The muscle inhibitory period by transcranial magnetic stimulation. Study in stroke patients

Motor evoked potentials (MEPs) elicited over hand muscles by transcranial magnetic stimulation (TMS) were studied in healthy individuals and, bilaterally, in patients with cerebral infarction. Conduction time of the central motor pathways (CMCT), threshold intensity, and amplitude of the MEPs were correlated with recovery motor hand function after stroke. Following MEPs by TMS during tonic muscle contraction, there is a transient suppression of muscle action. This inhibitory period (IP) was significantly shorter in the upper paretic limb of stroke patients with spasticity than in normal limb of the patients and healthy individuals. Shortening of the IP duration was correlated to degree of upper limb spasticity (Ashworth scale) and may be due to supraspinal level reduction of the inhibitory function. The IP study contributes to a better quantification of the hand function in stroke patients.