Interhemispheric connectivity in congenital hemiparesis

Aims: Early unilateral brain lesions can lead to different types of corticospinal (re-)organization. In some patients, the contralesional hemisphere exerts motor control over the (ipsilateral) paretic hand, as the primary motor cortex is (re-)organized in the contralesional hemisphere, whereas there are also patients with early unilateral lesions but normal contralateral motor projections. Here, we report on how cortical (re-)organization affects interhemispheric transcallosal connectivity in congenital hemiparesis.

Methods: Transcallosal interhemispheric connectivity was examined by diffusion tensor imaging (DTI) in eight patients with ipsilateral motor projections (IPSI) versus seven patients with normal contralateral motor projections (CONTRA). On the midsagittal layer, the corpus callosum (CC) was subdivided according to the classification of Hofer & Frahm (2006) in five different ROIs. DTI parameters for fractional anisotropy (FA), relative anisotropy, Trace, as well as structural parameters (count, volume) were calculated for areas I to V of the CC.

Results: The structural composition of the CC (volume, count) showed no differences between the IPSI and the CONTRA group. Differences were detected for DTI parameters: in area III, where callosal motor fibers cross the CC, group CONTRA showed significantly higher values for FA, paralleled by lower values for Trace. No differences were detected for area IV, where somatosensory fibers cross the CC.

Conclusion: The results demonstrate that cortical (re-)organization in patients with early unilateral lesions affects interhemispheric transcallosal connectivity. First, these findings help to further characterize different neurophysiological properties of patients with congenital hemiparesis. Second, they help to better understand the implications of interhemispheric connectivity for motor learning during the application of specific therapies in congenital hemiparesis.