Disinhibition in the Unaffected Hemisphere Is Related with the Cortical Involvement of the Affected Hemisphere

To investigate whether the disinhibition of the unaffected hemisphere (UH) is related with the lesion location or integrity of the corticospinal tract, we evaluated the intracortical excitability of hand motor cortex in the UH using a paired-pulse transcranial magnetic stimulation paradigm short intracortical inhibition (sICI) and intracortical facilitation (ICF) in 30 subacute stroke survivors. The participants were then classified according to the lesion locations (cortical versus subcortical) and the presence of motor-evoked potential (MEP) response on the paretic hand (MEP+ versus MEP-). The sICI and ICF in the UH were compared according to lesion location and presence of paretic MEP. The sICI and ICF in the UH were comparable between MEP+ and MEP-groups. However, in terms of lesion location, intracortical inhibition was present in patients with subcortical lesions, whereas the patients with cortical lesions showed significant disinhibition in the UH. In conclusion, these findings support that the disinhibition of UH in subacute stage is related to the location of lesion rather than the integrity of the corticospinal tract.