Abstract
Scientific studies addressing anatomical variations in meditators' brains have emerged rapidly over the last few years, where significant links are most frequently reported with respect to gray matter (GM). To advance prior work, this study examined GM characteristics in a large sample of 100 subjects (50 meditators, 50 controls), where meditators have been practicing close to 20 years, on average. A standard, whole-brain voxel-based morphometry approach was applied and revealed significant meditation effects in the vicinity of the hippocampus, showing more GM in meditators than in controls as well as positive correlations with the number of years practiced. However, the hippocampal complex is regionally segregated by architecture, connectivity, and functional relevance. Thus, to establish differential effects within the hippocampal formation (cornu ammonis, fascia dentata, entorhinal cortex, subiculum) as well as the hippocampal-amygdaloid transition area, we utilized refined cytoarchitectonic probabilistic maps of (peri-) hippocampal subsections. Significant meditation effects were observed within the subiculum specifically. Since the subiculum is known to play a key role in stress regulation and meditation is an established form of stress reduction, these GM findings may reflect neuronal preservation in long-term meditators—perhaps due to an attenuated release of stress hormones and decreased neurotoxicity.
Highlights
Numerous studies have revealed meditation effects in the vicinity of the hippocampus, such as more hippocampal and parahippocampal gray matter (GM), larger hippocampal dimensions—both globally and locally—as well as enhanced fiber integrity in white matter pathways connecting with the hippocampus (Holzel et al, 2008; Luders et al, 2009b, 2011, 2012c; Murakami et al, 2012; Leung et al, 2013)
Our study revealed robust meditation effects, with more GM in meditators than in controls within the hippocampal complex as well as positive associations between hippocampal GM and number of practice years
Several studies have demonstrated the hippocampus to be anatomically altered in meditation practitioners, with more hippocampal or parahippocampal GM (Holzel et al, 2008; Leung et al, 2013), larger hippocampal volumes globally (Luders et al, 2009b, 2012c), larger hippocampal radial distances locally (Luders et al, 2012c), as well as enhanced fiber integrity in white matter pathways connecting with the hippocampus (Luders et al, 2011)
Summary
The scientific literature recording anatomical variations in meditators’ brains has grown rapidly in recent years (Lazar et al, 2005; Pagnoni and Cekic, 2007; Holzel et al, 2008, 2010; Luders et al, 2009b, 2011, 2012a,b,c; Vestergaard-Poulsen et al, 2009; Grant et al, 2010; Tang et al, 2010, 2012; Murakami et al, 2012; Kang et al, 2013; Leung et al, 2013). Numerous studies have revealed meditation effects in the vicinity of the hippocampus, such as more hippocampal and parahippocampal GM, larger hippocampal dimensions—both globally (total hippocampal volume) and locally (radial hippocampal distances)—as well as enhanced fiber integrity in white matter pathways connecting with the hippocampus (Holzel et al, 2008; Luders et al, 2009b, 2011, 2012c; Murakami et al, 2012; Leung et al, 2013) This suggests GM to be a sensitive anatomical marker for determining links between mindfulness practices and brain anatomy, with the hippocampal complex implicated as a structure of particular interest. Since the hippocampal formation represents a complex of anatomic divisions varying in size and shape, we utilized a second volumetric approach refined by cytoarchitectonic probabilistic mapping to establish differential effects within (peri-) hippocampal subregions
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