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Meditation experience is associated with increased
cortical thickness
Sara W. Lazar
a
,CatherineE.Kerr
b
, Rachel H. Wasserman
a,b
, Jeremy R. Gray
c
,DouglasN.Greve
d
,
Michael T. Treadway
a
,MettaMcGarvey
e
,BrianT.Quinn
d
,Je¡eryA.Dusek
f,g
,HerbertBenson
f,g
,
Scott L. Rauch
a
,Christopher I.Moore
h,i
and Bruce Fischl
d,j
a
Psychiatric Neuroimaging Research Program, Massachusetts General Hospital,
b
Osher Institute, Harvard Medical School, Boston,Massachusetts
c
Departmentof Psychology, Yale University, New Haven, Connecticut,
d
Athinoula A.Martinos Center for Biomedical Imaging, Massachusetts
General Hospital, Boston,
e
Graduate Schoolof Education, Harvard University, Cambridge,
f
Mind/B ody Me dical Ins titute, Ch estnut Hill,
g
Departmentof Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston,
h
Departmentof Brain and Cognitive Sciences,
Massachusetts Institute of Technology,
i
McGovern Institute for Brain Res earch and
j
Computer Science and AI Lab (CSAIL),
Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Correspondence and requests for reprints to Sara W. Lazar, PhD, Room 2609, 14913th St.Charlestown, MA 02129, USA
Tel: + 1617 724 7108; fax: + 1617 726 4078; e-mail: lazar@nmr.mgh.harvard.edu
Sponsorship:This work was supported by NIH/NCCAM K01AT00694- 01, NCRR (P41RR14075), the MINDInstitute, and CDC Grants H75/CCH119124 and
H75/CCH 123424. C.K. was supported by Grant R21AT002860 - 02.
Received 26 August 2005; revised 16 September 2005; accepted 19 September 2005
Previous research indicates that long-term meditation practice is
associated with altered resting electroencephalogram patterns,
suggestive of long lasting changes in brain activity. We hypothe-
sized that meditation practice might also be associated with
changes in the brain’s physical structure. Magnetic resonance
imaging was used to assess cortical thickness in 20 participants
with extensive Insight meditation experience, which involves
focused attention to internal experiences.Brain regions associated
with attention, interoception and sensoryprocessing were thicker
in meditation par ticipants than matched controls, including the
prefrontal cortex and right anterior insula. Between-group di¡er-
ences in prefrontal cor tical thickness were most pronounced
in older participants, suggesting that meditation might o¡set
age-related cortical thinning. Finally, the thickness of two regions
correlated with meditation experience. These data provide the
¢rst structuralevidence for experience-dependent corticalplasticity
associa ted with meditation pr actice. NeuroReport 16:1893^1897
c2005 Lippincott Williams & Wilkins.
Key wor ds : insula, meditation, plasticity, prefrontalcortex
Introduction
Meditation is a form of mental exercise that has become a
popular US health practice. Regular practice of meditation is
reported to produce changes in mental state and resting
electroencephalogram patterns that persist beyond the time-
period of active practice [1]. We hypothesized that regular
meditation practice should also result in significant changes
in the cortical structure in regions that are routinely engaged
during this mental exercise. To test this hypothesis, we used
magnetic resonance imaging to visualize differences in the
thickness of the cerebral cortex of experienced Buddhist
Insight meditation practitioners. This form of meditation
does not utilize mantra or chanting. Rather, the main focus
of Insight meditation is the cultivation of attention and a
mental capacity termed ‘mindfulness’, which is a specific
nonjudgmental awareness of present-moment stimuli with-
out cognitive elaboration [2]. Formal practice involves
sustained mindful attention to internal and external sensory
stimuli. Thus, we tested the hypothesis that between-group
and experience-dependent differences in cortical thickness
would be found in brain regions involved in attention and
sensory processing, thereby showing evidence of cortical
plasticity.
Par ticipants and methods
Twenty participants with extensive training in Insight
meditation were recruited from local meditation commu-
nities. These participants were not monks, but rather typical
Western meditation practitioners who incorporate their
practice into a daily routine involving career, family, friends
and outside interests. Two participants were full-time
meditation teachers, three were part-time yoga or medita-
tion teachers and the rest meditated an average of once a
day for 40 min, while pursuing traditional careers in fields
such as healthcare and law. On average, participants had
9.177.1 years of meditation experience and practiced
6.274.0 h per week. Participants were required to have
participated in at least 1 week-long Insight meditation
retreat, which entails approximately 10 h of meditation per
day. Fifteen control participants with no meditation or yoga
experience were also recruited. The meditation and control
AGEING NEUROREPORT
0959 -4965 cLippincott Williams & Wilkins Vol 16 No 17 28 November 2005 1893
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
participants were matched for sex (meditators 65% male,
controls 67%), age (meditators 38.2 years old, controls 36.8
years old), race (both groups 100% Caucasian) and years of
education (meditators 17.3 years, controls 17.4 years). All
participants were physically and psychologically healthy.
Two meditation participants were left-handed; exclusion of
the left-handed participants did not significantly alter
results. All participants provided written, informed consent
and the study was approved by the Institutional Review
Board at the Massachusetts General Hospital.
The present methods utilized a well-validated computa-
tional approach to measure the thickness of the cerebral
cortex [3,4]. Cortical thickness was estimated from two
magnetization prepared rapid gradient echo (MPRAGE)
structural images collected from each participant that were
then motion-corrected and averaged together to form a
single high-resolution image [3–5]. An initial estimate of the
gray/white matter boundary was constructed by classifying
all white matter voxels in a magnetic resonance imaging
volume using a combination of geometric and intensity-
based information. A surface-deformation procedure was
then used to obtain subvoxel resolution in the gray/white
boundary and in the pial surface using a combination of
smoothness constraints and intensity terms. The resulting
cortical surface models for all participants were aligned to
an atlas of cortical folding patterns using a high-dimen-
sional nonlinear registration technique.
Results
The mean thickness across the entire cortex did not differ
significantly between the groups for either hemisphere
(P40.10), indicating that it was not the case that the cortex
of meditators is nonspecifically thicker everywhere. Statis-
tical thickness-difference maps constructed using the
Kolmogorov–Smirnoff statistics (one-tailed, a-level
P¼0.05), however, indicated that significant differences in
the ‘distribution’ of thickness existed between groups across
both hemispheres (k¼3.89, P¼0.0001), and in each hemi-
sphere separately (k¼3.02, P¼0.0025 for left hemisphere;
k¼2.49, P¼0.013 for right hemisphere). This finding indi-
cates that the pattern of relative thickness across each
hemisphere was different between groups. Protected by
significant unidirectional results for the omnibus test for
each hemisphere, an unpaired t-test was performed to test
for specific loci of significant between-group differences in
regional cortical thickness. Specifically, we tested the a priori
hypotheses that differences would be observed within
prefrontal, interoceptive and unimodal sensory cortical
regions. A false discovery rate of 0.05 corresponding to an
uncorrected P¼3.5 10
4
was used to correct for multiple
comparisons [6].
Within the search territory, a large region of right anterior
insula (P¼1.2 10
5
) and right middle and superior frontal
sulci corresponding approximately to Brodmann areas (BA)
9 and 10 (P¼1.8 10
5
) were significantly thicker in
meditators than in controls (Fig. 1). The left superior
temporal gyrus (auditory cortex, P¼3.7 10
4
) and a small
region in the fundus of the central sulcus, (BA 3a,
somatosensory cortex, P¼6.0 10
4
) showed trends towards
a significantly thicker cortex in meditation participants than
in controls. Analysis of the right frontal BA 9/10 subregion
resulted in a significant age by group interaction,
F(1,31)¼10.85, P¼0.002, with typical age-related decreases
observed in the control group [r(13)¼0.76, P¼0.001] but
not in the meditation group [r(18)¼0.05, P¼0.83]. Sig-
nificant interactions were not observed in any other brain
region.
As a further confirmation that meditation can influence
experience-dependent plasticity, we tested whether objec-
tive measures of meditation experience correlated with
cortical thickness. As frequency of daily practice varies
2.2
P<10−3
(d)(c)
(b)
(a)
P<10−
4
3
12
4
2
1.9
Thickness
1.520 25 30 35 40 45 50 55
20
1.7
Thickness (mm)
1.9
2.1
2.3
2.5
25 30 35
Age Age
40 45 50 55
Fig. 1 Cortical regions thicker in meditators than in controls. (a and b)
Statistical map depicting between-group di¡erences in thickness at each
point on the cor tical surface overlaid on the in£ated average br ain. All
points meeting a Po0.01 threshold (uncorrec ted) are displayed to be tter
illustrate the anatomic extent of the areas and the relative speci¢city of
the ¢ndings. Numbered regions: (1) insula, (2) Brodmann area (BA) 9/10,
(3) somatosensory cortex, (4) auditory cortex. (c and d) Scatter plot
of mean cortical thickness of each participant in the subregion above
threshold within each circled region of (c) insula and (d) BA 9/10, plotted
versus age.Meditation participants: blue circles; control participants: red
squares.
1894 Vol16No1728November2005
NEUROREPORT LAZAR ETAL.
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
between meditation practitioners, using the total number of
years of practice is not a sensitive metric of experience. One
effect of regular meditation practice is a significant drop in
respiration rate during formal practice [7,8]. We therefore
tested whether changes in respiration rate between rest and
meditation could serve as an objective measure of medita-
tion experience. The change in mean respiration rate from a
6-min baseline period to the first 6 min of the meditation
period was calculated for each participant and then
correlated with the self-reported total number of hours of
formal sitting meditation over the participant’s lifetime
(r¼0.75, Po0.001). The correlation between respiration
rate and total number of years the participant had been
practicing was also significant (r¼0.57, P¼0.009); however,
the correlation with total hours of formal sitting practice
resulted in a higher coefficient.
To directly test for cumulative effects of meditation
experience on brain structure, a correlation was performed
between cortical thickness and change in respiration rate.
After correcting for multiple comparisons using a false
discovery rate associated with a P¼0.05, the analysis
revealed one significant region within the inferior occipito-
temporal visual cortex (Fig. 2). Among the meditation
group, the zero-order correlation between thickness in this
region and change in respiration rate was r(18)¼0.72,
Po0.001, which was effectively unchanged when control-
ling for individual right-hemisphere mean thickness (as a
measure of nonspecific effects on cortical thickness), partial
r(17)¼0.73, Po0.001, and still further when controlling for
age, partial r(16)¼0.75, Po0.001. When controlling for age
and individual right-hemisphere average thickness, a partial
correlation between thickness in this region and years of
experience remained significant [partial r(15)¼0.627,
P¼0.007]. These findings are consistent with the hypothesis
that meditation practice promoted thickening in this region.
The most experienced participants were also among the
oldest. As age-related decreases in cortical thickness are
greatest in frontal regions [5], it is possible that the effect of
age may obscure the modest effects of meditation practice in
these areas. The Pearson correlations between respiration
rate and cortical thickness in the insula and BA 9/10 were
not significant (r¼0.36, P¼0.12 and r¼0.23, P¼0.33,
respectively), although they became so in the insula after
controlling for age [partial r(17)¼0.48, P¼0.04]. The correla-
tion between these parameters for the BA 9/10 region was
essentially unchanged [partial r(17)¼0.25, P¼0.30].
Discussion
Our data indicate that regular practice of meditation is
associated with increased thickness in a subset of cortical
regions related to somatosensory, auditory, visual and
interoceptive processing. Further, regular meditation prac-
tice may slow age-related thinning of the frontal cortex.
Previous studies of cortical plasticity in animals and
humans have shown that when a task requires that attention
be consistently directed towards a behaviorally relevant
sensory stimulus (e.g. a somatosensory [9] or auditory
stimulus [10]) over repeated practice sessions [11], robust
changes in sensory cortical maps result ([12] and Kerr CE,
Wasserman RH and Moore CI. Cortical plasticity as a
therapeutic mechanism for touch healing, under reveiw).
Additional studies suggest that relaxation facilitates the
learning-based process that underlies such cortical plasticity
[13]. It may be useful to conceptualize meditation practice as
engaging in an analogous set of cortical remodeling
processes: namely, directing attention towards behaviorally
relevant sensory stimuli within a relaxing setting over
repeated practice sessions [2,7]. Increased cortical thickness
could be due to greater arborization per neuron, increased
glial volume or increased regional vasculature. The methods
employed do not distinguish between these possibilities;
however, each of these mechanisms is supportive of
increased neural function.
We hypothesized that meditation practice should promote
neural plasticity in regions that are routinely engaged
during formal practice. Many factors including age, sex,
genetics, neuropathology and psychopathology [4,5,14,15],
however, influence the thickness of cortex nonspecifically,
confounding these analyses. Perhaps the largest of these
confounds is the effect of age. The rate of age-dependent
thinning is highly variable across the cortical surface [5].
Meditation-related effects on thickness may have been
counterbalanced by the effects of age on cortical thinning,
thereby minimizing our ability to detect significant correla-
tions. Thinning is most pronounced in the frontal lobe, and
indeed there were many regions in the parietal, temporal
and occipital lobe where there was little if any difference in
the average thickness in our older and younger participants
(data not shown). Such age-related effects may account for
−10
1.5
(b)
1.7
1.9
2.1
2.3
−5
Change in breathing rate (bpm)
Thickness (mm)
05
(a)
Fig. 2 Visual area correlated with meditation experience. (a) Statistical
map depic ting cor tical thickness c orrelated with change in respiration
rate. (b) Scatter plot of mean cortical thickness of each participant from
the circled region within the inferior occipitotemporal lobe plotted
versus change in respiration rate.Note: negative change inbreathing rate
(left side) is associated with more hours of meditation experience and a
thicker cor tex.
Vol 16 No17 28 November 2005 1895
MEDITATION AND CORTICAL THICKNESS NEUROREPORT
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
the fact that the strongest correlation with experience was
found in the occipitotemporal region, while other regions of
interest, which all lie in frontal regions, had only low
correlation with experience. Interestingly, despite the effects
of aging on the prefrontal cortex, in one focal region of BA
9/10 the average cortical thickness of the 40–50-year-old
meditation participants was similar to the average thickness
of the 20–30-year-old meditators and controls, suggesting
that regular practice of meditation may slow the rate of
neural degeneration at this specific locus. Future long-
itudinal studies will be required to verify this finding.
Another factor possibly confounding our ability to detect
correlations between thickness and experience is hetero-
geneity in the specific mental exercises that Insight practi-
tioners engage in over time. Beginners are taught to
maintain focused awareness on interoceptive stimuli and
then are gradually taught to expand their awareness to
focus on thoughts, emotions and external stimuli
such as sounds, although there is no prescribed schedule
or order in which these practices are taught. Correspond-
ingly, the insula, an area associated with the interoceptive
processes and breath awareness techniques common to
beginning and experienced meditators, had the largest and
most significant between-group difference, while unimodal
sensory areas, which may be associated with more
advanced and heterogeneous practices, had less significant
differences.
As a result of the cross-sectional nature of the study, the
findings are necessarily correlational, and a causal relation-
ship between cortical thickness and meditation cannot be
inferred. For example, it is possible that people with thicker
sensory cortex are for some reason drawn to meditation.
Several factors, however, suggest that these findings relate
to the meditative practice itself. First, although there were
significant ‘regional’ differences in thickness between
groups, there was no between-group difference in ‘global’
mean cortical thickness, indicating that these findings are
unlikely to be due to spurious between-group differences
that might impact cortical structure nonspecifically. Second,
the regions of cortical thickening correspond well to the
specific activities that practitioners of Insight repeatedly
engage in over time – paying attention to breathing
sensations and sensory stimuli. It is unlikely that nonspe-
cific lifestyle effects such as diet would be associated with
the specific pattern of differences found. The most plausible
explanation for the specific pattern observed is experience-
dependent cortical plasticity.
Finally, both years of practice and change in respiration
rate (a physiological measure of cumulative meditation
experience) were correlated with cortical thickness in two
regions, the inferior occipitotemporal visual cortex and right
anterior insula. These findings are consistent with other
cross-sectional reports of experience-dependent differences
in neural volume [16,17]. In addition, a longitudinal study
[18] has demonstrated that learning to juggle is associated
with increases in visual motion cortical areas. Our finding of
a correlation between the thickness in two regions and
amount of experience lends support to the hypothesis that
the observed differences are acquired through extensive
practice of meditation, and are not simply due to pre-
existing or incidental between-group differences.
Most of the regions identified in this study were found in
the right hemisphere. The right hemisphere is essential for
sustaining attention [19], which is a central practice of
Insight meditation. The largest between-group difference
was in the thickness of right anterior insula. Functional
imaging and electrophysiological studies in humans and
monkeys have implicated the right anterior insula in tasks
related to bodily attention and increased visceral awareness
[20,21]. Structural measures of gray matter volume of the
right anterior insula predict accuracy of objective measures
of interoceptive performance, as well as subjective ratings of
global visceral awareness [21]. The differential thickness
between groups in this region is consistent with increased
capacity for awareness of internal states by meditators,
particularly awareness of breathing sensations. Right BA
9/10 has been shown to be involved in the integration of
emotion and cognition [22]. It has been hypothesized that by
becoming increasingly more aware of sensory stimuli
during formal practice, the meditation practitioner is
gradually able to use this self-awareness to more success-
fully navigate through potentially stressful encounters that
arise throughout the day [2,23]. This eastern philosophy of
emotion dovetails with Damasio’s theory that connections
between sensory cortices and emotion cortices play a crucial
role in processing of emotionally salient material and
adaptive decision making [24].
Other forms of yoga and meditation will likely have a
similar impact on cortical structure, although each tradition
would be expected to have a slightly different pattern of
cortical thickening based on the specific mental exercises
involved [7,8,25]. Although numerous studies have
shown that indices of cortical size can decrease as a result
of aging and pathology (e.g. [4,5]), there are limited data
indicating mechanisms that promote cortical thickening
[16–18]. Our findings suggest that cortical plasticity can
occur, in adults, in areas important for cognitive and
emotional processing.
Conclusion
Our initial results suggest that meditation may be associated
with structural changes in areas of the brain that are
important for sensory, cognitive and emotional processing.
The data further suggest that meditation may impact age-
related declines in cortical structure.
Acknowledgements
We thank R. Gollub, D. Salat, M. Bar, G. Kuperberg and
S. Stufflebeam for helpful discussions. We also thank
I. Rosman for technical assistance, J. Zaki for manuscript
editing, and D. Salat and D. Rosas for access to data.
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