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The Right Hemisphere’s Capacity for Language: Evidence from Primary Progressive Aphasia

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Poster B60 in Poster Session B, Tuesday, October 24, 3:30 - 5:15 pm CEST, Espace Vieux-Port

Kyriaki Neophytou1,2, Robert Wiley1,3, Celia Litovsky1, Kyrana Tsapkini1,2, Brenda Rapp1; 1Johns Hopkins University, 2Johns Hopkins Medicine, 3University of North Carolina Greensboro

Introduction: The role of right hemisphere (RH) in language processing is still vigorously debated. This study provided additional evidence from analyzing white matter (WM) tract integrity in Primary Progressive Aphasia (PPA). Specifically, we studied: (1) the WM integrity of the left hemisphere (LH) language tracts and their RH homologues, (2) the overall relationship between language performance and WM integrity in the two hemispheres, (3) the domain-specificity of the RH contributions (i.e., specificity to language versus general cognitive processing) and (4) whether the RH uniquely contributes to language, independently of LH contributions. Methods: Participants were 33 PPA individuals and 20 healthy controls (HC). Language scores on naming, syntax and spelling, and non-language scores on spatial span were collected from the PPA group. DTI data were collected from both groups, and mean diffusivity (MD) – a measure of WM integrity - was calculated for seven language tracts and one non-language tract: anterior and posterior inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus, uncinate fasciculus (UF), long, anterior and posterior arcuate fasciculus and spino-thalamic tract (non-language), bilaterally. Analyses evaluated: (1) MD differences between PPA and HC in both hemispheres. (2) Associations of language scores with tract integrity and (3) domain-specificity in each hemisphere by comparing models with and without language scores. For (3), all models included non-language scores. (4) The unique contribution (unique-R2) of each hemisphere’s tract integrity to explaining variability in language scores was assessed by using the hemispheric difference in unique-R2 between homologous tracts to determine if: (i) the magnitude of unique-R2 differences of homologous tracts significantly favored the LH or the RH for specific tracts and (ii) the distribution across tracts of unique-R2 differences significantly favored the LH or the RH. Results: (1) We found significantly higher MD values for PPA versus HC groups in the LH (p=0.006) for the language tracts. No significant differences were found in the RH for the language tracts, nor for the non-language tract in either hemisphere. (2) For the language tracts, the R2 attributable to language was 10.3% and 5% for the LH and RH, respectively (p’s<0.001), indicating a significant association between language and tract integrity in both hemispheres. For the non-language tract, no significant associations were found. (3) The R2 attributable to language after considering the spatial span scores was 10.7% and 4.2% for the LH and RH, respectively (p’s<0.04), indicating a significant association between language and tract integrity beyond general cognitive functioning. (4) Regarding the magnitude of unique-R2, greater variance for Naming was uniquely explained by two LH tracts compared to their RH homologues: (i) UF (p=0.026), and (ii) anterior IFOF (p=0.021). For the distribution of unique-R2 difference values, we found that 67% of the RH tracts explained more unique variance in language performance than their LH counterparts (p<0.05). Conclusions: These results extend previous findings of the effects of PPA on the WM integrity of the language tracts in the LH and provide strong evidence of the relationship between language processing and WM integrity in both hemispheres in the context of LH damage.

Topic Areas: Disorders: Acquired,

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