The impact of localized gray matter damage on connectivity: Posterior Cortical Atrophy study (P3.186)

Objective: To utilize diffusion tensor imaging (DTI) and resting state functional MRI (rsfMRI) to study the effect of localized gray matter damage on white matter networks integrity through the model of posterior cortical atrophy (PCA). Background: In contrary to long-held beliefs, white-matter involvement in predominantly gray-matter diseases is well accepted. However, whether the mechanism to explain fibers’ degeneration is or is not gray-matter dependent is a matter of debate. PCA is a localized neurodegenerative syndrome. The involved visual system is also well defined, especially in contrast to other neuronal systems prone to degeneration. These characteristics put forward PCA as a fine model for tracking tissue degeneration and reorganization. Design/Methods: Fibers integrity was assessed in 10 PCA patients and 14 controls via DTI. The visual pathways and corticospinal tracts were delineated and their microstructural properties were evaluated. Functional connectivity within the visual network was measured, using rsfMRI. Dorsal related visual functions were tested and correlation with network integrity was examined. Results: Impaired integrity was evident in patients’ optic radiations and splenial fibers, in the segments located in close proximity to the occipital cortex, suggesting a localized damage. Degeneration did not proceed to the optic tracts, opposing trans-synaptic changes and was not evident in the corticospinal tracts, suggesting specificity to the visual pathways. rsfMRI revealed reduced connectivity within the visual network, however, this reduction was gray matter volume dependent. Patients’ motion perception abilities were correlated with the integrity of the affected fibers: the worse the integrity, the worse the ability to identify coherent motion. Conclusions: Impaired white matter integrity, was found only within fibers in close proximity to damaged gray matter areas, with no evidence of distal changes. Nevertheless, correlations were found between the integrity of the affected fibers and patients’ visual abilities suggesting that fibers’ integrity plays a role in determining behavioral manifestation. Disclosure: Dr. Glick-Shames has nothing to disclose. Dr. Backner has nothing to disclose. Dr. Raz has nothing to disclose. Dr. Levin has nothing to disclose.