Repetitive Transcranial Magnetic Stimulation of the Primary Motor Cortex Expedites Recovery in the Transition from Acute to Sustained Experimental Pain: a Randomised, Controlled Study

Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) is increasingly being investigated as a means of alleviating chronic pain. However, rTMS interventions are typically initiated once pain has already become chronic and maladaptive patterns of neural activity are likely to have been established. A critical question is whether M1 rTMS applied soon after pain onset can prevent the development of maladaptive neural activity and promote recovery. This study investigated the effect of 5 consecutive days of excitatory M1 rTMS on pain, functional limitation, mechanical hyperalgesia, descending inhibitory pain control, and M1 organisation in the transition from acute to sustained pain. Thirty healthy participants attended 8 sessions over a 16-day period. On days 0, 2, and 4, nerve growth factor was injected into the right forearm to induce progressively developing muscle soreness and mechanical hyperalgesia. Active or sham excitatory rTMS was delivered on days 4 to 8. Clinical and neurophysiological outcomes were recorded on days 0, 2, 4, 6, 8, 11, and 14. Active rTMS promoted recovery of muscle soreness, pain, and mechanical hyperalgesia when compared with sham rTMS (all between-group P < 0.05). Corticomotor excitability and descending inhibitory pain control did not differ between groups. These findings suggest that active excitatory M1 rTMS promotes recovery of muscle soreness, pain, and mechanical hyperalgesia in the transition from acute to sustained experimental pain. The analgesic effects of M1 rTMS do not seem to be modulated by descending inhibitory pain control or local changes in corticomotor excitability.