Diffusion weighted callosal integrity reflects interhemispheric communication efficiency in multiple sclerosis.

We aimed to investigate the relation between damage in the corpus callosum and the performance on an interhemispheric communication task in patients with multiple sclerosis (MS). Relative callosal lesion load defined as the ratio between callosal area and the total lesion load in the total corpus callosum, and the diffusion tensor imaging (DTI) derived measures fractional anisotropy (FA) and transverse and longitudinal diffusivity were calculated in sixteen female MS patients and sixteen age and education matched female controls. The redundancy gain task was used to behaviorally evaluate interhemispheric communication efficiency. During this task, simple reaction times to uni- and bilateral presented stimuli are recorded. The advantage in reaction time for bilateral as compared to unilateral trials, the redundancy gain, was significantly larger for the MS-group. The DTI data showed significantly decreased FA and increased diffusivity parameters in the corpus callosum for the MS patients compared with the control group. Moreover, we found a significant correlation between the DTI-derived measures in the corpus callosum and the redundancy gain effect. Callosal damage in MS, as measured by DTI and defined as transverse diffusivity, is associated with alterations in a behavioral task that relies on interhemispheric transfer and communication.