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Lesion site predictors of syntactic deficits in aphasia

Poster A14 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall

Dirk Den Ouden¹, William Matchin¹, Gregory Hickok², Julius Fridriksson¹; ¹University of South Carolina, ²University of California, Irvine

Introduction: Syntactic problems in aphasia are multidimensional, yet syntactic abilities do not dissociate well along the major aphasia types (Den Ouden et al., 2019). In the present study, we leveraged the largest sample of stroke survivors with aphasia reported to date who were tested with the Northwestern Assessment of Verbs and Sentences (NAVS; Cho-Reyes & Thompson, 2012). In addition, participants’ spontaneous speech samples were rated on a scale for presence and severity of morphosyntactic and phrase-structure production deficits. We then investigated lesion predictors of relative impairments in these subcomponents: syntactic comprehension, complex-sentence production, verb-argument-structure production, phrase-structure production, and morphosyntactic production. Methods: 112 Left-hemisphere stroke survivors with aphasia in the chronic stage (>6 months post stroke) participated in several studies from which these data were leveraged (39.3% female; Mean age 60.4, sd 10.7; Mean WAB-R AQ 64.0, sd 22.3). All participants were tested with the following NAVS subtests: the Argument Structure Production Test “A” score (ASPT-A), the Sentence Production Priming Test (SPPT), and the Sentence Comprehension Test (SCT). For a subset of participants (30%), investigators blindly rated discourse production for the presence and severity of morphosyntactic simplifications (deletion of inflections and function words) and the presence and severity of sentence simplifications (short sentences, absence of embeddings and noncanonical structures), each on a scale from 0-10 (see Matchin et al., 2020). All underwent neuroimaging (Siemens 3T MRI), collecting T1-Weighted images. Lesions were manually drawn based on visual examination of structural images. Voxel-based univariate lesion-symptom mapping was then performed using linear regression analysis with permutation thresholding (3000 permutations) and a one-tailed alpha level of .05. Results: Syntactic comprehension (SCT) was affected by lesions in mid to posterior middle and superior temporal regions, argument structure production (ASPT-A) was dependent on integrity of posterior temporal to inferior parietal regions, complex-sentence production (SPPT) was dependent on integrity of superior temporal and supramarginal regions, morphosyntactic deficits were predicted by lesions in inferior to middle frontal and prefrontal regions, and phrase-structure production problems were predicted by lesions covering the inferior frontal operculum. Conclusions: Results show a syntactic continuum along left-hemisphere perisylvian cortex, in line with the model for the cortical organization of syntax proposed by Matchin and Hickok (2020). This model places the greatest load for hierarchical syntactic computations on (middle) posterior temporal cortex in both comprehension and production, for argument-structure computations on the superior posterior temporal and angular gyrus, with a role for inferior frontal cortex in morphosyntactic computations and linearization of sentence elements in production. One notable exception is that reduced morphosyntactic production as well as simplified sentence productions were predicted by lesions to the inferior-frontal pars opercularis, rather than the pars triangularis. This latter result is somewhat more in line with the neurolinguistic model of Friederici (2012), who particularly emphasizes the role of pars opercularis (BA44) in ‘syntactic processing’. Overall, these findings confirm that different lesions will affect different functional abilities that are part of the syntactic domain. The neural basis for these behavioral dissociations may inform the differential treatment of specific syntactic impairments.

Topic Areas: , Disorders: Acquired