Brain Structure and Meditation
How Spiritual Practice Shapes the Brain
Ulrich Ott (1), Britta K. Hölzel (1, 2) & Dieter Vaitl (1)
1 Bender Institute of Neuroimaging, University of Giessen, Germany
2 Massachusetts General Hospital, Harvard Medical School, Boston, MA, U.S.A.
Abstract Meditation practices can be conceived as specific types of mental train-
ing with measureable effects on the function and structure of the human brain.
This contribution narratively reviews recent morphometric studies that compared
experienced meditators with matched controls. While meditation types and meas-
ures differed between studies, results were remarkably consistent. Differences in
gray matter (GM) volume and density were found in circumscribed brain regions
which are involved in interoception and in the regulation of arousal and emotions,
namely insula, hippocampus, prefrontal cortex, and brainstem. The normal age-
related decline in GM volume and in attentional performance was present in con-
trols but not in meditators. These findings need to be replicated in longitudinal
studies in order to confirm the causal role of meditation training. Future research
has to elucidate effects of these structural changes on neural activity and mental
functioning during behavioral tasks.
Introduction
For many centuries, meditation has been practiced by mystical branches of ma-
jor religions for promoting spiritual development, for gaining insight into reality,
and for attaining transcendental states of consciousness. From a scientific perspec-
tive, the effects of these traditional exercises are based on the plasticity of the
brain. Sustained efforts to focus attention and to cultivate emotional balance leave
traces in the underlying neural substrate and circuitry. Over time, these changes in
brain structure in turn support the intended changes in mental faculties and per-
sonality.
The current contribution reviews findings of structural differences in the brains
of advanced meditation practitioners when compared to non-meditating controls.
Increases in GM density and cortical thickness of specific brain regions may pro-

2
vide objective indicators for the enhancement of particular self-regulation skills.
Meditation techniques involve the training and development of certain mental ab-
ilities or qualities, e.g. awareness of bodily sensations, focusing of attention, emo-
tion regulation etc. Often such heightened skills and improved cognitive abilities
are referred to as “expansion of consciousness”. Significant improvements detect-
able at the cognitive-behavioral level, such as one’s ability to control attention, re-
gulate emotion, and bring awareness to bodily sensations, should also be mirrored
in morphological changes at the neural level. The popular idea of "consciousness
expansion through meditation" can thus be understood more scientifically by un-
derstanding how the underlying neural structures are modified by meditation prac-
tices.
Morphological differences in meditation practitioners
Up to now, five studies on structural differences between meditation practitio-
ners and controls have been conducted and will be reviewed here (for a summary
of findings, see Figure 1 and Table 1 and 2).
The first study by Lazar et al. (2005) compared cortical thickness of 20 Bud-
dhist insight meditation practitioners and 15 matched controls. Insight meditation
practice aims at cultivating a nonjudgmental awareness of the internal and external
stimuli present in each moment (“mindfulness”). On average, participants medi-
tated for 9.1 years (SD = 7.1 years), practicing about 40 minutes per day.
Statistical analyses revealed differences in cortical thickness between groups in
the right anterior insula and the right middle and superior frontal sulci. The cortex
of meditation practitioners was significantly thicker in both regions. In the pre-
frontal cortex, the effect was most likely caused by an age-related decrease of cor-
tical thickness in the control group which was absent in the meditation group. The
authors argue that the strong effect in the right anterior insula could be due to the
extensive training in breath awareness and in maintaining attention to visceral sen-
sations.
Slowing of the breathing rate between a baseline condition and the first six mi-
nutes of meditation showed a strong correlation with the amount of practice and
was taken as a physiological indicator of meditation experience. Within the medi-
tation group this measure was correlated with cortical thickness in a region in the
inferior occipito-temporal visual cortex and, when controlling for age, also with
cortical thickness in the right anterior insula. The latter finding was taken as fur-
ther evidence that training in interoceptive awareness during meditation could be
responsible for increased cortical thickness in the right anterior insula, since this
structure is involved in the meta-representation of the body scheme, homeostasis,
and associated visceral sensations.
Effects of meditation on GM volume and on cognitive performance were inves-
tigated in a subsequent study by Pagnoni and Cekic (2007). Here, 13 Zen medita-