The motor cortex is the specific region in the brain involved in planning, controlling and executing voluntary movements. This is important for skill acquisition. Interestingly it also plays a role in varying bodily movements to reduce areas of joint loading and muscle stress.(Summers et al., 2019) For this reason we want the motor cortex to be very responsive or ‘excitable’ to maximise skill performance but also to reduce the risk of injury.
Corticomotor responses to pain have been an area of interest for researchers as we try to understand the vicious cycle that is chronic pain. Researchers use transcranial magnetic stimulation (TMS) to elicit corticomotor responses to painful stimuli. Some subjects show short-term facilitation (a more excitable responsive cortex) while others show depression.(Cavaleri et al., 2021) Those with corticomotor depression could be reflective of a more protective response – if the motor cortex is depressed it will reduce variability of bodily movements. You can imagine if this state were to persist it would be detrimental for not only skill acquisition but reducing the load on joints and muscles. This can be observed in patients presenting with low back pain who display very stiff, global movements rather than flexible, nuanced movements.
There are several factors that may contribute to the variability in corticomotor responses to pain. One is individual differences in pain sensitivity and tolerance. Studies have shown that individuals with higher pain sensitivity exhibit more depressive corticomotor responses to painful stimuli compared to those with lower pain sensitivity.(Seminowicz et al., 2019)
Another factor is the location of the painful stimulus. Studies suggesting that responses are different when the stimulus is applied to the upper limb versus the lower limb.(Rice et al., 2021)
What does this mean for addressing chronic pain? Simply having an awareness that patients may have depressed corticomotor responses supports the approach of exploring different movements through exercise. We must also demonstrate patience while retraining strength and coordination – aiming to induce beneficial neuroplasticity takes time!
Cavaleri, R., Chipchase, L. S., Summers, S. J., Chalmers, J., & Schabrun, S. M. (2021). The Relationship Between Corticomotor Reorganization and Acute Pain Severity: A Randomized, Controlled Study Using Rapid Transcranial Magnetic Stimulation Mapping. Pain Medicine (United States), 22(6). https://doi.org/10.1093/pm/pnaa425
Rice, D. A., Lewis, G. N., Graven-Nielsen, T., Luther, R., & McNair, P. J. (2021). Experimental Hand and Knee Pain Cause Differential Effects on Corticomotor Excitability. Journal of Pain, 22(7). https://doi.org/10.1016/j.jpain.2021.01.006
Seminowicz, D. A., Thapa, T., & Schabrun, S. M. (2019). Corticomotor Depression is Associated With Higher Pain Severity in the Transition to Sustained Pain: A Longitudinal Exploratory Study of Individual Differences. Journal of Pain, 20(12). https://doi.org/10.1016/j.jpain.2019.06.005
Summers, S. J., Chipchase, L. S., Hirata, R., Graven-Nielsen, T., Cavaleri, R., & Schabrun, S. M. (2019). Motor adaptation varies between individuals in the transition to sustained pain. Pain, 160(9). https://doi.org/10.1097/j.pain.0000000000001604