Poster C45, Friday, August 17, 10:30 am – 12:15 pm, Room 2000AB
Apraxia of speech in aphasia maps to lesions in the arcuate fasciculus
Sebastien Paquette1, Karen Chenausky1, Andrea Norton1, Gottfried Schlaug1;1Music, Stroke Recovery, and Neuroimaging Laboratory, Beth Israel Deaconess Medical Center - Harvard Medical School
Introduction. The contribution of lesion location to signs of apraxia of speech (AOS) and aphasia in individuals who have suffered a stroke, and the contribution of AOS to their communication impairments, are challenging to determine because of the overlap of both lesion location and symptomatology between AOS and aphasia. We began investigating these questions by (1) estimating the prevalence of AOS in a large group of patients with aphasia and (2) performing voxel‐based lesion–symptom mapping (VLSM) analyses to determine whether the spatial location of brain lesions can predict symptoms of AOS (Rorden et al., 2007). VLSM tests each voxel to statistically determine whether individuals with lesions in a particular location are more likely to experience the deficit of interest than those without injury at that location. Methods. The Apraxia of Speech Rating Scale (ASRS; Strand et al. 2014) was used to rate video of 39 individuals (out of a final sample of 60) with chronic-stage aphasia. Tasks used were: conversation, how-to and picture descriptions, word/sentence repetition, and diadochokinesis. The ASRS contains 16 items corresponding to characteristic features of AOS. Each item is rated on a scale from 0 (not present) to 4 (nearly always evident and marked in severity). The overall ASRS score is a sum of all 16 items, with scores > 8 indicating the presence of AOS. Participant performance on the Boston Naming Test (BNT; not used for ASRS ratings) was used for a second VLSM analysis to contrast maps with the AOS maps. In order to perform VLSM analyses, lesions masks were first drawn manually on T1-weighted images by an experienced investigator, blinded to the question of interest, and normalized using SPM8. The Non-Parametric Mapping (NPM) software included in MRIcron (z-scores; Brunner-Munzel test) with a false discovery rate correction set at p ≤ 0.01 was used to determine significant relationships between left-hemisphere lesioned voxel clusters and ASRS scores. A critical threshold of 26% was applied (i.e., voxels were ignored unless they were involved in at least 10 cases). Results. 10% of videos were coded by two investigators to establish ASRS scoring reliability. Two-way random-effects ICCs for absolute agreement on single measures yielded a between-judge ICC of 89.7 on overall ASRS score, indicating excellent reliability on the identification of features of AOS. 35 of 39 participants were identified as having AOS. No participants had dysarthria. VLSM analysis revealed a distinct white-matter voxel cluster in the longitudinal portion of the left dorsal arcuate fasciculus that was significantly associated with overall ASRS score and was distinct from the large voxel clusters associated with performance on the BNT (% correct). Conclusions. Our findings associate the expression of apraxia of speech in aphasia to damage circumscribed to the arcuate fasciculus, distinct from the cluster of regions identified using the BNT and reinforce the hypothesis that lesions of the dorsal stream, connecting Wernicke’s and Broca’s areas, plays a critical role in the disordered mapping of acoustics to articulation.
Topic Area: Language Disorders