Lateralization of motor cortex excitability in stroke patients during action observation: a TMS study

Action observation activates the same motor areas as those involved in the performance of the observed actions and promotesfunctional recovery following stroke. Movement observation is now considered a promising tool for motor rehabilitation, byallowing patients to train their motor functions when voluntarymovement is partially impaired.We asked chronic-stroke patients,affected by either left (LHD) or right hemisphere (RHD) lesions, to observe either a left or right hand, while grasping a small target(eliciting a precision grip) or a large target (eliciting a whole hand grasp directed towards a target object). To better understandthe effects of action observation on damaged motor circuits, we used transcranial magnetic stimulation (TMS) to induce motorevoked potentials (MEP) from two muscles of the unaffected hand in 10 completely hemiplegic participants. Results revealed thatLHD patients showed MEP facilitation on the right (contralesional) M1 during action observation of hand-object interactions. Incontrast, results showed no facilitation of the left (contralesional) M1 in RHD patients. Our results confirm that action observationmight have a positive influence on the recovery of motor functions after stroke. Activating the motor system by means of actionobservation might provide a mechanism for improving function, at least in LHD patients.