Study of Pain Processing in Experienced Yoga Practitioners

Objective: Pain perception is characterized by substantial differences between individuals.
We recently showed that a group of experienced yogis tolerated pain much longer than matched
controls. To tolerate pain yogis reported using strategies involving interoceptive awareness
and parasympathetic activation while nearly all controls did not. Yogis had more gray matter
in multiple brain regions, but only mid-insular gray matter correlated with pain tolerance.
They also had higher left intra-insular white matter connectivity than controls. Given that
autonomic integration occurs in the mid-insula, these observed insular adaptations could be
related to successful pain affect regulation mediated by increased interoceptive processing
and parasympathetic regulation. Our findings are consistent with a recent theory suggesting
that yoga s benefits are achieved by reducing allostatic load in stress response systems (
wear and tear on the body ), thus restoring optimal homeostasis. Specifically, the beneficial
effects of yoga on many conditions, including chronic pain, may be attributable to increased
parasympathetic activation. Indeed, all the conditions benefiting from yoga practice are
exacerbated by stress and exhibit a high sympathetic/parasympathetic balance, as measured by
low heart rate variability (HRV). Increased sympathetic activity is known to increase
hypothalamo-pituitary-adrenal (HPA) axis function. Additionally, it has been proposed that
people respond to uncertainty by activating the sympathetic nervous system, and that this
default response is related to the well-known negativity bias, the tendency to prioritize
negative information over positive. Yoga teaches a more neutral appraisal of the world which
might be a better adaptive response to uncertainty not involving as much sympathetic
activation and requiring less energy from the organism than prioritizing negative information
in a reactive way. This should promote a better control over stressful events including pain.
Thus, the proposed studies will first pilot the psychophysical procedures before proceeding
to the full study testing general hypothesis that the differences in pain processing and the
related neurostructural and neurophysiological differences expected to be found in
experienced yogis are related to more flexible autonomic and HPA axis control. We will also
document personality traits, including pain-related behaviors, and mental states associated
with the observed differences.

Study population: In the pilot sub-study 19 experienced yogis will be compared to 19 healthy
volunteers who will serve as controls. The full protocol will include 49 participants per
group.

Design: A pilot sub-study will be followed by the full cross-sectional study. In the full
cross-sectional study experienced yogis will be matched on a number of variables with healthy
controls not practicing any type of mind-body techniques. After screening, participants will
be fitted with an ambulatory electrocardiography device (Holter monitor) for 24 hours to
characterize their HRV in natural settings. They will also provide saliva samples at
pre-determined intervals for seven consecutive days to measure cortisol, an index of the HPA
axis function. Each subject will undergo two testing sessions. Session 1 will evaluate how
participants anticipate and process warm and painful stimuli in certain and uncertain
contexts by measuring perception while monitoring physiological responses such as
respiration, heart rate, blood pressure, skin conductance and cortisol response. In session
2, functional magnetic resonance imaging (fMRI) will be used to assess potential differences
in brain resting state activity between groups, as well as to document neural responses
related to the anticipation and processing of warm and painfully hot stimuli in certain and
uncertain contexts using a similar paradigm as in session 1. Once again, physiological
monitoring will be performed. Anatomical MRI scans will be acquired for co-registration of
the fMRI findings as well as to measure gray matter volume and cortical thickness differences
between groups. Questionnaires evaluating the participants mental state and personality
traits will be acquired throughout the sessions.

Outcome measures: Ratings of warm and painfully hot stimuli in certain and uncertain contexts
will be compared between groups. Baseline HRV and cortisol levels will also be compared
between groups. Functional and anatomical MRI data will be analyzed to examine differences
between yogis and healthy volunteers for 1) gray matter volume and cortical thickness; 2)
thermal anticipation and thermal-evoked activation patterns in certain and uncertain
contexts; 3) functional connectivity during both anticipation and processing of thermal
stimuli in certain and uncertain contexts; 4) resting state activity; and 5) functional
connectivity during resting state. We will examine whether the behavioral, functional, or
structural differences found are related to HPA axis function, autonomic function,
personality traits and mental state.

- FOR YOGA PRACTITIONERS:

You may qualify if you are:

- at least 30 years old

- an experienced yoga practitioner and practice regularly

- fluent in English

- right-handed

- in good health

You may not qualify if you:

- have a major medical condition

- suffer from chronic pain

- are pregnant or breast-feeding

- have a fear of enclosed spaces (claustrophobia)

FOR HEALTHY CONTROLS:

You may qualify if you are:

- at least 30 years old

- fluent in English

- right-handed

- in good health

You may not qualify if you:

- practice yoga, meditation, or martial arts

- have a major medical condition

- suffer from chronic pain

- are pregnant or breast-feeding

have a fear of enclosed spaces (claustrophobia)