Brain metabolic connectivity reconfiguration in the semantic variant of primary progressive aphasia

Functional network-level alterations in the semantic variant of Primary Progressive Aphasia (sv-PPA) are relevant to understanding the clinical features and the neural spreading of the pathology. We assessed the effect of neurodegeneration on brain systems reorganization in early sv-PPA, using advanced brain metabolic connectivity approaches. Forty-four subjects with sv-PPA and forty-four age-matched healthy controls (HC) were included. We applied two multivariate approaches to [18F]FDG-PET data -i.e., sparse inverse covariance esti-mation and seed-based interregional correlation analysis -to assess the integrity of (i) the whole-brain metabolic connectivity and (ii) the connectivity of brain regions relevant for cognitive and behavioral functions. Whole-brain analysis revealed a global-scale connec-tivity reconfiguration in sv-PPA, with widespread changes in metabolic connections of frontal, temporal, and parietal regions. In comparison to HC, the seed-based analysis revealed a) functional isolation of the left anterior temporal lobe (ATL), b) decreases in temporo-occipital connections and contralateral homologous regions, c) connectivity in-creases to the dorsal parietal cortex from the spared posterior temporal cortex, d) a disruption of the large-scale limbic brain networks. In sv-PPA, the severe functional derangement of the left ATL may lead to an extensive connectivity reconfiguration, encompassing several brain regions, including those not yet affected by neurodegeneration. These findings support the hypothesis that in sv-PPA the focal vulnerability of the core region (i.e., ATL) can potentially drive the widespread cerebral connectivity changes, already present in the early phase.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

In the semantic variant of Primary Progressive Aphasia (sv-PPA), there are extensive brain metabolic connectivity reorganization and functional alterations, particularly affecting frontal, temporal, and parietal regions. Compared to healthy controls, sv-PPA patients show functional isolation of the left anterior temporal lobe, decreased connections in temporo-occipital regions and contralateral homologous regions, increased connectivity to the dorsal parietal cortex from the spared posterior temporal cortex, and disruption of large-scale limbic brain networks. The severe functional derangement of the left anterior temporal lobe in sv-PPA may lead to extensive connectivity reconfiguration involving multiple brain regions.