Upper extremity weight-bearing effect on corticospinal excitability following stroke

The effects of upper extremity weight-bearing on the excitability of corticospinal neurons projecting to the flexor carpi ulnaris (FCU) muscle of patients having had cerebrovascular accidents (strokes) were examined. Alternate transcranial magnetic and ulnar nerve stimulation were applied and peristimulus time histograms of single FCU motor unit discharge times were generated to provide information about the cortical and segmental postsynaptic potentials (PSPs), respectively. Recordings from 10 patients and 5 control subjects indicated the cortically evoked PSPs were initially abnormally small in the stroke group (p < .01). Following weight-bearing the cortical projection strength to FCU motoneurons increased in stroke patients (p < .05) only. The composite group Ia PSP was reduced in 2 patients, but data could not be obtained from the remaining subjects. It is concluded that upper extremity weight-bearing normalizes corticospinal facilitation of FCU motor units in stroke patients. A sustained increase in motor cortical excitability through augmented afferent input may be responsible.