P 91. Physiologic mechanism of motor learning induced by action observation

Abstract

Our previous report ( Nojima et al., 2012 ) indicated that repetitive training with mirror visual feedback can improve the motor performance of the non-moving hand and facilitate the primary motor cortex (M1) function. However, that experiment could not rule out the influence of the intermanual transfer from the training hand on motor learning of the non-moving hand. Therefore, we executed the present study to elucidate how a visual feedback itself works on the motor performance and cortical excitability. We used transcranial magnetic stimulation (TMS) to evaluate the plastic changes of the excitability of the right M1 by action observation (AO). Twenty-one neurologically healthy subjects were participated in this experiment. Each subject was asked to rotate two cork-balls in a counter-clockwise direction with the left hand as fast as possible before and after the intervention, and the number of ball-rotation was counted for 30 s. Subjects were assigned to the AO group (n = 11) and the control group (n = 10), respectively. AO intervention was executed placing PC monitor over subject’s left hand. For the control cocndition, subjects watch the stationary hand picture instead of motion picture. To measure the effect of the intervention on the excitability of M1, motor evoked potentials (MEP) and short intracortical inhibition (SICI), intracortical facilitation (ICF) were obtained from the left first dorsal interosseous (FDI) muscle. The pre/post ratio of the number of ball rotation in the AO group was significantly larger than that of the control group. With regard to functional changes of M1, the mean MEP amplitude and the ICF for the left FDI revealed significant increase after intervention in the AO group but not in the control group. In addition, there was a significant positive correlation between behavioral improvement and the subjective strength of kinesthetic illusion. The present results showed that the visual image of the moving hand significantly improved the motor performance of the left hand and increased the excitability of M1 regardless of actual movement of target hand. Especially, it was suggested that this behavioral improvement was associated with the facilitation of the excitatory function of corticospinal pathway since ICF was significantly increased by AO intervention. This plastic change in M1 might be associated with the subjective kinesthetic illusion. This approach may be a promising tool to improve motor performance as rehabilitation.