The impact of localized grey matter damage on neighboring connectivity: posterior cortical atrophy and the visual network.

Posterior cortical atrophy (PCA), a localized neurodegenerative syndrome involving the occipito-parietal cortices, can serve as a good model to elaborate on the consequence of a localized damage on the anatomical and functional connectivity within an affected system. Ten PCA patients and 14 aged-matched controls were enrolled. Structural connectivity was measured via Diffusion Tensor Imaging (DTI) and probabilistic tractography. The optic tracts and radiations and the splenial fibers were delineated and their microstructural properties were evaluated. Functional connectivity was measured by resting state functional MRI (rsfMRI). Voxel-based morphometry (VBM) was used to assess atrophy. Dorsal stream visual functions were tested and correlation between these behavioral data, volume measures, white matter integrity and connectivity were examined. Impaired white matter integrity was evident in patients' optic radiations and occipito-callosal 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. rsfMRI revealed reduced connectivity within the visual network and between the visual and other related areas such as the frontal eye field. Correlations were found between grey matter volume and spatial perception abilities and between the integrity of the affected fibers and motion perception. White matter involvement in PCA seems to be grey matter dependent. Functional connectivity, on the other hand, showed a more diffuse pattern of damage. Correlations were found between the integrity of the affected fibers and patients' visual abilities suggesting that fiber integrity plays a role in determining behavioral manifestation.