Enhanced brain connectivity in long-term meditation practitioners
Research Highlights
► Little is known about the cerebral characteristics that underlie meditation. ► Our DTI study revealed enhanced structural connectivity in meditators. ► FA was larger within projection, commissural, and association pathways. ► Largest effects were observed bilaterally within CST and UNC, and within left tSLF. ► Meditation might be a powerful tool to change the physical structure of the brain.
Introduction
Meditation is a cognitive practice directed at stilling the fluctuations of the mind (Baerentsen et al., 2009). Meditators, especially long-term practitioners, provide an ideal human model for investigating brain plasticity given their ongoing, frequent, and regular cognitive efforts. The effect of meditation on brain function has been addressed in a large number of functional studies (Cahn and Polich, 2006). However, research exploring possible links between meditation and brain structure is still surprisingly sparse. With only a small number of structural MRI studies published, existing findings point to larger brain regions (thicker cortices, more brain tissue, and a diminished age-related atrophy, respectively) in meditators compared to control subjects (Grant et al., 2010, Luders et al., 2009b, Holzel et al., 2008, Vestergaard-Poulsen et al., 2009, Pagnoni and Cekic, 2007, Lazar et al., 2005). Recent longitudinal MRI studies complement these cross-sectional outcomes by revealing actual meditation-induced increases in gray matter (GM) density as a consequence of mindfulness-based stress reduction interventions over eight weeks (Holzel et al., 2011). Interestingly, existing findings appear to support the notion that significant links between meditation and brain anatomy are wide-spread throughout the entire brain involving both cortical and subcortical regions (e.g., superior, middle and inferior frontal gyrus, orbito-frontal cortex, paracentral regions [including somatosensory cortex], inferior temporal, superior temporal, fusiform, and cingulate gyrus, insula, thalamus, putamen, and hippocampus) as well as the brain stem and the cerebellum. Consequently, one might also expect enhanced brain connectivity in meditators, particularly with respect to fiber tracts connecting those aforementioned brain regions shown to be linked to meditation.
Diffusion tensor imaging (DTI) is an exciting, relatively new imaging modality providing valuable insights into the structural connectivity of the brain by quantifying the overall orientation of white matter bundles. Nevertheless, DTI studies in meditators are surprisingly rare. In fact, to our knowledge, only one study incorporated DTI-based data and assessed the effect of an Integrative Body–Mind Training (IBMT) in a subsample of 22 subjects (Tang et al., 2010). Indeed, this longitudinal study demonstrated that as few as 11 h of IBMT (spread over one month) is sufficient to raise the fractional anisotropy (FA) – an indicator of white matter integrity – of several fiber tracts, including the superior and anterior corona radiata, the genu and body of the corpus callosum, and the superior longitudinal fasciculus. However, given the lack of any additional reports regarding DTI-based findings, further studies are clearly necessary to advance this field of research. Thus, we set out to compare fiber characteristics utilizing DTI and atlas-based tract mapping methods in a relatively large sample of long-term meditators and well-matched controls. To expand the extremely sparse literature with respect to DTI-based findings and to provide a foundation against which future outcomes can be compared, we applied a broad field mapping approach and investigated 20 different fiber tracts (i.e., 9 tracts in each hemisphere and 2 inter-hemispheric tracts).
Section snippets
Subjects
Our sample consisted of 27 active meditation practitioners (mean age ± SD: 51.6 ± 12.3 years) and 27 sex- and age-matched controls (mean age ± SD: 51.4 ± 12.4 years). Both the meditation and the control group contained 11 men and 16 women. The maximum allowed age difference within a sex-matched pair across groups was two years. Altogether, age ranged between 25 and 71 years. Both groups were comparable with respect to their educational background with 89% of all mediators and 93% of all controls having,
FA Differences between long-term meditators and controls
The repeated-measures omnibus model including the 9 bilateral tracts yielded a significant Group-by-Tract Interaction (F[8,44] = 3.332; p = 0.005) and a significant Group-by-Tract-by-Hemisphere interaction (F[8,44] = 2.452; p = 0.027).
As summarized in Table 1 (Group), we detected significantly larger FA in meditators than in controls within the following fiber tracts: anterior thalamic radiation (ATR), cingulum–hippocampus (CgH), corticospinal tract (CST), inferior fronto-occipital fasciculus (IFO),
Discussion
We detected larger FA throughout the entire brain when comparing long-term meditators against a well-matched sample of healthy controls. FA is a measure of how anisotropic (cigar-shaped) the fitted tensor is within a given voxel. That is, FA indicates the degree of directional sensitivity of water diffusion within the voxel (Basser and Pierpaoli, 1996). As summarized recently (Thomason and Thompson, 2011), higher FA measures reflect fibers that are more numerous, more dense, more myelinated, or
Acknowledgments
We warmly thank all participants for their dedication and partaking in our study. We are also grateful to Trent Thixton who assisted with the acquisition of the image data. For generous support the authors thank the Brain Mapping Medical Research Organization, the Robson Family and Northstar Fund, and the following Foundations: Brain Mapping Support, Pierson-Lovelace, Ahmanson, Tamkin, William M. & Linda R. Dietel Philanthropic Fund at the Northern Piedmont Community, Jennifer Jones-Simon, and
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