The Effect of Meditation on Brain Structure

Cortical Thickness Mapping and Diffusion Tensor Imaging

Do-Hyung Kang, Hang Joon Jo, Wi Hoon Jung, Sun Hyung Kim, Ye-Ha Jung, Chi-Hoon Choi, Ul Soon Lee, Seung Chan An, Joon Hwan Jang and Jun Soo Kwon

Soc Cogn Affect Neurosci. 2013;8(1):27-33. 

http://www.medscape.com/viewarticle/781577

Abstract and Introduction

Abstract

A convergent line of neuroscientific evidence suggests that meditation alters the functional and structural plasticity of distributed neural processes underlying attention and emotion. The purpose of this study was to examine the brain structural differences between a well-matched sample of long-term meditators and controls. We employed whole-brain cortical thickness analysis based on magnetic resonance imaging, and diffusion tensor imaging to quantify white matter integrity in the brains of 46 experienced meditators compared with 46 matched meditation-naïve volunteers. Meditators, compared with controls, showed significantly greater cortical thickness in the anterior regions of the brain, located in frontal and temporal areas, including the medial prefrontal cortex, superior frontal cortex, temporal pole and the middle and interior temporal cortices. Significantly thinner cortical thickness was found in the posterior regions of the brain, located in the parietal and occipital areas, including the postcentral cortex, inferior parietal cortex, middle occipital cortex and posterior cingulate cortex. Moreover, in the region adjacent to the medial prefrontal cortex, both higher fractional anisotropy values and greater cortical thickness were observed. Our findings suggest that long-term meditators have structural differences in both gray and white matter.

Introduction

One of the biggest challenges for modern neuroscience is the identification of the neuroanatomical correlates of experience-induced neuroplasticity. Experience-induced structural brain changes highlight the relationship between behavior and underlying cortical structures (Draganski et al., 2004; Driemeyer et al., 2008). Indeed, structural brain studies have demonstrated learning-dependent alterations in the adult human brain (Draganski et al., 2006), and the anatomical correlates of navigation (Maguire et al., 2000), arithmetic (Aydin et al., 2007), music acquisition (Han et al., 2009; Hyde et al., 2009), working memory (Takeuchi et al., 2010) and a board game called Baduk in Korea (Lee et al., 2010) have been identified.
Meditation can be conceptualized as a family of complex emotional and attentional regulatory training practices developed for various ends. Recently, the therapeutic use of meditation, including mindfulness-based techniques, has become increasingly important in the treatment of physiological and psychological conditions (Ludwig and Kabat-Zinn, 2008). Furthermore, a convergent body of neuroscientific evidence suggests that meditation alters the function and structure of distributed neural processes underlying attention and emotion (Brefczynski-Lewis et al., 2007; Pagnoni and Cekic, 2007; Lutz et al., 2008). In particular, the altered synaptic structure of the brain circuits associated with attention and emotion might be the one of the essential pathophysiological conditions underlying some major psychiatric disorders such as schizophrenia and depression (Goto et al., 2010).
Previous studies using structural magnetic resonance imaging (MRI) in meditators compared to controls have provided inconsistent results, especially in the frontal cortex (Lazar et al., 2005; Pagnoni and Cekic, 2007; Hölzel et al., 2008; Luders et al., 2009; Vestergaard-Poulsen et al., 2009). Luders et al. (2009) investigated 22 active practitioners of meditations, including Zazen, Samatha and Vipassana and found larger gray matter (GM) density in the orbitofrontal cortex (OFC), which is related to emotional regulation processing (Quirk and Beer, 2006). Lazar et al. (2005) compared 20 insight meditation practitioners to controls using cortical thickness analysis and detected greater cortical thickness in the middle and superior frontal cortices, which is associated with attention processing. There have been studies investigating the relationship between the duration of meditation practice and brain structure. Some studies demonstrated that there is an effect of the duration of meditation practice on local GM, suggesting longer meditation might induce greater changes in brain structure (Hölzel et al., 2008; Grant et al., 2010). However, other studies failed to find any significant correlation between local GM and meditation experience (Luders et al., 2009; Vestergaard-Poulsen et al., 2009). These mixed results may be due to relatively small sample sizes employed in previous studies. In an effort to overcome the limitations of previous studies, in the present study, a large sample of subjects were trained in an identical method of meditation, 'Brain Wave Vibration (BWV)'. Recent studies have reported positive effects of BWV with respect to stress, emotional regulation and neurohormonal levels (Jung et al., 2010, 2012; Bowden et al., 2012).
Diffusion tensor imaging (DTI) is a quantitative method used to assess the integrity of anatomical connectivity in white matter (WM) through the examination of the degree of fractional anisotropy (FA). To our knowledge, only two studies have previously used DTI to examine WM changes in meditators (Tang et al., 2010; Luders et al., 2011). Recently, our group reported training-related alterations in functional connectivity using resting-state functional MRI. Specifically, we found greater default mode network (DMN) connectivity associated with meditation, particularly in the medial prefrontal cortex (MPFC) (Jang et al., 2011). As our previous findings indicated alterations in functional connectivity, we believed that investigating the impact of meditation on alterations in anatomical connectivity is crucial.
The primary focus of the present study was to determine structural brain differences between a group of experienced meditators and a meditation-naive group. Whole-brain cortical thickness analysis based on structural MRI was conducted to investigate GM differences between two groups. WM differences were also examined using DTI. The relationship between structural brain differences and individual characteristics, including practice duration, was conducted in the experienced meditation group to explore the reciprocal interplay between meditation training and underlying cortical structures. We hypothesized that experienced meditators would demonstrate structural differences in the MPFC, orbitofrontal cortex and parietal areas that associated with attention and emotional regulations.