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Clustering and Switching on Verbal Fluency in the Logopenic Variant of Primary Progressive Aphasia

Poster A30 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall

Fatima Jebahi¹, Katlyn Nickels¹, Noah Frazier¹, Aneta Kielar¹; ¹The University of Arizona

Introduction: A defining feature of the logopenic variant of primary progressive aphasia (lvPPA) is significant lexical retrieval difficulties, which are often characterized using confrontation naming tasks. Other lexical retrieval measures that have been less studied are verbal fluency (VF) tasks, which examine the ability to produce as many unique words as possible that begin with a specific letter (letter fluency) or that belong to a specific category (semantic fluency) in 60 seconds. Importantly, performance on VF tasks offer a unique opportunity to investigate the nature of lexical retrieval difficulties. Optimal VF performance depends on generating words within a subcategory (clustering) and, when a subcategory is exhausted, shifting to a new subcategory (switching). Only a few studies have investigated the qualitative (clustering and switching) aspect of this task in lvPPA. Indeed, a reduction in the number of words generated on VF tasks has been well documented, but limited research has examined the qualitative aspect of their performance. This examination can offer important insights into the organization of the lexical-semantic system in lvPPA. The purpose of this study was to examine clustering and switching on a semantic VF task (animal fluency) in patients with lvPPA and examine their relationship to gray matter atrophy. Methods: Participants with lvPPA (n =13; mean age=68.69±5.27 years; mean education=17.31±4.48 years) and 21 age- (t(32)=.049, p=.481) and education- (t(32)=-.660, p =.257) matched controls were recruited from the University of Arizona. All participants underwent neuropsychological and language testing and a magnetic resonance imaging (MRI) scan. On animal fluency, participants named as many animals as possible in 60 seconds. We calculated the number of correct words, number of clusters, mean cluster size, and number of switches based on established guidelines. Differences between the lvPPA and controls were assessed using independent sample t-tests. Additionally, voxel-based morphometry (VBM) will be implemented to identify areas of gray matter atrophy in lvPPA. These VBM maps will be entered into multiple regression to investigate the relationship between gray matter volumes and clustering and switching measures. Results: Our results indicate that number of words (t(32)=-9.37, p<0.001), number of clusters (t(32)=-6.74, p<0.001), average cluster size (t(32)=-4.13, p<0.001), and number of category switches (t(32)=-8.08, p<0.001) were significantly reduced in participants with lvPPA. VBM will be computed to identify patterns of gray matter atrophy and to investigate the relationship between regional gray matter volume and fluency measures. Conclusion: The present study examined differences in quantitative and qualitative features of VF in patients with lvPPA and neurotypical controls. Patients with lvPPA generated fewer words than their respective controls and demonstrated significant impairment on clustering and switching measures. This is consistent with involvement of frontal lobe functions during switching and temporal regions for clustering. Our findings are consistent with the literature on lvPPA and align with the patterns observed in Alzheimer’s Disease (AD). Interestingly, lvPPA is often associated with underlying AD pathology and show similar behavioral patterns to those observed in AD. Our results offer clinically and empirically important insights regarding the organization of the lexical-semantic system in lvPPA.

Topic Areas: Disorders: Acquired, Language Development/Acquisition