Mapping Descending Motor Pathways After Stroke in Humans

After severe corticospinal tract damage poststroke in humans, alternate motor pathways may support some recovery of strength and movement in the arm. Here we investigated whether one candidate pathway, the reticulospinal tract, is modulated in people with mild to severe corticospinal damage after stroke. We used a novel startle transcranial magnetic stimulation paradigm to elicit ipsilateral motor evoked potentials. We found that ipsilateral motor evoked potential presence (i.e., reticulospinal excitability) was higher in the paretic arm of people with severe corticospinal tract damage compared to people with mild corticospinal tract damage and age-matched controls. Further, ipsilateral motor evoked potential presence was correlated with motor impairment across the entire stroke cohort, whereby individuals with worse impairment exhibited higher reticulospinal tract excitability. These findings are important because interventions aimed at modulating the reticulospinal tract could be beneficial or detrimental depending on the degree of reliance on this pathway for residual motor output.