Lab Talk

EEG and Meditation

Neuroscientific studies, particularly EEG, are revealing much about the neural correlates of meditation in the hopes of understanding why it has therapeutic value, and as a way to probe the nature of self and consciousness.

Red-and-orange robed Tibetan monks sit placidly under electrode caps.  Next to them on laptops their EEG data crawls across the screens. The monks are pursuing their goal-less goal—a state of consciousness relaxed, attentive, and sensitive, yet imperturbable—a pursuit that has interested scientists for at least 60 years. The recent Dalai Lama’s active support for the neuroscience of meditation joins with a long tradition of collaboration between meditation masters and neuroscientists in pursuit of knowledge about the human mind and brain.

Towards a Definition of Meditation

Meditation is the English catch-all term for a wide variety of contemplative practices including mindfulness, zen, ch’an, transcendental meditation, qi gong, vipassana, and Tibetan Buddhist practices. Generally, the cultures / languages of these practices’ origins do not possess a blanket term like meditation, referring instead to more specific practices and states. Western researchers are free to define meditation as they wish, but all agree it’s something like any contemplative practice involving mental relaxation and a conscious regulation of attention, thought, and/or emotion (in my own words). Meditation is by now well-recognized by scientific medicine as bringing both short- and long- term benefits to practitioners including subjective feelings of peace and happiness, reduction of anxiety, and improvements in heart condition and immune function.

Contemporary research literature recognizes two main types of meditation – “concentrative” and “open,” which correspond roughly with the traditional Buddhist categories of “meditation on an object” and “objectless meditation.” The two types are distinct but most often represent stages in a person’s meditative development. Few people (if any) can hold their minds empty and relaxed without training and it is easier at first to focus on one object, such as one’s own breath or posture, mantras, or visualizations.

EEG Correlates of Meditation

EEG studies of meditation typically compare experienced meditators to novices.  In novice meditators, the most commonly used meditative paradigm is breath counting.  One can imagine that the many variants of meditative practice and depth of meditation, generally subjectively scored by participants, can introduce variability and confounds.  Nonetheless, the most general and consistently observed EEG correlate of meditation is an increase in the power of lower frequencies between 4 and 10 Hz corresponding to the theta band (4-8 Hz) and the lower end  of the alpha band (8-10 Hz)  (reviews in Aftanas 2004; Cahn 2006; Chiesa 2010; Lomas 2015).  (For a primer on brain frequencies see here). The general amplification of lower alpha frequencies, even as compared to a ‘non-meditative’ eyes closed resting state, is the most universal EEG signature of meditation.

Alpha frequencies have been studied extensively in the literature.  Alpha oscillations are highly variable among human populations and alpha band activity in general is correlated to focused attention (when eyes are open) and to mental imagery when eyes are closed as well as to creativity.  This prompts the obvious question: if alpha activity is so ubiquitous then what is its relevance to meditation specifically?

First Inklings: Alpha Blocking

Alpha blocking in EEG refers to the reduction in alpha and increase in beta which normally occurs in response to sudden stimuli (such as noises).  It occurs most prominently  in the transition from eyes closed to eyes open when visual stimulus floods the brain. The presence of stimulus perhaps shifts the attention from internal imagery to external stimuli.

If you can recall the 1970s, you may remember first hearing about meditation in the popular media in association with the astounding abilities of yogis and zen masters to placidly ignore stimuli, such as large unexpected noises, and otherwise to control normally automatic human neurological activity (such as by slowing their hearts at will).

Alpha ‘Unblocking’ and Regulation of Attention

EEG studies at that time showed that meditators were (what I will call) “alpha unblocking” — maintaining consistent alpha rhythms at times that most of us would alpha block. Interestingly, a few studies showed a converse effect – subjects reacting to repeated stimuli with undiminished alpha-blocking instead of habituating to them as we normally do—their brains reacting as if hearing the noise for the first time, each time. While “alpha unblocking” seems to demonstrate a deeply introspective state of consciousness, this alpha de-habituation seems to demonstrate radical “being-in-the-moment”; both are goals of almost all kinds of meditation. The seeming contradiction between the two results has not been much studied but has been further observed. Do they indicate different kinds of meditation, stages of development, or other individual differences? There are also singular reports of meditation masters who can generate much higher levels of alpha activity or shift localized alpha activity in the brain.

Thus even as we are beginning to understand the role of alpha oscillations (and perhaps by methodological oversights alpha band activity in general ),  the primary outcome of meditation may be to control attention and internal state in the face of the barrage of stimuli, negative and otherwise, that we experience everyday.

Beyond Alpha

Alpha oscillations are not the end of the story.  Other and especially recent research is discovering further meaningful phenomena in other frequency bands, especially gamma,  as well as neural synchrony and complexity in particular sub-networks of the brain and also differences in hemispheric symmetry.  These are for future discussion.

 

2 thoughts on “EEG and Meditation

  1. You can see in the book O Homem Holístico , Efitora Vozes a more deep review of Meditation and EEG

    1. As indicated, this post focuses on only the first recognized correlate of meditation — alpha — because it’s a complex subject in itself. As indicated at the end of the post, this is only the beginning of the story; part II will be out soon, and that won’t cover it all either; it is such a rich subject! 🙂

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