運動イメージによる運動誘発電位の出現動態 : 剣道の鍛錬者と非鍛錬者の運動誘発電位(MEP)による検討

Abstract

Objectibe: To understand the neural mechanisms of motor imagery, we examined differences in cortical excitability (primary motor cortex) induced by motor imagery between highly skilled and less skilled exponents of Kendo (Japanese fencing). Methods: First, to confirm differences in Kendo skills between the highly skilled and less skilled Kendoists, EMGs from four muscles (two intrinsic and two forearm muscles) and grip forces on the left and right sides were recorded simultaneously while performing Kendo. Second, to investigate changes in excitability of the motor cortex induced by motor imagery, motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) were recorded from the left and right first dorsal interosseous (FDI), abductor digiti minimi (ADM), extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles. During motor imagery of Kendo skills, MEPs were recorded under the following three conditions: (1) The subjects imaged Menuchi-movements (hitting the head with a bamboo sword) without a visual aid (V^- ), (2) the subjects imaged Menuchi-movements with the aid of a video system (V^+), (3) the subjects imaged the maximum muscle contraction of each of the four muscles, related to Menuchi-movements, respectively. Results: During motor imagery of Menuchi-movements under condition V^-, MEP amplitudes were larger in the highly skilled Kendoists than those in the less skilled Kendoists. Moreover, MEP amplitudes in the less skilled Kendoists were larger under condition V^+ than under condition V^-, whereas the opposite was true in the highly skilled Kendoists although the defference did not attain statistical significance. In both sets of subjects, however, the MEP amplitudes during motor imagery of individual muscle contraction were the same, i.e., the differences in MEP amplitude between the highly skilled and less skilled Kendoists disappeared. Conclusion: The brain function for imaging motor skills differs between highly skilled and less skilled Kendoists. That is, the motor imagery of highly skilled Kendoists invdves performing concrete movement (internal imagery) whereas that of less skilled Kendoists involves looking at the movement (external imagery).