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To explore the effect of mirror box therapy based on the mirror neuron (MN) system of the primary motor cortex (M1), we examined if direct (without a mirror) and indirect (with a mirror) observation of self-movement in healthy subjects induced changes in motor evoked potential (MEP) evoked by transcranial magnetic stimulation (TMS). MEPs were elicited from the first dorsal interosseous (FDI) and the flexor carpi radialis (FCR) muscles. Somatosensory evoked potentials (SEPs) during self-movement observation were also recorded. Both observations of self-movement with and without a mirror increased MEP amplitude. In addition, increase in MEP amplitude was specific to the prime mover muscle involved in the observed movement. The SEPs increased similar to the MEPs during both observations of self-movement with and without a mirror. We conclude that although the MN system can be activated by observing self-movement in a manner similar to that achieved by observing movement of another person, there were no detectable effect on corticospinal excitability that were specific to movements observed with a mirror.

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Morishita T, Uehara K, Funase K. Changes in interhemispheric inhibition from active to resting primary motor cortex during a fine-motor manipulation task. J Neurophysiol 107: 3086 -3094, 2012. First published March 14, 2012 doi:10.1152/jn.00888.2011.-The effect of performance of a sensorimotor task on the interhemispheric inhibition (IHI) induced from the active primary motor cortex (M1) to the resting M1 was examined in 10 right-handed subjects. Transcranial magnetic stimulation (TMS) was performed to produce motor evoked potentials (MEP) in the resting right (Rt)-first dorsal interosseous (FDI). For the paired-TMS paradigm, a conditioning stimulus (CS) was delivered to the Rt-M1, and its intensity was adjusted from 0.6 to 1.4 times the resting motor threshold of the MEP in the left (Lt)-FDI in 0.2 steps. The test stimulus was delivered to the Lt-M1, and its intensity was adjusted to evoke similar MEP amplitudes in the Rt-FDI among the task conditions. The interstimulus interval was fixed at 10 ms. As a sensorimotor task, a fine-motor manipulation (FM) task (using chopsticks to pick up, transport, and release glass balls) was adopted. In addition, an isometric abduction (IA) task was also performed as a control task. These tasks were carried out with the left hand. The IHI from the active to the resting M1 observed during the FM task was markedly increased compared with that induced during the IA task, and this effect was not dependent on the MEP amplitude evoked in the active Lt-FDI by the CS. The present findings suggest that the increased IHI from the active to the resting M1 observed during the FM task was linked to reductions in the activity of the ipsilateral intracortical inhibitory circuit, as we reported previously.

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