Induction of Cortical Plastic Changes in Wrist Muscles by Paired Associative Stimulation in the Recovery Phase of Stroke Patients

Background. Paired associative stimulation (PAS) combining peripheral nerve and transcranial magnetic stimulation (TMS) have been proposed to induce long-term changes in excitability of the cerebral cortex and potentially optimize motor recovery in stroke patients. Objective. This pilot study examined whether short-lasting changes in cortical excitability could be induced by a single session of PAS within the first months after stroke. Methods. Six hemiparetic patients with a subcortical stroke were included. The single session PAS protocol was applied at 1, 5, and 12 months after stroke. During the follow-up, the clinical recovery of wrist function was assessed in parallel to the PAS study by the Fugl-Meyer motor scale and dynamometry of wrist extension. Results. The PAS protocol induced a significant extensor carpi radialis motor evoked potential facilitation (mean +78.5%) on the paretic side 5 months after stroke. The facilitation was still present 12 months after stroke but on average smaller (+30%). Conclusions. These electrophysiological findings suggest that patients with subcortical infarcts may respond to PAS in an earlier than later period after stroke. If the clinical efficacy of interventions such as PAS is confirmed, it could be proposed early as add-on therapy to optimize training-induced plasticity processes.