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Poster C29, Thursday, November 9, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Oscillatory Abnormalities in Primary Progressive Aphasia

Aneta Kielar1,3, Tiffany Deschamps2, Regina Jokel2,4, Jed Meltzer2,3,4;1University of Arizona, 2Baycrest Health Sciences Toronto, Ontario, Canada, 3Canadian Partnership for Stroke Recovery, Ottawa, Ontario, Canada, 4University of Toronto, Toronto, Ontario, Canada

Introduction: Primary progressive aphasia (PPA) is a neurodegenerative disorder characterized by deterioration of language functions, with initial preservation of other cognitive processes. In dementia, functional disruption can extend beyond the regions of frank atrophy that can be detected with structural imaging. Electrophysiological abnormalities in structurally intact tissue may constitute a useful biomarker for early diagnosis and assessment of interventions. In the present study we evaluated oscillatory responses to language stimuli and spontaneous brain electrical activity in patients with PPA compared to age-matched controls. Methods & Procedure: Participants performed a sentence comprehension task while their brain responses were examined using magnetoencephalography (MEG). The sentences included semantically and syntactically anomalous words that evoked distinct electrophysiological responses. Results: In comparison to age-matched controls, oscillatory responses (8-30 Hz event-related desynchronization for anomalous vs. control words) for PPA patients had delayed peak latencies, attenuated amplitude, and in the left parietal region, reversed sensitivity to semantic anomalies, with greater event-related desynchronization for control words instead. Correlational analyses indicated that recruitment of right hemisphere temporo-parietal areas is associated with better semantic performance, demonstrating a compensatory role for right-hemisphere activation. Resting-state MEG analyses showed that patients with PPA exhibit altered spontaneous electrical activity, with a general shift to slower spontaneous dynamics. These abnormalities go in the opposite direction of changes seen in the healthy aging process, and were correlated with slowed neural responses to language stimuli, suggesting that degenerative pathology is linked with slower brain dynamics in both task-related and spontaneous activity. The task-related activity and the resting-state results showed little overlap with gray matter volume measures obtained with VBM analysis. This suggests that in PPA, the atrophied regions may not contribute to information processing in a significant way, but also that additional neural dysfunction may occur in regions far beyond the zone of frank atrophy. Conclusions: The present results indicate that neuropathological changes in the brains of PPA patients result in slowed information processing, which, in turn, is linked with progressive cognitive decline. Abnormalities in both resting-state and task-evoked oscillations can serve as sensitive indicators of neuronal damage associated with neurodegenerative conditions such as PPA. The combination of these measures can reveal the extent of the neural tissue that is not directly atrophied, but is functionally compromised.

Topic Area: Language Disorders

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