Increased gray matter volume in the right angular and
posterior parahippocampal gyri in loving-kindness
Mei-Kei Leung,1,2Chetwyn C. H. Chan,3,4Jing Yin,4,5Chack-Fan Lee,4,5Kwok-Fai So,4,6,7and Tatia M. C. Lee1,2,4,7,8
1Laboratory of Neuropsychology, The University of Hong Kong, 852 Hong Kong, China,2Laboratory of Cognitive Affective Neuroscience,
The University of Hong Kong, 852 Hong Kong, China,3Applied Cognitive Neuroscience Laboratory, Department of Rehabilitation Sciences,
The Hong Kong Polytechnic University, 852 Hong Kong, China,4Social Neuroscience Research Network, The University of Hong Kong, 852 Hong
Kong, China,5Centre of Buddhist Studies, The University of Hong Kong, 852 Hong Kong, China,6Department of Anatomy, The University of
Hong Kong, 852 Hong Kong, China,7The State Key Laboratory of Brain and Cognitive Sciences, The University of Hong Kong, 852 Hong Kong,
China, and8Institute of Clinical Neuropsychology, The University of Hong Kong, 852 Hong Kong, China
Previous voxel-based morphometry (VBM) studies have revealed that meditation is associated with structural brain changes in regions underlying
cognitive processes that are required for attention or mindfulness during meditation. This VBM study examined brain changes related to the practice
of an emotion-oriented meditation: loving-kindness meditation (LKM). A 3T magnetic resonance imaging (MRI) scanner captured images of the brain
structures of 25 men, 10 of whom had practiced LKM in the Theravada tradition for at least 5years. Compared with novices, more gray matter volume
was detected in the right angular and posterior parahippocampal gyri in LKM experts. The right angular gyrus has not been previously reported to have
structural differences associated with meditation, and its specific role in mind and cognitive empathy theory suggests the uniqueness of this finding for
LKM practice. These regions are important for affective regulation associated with empathic response, anxiety and mood. At the same time, gray matter
volume in the left temporal lobe in the LKM experts appeared to be greater, an observation that has also been reported in previous MRI meditation
studies on meditation styles other than LKM. Overall, the findings of our study suggest that experience in LKM may influence brain structures associated
with affective regulation.
Keywords: temporo-parietal junction; voxel-based morphometry; metta meditation; empathy; affective regulation
It is well known that the human brain is a malleable organ. This sug-
gests that intense training can induce structural changes in brain
regions that are needed to produce the trained behavior (Draganski
and May, 2008). Indeed, scientists coined the term ‘neuroplasticity’ to
describe the fact that the human brain changes in response to experi-
ential learning. The classic study of London taxi drivers is one of the
best illustrations of experience-induced neuroplastic change. In their
study, Maguire et al. (2000) demonstrated that experience navigating
London streets was associated with significantly larger bilateral poster-
ior hippocampi. The hippocampus is known to be a spatial navigation
center (Maguire et al., 1998). Along similar lines, Aydin et al. (2007)
found that math experts have higher gray matter density in the parietal
cortex than did controls. In fact, the parietal cortex is known for its
involvement in arithmetic calculations and visuospatial processing
(Dehaene et al., 1999).
Meditation is a process of training mental states, and such experi-
ential learning may affect the human brain. Lazar et al. (2005) were the
first to investigate the relationship between meditation and structural
brain changes. They found that expert insight meditators had a thicker
prefrontal cortex and right anterior insula than novice meditators.
Since then, other studies have reported differences in brain structures
between experts and novices in a number of meditation practices,
including Zen (Pagnoni and Cekic, 2007; Grant et al., 2010), insight
(Ho ¨lzel et al., 2008), concentrative practices and open awareness
(Vestergaard-Poulsen et al., 2009) and a mixed style (Luders et al.,
2009). Zen experts have a thicker anterior cingulate cortex (ACC)
compared with novices (Grant et al., 2010). The ACC actively helps
people focus and refocus attention voluntarily in response to distrac-
tion and, thus, may help Zen meditators maintain their state of ‘emp-
tiness’ (Pagnoni et al., 2008). In insight experts, the right anterior
insula is cortically thicker than in novices (Lazar et al., 2005). The
insula is important for interoceptive awareness, which connects us
with our subjective internal states (Ho ¨lzel et al., 2008). Some studies
have reported that cortical thickness/gray matter volume is associated
with years/hours of meditation practice (Lazar et al., 2005; Ho ¨lzel et al.,
2008) while other studies have failed to identify any relationship
between these two variables (Luders et al., 2009; Vestergaard-Poulsen
et al., 2009).
In general, scientific studies have focused on types of meditation
that train attention regulation to produce a calm mind. Therefore, it
should be no surprise that they have found differences in the brain
regions in the attention system. Following this line of thought, medi-
tation that focuses on affective processing should have an effect on the
emotion-processing system. If meditation really can change how the
brain processes emotions, the finding could influence how clinicians
design interventions for clinical affective dysregulation.
Loving-kindness meditation (LKM) is a form of meditation that
trains emotion regulation. LKM practitioners explicitly cultivate posi-
tive feelings, generating an emotional state that is full of unconditional
love, compassion and empathy toward the self and others, without any
discursive thoughts (Salzberg, 1995). Previous research has shown that
a short LKM practice in the laboratory was sufficient to induce
Received 18 January 2012; Accepted 8 July 2012
Advance Access publication 18 July 2012
This work was supported by the May Endowed Professorship, a Research and Conference Grant (#10401362 to
T.L.), research funding from the Centre of Buddhist Studies of The University of Hong Kong (to T.L.) and the
Research Grant Council General Research Fund (HKU747612H to T.L.). There are no conflicts of interest including any
financial, personal or other relationships with persons or organizations for any author related to the work described
in this article.
Correspondence should be addressed to Tatia M. C. Lee, May Professor in Neuropsychology, Laboratory of
Neuropsychology, The University of Hong Kong, Room 610, Knowles Building, Pokfulam Road, Hong Kong, China.
doi:10.1093/scan/nss076SCAN (2013) 8, 34^39
? TheAuthor (2012).PublishedbyOxfordUniversity Press.
‘feelings of social connection and positivity towards strangers on both
explicit and implicit levels’ (Hutcherson et al., 2008). Furthermore,
after completing a 12 week focused-attention meditation (FAM) and
LKM intervention, college students had significantly less anxiety and
negative affect (Sears and Kraus, 2009). LKM’s unique focus on culti-
vating positive emotions and heartfelt care for self and others makes it
a valuable technique to counteract negative symptoms such as anhe-
donia and blunted affect from which people with schizophrenia suffer
(Johnson et al., 2009; Garland et al., 2010). However, despite the po-
tential value of LKM in reducing negative emotions and improving
mental well-being and social connectedness, it has received only sparse
scientific attention. In particular, it is important to understand how
LKM might affect brain structure, yet this issue has remained unex-
plored. To date, only a few functional magnetic resonance imaging
(fMRI) studies have addressed the neural correlates of LKM. Lutz
et al. (2008) had LKM experts and novices listen to neutral and emo-
tional (including positive and negative) human vocalizations during
meditation and rest states, respectively. They found significantly higher
activation in LKM experts than in novices during meditation than in
the rest state (i.e. state-by-group interactions) in the amygdala and
temporo-parietal junction (TPJ), which is constituted by the inferior
parietal lobule (IPL), superior temporal gyrus (STG) and posterior
superior temporal sulcus (pSTS) during all sounds; in limbic regions
such as the insula and cingulate cortices during emotional sounds and
in the insula during negative sounds. These results are in agreement
regarding the networks that are important for social cognition, for
instance, mind and empathy theory (Saxe and Kanwisher, 2003;
Decety and Lamm, 2007). This has led to speculation that long-term
LKM practice may enhance mentation toward human voices and
emotion sharing (Lutz et al., 2008). In their follow-up study, Lutz
et al. (2009) further investigated the relationship between the brain
and the cardiovascular system on the same group of subjects, listening
to emotional sounds during the compassion state. The neural activity
in the right insula, somatosensory cortices, right IPL and premotor
areas was found to be positively associated with heart rate; also, this
positive association was especially strong in LKM experts compared
with novices during the compassion state. These data suggest that LKM
training may change brain representations toward affective stimuli and
these functional brain changes may be tied to the visceral system.
To verify the possibility that the devoted cultivation of positive
emotion and compassion could bring about changes in brain struc-
tures, on top of that provided by mindfulness training, we adopted
automated voxel-based morphometry (VBM) to examine differences
in gray matter volume between LKM experts and novices on a
whole-brain voxel-by-voxel basis. In general, meditation practitioners
usually commence their practice in forms that train attention or mind-
fulness and then move on to the forms of practice they want to pursue.
Different forms of meditation are thought to reinforce one another.
Therefore, we hypothesized that LKM experts would have more gray
matter volume than novices not only in brain regions previously indi-
cated for attention or mindfulness meditation but also in those regions
related to social cognition and affective processing as reviewed above,
such as the right TPJ (including the IPL, STG and pSTS) and the
amygdala. Furthermore, we examined the relationship between hours
of meditation practice and gray matter volume in our LKM experts.
MATERIALS AND METHODS
Twenty-five healthy Chinese men participated in this study, 10 of
whom were LKM experts, while the remaining 15 were novices without
long-term meditation experience. Both groups were matched on age
and education levels. The experts were recruited from a Buddhist
meditation network in Hong Kong and had at least 5years of LKM
practice based on the Theravada tradition. To control for any possible
confounding variance introduced by different motivations for medita-
tion practice, for the comparison group for the LKM experts, we used
novices interested in meditation who had undergone a total of 7h of
training in basic meditation self-practice. The home-based meditation
self-practice was carried out based on written instructions for practi-
cing concentration/calming/kindness-cultivation skills prepared by our
co-investigator, the Venerable Jing Yin, who is himself an expert in
meditation. The instruction was similar to that offered by the
Venerable Dr M. Ricard, who has a great deal of experience practicing
and teaching meditation. All subjects were right-handed, measured
with the Edinburgh Handedness Inventory (Oldfield, 1971). The sub-
jects had no history of traumatic brain injury, medical conditions or
psychiatric disorders that could have affected their brain structure at
the time of the study. All subjects gave their written informed consent
to take part in this study, which was approved by the Institutional
Review Board of The University of Hong Kong/Hospital Authority
Hong Kong West Cluster.
High-resolution MRI brain images were acquired via a 3.0 Tesla
Philips Medical Systems Achieva scanner with an eight-channel
SENSE head coil. A three-dimensional, T1-weighted, magnetization-
prepared rapid acquisition gradient-echo sequence was used with 164
contiguous sagittal slices 1mm in thickness, time to repetition¼7ms,
time to echo¼3.2ms, flip angle¼88, field of view¼164mm, ma-
trix¼256?240mm and voxel size¼1?1?1mm.
Image processing (VBM-Dartel)
The MRI images were processed using the VBM8 toolbox (Christian
SPM8 (Wellcome Department of Cognitive Neurology, London, UK;
http://fil.ion.ucl.ac.uk/spm) in MATLAB 7.7.0 (Mathworks Inc.,
Natick, MA, USA). The default settings were used unless otherwise
specified. Each MRI image was first displayed in SPM8 to screen for
artifacts or gross anatomical abnormalities. For better registration, the
orientation of the images was adjusted to match the template and the
image origin was manually set to a position as close to the anterior
commissure as possible. In the spatial normalization step, the
high-dimensional Dartel normalization approach (VBM-Dartel) was
chosen (Ashburner, 2007). This deformation technique has much
inter-subject alignment, especially for small inner structures (Yassa
and Stark, 2009), and it is more sensitive to regional differences,
such as those that appear in the hippocampus (Bergouignan et al.,
2009). It is thought to be a better alternative to the standard
VBM-SPM normalization approach (Ashburner and Friston, 2000).
To preserve the actual gray matter values locally and account for in-
dividual differences in global brain size, modulated gray matter seg-
ments were generated by multiplying them with the non-linear
components derived from the normalization matrix instead of the
linear components. The covariance between all normalized modulated
images was visualized using a boxplot and covariance matrices to check
for homogeneity and, thus, inspect for outliers. Finally, the normalized
modulated images were smoothed with a standard Gaussian kernel of
8mm, full width at half maximum. Smoothing rendered the data more
normally distributed so that the assumption of parametric statistical
comparisons was not violated (Worsley et al., 1996). Normalized and
bias-corrected images of all subjects were also obtained and further
averaged to create a study-specific template to visualize the results.
Morphometryof LKM practitionersSCAN (2013)35
A series of statistical analyses were performed on the smoothed, nor-
malized and modulated gray matter images in SPM8. Two-sample in-
dependent t-tests were run to identify group differences in whole-brain
gray matter volume between experts and novices. An absolute thresh-
old masking of 0.1 was used, meaning that only voxels with gray matter
values >0.1 were counted. Global normalization was not needed in the
statistical model because we applied the correction directly to the data
during the modulation step using the non-linear (instead of the linear)
component, as recommended in the VBM8 manual. Clusters were
considered significant at the combined voxel-extent threshold of an
uncorrected voxel level of P<0.01 and cluster extent >530voxels, as
determined based on Monte Carlo simulations with AlphaSim equiva-
lent to P<0.05, corrected for multiple comparisons. A more lenient
corrected P<0.1 was then adopted to detect trend-level results, which
corresponded to P<0.01 and a cluster extent of >463voxels. To fur-
ther examine the relationship between the duration of meditation
training and gray matter volume, correlation analysis was conducted
between hours of meditation practice and average gray matter volume
extracted from the significant cluster(s) using the REX toolbox for the
LKM experts (Susan Whitfield-Gabrieli; http://web.mit.edu/swg/soft
Table 1 presents the demographic information for all subjects. The
LKM experts were matched with the novices by age [t(23)¼0.651,
P>0.5] and years of education [t(23)¼?1.704, P>0.1]. The experts
had 6456.2h of experience in LKM practice on average.
When LKM meditators were compared with novices, more gray matter
volume was detected in the right angular gyrus [Brodmann area (BA)
39; Figure 1A, Table 2] and right posterior parahippocampal gyrus
(BA 36; Figure 1B, Table 2) at a significant level (corrected P<0.05).
With a more lenient threshold, more gray matter was also detected in
the left inferior temporal gyrus (ITG) and middle temporal gyrus
(MTG) (BA 20 and 21; Figure 1C, Table 2) at a trend level (corrected
P<0.1). The same results persisted even after controlling for age and
years of education. Novices had no regions with significantly more gray
matter than the LKM experts, even after controlling for age or years of
education (Table 2). The same results persisted when another group of
subjects who did not have any experience in meditation (i.e. zero
hours) was used as the control comparison group (for details, please
see the Supplementary Data).
The results of the correlation analysis showed that the number of
meditation hours of the LKM experts was negatively related (at a trend
level) to the gray matter volume of the right angular gyrus (r¼?0.618,
P¼0.057) and the left MTG (r¼?0.593, P¼0.071), but not with the
right parahippocampal gyrus (r¼?0.079, P¼0.828). When the effects
of age and education were removed, only the correlation between
number of meditation hours and the gray matter volume of the
right angular gyrus remained significant (r¼?0.761, P¼0.028).
This study examined the effect of experience in LKM meditation on
brain morphometry in expert Chinese male meditators. We used the
VBM-Dartel inter-subject alignment (VBM-Dartel) to minimize the
threat of registration errors. The LKM experts appeared to have
more gray matter in the left temporal lobe (ITG and MTG) at a
trend level. Previous meditation research has reported similar results
in the left ITG (Ho ¨lzel et al., 2008; Luders et al., 2009). Thus, this
finding may be attributable to the general effect of meditation practice.
At the same time, we found that the LKM experts had significantly
more gray matter than novices in the right angular and right posterior
parahippocampal gyri. It is noted that not all hypothesized regions
(identified based on previous fMRI studies on normal controls) had
more gray matter volume in LKM experts than in novices, no matter
how lenient a threshold was used. This observation suggests that the
mechanisms involved in structural and functional changes are likely
different. An alternative explanation is that the neural correlates of
social cognition in LKM experts may differ from those in the partici-
pants of these fMRI studies. The structural difference in the right
angular gyrus was not observed in previous MRI studies on FAM or
mindfulness meditation. Because of the specific role of the right
Fig. 1 Increased gray matter volumes in LKM experts compared with novices as revealed
by VBM-Dartel. On the left side are the group differences (LKM experts>novices) overlaid on
the average of the bias-corrected images of all subjects. On the right side are the glass brains
showing all the clusters that survived corrected P<0.05 or P<0.1. Significant effects (P<0.05,
corrected) were detected in the (A) right angular and (B) posterior parahippocampal gyri. Trend-level
effect (P<0.1, corrected) was detected in the (C) left temporal lobe. No significant group differences
were found for the opposite contrast (LKM experts<novices). Controlling for age or years of
education did not affect the results.
Table 1 Descriptive statistics of subject demographics and questionnaire data
LKM experts LKM novicesP-value
Years of education
Range in hours
P-values represent group differences between LKM experts and novices using independent samples
36SCAN (2013) M.-K.Leungetal.
angular gyrus in mind and cognitive empathy theory, we consider this
finding to be unique to LKM. All these structural differences cannot be
explained by individual variations in global brain volume, age or years
of education. Previous reports have suggested that LKM is associated
with a reduction in anxiety and negative affect (Johnson et al., 2009;
Sears and Kraus, 2009; Goldin and Gross, 2010). Taking these findings
together, we speculate that the enlarged right angular and right para-
hippocampal gyri (and the left temporal lobe at a trend level) in
LKM experts may play a role in counteracting anxiety and negative
Right angular gyrus
The finding of an enlarged right angular gyrus is novel. Previous studies
on insight, Zen and Tibetan Buddhism and a mixed style of meditation
practice have demonstrated increased gray matter in the insula, hippo-
campus, inferior temporal lobe, cingulate cortex, prefrontal regions,
brain stem and some other regions (Lazar et al., 2005; Pagnoni and
Cekic, 2007; Ho ¨lzel et al., 2008; Luders et al., 2009; Vestergaard-Poulsen
et al., 2009; Grant et al., 2010), but none has reported gray matter
changes in the parietal structures. Although a recent longitudinal
study reported an increase in gray matter concentration in the left
TPJ after 8weeks of mindfulness-based stress reduction training, this
cluster, in fact, peaked in the left MTG [Montreal Neurological Institute
(MNI) coordinates: ?50, ?48 and 20] (Holzel et al., 2011), whereas the
peak coordinates of our angular gyrus cluster were on the right side and
more posterior and superior (41, ?63 and 46). On the other hand,
diffusion tensor imaging offers in vivo examination of whitematter
connectivity. A recent study revealed greater connectivity in the left
superior longitudinal fasciculus (SLF) and its temporal component
(tSLF) in meditators who practiced different forms of meditation com-
pared with control subjects (Luders et al., 2011). Since the SLF connects
the frontal and the temporo-parietal regions, the finding of Luders
et al.’s (2011) study lays the groundwork for speculation regarding
some changes in the parietal lobe associated with meditation.
However, the nature and mechanisms of the coupling of the parietal
and the fronto-temporal activity for affective regulation in people prac-
ticing LKM meditation await verification in future research.
The right angular gyrus may be related to meditation practices that
involve LKM in multiple ways. It is one of the main regions that form
the TPJ, which has been repeatedly implicated in social cognition, such
as mind and empathy theory (Decety and Lamm, 2007). In particular,
the right TPJ is believed to be selectively recruited to understand
others’ thoughts, desires and feelings (Saxe and Wexler, 2005).
Together with the medial temporal lobe and ventromedial prefrontal
cortex, it forms a cognitive system that is important for cognitive
empathy. In particular, the role of the right TPJ in the self–other dis-
tinction is fundamental to the mentalizing ability that is central to
cognitive empathy (Saxe and Kanwisher, 2003); this may be important
for understanding the affective states of others and for sharing com-
passionate loving kindness to truly recognize the wisdom that all
human beings are equal and to appreciate oneness with others
Lutz et al. (2008) observed that LKM experts had more activity than
novices in the right angular gyrus of the TPJ and a number of other
brain regions when listening to emotional human vocalizations during
compassion meditation. The authors reasoned that long-term LKM
may enhance emotion sharing and perspective taking, especially
since the increase was strongly modulated by meditation expertise.
Their follow-up study further highlighted the importance of the
right angular gyrus/IPL in LKM because of the stronger coupling be-
tween its activity and heart rate during the compassion state in LKM
experts than in novices (Lutz et al., 2009). These findings are in line
with our observation of increased gray matter in the right angular
gyrus with LKM practice.
The increased gray matter volume of the right angular gyrus in LKM
experts corroborates previous findings regarding the benefits of LKM
for affective processing (Johnson et al., 2009; Sears and Kraus, 2009;
Garland et al., 2010), leaving room for speculation regarding the po-
tential therapeutic effect of LKM on counteracting affective disturb-
ances. On the other hand, we found a negative correlation between
hours of meditation practice and the gray matter volume of the angu-
lar gyrus in the LKM experts. Previous VBM studies on meditation
experts have shown inconsistent results regarding the relationship be-
tween brain structure and the duration of meditation practice (Lazar
et al., 2005; Ho ¨lzel et al., 2008; Luders et al., 2009; Vestergaard-Poulsen
et al., 2009). Previous fMRI studies have revealed an inverted U-shaped
relationship between meditation expertise and neural activity. For
example, Brefczynski-Lewis et al. (2007) observed that experts with
an average of 19000h of practice, relative to meditation novices,
showed stronger blood-oxygen-level-dependent (BOLD) signals in
the attentional default network. However, BOLD signals in the same
regions were weaker for those experts who had an average of 44000h
of practice. This inverted U-shaped function may be explained by the
process of skill acquisition?a pattern that has been observed in other
domains of expertise (Doyon et al., 2002). It is also consistent with the
description in meditation texts that the practice of concentration
meditation will become less effortful as one becomes more skillful at
the practice. We speculate that, based on the prediction set forth by the
inverted U-shaped pattern, it is entirely possible that a positive rela-
tionship is revealed during the early stage of meditation practice (e.g.
<2000–5000h). Further research to verify the direction of the relation-
ship between the duration of meditation practice and gray matter
volume may consider a longitudinal design or employing cohorts at
various levels of meditation expertise.
Table 2 Increased gray matter volumes in LKM experts compared with novices as revealed by VBM-Dartel
Contrast Brain regions (Brodmann area)Peak coordinates Corrected P-valuet-ValueCluster size
Experts>novicesRight angular gyrus (39)
Right posterior parahippocampal gyrus (36)
Left ITG (20)
Left MTG (21)
Experts<novices No suprathreshold voxels
The corrected P-value was determined by combining the voxel-level and cluster-level thresholds by AlphaSim. For Experts>novices, experts had significantly more gray
matter volume than novices in the right angular and right posterior parahippocampal gyri, while more gray matter volume was also detected in the left temporal lobe (the
ITG and MTG) at trend-level onlya. For experts<novices, no significant group differences were detected. Controlling for years of education did not affect the results.
Coordinates are in MNI space.
Morphometryof LKM practitioners SCAN (2013)37
Right posterior parahippocampal gyrus
The finding of an enlarged posterior parahippocampal gyrus is unique
to LKM in our study. No gray matter change was found in this region
in previous structural studies on FAM or mindfulness meditation. The
parahippocampal gyrus together with the temporopolar area, cingulate
cortex, orbitofrontal cortex and insula forms the paralimbic system
(Brodmann, 1909, 1994). Having dense connections with the limbic
system, especially the amygdala, the paralimbic system is an important
transition area that supports communication between the limbic
system and the neocortex (Mesulam, 2000), which is important for a
range of higher order cognitive affective functions, such as emotion/
mood regulation, self-control and motivational behavior (Kiehl, 2006).
As proven by effective connectivity analysis, the parahippocampal
gyrus has strong interactions with the amygdala (Stein et al., 2007).
Abnormalities such as decreased gray matter volume or altered activity
in these two regions are linked with various conditions of emotional
dysfunction, such as depression (Gilbert et al., 2010), bipolar disorder
(Chen et al., 2011) and schizophrenia (Gradin et al., 2011). A recent
study that revealed gender-related differences in neural activity toward
the compassion experience is in line with our findings. Pictures of
human suffering selectively activated the parahippocampal gyrus and
the occipital regions in male participants (Mercadillo et al., 2011).
Another VBM study on insight meditators with a relatively high
male composition (80%) also reported higher gray matter volume in
the right medial temporal (hippocampus) and left temporal (ITG)
lobes (Ho ¨lzel et al., 2008).
Left temporal lobe
The left temporal lobe has repeatedly been reported to have structural
and functional changes associated with meditation. Insight experts had
significantly more gray matter in the left ITG than novices, and their
ITG size positively correlated with hours of meditation practice
(Ho ¨lzel et al., 2008). Another study on the common effects of different
meditation styles on brain structure also found more gray matter in the
left ITG when the statistical threshold was lowered (Luders
et al., 2009). The temporal lobe was further found to be activated
during the mindfulness meditation state (Holzel et al., 2007). It ap-
pears that the temporal lobe is involved in the experience of the mind-
ful state and ‘insight into the unity of all reality’ (Ho ¨lzel et al., 2008).
Luders et al. (2011) also observed that meditators (who practiced vari-
ous forms of meditation) showed higher connectivity in the left tSLF,
which traverses through the left middle/superior temporal lobe. This
finding corroborates our observation that experts have increased gray
matter volume in the left temporal lobe. Future studies should be
conducted to examine whether there is enhanced connectivity in the
tSLF/SLF in LKM meditators and, if so, how this enhanced connect-
ivity relates to the enlargement of the left temporal lobe. These data
suggest that the left temporal lobe is not exclusively implicated in a
specific style of meditation but, instead, is involved in various styles
ranging from attention to mindfulness to LKM. Caution must be
taken, however, in interpreting this structural difference since it
appeared as a trend-level result in both the current and previous stu-
dies (Luders et al., 2009).
This study has several limitations. First, the sample size of LKM experts
was rather small because of the difficulty of subject recruitment.
Insufficient power may have led to the negative findings in some
emotion-related brain regions, for example, the medial orbitofrontal
cortex and the insula. The level of expertise of our LKM experts may
also explain these negative findings because specific neural changes
may take place at different stages of LKM practice and levels of LKM
competence. These speculations may be verified in future longitudinal
studies of large sample sizes. Second, like other cross-sectional studies
comparing brain structure between experts and novices, we cannot
definitively say that long-term LKM caused the gray matter differences
observed in this study or that people with these brain differences are
more inclined to practice LKM. Longitudinal studies are needed to
explore the causal relationship between LKM practice and brain struc-
ture. Third, the current findings have yet to be generalized to female
LKM experts since this study recruited only male LKM experts.
The purpose of recruiting men was to avoid potential gender con-
founds, especially since this is the first exploratory study of LKM
and brain structure. Future studies may recruit female participants
or people of both genders to address this limitation.
This study found that LKM experts had significantly more gray matter
volume in the right angular gyrus, which may be unique to the effect of
LKM training. Neuroscience studies have linked the right angular
gyrus (a part of the right TPJ) with empathy for others during medi-
tation. Our LKM experts also had more gray matter volume in the
right posterior parahippocampal gyrus. It is part of the paralimbic
system, which works with the limbic and neocortical regions to regu-
late emotional or empathic responses, and this may be specific to men.
Although more gray matter was also detected in the left temporal lobe
in LKM experts at a trend level, this difference may not be specific to
LKM since it has also been observed for other meditation styles.
Despite some limitations, our findings provide an important initial
clue that LKM may be associated with increased gray matter volume
in regions that are important for emotion regulation. Future research
should investigate the neural processes and mechanisms underlying
LKM training to examine its therapeutic potential as an intervention
for affective dysregulation.
Supplementary data are available at SCAN online.
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