Effect of pain and pain expectation on primary motor cortex excitability

The study aimed to test whether pain and pain expectation affect corticospinal excitability.

Transcranial magnetic stimulation was used to measure corticospinal excitability among 15 subjects in five experimental conditions in which thermic stimulations were applied to the hand: (1) neutral stimulus; (2) actual heat; (3) actual pain; (4) expected heat; and (5) expected pain. Motor-evoked potentials were recorded in two intrinsic hand muscles.

A significant difference was found between experimental conditions for both muscles (p<0.005). Contrast analysis showed that actual pain led to a significant corticospinal inhibition compared with both neutral and actual heat conditions, whereas no effect was observed during pain expectation.

Our results suggest that acute pain (low-to-moderate intensity (∼3/10)) does elicit motor inhibition but that its expectation does not.

The fact that low and short-lasting pain can induce motor inhibition suggests that even moderate pain might interfere with optimal motor function in patients with both pain and motor deficits.