Abstract
The amplitude of motor-evoked potential (MEP) is increased during action observation and motor imagery. The present study investigated whether the excitability of the corticospinal tract is further increased when subjects observe an action while they image the same action. MEP induced by transcranial magnetic stimulation were recorded from the biceps brachii (BB) and brachioradialis (BR) muscles in four different conditions: (1) relax (control), (2) observation of flexion-extension of the elbow attentively (OBS), (3) imagery of flexion-extension of the elbow (IMAG), (4) observation of flexion-extension of the elbow with imagery of the same action (OBS + IMAG). The amplitudes of MEP in BB during IMAG and OBS + IMAG were significantly increased compared to that during the control. In addition, facilitation of MEP size during OBS + IMAG was significantly greater than that during IMAG. And the degree of increase in MEP size during OBS + IMAG was significantly larger than the sum of the values obtained from OBS and IMAG. However, when the subjects imaged the elbow flexion-extension while they observed different actions, MEP amplitudes were not increased compared to that during only imagery of the flexion-extension of the elbow. For BR, the amplitudes of MEP were not changed among four conditions. These findings suggest that the combination of action observation and motor imagery could enhance the excitability of corticospinal tract, possibly through modulation of the mirror neuron systems. [J Physiol Sci. 2008;58 Suppl:S193]
