Meditation experience predicts less negative appraisal of pain: Electrophysiological evidence for the involvement of anticipatory neural responses

Pain and the Brain

Anticipation of Pain Anticipation of events can allow one to cope with emotional and physiological states Anxiety can predict pain severity and pain behavior Placebo experiments show decreased activity in anterior insula and cingulate and contralateral thalamus but increases in prefrontal cortex activity

Meditation Numerous types: Western Culture separates into concentrative meditation and mindfulness meditation Training to minimize distractions and focus attention Believed to have greater cognitive control on directing attention Reduce anticipatory and emotional aspects of pain by focusing attention on present

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Purpose Previous studies show responses to pain in meditators in the thalamus, primary and secondary somatosensory cortices, insula, prefrontal cortex, and anterior cingulate cortex Determine if differences in pain responses occur during anticipation period or as part of pain-evoked response.

Methods Formal meditation experience recorded based on weeks over a lifetime Emotional aspect of pain gauged on a numerical scale 0-10 Painful sensations delivered via laser stimuli on skin Determined pain threshold and moderate pain levels for each subject The experiment included groups of both meditators and non-meditators. Meditators were questioned on type of meditation they engage in and how long they have done their chosen form of meditation. The number of weeks they have committed to formal meditation was recorded as the means for formal meditation. Meditation practices included mindfulness meditation (5 subjects) Samatha (2) a Buddhist form of meditation Tantra-Yoga (2- non-Buddhist) –visualization and repetition of personal mantra in time with the breathing Zen (2) meditation- focus on breathing and some body sensations Sahaj Marg (1)- focus on body sensations and a feeling of lightness and peacefulness in the heart Pain was induced by a carbon dioxide laser stimulator which applied a heat stimuli for 150 millisecond the dorsal surface of the right forearm (15mm diameter). The stimuli were randomly delievered to different positions on the arm over a 3 cm x 5 cm area Asked to rate the pain on the scale of 0-10 (4 being theshold or just painful) and 10 being the most painful (tolerance) Determined the pain threshold and moderate pain levels for each subject by varying the intensity of the laser.

Methods cont… Visual cues given beginning at 3 s before painful stimuli administered EEG recordings were taken and data analyzed before visual cue, during early period, late period, and P2 peak Low-resolution electromagnetic tomography (LORETA) source analysis and VOI determined Pain anticipation: MCC, IPC,mPFC, pACC Pain experience: contralateral insula and ipsilateral S2 cortex

Results Laser intensities Meditation Group: Control Group: Pain threshold mean= 2.02 Joules Moderate Pain = 3.62 Joules Control Group: Pain threshold mean= 1.8 Joules Moderate Pain= 3.02 Joules Not significant

When data was baseline-corrected to the pre-anticipation period there was lower activation in the right somatosensory cortex and the left posterior insula in meditation groups but may have included anticipatory activity. When used with pre-stimulus there was no significant difference between groups Diagram c shows group differences in the effects of anticipation during pain-evoked response. Anticipatory MCC activity lower in meditation group during pain processing - mPFC activity was higher in meditation group Differences in cortex between groups during late anticipation and pain experience Meditation group lower activation in MCC and right IPC during late anticipation Lower activation in meditation group in right somatosensory cortex (S2) and left posterior insula than in controls

Shows time-course plots of volumes of interest to compare the time at which neuronal activity diverges between the groups In the MCC and left posterior insula the differences didn’t appear until late anticipation Insula activity did not peak in meditation group; peaked during pain-evoked response in control group In the right IPC and S2 cortex neuronal activity began to diverge during early anticipation but was not significant until late anticipation and pain. The divergence of these two areas may explain why these effects did not appear to be significant after base correcting the pain-evoke data to the pre-stimulus period Activity in mPFC showed early increases in both groups but diverged in late anticipation to be greater in meditation group

Anticipatory neural activation related to pain unpleasantness in mPFC/pACC meditators have negative relationship with pain and control has strong positive relationship There were also differences between groups of pain unpleasantness ratings and cortical activation during late anticipation Remember that activity in the mPFC increases during late anticipation in the meditation group and decreases in the control group. Lower anticipatory MCC activity predicted lower pain unpleasantness in the meditation group but not in the control It was also found that meditation experience predicted lower activation of inferior parietal and midcingulate cortices during late anticipation of pain. It is possible the MCC is a mediating variable

Conclusions More meditation experience correlated with lower perception of pain unpleasantness Significant group differences in activation found mainly in anticipatory neural responses Meditation groups had lower anticipation-evoked potential resulting from lower activation of IPC and MCC

Conclusion cont…. Differences between groups also part of pain-evoked response related to anticipatory activity Low activity in MCC but higher in mPFC Meditation associated with lower activation of right (ipsilateral) S2 and left (contralateral) insula Differences may be due to differencing in anticipatory processing

Lower MCC activity and lower pain unpleasantness were part of meditation experience Meditation reduces negative appraisal of pain during anticipation Increase in activity in mPFC/pACC in meditation groups Reduction in anticipation in meditators may be due to controlling attention and attitude of acceptance which reduces emotional appraisals of events Also be due to less focus on the pain or task but unlikely since not part of practice

The End