(Cerebral resting state networks - MBI Siements Skyra 3T Human MRI)
Connectivity-based segmentation of the striatum in Huntington's disease: vulnerability of motor pathways
The striatum, the primary site of degeneration in Huntington's disease (HD), connects to the cerebral cortex via topographically organized circuits subserving unique motor, associative and limbic functions. Currently, it is not known whether all cortico-striatal circuits are equally affected in HD. We aimed to study the selective vulnerability of individual cortico-striatal circuits within the striatum in HD, and hypothesized that motor cortico-striatal pathways would be most affected, consistent with HD being a primarily motor disorder. Diffusion Tensor Imaging (DTI) tractography was used to identify connections between the striatum and seven major cortical regions in 12 HD patients and 14 matched controls. The striatum of both groups was parcellated into subregions based on connectivity with the cerebral cortex. Volumetric and DTI microstructural measures of Fractional Anisotropy (FA) and Mean Diffusivity (MD) were obtained within each subregion and compared statistically between groups. Tractography demonstrated the topographic organization of cortical connections in the striatum of both controls and HD patients. In HD patients, the greatest difference from controls in volume, FA and MD was observed in M1 and S1 subregions of the caudate and putamen. Motor symptoms correlated with volume and MD in sensorimotor striatal subregions, suggesting that sensorimotor striatal degeneration is closely related to motor dysfunction. DTI tractography provides a novel approach to sensitively examine circuit-specific abnormalities in HD and has identified that the motor cortico-striatal circuit is selectively vulnerable in HD.
Diffusion Tensor Imaging in Huntington's disease reveals distinct patterns of white matter degeneration associated with motor and cognitive deficits
White matter (WM) degeneration is an important feature of Huntington's disease (HD) neuropathology. To investigate WM degeneration we used Diffusion Tensor Imaging and Tract-Based Spatial Statistics to compare Fractional Anisotropy, Mean Diffusivity (MD), parallel diffusivity and perpendicular diffusivity (λ ⊥) in WM throughout the whole brain in 17 clinically diagnosed HD patients and 16 matched controls. Significant WM diffusivity abnormalities were identified primarily in the corpus callosum (CC) and external/extreme capsules in HD patients compared to controls. Significant correlations were observed between motor symptoms and MD in the CC body, and between global cognitive impairment and λ⊥ in the CC genu. Probabilistic tractography from these regions revealed degeneration of functionally relevant interhemispheric WM tracts. Our findings suggest that WM degeneration within interhemispheric pathways plays an important role in the deterioration of cognitive and motor function in HD patients, and that improved understanding of WM pathology early in the disease is required.