Disrupted brain connectome in semantic variant of primary progressive aphasia

Using resting-state functional magnetic resonance imaging and graph analysis, the topological organization of the functional brain network connectivity was explored in patients with left-sided onset semantic variant (SV) of primary progressive aphasia relative to healthy controls. Functional brain networks in SV patients were characterized by a significantly lower mean network degree, clustering coefficient, and global efficiency, longer characteristic path length and higher assortativity compared with controls. SV patients showed also a strongly left-lateralized loss of hubs, and reduced nodal degree in the inferior and ventral temporal regions and occipital cortices. In SV, the decreased nodal degree extended into the medial and ventral frontal cortex bilaterally, left amygdala and/or hippocampus, and left caudate nucleus. These findings provide evidence that the focal structural degeneration of the inferior temporal, and perysilvian language regions in SV patients ultimately results in a distributed pattern of functional connectivity abnormalities. The local network analysis shows that SV is associated with a functional degradation in the "pan-modal" inferior and/or ventral temporal regions, and the "modality-specific" visual cortical origin of the ventral processing pathway.