Human ventromedial prefrontal cortex lesions enhance expectation-related pain modulation

Abstract

Pain is strongly modulated by expectations and beliefs. Research across species indicates that subregions of the ventromedial prefrontal cortex (VMPFC) play a fundamental role in learning and generating predictions about valued outcomes. Consistent with this overarching framework, neuroimaging studies of experimental pain indicate that VMPFC activation tracks expectations of pain relief and statistically mediates expectation-related reductions in responses to painful stimuli across a distributed pain processing network. However, lesion studies in preclinical models and in humans with refractory chronic pain suggest that VMPFC may play a more general role in representing the affective and motivational qualities of pain that contribute to its strong aversive drive. To test whether VMPFC is necessary for pain processing in general, or instead plays a more specific role in the modulation of pain by expectations, we studied responses to experimental heat pain in five adults with bilateral surgical lesions of VMPFC and twenty healthy adults without brain damage. All participants underwent quantitative sensory testing (QST) to characterize pain sensitivity, followed by a pain expectancy task. Participants were instructed that auditory cues would be followed by heat calibrated to elicit low or high pain. Following a conditioning phase, each cue was intermittently paired with a single temperature calibrated to elicit moderate pain. We compared ratings of moderate heat stimuli and subjective expectancy ratings as a function of cue to evaluate whether VMPFC lesions impact cue-based expectancy and expectancy effects on pain intensity and unpleasantness. We also analyzed QST measures to evaluate whether VMPFC lesions were associated with overall shifts in pain sensitivity. Compared to adults without brain damage, individuals with VMPFC lesions reported larger differences in expectations as a function of pain-predictive cues, and stronger cue-based modulation of pain ratings, particularly for ratings of pain unpleasantness. There were no group differences in pain sensitivity, nor in the relationship between pain and autonomic arousal, indicating that the impact of VMPFC lesions is specific to expectancy-based modulation of pain unpleasantness. Our findings suggest that the VMPFC is not essential for basic subjective and physiological responses to painful stimuli. Rather, our findings of significantly enhanced cue- related expectancy effects may suggest that VMPFC plays an important role in updating expectations or integrating sensory information with expectations to guide subjective judgements about pain. Taken together, these results expand our understanding VMPFCs contribution to pain and highlight the role of VMPFC in integrating cognitive representations with sensory information to yield affective responses.