Learning the time of pain in the human motor system.

Abstract

Although traditionally conceptualized as a sensory phenomenon, pain could also be framed as a motor issue. Yet, the role of the motor system in pain prediction remains poorly understood. Here, we test whether the human motor system can learn to predict the time of pain. In 2 experiments, distinct groups of participants learned that different visual cues predicted pain occurrence either shortly or long after cue onset. Single-pulse transcranial magnetic stimulation was administered over the primary motor cortex to probe corticospinal excitability at 3 critical timepoints during cues presentation, namely long before, immediately before, and long after the time of pain. Bayesian informative hypothesis testing supported, for both experiments, the hypothesis that the motor system learns pain timing through sustained motor inhibition during pain anticipation. Specifically, independently of actual pain occurrence, corticospinal excitability decreased from cue onset, long before the time of pain, until the time of pain, and recovered once this had passed. In addition, stronger corticospinal inhibition long before the time of pain correlated with greater subjective temporal anticipation of pain occurrence, suggesting a role for the motor system in transforming physical time into subjective time. Sustained motor inhibition during pain anticipation may be adaptive for the preparation of prompt defensive behaviors. However, exaggerated motor inhibition may become maladaptive creating an anticipated sense of a pain that may never occur. In clinical settings, enhanced motor inhibition may interfere with therapeutic interventions aimed at restoring motor function and pain resolution.