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The Relationship Between Right Hemisphere White-Matter Tracts and Information Content in Parkinson’s Disease

Poster D34 in Poster Session D, Wednesday, October 25, 4:45 - 6:30 pm CEST, Espace Vieux-Port

Federico Rodriguez-Porcel¹, Deena Schwen Blackett¹, Daniel Lench¹, Travis Turner¹, Ezequiel Gleichgerrcht¹, Hickok Gregory², Leonardo Bonilha³; ¹Medical University of South Carolina, ²University of California, Irvine, ³Emory University

Introduction: Communication impairments are common in Parkinson's disease (PD). The nature of this impairment is multifaceted, encompassing motor control, cognition, and language-specific domains. Although PD is associated with impairments at the motor and single-word production levels, little is known about its effect on connected speech. Early work has shown deficits in discourse productivity, fluency, lexical diversity, and information content. However, the structural correlates of these deficits have not been evaluated. In this study, we sought to evaluate the association between discourse abilities in PD and the degeneration of basal ganglia and language-specific fiber tracts. Methods: We collected discourse samples of the Cinderella story from 19 patients with PD who were being evaluated for deep brain stimulation candidacy. Discourse samples were transcribed and coded in CLAN and discourse metrics were extracted, including measures of discourse productivity (total utterances and mean length of utterance), fluency (words per minute, retracings, repetitions, and pauses), word-level and utterance errors, lexical diversity (type-token ratio) and information content (propositional density and open to closed class ratio). Diffusion Kurtosis Imaging (DKI) using 30 diffusion encoding directions and three b-values (0,1000,2000 s/mm2) was acquired on a Siemens Verio or Skyra 3T MRI scanner. DKI scans were processed with the open-source PyDesigner pipeline and tractography was performed using DSI studio’s autotracking across 12 major white-matter bundles associated with language production on each hemisphere. Diffusion metrics extracted along defined tracts included fractional anisotropy (FA), mean diffusivity (MD), and mean kurtosis (MK). Pearson correlations were used to determine the relationship between the diffusion metrics of tracts and the discourse metrics. For significant correlations, follow-up multiple linear regressions were conducted including motor speech ratings as a predictor to determine if the relationship between tract integrity and discourse remained after controlling for motor speech. P-values associated with each model and independent variable were adjusted using the false discovery rate. Results: Information content metrics, such as propositional density and open-closed ratio correlated with degeneration of right-hemisphere tracts. Specifically, the integrity of the third segment of the superior longitudinal fasciculus (SLF-III) was negatively associated with an open-closed ratio (MD: r=-0.709; p=0.048; MK: r=0.645; p=0.036) and positively associated with propositional density (MK: r=-0.636; p-value=0.036) while the right superior corticostriatal pathway was negatively associated with open-closed ratio (MK: r=0.719; p=0.036) and the right arcuate fasciculus was positively associated with propositional density (MK: r=-0.631; p=0.038). Conclusion: Our data provide preliminary evidence regarding the role of right hemisphere white matter tracts in connected speech in PD. Specifically, our results suggest that in PD, degeneration of the SLF-III and the superior corticostriatal pathway are associated with a decline in information content metrics. The latter also hints towards the non-motor role of the basal ganglia in language production. Further studies with larger samples and control groups are needed to assess the role of the right hemisphere in connected speech in PD.

Topic Areas: Disorders: Acquired, Meaning: Discourse and Pragmatics