How does meditation experience functionally change the brain, and what effects does this have on distractibility? These are the questions addressed in a 2006 PNAS article from Brefczynski-Lewis et al, who compare expert meditators (between 10,000 and 54,000 hours of meditation experience) with two age-matched novice groups, one paid to help control for any motivation-related differences between groups.
As compared to a resting condition, the neural correlates of meditation changed with experience according to a U-shaped function: those with the most and least meditation experience show relatively little activation of the neural networks involved in attention (left superior & middle frontal gyrus, among other regions), as though meditation requires additional effort only during an intermediate stage of expertise. The most experienced meditators showed only an initial 10s spike of activity in the dorsalateral prefrontal cortex, whereas those with less experience sustained this activity throughout the meditation period.
In response to distracting events (oddball sounds played during the meditation, as compared with random null events), all subjects showed activation of a right-lateralized ventral attentional network, but only novice meditators showed a greater activation of a default mode network in response to these events (perhaps indicating greater "mind wandering" as a result of distraction). The finding of increased ventral network activity was surprising to the authors, who suggested this network (and the changes in pupil diameter also observed) may have reflecting some kind of "monitoring" process among meditators.
As with all studies, there are a few caveats: the differences seen here might reflect self-selection on the behalf of the expert meditators, and the "resting" baseline comparison condition is conceivably a poor one. On the other hand, the authors rightfully suggest that until we know more about what meditation is actually doing, other baseline conditions may have their own confounds.
The authors conducted various analyses to rule out other potential caveats, such as that these effects could be due to structural differences between the expert and novice meditators' brains, to motivational influences, or to age differences between groups.
I would think the only way to really study the change question would be a longitudinal study. As a moderately experienced practitioner of TM, and a people watcher of and from the early days of the movement, I submit there is a measure of self-selection in becoming an experienced meditator, so there may be a native structural difference between the populations. One that may be buried below the noise level of individual variations. I would expect that if they found any significant differences, that would just show that there is a difference, not that it was engendered by the practice.
However, I would agree that something changes. And after reading about Dr. Jeffrey Schwartz's work with OCD patients, I am willing to accept structural changes following consistent and persistent mental exercises.
Gray, these are great points!
Todays' post addresses the self selection component and comes up with some discrepant results from Jha et al - in summary, they find completely nonoverlapping attentional improvements when subjects are randomly assigned vs. recruited based on their prior interest.
Not clear what the cause of this is, as the study also uses a much shorter training period than Jha et al (5 days vs. 8 days & 1 month).