Interhemispheric inhibition predicts the size of a cortical hand muscle representation during active contraction

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IHI between motor cortices can be assessed using paired-pulse TMS, and may be related to the size of the cortical representation for a given muscle. 15 healthy, individuals participated. IHI was examined in the right FDI by delivering conditioning TMS to ipsilateral M1 followed by TMS to contralateral M1. The size of the FDI representation in M1 was found by delivering TMS over a grid centred on the FDI motor hotspot of the left M1. Both IHI and cortical territory were obtained during rest, contralateral and ipsilateral FDI contraction. Results indicate that reduced IHI corresponded to larger cortical FDI representations during both contralateral and ipsilateral contraction, and not during rest.