Elsevier

Consciousness and Cognition

Volume 19, Issue 4, December 2010, Pages 899-905
Consciousness and Cognition

Cerebral blood flow differences between long-term meditators and non-meditators

https://doi.org/10.1016/j.concog.2010.05.003Get rights and content

Abstract

We have studied a number of long-term meditators in previous studies. The purpose of this study was to determine if there are differences in baseline brain function of experienced meditators compared to non-meditators. All subjects were recruited as part of an ongoing study of different meditation practices. We evaluated 12 advanced meditators and 14 non-meditators with cerebral blood flow (CBF) SPECT imaging at rest. Images were analyzed with both region of interest and statistical parametric mapping. The CBF of long-term meditators was significantly higher (p < .05) compared to non-meditators in the prefrontal cortex, parietal cortex, thalamus, putamen, caudate, and midbrain. There was also a significant difference in the thalamic laterality with long-term meditators having greater asymmetry. The observed changes associated with long-term meditation appear in structures that underlie the attention network and also those that relate to emotion and autonomic function.

Introduction

Meditation, in general, is a complex neurocognitive task that is often associated with alterations in body physiology and psychological measures. Over the past 30 years, there have been a number of studies which have explored the physiological correlates of different types of meditation. It is important to note here that meditation refers to a large variety of practices that range from purely relaxation based to those performed with the goal of attaining powerful spiritual experiences. This variation, in itself, makes the study of such practices difficult. However, we have tried to find similarities among these practices, and feel that enough prior studies have demonstrated changes associated with these practices, that it seems worthwhile to continue to explore them.

We have previously argued that meditation practices might be regarded as “belief promoting” practices since their content – e.g. Buddhist or Christian ideals – are what the participants focus upon. If such practices alter beliefs and cognitions, then one would expect differences in brain function in individuals who performed such practices for many years compared to those who have not performed these practices. For e.g. the frontal lobes play an important role modulating emotions, engaging cognitive processes, and developing a sense of self. Neuroimaging studies have generally shown increased frontal lobe activity during meditation practices suggesting that meditation may promote beliefs and help reinforce specific religious or spiritual ideals. In addition, meditation techniques often result in alterations in the state of consciousness of the individual (Baijal and Srinivasan, 2010, Lehmann et al., 2001, Travis et al., 2002). Such alterations may be mild, such as a state of relaxation or alertness (Lazar et al., 2000). Sometimes meditation results in profound changes in consciousness leading individuals into trance-type states, states of self-hypnosis, or mystical states (Newberg and Iversen, 2003, Travis et al., 2002). It is also possible that over time, repetitive meditation practice might produce permanent changes in the state of the brain with respect to consciousness (Lutz et al., 2008, Lutz et al., 2009). Furthermore, it has been suggested that meditation affects the brain’s default network (Travis et al., 2010) which is associated with baseline brain function and mediates many basic brain functions. Its subsystems include part of the medial temporal lobe for memory, part of the medial prefrontal cortex for mental simulations, and the posterior cingulate cortex for integration, along with the adjacent precuneus and the medial, lateral and inferior parietal cortex (Buckner et al., 2008, Raichle et al., 2001). If meditation does result in long term changes in brain activity, one might expect that the default network is also changed.

Neuroimaging studies utilizing positron emission tomography (PET), single photon emission computed tomography (SPECT), and functional magnetic resonance imaging (fMRI) have all demonstrated specific changes in cortical and sub-cortical structures when subjects were actively meditating (Herzog et al., 1990-1991, Lou et al., 1999, Lazar et al., 2000, Newberg et al., 2003, Newberg et al., 2001). However, we are aware of a limited number of neuroimaging studies that have evaluated the long-term effects of meditation practices. A study by Lutz, Greischar, Rawlings, Ricard, and Davidson (2004) suggested that the practice of meditation for a period of time can cause longer lasting changes in the brain. Another study (Davidson et al., 2003) showed that there were significant changes over time in the brain’s electroencephalogram. In addition, a study by Lazar et al. (2005) utilizing structural MRI demonstrated that long-term meditators had thicker cerebral cortexes than non-meditators. Other studies showed increased gray matter concentration in meditators compared to non-meditators in the insula, inferior temporal lobe, frontal lobe, and hippocampus (Hölzel et al., 2008, Luders et al., 2009). A different study found that long-meditators did not experience a significant negative correlation between brain volumes and aging as did non-meditating controls subjects (Pagnoni & Cekic, 2007).

This current study retrospectively evaluated all of the meditation subjects that we have studied to date using SPECT imaging and compared the cerebral blood flow (CBF) to whole brain ratios during the baseline (or resting) scan between long-term meditators and non-meditators. In this way, we hoped to evaluate whether there were differences in specific brain areas in long-term meditators compared to non-meditators. If such differences are observed, there remain two intriguing possibilities. One possibility is that meditators have brains that are fundamentally different to begin with which predisposed them to finding such practices beneficial. This might have contributed substantially to these individuals seeking out such practices and making them an important part of their daily lives. The second possibility is that the meditators affected their brains over the course of many years of performing their practice. In either case, if the brains of long-term meditators are different from non-meditators, this finding has potentially important implications for understanding the relationship between the brain and meditation practices.

The purpose of this study was to determine the differences in the brain associated with those individuals performing meditation for many years. What is not yet known is whether changes observed during the acute phase of meditation practice will become more permanent and will be in a similar direction of either increased or decreased activity. Based upon specific areas of the brain previously observed to be affected during meditation and also based upon areas observed to be structurally different in long-term meditators, we elaborated several hypotheses that would be the focus of this study: (1) we expected to observe relatively higher baseline frontal lobe CBF in long-term meditators because we have previously observed increased activity in the frontal lobe regions during active meditation (Newberg et al., 2003, Newberg et al., 2001) and because existing studies have found differences in these structures between meditators and non-meditators (Lazar et al., 2005, Luders et al., 2009); (2) we expected to see relatively lower baseline parietal lobe activity in long-term meditators since meditation is also associated with alterations in the subjective experience of personal space and we have postulated and have found decreased activity in the parietal lobes during active meditation (Newberg et al., 2003, Newberg et al., 2001, Herzog et al., 1990-1991); (3) we expected differences in the midbrain since this structure is related to autonomic changes associated with meditation (Jevning et al., 1992, Sudsuang et al., 1991); (4) we expected to see higher baseline CBF in the basal ganglia and limbic system since these areas are related to emotional processing which has been found to be an important component of meditation (Luders et al., 2009, Lutz et al., 2008); and (5) we expected to see higher thalamic activity since this structure is involved with sensory processing and also for integrating higher cognitive processes and has previously been shown to be activated during meditation (Newberg and Iversen, 2003, Newberg et al., 2001).

Section snippets

Subjects and imaging acquisition

The study protocol and consent form were approved by the human Institutional Review Board. Twelve long-term meditators, with no history or clinical evidence of medical, neuropsychological, or drug abuse that would potentially alter cerebral blood flow, were recruited to participate in this study. Seven were women and five men with ages ranging from 38–52 years with a mean age of 45 years. Each subject described himself or herself as practicing meditation or prayer for more than fifteen years

Region of interest analysis

The scans were reconstructed and resliced, using an oblique reformatting program, according to the anterior-posterior commissure line so that all scans were at comparable orientations for the analysis. A previously validated template methodology consisting of regions of interest (ROI) corresponding to the major cortical and sub-cortical structures was placed over the baseline scan (Resnick, Karp, Tretsky, & Gur, 1993). For the purposes of this study, we examined the CBF as measured in a

Statistical parametric mapping (SPM)

The image volumes of transverse slices were made compatible with SPM by creation of usable headers for the images. For each image, a file was created that contained data on image size, number of slices, pixel depth, maximal pixel value, and voxel size. All slices of a brain image were sampled and averaged to arrive at a mean pixel intensity for that image. The intensity threshold was set at 60% of the whole brain value. The images were spatially normalized in SPM to a standardized stereotactic

Results

Using the ROI analysis, the CBF ratios of long-term meditators was found to be significantly higher (p < .05) compared to non-meditators in the prefrontal cortex (see Fig. 1), parietal cortex, thalamus, putamen, caudate, inferior temporal lobe, cerebellum, and brainstem regions (see Table 1).

SPM analysis confirmed many of these regions to be affected (see Table 2). In particular, SPM found significant higher CBF in the long-term meditators in the parietal lobes, cerebellum, middle frontal lobes,

Discussion

Overall, the findings of this study suggest that long-term meditators have significantly different patterns of CBF at baseline compared to non-meditators. Regarding our initial hypotheses, the first was that we expected to observe a higher level of activity in the frontal cortices in long-term meditators. There have been several studies that have examined the effects of the complex neurocognitive task of meditation on brain activity. Several brain imaging studies have shown changes in frontal

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