Dynamic Corticospinal White Matter Connectivity Changes During Stroke Recovery: A Diffusion Tensor Probabilistic Tractography Study
Reorganisation of the brain after stroke involves recruitment of motor regions within the ipsilesional and, in some cases, contralesional cortex. Diffusion tensor imaging (DTI) tractography studies have provided important information about alterations within corticospinal tracts during stroke recovery. However, little is known about motor connectivity changes at the cortical surface, i.e. evaluating fibre pathways that directly project into the motor cortex. We have developed an automated method to quantify cortical surface motor connectivity that involves the use of the entire cortical surface as a seed mask with target regions defined within the corticospinal tracts to initiate a probabilistic tractography algorithm. The advantage of this novel approach is that cortical surface connectivity changes within multiple motor regions can be investigated, independently of the location and size of the ischemic infarct. Using data from six elderly controls as a measure of reproducibility, we found no change in volume overlap of the generated corticospinal tracts in ten stroke patients (4 subcortical) compared to controls, but significant connectivity changes at the cortical surface, especially within the ipsilesional hemisphere of stroke patients over time. When using the cortical regions with significantly enhanced connectivity as a seed mask, we found evidence of fibre tracts directly linking the contralesional motor cortex with the ipsilesional corticospinal pathways. Measures of uncertainty in fibre orientation within these fibre tracts significantly correlated with functional outcome. The novel findings from this study highlight the robustness of this methodology to study white matter repair / reorganisation during recovery from stroke.