Age effects on gray matter volume and attentional performance in Zen meditation

Abstract

Zen meditation, a Buddhist practice centered on attentional and postural self-regulation, has been speculated to bring about beneficial long-term effects for the individual, ranging from stress reduction to improvement of cognitive function. In this study, we examined how the regular practice of meditation may affect the normal age-related decline of cerebral gray matter volume and attentional performance observed in healthy individuals. Voxel-based morphometry for MRI anatomical brain images and a computerized sustained attention task were employed in 13 regular practitioners of Zen meditation and 13 matched controls. While control subjects displayed the expected negative correlation of both gray matter volume and attentional performance with age, meditators did not show a significant correlation of either measure with age. The effect of meditation on gray matter volume was most prominent in the putamen, a structure strongly implicated in attentional processing. These findings suggest that the regular practice of meditation may have neuroprotective effects and reduce the cognitive decline associated with normal aging.

Introduction

Buddhist meditative practices have received considerable attention recently (Barinaga, 2003, Knight, 2004), for their potential phenomenological and epistemological contributions to cognitive science (Varela et al., 1991) and as a context in which to investigate neural plasticity related to mental practice (Lutz et al., 2004). The latter point is particularly relevant here: not unlike learning a second language or a musical instrument, meditation traditionally requires a long-term commitment to daily practice and therefore has the potential to induce changes in neural function and structure. While meditative practices can vary greatly, even within the Buddhist tradition itself, a core characteristic is the importance assigned to attentional and postural self-regulation, indicating the engagement of voluntary selection and inhibition processes common to many training situations. Zen meditation, in particular, is performed by sitting cross-legged (in the “lotus” or “half-lotus” position) and trying to maintain throughout the session a straight posture, a normal breathing pattern, and a mental attitude of openness to one's own mental processes while recognizing the occurrences of episodes of mind-wandering and distraction.

The recent development of imaging techniques has allowed researchers to observe learning-related morphological brain changes in domains as diverse as spatial navigation (Maguire et al., 2000), music (Gaser and Schlaug, 2003), language (Mechelli et al., 2004), and juggling (Draganski et al., 2004). While structural effects of training, typically observed as regional increases in gray matter volume or thickness of the cortical sheet, represent one facet of normal brain plasticity, an equally important and counteracting factor is age. Gray matter volume and cortical thickness have been shown to decrease starting at or immediately after adolescence (Good et al., 2001, Sowell et al., 2003), a loss that is partially echoed by some aspects of cognitive function, particularly in the attentional and executive domains (Chao and Knight, 1997). In the present study, we used voxel-based morphometry (VBM) (Ashburner and Friston, 2000) and a computerized neuropsychological test to examine the putative effect of regular meditative practice on the age-related decline in gray matter volume and attentional performance observed in healthy subjects. Given the cross-sectional design of the study, the use of terms such as “decline” or “rate of change” should be generally interpreted here as between-subjects inferences rather than directly observed longitudinal effects.