Motor excitability changes during action observation in stroke patients

To explore whether stroke patients exhibit increases in motor excitability during action observation, whether differences exist between the affected and non-affected sides, and between pure motor strokes and predominantly sensory strokes. In 18 patients (10 pure motor strokes, 8 predominantly sensory strokes, < 6 months after the stroke) transcranial magnetic stimulation was used to test motor excitability while the patients viewed a video showing a hand performing pinch grips. Transcranial magnetic stimulation pulses were applied at 120% of the individual motor threshold at rest, as obtained from the affected hemisphere. Recordings were taken simultaneously from the first dorsal interosseous muscle of both hands. Motor performance was evaluated with the Box and Block Test. Transcranial magnetic stimulation-evoked muscle responses obtained from the affected and the unaffected sides were significantly higher during action observation than during rest (p = 0.024 and p = 0.004, respectively). This effect was significantly stronger when measuring the same hand as the one viewed in the video (p = 0.019). No difference was found between motor and sensory strokes. In 11 patients there was an action observation-associated increase in the amplitudes of motor evoked potentials in the affected side. In 15 patients there was an action observation-associated increase in motor evoked potentials amplitudes in the unaffected side. The results are potentially relevant for the use of action observation as a treatment strategy.