Lazar and colleagues at Harvard Medical School used MRI to compare cortical thickness in 20 experienced Insight meditation practitioners (average 9 years of practice) against 15 matched controls. Meditators had significantly thicker cortex in the prefrontal cortex and right anterior insula, two regions involved in attention and awareness of internal body signals. The thickness difference was most striking in older participants, suggesting that meditation may slow age-related thinning of the brain. The amount of cortical thickness correlated with the amount of meditation experience. Published in NeuroReport (Vol. 16, pp. 1893-1897). This was one of the first studies to link meditation to measurable physical differences in the brain.

Holzel and colleagues scanned the brains of 16 people before and after an 8-week Mindfulness-Based Stress Reduction (MBSR) course and compared them to 17 people on a waitlist. The meditation group showed significant increases in gray matter concentration in the left hippocampus, which is important for learning and memory, as well as in the posterior cingulate cortex, temporo-parietal junction, and cerebellum. The control group did not show these changes. Gray matter is the tissue in the brain that contains nerve cell bodies, so an increase suggests more nerve cells or denser connections. Published in Psychiatry Research: Neuroimaging (Vol. 191, pp. 36-43).

Fox and colleagues at the University of British Columbia reviewed 21 studies that used brain scans to compare the brains of meditators with non-meditators. They found that 8 brain regions consistently showed differences, including the prefrontal cortex (involved in planning and self-control), the insula (involved in body awareness), the hippocampus (involved in memory), and the corpus callosum (the bridge connecting the two brain halves). They calculated an overall effect size of 0.46 (a medium-sized effect, where 0.2 is small and 0.8 is large), based on 132 measurements across 16 studies. The authors noted that while the pattern was consistent, publication bias was a concern. Published in Neuroscience and Biobehavioral Reviews (Vol. 43, pp. 48-73).

Luders and colleagues at UCLA compared brain scans of 22 long-term meditators (averaging 24 years of practice, ranging from 5 to 46 years) with 22 people matched for age, handedness, and sex who did not meditate. The meditators had significantly more gray matter in the right orbito-frontal cortex (involved in emotional regulation), right thalamus (a relay station for sensory information), left inferior temporal gyrus (involved in visual processing), and right hippocampus (involved in memory). These are regions linked to emotional regulation, response control, and sustained attention. Published in NeuroImage (Vol. 45, pp. 672-678).

Luders and colleagues measured cortical gyrification, which is the degree of folding on the brain surface, in long-term meditators versus controls. Greater folding is thought to allow the brain to process information faster. Meditators showed significantly more gyrification in the left precentral gyrus, right fusiform gyrus, right cuneus, and both sides of the anterior insula. The amount of extra folding correlated with the number of years the person had been meditating, meaning people who meditated longer had more folded brains. Published in Frontiers in Human Neuroscience (Vol. 6, Article 34).

Gotink and colleagues analyzed brain scans from 3,742 participants in the Rotterdam Study, a large ongoing population health study in the Netherlands. People who practiced meditation or yoga had significantly smaller right amygdala volume (31.8 cubic millimeters less, which is a small but measurable difference). The amygdala is the brain region most associated with processing fear and stress. Follow-up analysis over time confirmed the association, with a 24.4 cubic millimeter reduction in right amygdala volume in practitioners. This was by far the largest study to examine brain structure and meditation, making its findings more statistically reliable than smaller studies. Published in Brain Imaging and Behavior (Vol. 12, pp. 1631-1639).

Pagnoni and Cekic at Emory University compared brain scans of 13 regular Zen meditation practitioners with 13 matched controls. In the control group, gray matter volume decreased with age, following the normal pattern of brain aging. In the meditator group, this age-related decline was absent. The protective effect was especially strong in the putamen, a brain region involved in focused attention. The meditators also performed better on a rapid visual information processing task. While the study was small, it suggested that sustained meditation practice may protect against normal age-related loss of brain tissue. Published in Neurobiology of Aging (Vol. 28, pp. 1623-1627).

Luders, Thompson, and Kurth compared hippocampal dimensions in 30 meditators (15 men and 15 women, each averaging over 20 years of practice) with 30 non-meditating controls. The hippocampus is a brain structure essential for memory and emotional regulation. Both male and female meditators showed larger hippocampal dimensions than their respective control groups, but the specific location, side of the brain, and size of the difference varied between men and women. This suggests meditation-related brain changes may interact with sex-based biological differences. Published in Frontiers in Psychology (Vol. 6, Article 186).

Holzel and colleagues measured brain structure in 26 healthy but stressed adults before and after completing an 8-week MBSR program. They found that the amount of stress reduction each person reported correlated with decreases in gray matter density in the right basolateral amygdala, the part of the brain most involved in processing threats and stress responses. People who reported feeling less stressed showed more amygdala shrinkage. This suggests the brain physically reorganizes in response to stress reduction through meditation. Published in Social Cognitive and Affective Neuroscience (Vol. 5, pp. 11-17). However, the study did not find a significant overall change in amygdala volume for the whole group.

Desbordes and colleagues assigned healthy adults with no meditation experience to 8-week courses in either mindful attention meditation or compassion meditation, plus a control group. Before and after the courses, participants viewed emotional images while inside a brain scanner, and crucially, they were not meditating during the scan. The mindful attention group showed reduced amygdala activity in response to all images, while the compassion group showed increased amygdala activity to images of suffering. These changes persisted outside of formal meditation practice, suggesting that meditation training produces lasting changes in how the brain processes emotions, not just temporary shifts during meditation itself. Published in Frontiers in Human Neuroscience (Vol. 6, Article 292).