual brain EEG activity.
A second example below shows a milder arousing of pīti where the separation of physical and muscle artifacts is easier, though still not straightforward. This meditator had been practising this form of energisation practice for only a relatively short time, but had previous experience of developing pīti in other ways. In this example, because the meditator “comes out of” the energised state and back into meditation proper more cleanly than in the previous example, it is possible to compare the meditation state before and after the pīti “event”.
All the traces after the arousing of pīti are more intense than before, apart from those referenced to A1 – this is because the bodily tremors of the “seizure” partly dislodged the A1 ear reference during the recording! The intensification is particularly strong at site T3, the left temporal area, after the burst of pīti, compared to before arousing pīti.
To look at this more closely, a 2-dimensional spectral plot (marked 1) was computed for the four seconds “immediately-after” period, and shows intense focused activity in the left temporal lobe in the Theta band.
A second spectral plot (marked 2) was then computed a full minute later, after the meditator had performed two further arousings of pīti. Plot 1, from immediately after arousing and then calming the first pīti, confirms focused and intense energisation of the left temporal region in the Theta band. Plot 2, a minute later after two further pīti episodes shows that the meditator’s brainwaves have now slowed right down into the Delta band, still focused in the left temporal region, but much more extensive.
This sequence illustrates how consciously arousing pīti, then calming and tranquilising the energisation, sometimes over several sequences, intensifies and deepens a meditator’s practice. In a sense, the technique is a “short-cut” to access deeper levels of aborption or samādhi.
The process appears to correspond to the sequence of the final four stages of the Bojjangas, or the Buddhist Seven Factors of Enlightenment: pīti, pasaddhi, samādhi, upekkhā (joyful energisation, tranquillity, concentration, equanimity). Also, the study shows that the deeper stages of jhāna are characterised by very slow-wave electrical activity in the brain, normally only seen in unconscious deep sleep, but now experienced fully consciously.
© 2012, samadhieeg.org.uk