Sunday, 23 March 2014

Gamma: Vipassana Goenka style

A study by Cahn et al (2010) looks at EEG during Vipassana meditation in the Goenka style.  The lead-up discussion points to other studies of Vipassana that have more in common with the Mahasi style without, in my view, sufficiently highlighting the great difference between these two styles.

The style of meditation studied is described as follows:
"The specific Vipassana meditative technique involves attentional scanning of sensations
throughout the body in an iterative and cyclic fashion, scanning body sensations from the top of the head to the toes and back again repeatedly, with the concomitant adoption of an attitude of detached observation and non-reactivity to any sensations and thoughts that may arise."

16 subjects with an average of 20 years of daily meditation of at least 30 minutes daily were recruited for the study.  The authors used a 19-channel electrode cap with the following locations: Fp1, Fp2, F3, F4, F7, F8, Fz, C3, C4, T7, T8, Cz, P3, P4, P7, P8, Pz, O1, and O2.  The major bands were demarcated as follows:  delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–25 Hz), and gamma (35–45 Hz).  The contrasting conditions studies were eyes-closed meditation versus ‘‘everyday thinking.’’ However, the authors note that the meditators found it difficult not to slip into meditation when they sat quietly with their eyes closed, a common problem in these types of studies.

Band widths

Statistical differences

The following is a summary of what they found:
"The pattern of meditation-induced increase in parieto-occipital gamma activity, concomitant decrease in frontal delta power, and a shift to a more frontal distribution of theta activity suggests that sensory processing and cognitive processing were altered during meditation relative to the control state."

They entertain alternative hypotheses about what occurred with this increase in gamma activity.  It is possible that this is a specific effect of the iterative body scanning technique, or it may reflect the enhanced perceptual clarity often reported in open-monitoring techniques.

This study highlights several problems with studies of meditation.  First, there are very real differences between different meditation styles, even when they come with a similar label.  One cannot assume that the findings of this study would generalize to Mahasi style Vipassana, for instance.  Second, the band widths are not standardized across studies.  The gamma band (35-45 Hz.) in this study is not comparable to the gamma band in other studies:  25-42 Hz. in Lutz et al, (2004) and 25-35 Hz. in Berkowitz-Ohana et al (2011).  Third, the control conditions of "relaxation" or "everyday thinking" are highly problematic given that most seasoned meditators will meditate as soon as they sit quietly and close their eyes.

Berkovich-Ohana, A., Glicksohn, J., & Goldstein, A. (2012). Mindfulness-induced changes in gamma band activity–implications for the default mode network, self-reference and attention. Clinical Neurophysiology, 123(4), 700-710.

Cahn, B. R., Delorme, A., & Polich, J. (2010). Occipital gamma activation during Vipassana meditation. Cognitive Processing11(1), 39-56.

Lutz, A., Greischar, L. L., Rawlings, N. B., Ricard, M., & Davidson, R. J. (2004). Long-term meditators self-induce high-amplitude gamma synchrony during mental practice. Proceedings of the National Academy of Sciences of the United States of America101(46), 16369-16373.

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