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

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-iSP(mean)) 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-iSP(mean) accounted for 84% of variance in motor impairment (p < 0.01). Both transcallosal prefrontal tract FA (Delta R-2 = 0.12, p = 0.04) and NL-iSP(mean) (Delta R-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. (C) 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.