Article 14: Neural Mechanisms of Practice-Induced Improvement in Functional Reaching After Moderate Severity Stroke

Abstract

Objective: To identify neurophysiologic correlates of practice-induced improvements in reaching in moderately severe stroke patients. Design: Before-after trial. Setting: Government research institution. Participants: 9 subjects (4 women) with moderately severe arm impairment (Fugl-Meyer Assessment upper extremity, 26±6) due to chronic stroke; 6 had left hemisphere lesions. Intervention: Single session of paretic arm reaching practice. Main Outcome Measures: The behavioral outcome measure was response time, that is, time from a visual “go” signal until a large button placed in front of the subject was pressed. Neurophysiologic measures included lesioned hemisphere corticospinal excitability and intracortical inhibition, and interhemispheric inhibition from the nonlesioned to the lesioned hemisphere, as measured by motor-evoked potential (MEP) amplitudes, cortical silent periods, and ipsilateral silent periods, respectively. All measurements were made in the paretic arm biceps and triceps muscles. Results: Reaching response times significantly decreased with practice and improvements were maintained 24 hours after practice (P=.04). Practice-induced improvements were accompanied by increased MEP amplitudes (P=.02), decreased cortical silent period depth (P=.03), and decreased ipsilateral silent period depth (P=.007) in the triceps, but not in the biceps. Conclusions: People with moderately severe chronic stroke show practice-induced reaching improvements that are accompanied by muscle-specific increases in excitability of the lesioned hemisphere and decreases in inhibition from the nonlesioned hemisphere.