Pain-motor integration in chronic pain: A neurophysiological study

Objective: Chronic pain may lead to functional changes in several brain regions, including the primary motor cortex (M1). Our neurophysiological study aimed to probe M1 plasticity, through a non-invasive transcranial magnetic stimulation protocol, in a cohort of patients with chronic pain. Methods: Twenty patients with chronic pain (age & PLUSMN; SD: 62.9 & PLUSMN; 9.9) and 20 age- and sex-matched healthy controls (age & PLUSMN; SD: 59.6 & PLUSMN; 15.8) were recruited. Standardized scales were used for the evaluation of pain severity. Neurophysiological measures included laser-evoked potentials (LEPs) and motor-evoked potentials (MEPs) collected at baseline and over 60 minutes following a standardized Laser-paired associative stimulation (Laser-PAS) protocol. Results: LEPs and MEPs were comparable in patients with chronic pain and controls. The pain threshold was lower in patients than in controls. Laser-PAS elicited decreased responses in patients with chronic pain. The response to Laser-PAS was similar in subgroups of patients with different chronic pain phenotypes. Conclusions: M1 plasticity, as tested by Laser-PAS, is altered in patients with chronic pain, possibly reflecting abnormal pain-motor integration processes. Significance: Chronic pain is associated with a disorder of M1 plasticity raising from abnormal painmotor integration.