Friday, 4 January 2013

A review of meditation studies

A recent review of meditation studies (Fell et al, 2010) raises issues that are worth considering.

The authors reflect on the inconclusive results from previous studies (Cahn, B.R., Polich, J., 2006).  Meditation takes diverse forms, but the authors feel that during the development of meditation practice some common characteristics are shared and passed through.  They offer two hypotheses.  The first is that every meditative training involves a similar scheme of development.  The second is that the steps are similar, beginning with similar physical demands,  With increasing experience the student focuses on an object with consequent slowing of internal dialogue accompanied by greater relaxation.  With advanced practice, the student undergoes a change in the relationship between thoughts and feelings, and the student starts experiencing mental processes as temporary and transient.  The most advanced step in meditation practice occurs when the meditator achieves certain peak experiences and undergoes permanent changes and alterations of consciousness that last outside of the mediation experiences.

In terms of EEG correlates, the authors maintain that there is a state-related slowing of the alpha rhythm in combination with an increase in alpha power which is localized in frontal regions.  This pattern occurs early on in the development of meditation practice.  The alpha oscillations are thought to reflect an increase in internal attention.

A general increase in theta activity occurs with mediation practice and is associated with more advanced levels.  Sharp bursts or theta trains, proceeded and followed by alpha, have been observed in studies and are thought to distinguish the theta that occurs in meditation from the irregular theta that reflects drowsiness.  This type of theta activity has also been observed to occur after meditation when the meditators opened their eyes and were alert.

Synchronized gamma oscillations have been associated with meditation.  Studies with long-term meditators doing different forms of focused and compassion meditation found high levels of gamma activity.  The authors speculate that gamma activity may provide ideal conditions for cortical plasticity and the formation of neural circuits.

While these generalizations provide a context to look at meditation, the diversity of meditation practices and their neurophysiological correlates warrants examination.  And there is abundant evidence that the differences matter.

Cahn, B. Rael, and John Polich. "Meditation states and traits: EEG, ERP, and neuroimaging studies." Psychological bulletin 132.2 (2006): 180.

Fell, Juergen, Nikolai Axmacher, and Sven Haupt. "From alpha to gamma: Electrophysiological correlates of meditation-related states of consciousness."Medical hypotheses 75.2 (2010): 218-224.

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