Meditation and the brain

Chapter 9 endnote 41, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

Other studies find that meditation reduces stress, improves the detection and processing of prediction error, facilitates recategorization (termed “emotion regulation”), and reduces unpleasant affect, although the findings are often inconsistent from one study to the next because not all the experiments have been well-controlled. [...] How meditation helps one deconstruct the self and be mindful is an open question.

It’s still an open question whether or how meditation helps people to deconstruct the self and be mindful of sensations in the present moment, but we have some hints. One study showed that meditators had increased activity in the interoceptive network regions and control network regions. People who have been given training with mindfulness meditation (compared to those who receive relaxation training) show increased activity for many (but not all) of the interoceptive network regions and control network regions. Those receiving mindfulness training also showed improved efficiency in their ability to pay attention, reduced reports of negative emotion, increased reports of positive affect, but no improvement in general intelligence. During a stressful arithmetic task, both groups showed a strong cortisol response (meaning that the brain was signaling a metabolic need for glucose), but mindfulness training decreased the cortisol response compared to relaxation training. It also lowered the inflammatory response to the stressful task. A meta-analysis replicated these findings, covering 24 brain imaging experiments that compared meditators to control subjects with no meditation training. Therefore, meditation employs the same brain networks that are involved in constructing emotion and the self. These brain imaging results are consistent with better control over construction.

Meditators and non-meditators appear to have differences in brain structure, according to a meta-analysis in 2014 that summarized 21 experiments with over 300 meditation practitioners. A meditating brain is a (selectively) bigger, better-connected brain. Brain regions increased in cortical thickness. These changes in cortical thickness are probably due to new dendrites growing, new synapses forming, new glial cells growing, and new blood vessels forming, all of which allow neurons to communicate more effectively with each other. White matter changes are likely due to increased myelination, meaning that the protective covering around the axons thickens, so that neurons can send information to one another more quickly.

Key regions of the interoceptive and control networks are larger for meditators, as are regions in somatosensory cortex, representing touch and proprioception sensations (from muscles, tendons, and joints), as well as portions of the visual network. Several of these regions—namely the anterior insula and the ACC—are among the most highly connected in the brain, and they synchronize activity throughout the brain that is necessary for effective prediction and management of prediction error (chapter 4). In some studies, we see stronger connections after only a few hours of mediation training.

Brain changes with meditation may mediate the other biological changes that have been observed, including reduced inflammation.

We must be cautious about drawing hasty conclusions from these results. The science of meditation sees a fair degree of publication bias, where positive findings are preferred and negative results don’t get published. Also, most published meditation experiments have a Western focus, testing whether meditators do better at regulating during a stressful or compassionate task, or whether they improve in their ability to focus their attention. The experiments don’t attempt to deconstruct emotion or the “self,” which is what Buddhist philosophy and the theory of constructed emotion would predict. So more scientific study is needed.