A number of TMS studies have suggested that the activation of the ipsilateral primary motor cortex (M1) during the performance of a unilateral hand motor task is mediated by transcallosal pathways.
However, the effects of performing a sensorimotor task on interhemispheric neural mechanisms have not been examined in detail. We examined the changes in interhemispheric inhibition (IHI) from the active to the resting M1 during the performance of a finemotor manipulating task and compared them with those produced during a simple voluntary contraction task.
The effect of performing a fine-motor manipulation task as a sensorimotor task on the IHI induced from the active M1 to the resting M1 was examined in ten right-handed subjects , assessed by motor evoked potentials (MEP) evoked by transcranial magnetic stimulation (TMS) . As a result, a marked facilitation of the ipsilateral M1 excitability was observed during performing a fine-motor manipulation task than a simple finger muscle contraction.
The present findings suggest that the increased IHI from the active to the resting M1 observed during a fine-motor manipulation task was linked to reductions in the activity of the ipsilateral intracortical inhibitory circuit, as we reported previously.
In order to verify the actual effect of a fine-motor manipulating task performed by a healthy hand of hemiplegic patient, collaboration with the rehabilitation facility will be useful.
An actual daily motor task using chopsticks as a sensorimotor task is adopted in the present study. This fine-motor manipulation using chopsticks induces the marked facilitation of ipilateral M1 excitability innervating the contralateral hand muscle.
Changes in interhemispheric inhibition from the active to resting primary motor cortex during a fine-motor manipulation task. Morishita T, Uehara K, Funase K, Journal of Neurophysiology, in press, doi:10.1152/jn.00888.2011
Increased excitability and reduced intracortical inhibition in the ipsilateral primary motor cortex during a fine-motor manipulation task. Morishita T, Ninomiya M, Uehara K, Funase K, Brain Research, 1371: 65-73, 2011