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Brain. 2016 Oct;139(Pt 10):2778-2791. Epub 2016 Aug 6.

Healthy brain connectivity predicts atrophy progression in non-fluent variant of primary progressive aphasia.

Author information

1
1 Department of Neurology, Memory and Aging Center, University of California San Francisco, CA, USA.
2
2 Memory Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau - Biomedical Research Institute Sant Pau - Universitat Autonoma de Barcelona, Spain 3 Centro de Investigacion Biomedica en Red de Enfermedades Neurodegenerativas - CIBERNED, Spain.
3
4 Department of Communication Sciences and Disorders, Temple University, Philadelphia, Pennsylvania, USA.
4
5 Department of Communication Sciences and Disorders, University of Texas, Austin, USA.
5
6 Department of Neurology, University of California San Francisco, CA, USA 7 Bioengineering Graduate Group, University of California Berkeley, San Francisco, CA, USA 8 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA.
6
1 Department of Neurology, Memory and Aging Center, University of California San Francisco, CA, USA 9 Department of Pathology, University of California San Francisco, CA, USA.
7
1 Department of Neurology, Memory and Aging Center, University of California San Francisco, CA, USA MariaLuisa.Mandelli@ucsf.edu.

Abstract

Neurodegeneration has been hypothesized to follow predetermined large-scale networks through the trans-synaptic spread of toxic proteins from a syndrome-specific epicentre. To date, no longitudinal neuroimaging study has tested this hypothesis in vivo in frontotemporal dementia spectrum disorders. The aim of this study was to demonstrate that longitudinal progression of atrophy in non-fluent/agrammatic variant primary progressive aphasia spreads over time from a syndrome-specific epicentre to additional regions, based on their connectivity to the epicentre in healthy control subjects. The syndrome-specific epicentre of the non-fluent/agrammatic variant of primary progressive aphasia was derived in a group of 10 mildly affected patients (clinical dementia rating equal to 0) using voxel-based morphometry. From this region, the inferior frontal gyrus (pars opercularis), we derived functional and structural connectivity maps in healthy controls (n = 30) using functional magnetic resonance imaging at rest and diffusion-weighted imaging tractography. Graph theory analysis was applied to derive functional network features. Atrophy progression was calculated using voxel-based morphometry longitudinal analysis on 34 non-fluent/agrammatic patients. Correlation analyses were performed to compare volume changes in patients with connectivity measures of the healthy functional and structural speech/language network. The default mode network was used as a control network. From the epicentre, the healthy functional connectivity network included the left supplementary motor area and the prefrontal, inferior parietal and temporal regions, which were connected through the aslant, superior longitudinal and arcuate fasciculi. Longitudinal grey and white matter changes were found in the left language-related regions and in the right inferior frontal gyrus. Functional connectivity strength in the healthy speech/language network, but not in the default network, correlated with longitudinal grey matter changes in the non-fluent/agrammatic variant of primary progressive aphasia. Graph theoretical analysis of the speech/language network showed that regions with shorter functional paths to the epicentre exhibited greater longitudinal atrophy. The network contained three modules, including a left inferior frontal gyrus/supplementary motor area, which was most strongly connected with the epicentre. The aslant tract was the white matter pathway connecting these two regions and showed the most significant correlation between fractional anisotropy and white matter longitudinal atrophy changes. This study showed that the pattern of longitudinal atrophy progression in the non-fluent/agrammatic variant of primary progressive aphasia relates to the strength of connectivity in pre-determined functional and structural large-scale speech production networks. These findings support the hypothesis that the spread of neurodegeneration occurs by following specific anatomical and functional neuronal network architectures.

KEYWORDS:

connectivity; functional connectivity; longitudinal atrophy; primary progressive aphasia; tractography

PMID:
27497488
PMCID:
PMC5035819
DOI:
10.1093/brain/aww195
[Indexed for MEDLINE]
Free PMC Article

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