Papers of the Week

Aberrant motor cortex plasticity is hypothesised to contribute to chronic musculoskeletal pain, but evidence is limited. Critically, studies have not considered individual differences in motor plasticity or how this relates to pain susceptibility. Here we examined the relationship between corticomotor excitability and an individual's susceptibility to pain as pain developed, was sustained and resolved over 21 days. Nerve growth factor was injected into the right extensor carpi radialis brevis muscle of 20 healthy individuals on day 0, 2 and 4. Corticomotor excitability, pressure pain thresholds (PPTs) and performance on a cognitive conflict task were examined longitudinally (day 0, 2, 4, 6 and 14). Pain and disability were assessed on each alternate day (1,3…21). Two patterns of motor plasticity were observed in response to pain – corticomotor depression or corticomotor facilitation (p=0.009). Individuals who displayed corticomotor depression experienced greater pain (p=0.027), and had worse cognitive task performance (p=0.038), than those who displayed facilitation. PPTs were reduced to a similar magnitude in both groups. Corticomotor depression in the early stage of pain could indicate a higher susceptibility to pain. Further work is required to determine whether corticomotor depression is a marker of pain susceptibility in musculoskeletal conditions. Perspective: This article explores individual differences in motor plasticity in the transition to sustained pain. Individuals who developed corticomotor depression experienced higher pain and worse cognitive task performance than those who developed corticomotor facilitation. Corticomotor depression in the early stage of pain could indicate a higher susceptibility to pain.