The Functional Role of Response Suppression during an Urge to Relieve Pain.

Abstract

Being in the state of having both a strong impulse to act and a simultaneous need to withhold is commonly described as an "urge." Although urges are part of everyday life and also important to several clinical disorders, the components of urge are poorly understood. It has been conjectured that withholding an action during urge involves active response suppression. We tested that idea by designing an urge paradigm that required participants to resist an impulse to press a button and gain relief from heat (one hand was poised to press while the other arm had heat stimulation). We first used paired-pulse TMS over motor cortex (M1) to measure corticospinal excitability of the hand that could press for relief, while participants withheld movement. We observed increased short-interval intracortical inhibition, an index of M1 GABAergic interneuron activity that was maintained across seconds and specific to the task-relevant finger. A second experiment replicated this. We next used EEG to better "image" putative cortical signatures of motor suppression and pain. We found increased sensorimotor beta contralateral to the task-relevant hand while participants withheld the movement during heat. We interpret this as further evidence of a motor suppressive process. Additionally, there was beta desynchronization contralateral to the arm with heat, which could reflect a pain signature. Strikingly, participants who "suppressed" more exhibited less of a putative "pain" response. We speculate that, during urge, a suppressive state may have functional relevance for both resisting a prohibited action and for mitigating discomfort.