Diffusion imaging and transcranial magnetic stimulation assessment of transcallosal pathways in chronic stroke.

ABSTRACT

OBJECTIVE: To examine the relationship of transcallosal pathway microstructure and transcallosal inhibition (TCI) with motor function and impairment in chronic stroke. METHODS: Diffusion-weighted magnetic resonance imaging and transcranial magnetic stimulation (TMS) data were collected from 24 participants with chronic stroke and 11 healthy older individuals. Post-stroke motor function (Wolf Motor Function Test) and level of motor impairment (Fugl-Meyer score) were evaluated. RESULTS: Fractional anisotropy (FA) of transcallosal tracts between prefrontal cortices and the mean amplitude decrease in muscle activity during the ipsilateral silent period evoked by TMS over the non-lesioned hemisphere (termed NL-iSPmean) were significantly associated with level of motor impairment and motor function after stroke (p<0.05). A regression model including age, post-stroke duration, lesion volume, lesioned corticospinal tract FA, transcallosal prefrontal tract FA and NL-iSPmean accounted for 84% of variance in motor impairment (p<0.01). Both transcallosal prefrontal tract FA (ΔR(2)=0.12, p=0.04) and NL-iSPmean (ΔR(2)=0.09, p=0.04) accounted for unique variance in motor impairment level. CONCLUSIONS: Prefrontal transcallosal tract microstructure and TCI are each uniquely associated with motor impairment in chronic stroke. SIGNIFICANCE: Utilizing a multi-modal approach to assess transcallosal pathways may improve our capacity to identify important neural substrates of motor impairment in the chronic phase of stroke.