Functional demanded excitability changes of human hand motor area

概要

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The present study was performed to examine whether there are functional differences between the first dorsal interosseous (FDI) and abductor digit minimi (ADM)muscles depending on different muscle contractions, dynamic and static contraction of index and little finger abduction. We recorded motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) and simultaneously recorded force curves during the muscle contractions. We also defined rest motor threshold (RMT) and active motor threshold (AMT, during dynamic and static contraction) in two muscles. F-waves were recorded in same procedures as MEPs. In all trials of MEP and F-wave, background EMGs (B.EMGs) were kept at same level. Force matching errors of dynamic contraction were statistically smaller in FDI muscle than those in ADM. In the FDI muscle, AMT during dynamic contraction was significantly lower than that during static one. Additionally, we employed MEP/B.EMG ratio as an index to assess functional differences between two muscles. In the FDI muscle, the ratios were larger during dynamic contraction than those during static ones. But such results were not found in the ADM muscle. F-waves remained steady in either muscle. Thus, we conclude that there are functional demanded excitability changes between FDI and ADM muscles, although they share the same innervations of ulnar nerve.