With Comments from Russell H. Greenfield, MD Dr. Greenfield is Medical Director, Carolinas Integrative Health, Carolinas HealthCare System, Charlotte, NC, and Clinical Assistant Professor, School of Medicine, University of North Carolina, Chapel Hill, NC; he has no financial relationships with companies having ties to the material presented in this continuing education program.
Could Meditation Give You a Big Head?
Source: Lazar SW, et al. Meditation experience is associated with increased cortical thickness. NeuroReport 2005;16:1893-1897.
Goal: To determine whether regular insight meditation practice causes changes in cortical thickness in brain regions involved in attention and sensory processing (i.e., cortical plasticity).
Design: Cross-sectional study.
Subjects: Twenty people with extensive insight meditation experience and 15 controls with no experience with meditation or yoga.
Methods: Participants underwent magnetic resonance imaging (MRI), and a validated computational method for determining cortical thickness was employed. Results for those with meditation experience were compared to results for subjects in the control group. Change in mean respiratory rate (RR) from a six-minute baseline to the first six minutes of the meditation period was determined for each of the meditating participants and correlated with self-reported total number of hours of formal meditation during the person's lifetime. A correlation was also performed between change in RR and cortical thickness.
Results: The pattern of relative thickness across each hemisphere was significantly different in specific areas between the two groups. Increased cortical thickness was identified in regions involved with somatosensory, auditory, visual, and interoceptive (originating from within the body) processing in those meditating regularly (right anterior insula, right middle and superior frontal sulci). Typical age-related decreases in specific subregional cortical thickness were found in controls but not in the regular meditators. A correlation was found between total lifetime hours of meditation and RR, and at least a partial correlation was noted between change in RR and thickness of specific regions of the cortex (the insula and inferior occipito-temporal visual cortex).
Conclusions: Regular meditation practice results in an increased cortical thickness in a subset of brain regions associated with processing of stimuli. Regular meditation may also slow age-related thinning of the frontal cortex.
Study strength: Use of a validated measure to determine cortical thickness.
Study weaknesses: Small sample size; no mention of where control subjects were recruited from; the most experienced meditators were also among the oldest participants, so typical age-related changes in cortical thickness may have obscured modest effects of meditation practice in certain brain regions.
Of note: Mean cortical thickness across the entire cerebral cortex did not differ significantly between the two groups, indicating that meditation did not create generalized and nonspecific cortical thickening; the majority of cortical changes were detected in the right hemisphere; the primary focus of Buddhist insight meditation is to cultivate attention and mindfulness, or non-judgmental awareness of moment-to-moment stimuli both internal and external without the use of mantras or chants; subjects with prior meditation experience were "regular people" with jobs, family, and outside interests, not monks; two participants were full-time meditation instructors, three were part-time meditation/yoga instructors, the rest meditated an average of once a day for 40 minutes (subjects had been practicing meditation, on average, for more than nine years and had participated in at least one week-long insight meditation retreat); all subjects were healthy and were matched for age, sex, race, and education level; frequency of daily meditation practice varied widely among the meditators; the insula, an area of the brain associated with breath awareness techniques and interoceptive processing, showed the largest between-group differences with regard to cortical thickness.
We knew that: Many trials have shown that cortical thickness decreases as a result of aging and pathology; prior studies have shown that regular meditation alters a person's resting EEG, suggesting long-term changes in brain activity that persist beyond the time period of meditation practice; during formal meditation practice a drop in RR typically occurs; augmented cortical thickness can occur as the result of a combination of increased arborization per neuron, greater glial volume, or enhanced regional vascularization; learning to juggle has been shown to increase the thickness of the visual cortex; many factors influence cortical thickness including genetics, age, neuropathology, and gender; the rate of age-dependent thinning is highly variable across the cortex.
Clinical import: This intriguing trial offers compelling results that call out for corroboration. As the authors point out, cross-sectional studies can reveal correlations, but do not prove the existence of a cause-and-effect relationship. That stated, the differences in cortical thickness between the groups were not global in nature, but specific to regions associated with stimulus processing that are also active during the practice of insight meditation. The idea that changes in regional cortical plasticity could have been due to nonspecific lifestyle differences between the groups seems unlikely. Ample data do exist to support the practice of mindfulness meditation in specific clinical situations, but the notion that meditation could help prevent changes in the brain typically associated with aging should be of great interest to researchers. Future studies will need to focus on the duration and frequency of meditation needed to experience objective benefit; however, it would seem prudent to mention the promising results of meditation trials to our patients (and to explore the practice ourselves).
What to do with this article: Keep a copy on your computer.