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Neural correlates of Apraxia of Speech and their functions in speech production: Evidence from Primary Progressive Aphasia (PPA)
Poster Session D, Saturday, September 13, 5:00 - 6:30 pm, Field House
This poster is part of the Sandbox Series.
S.C. Angela Xu1, Donna Tippett1, Robert Wiley2,1, Brenda Rapp1, Kyrana Tsapkini1; 1Johns Hopkins University, 2University of North Carolina at Greensboro
INTRODUCTION Theories of word production posit multiple levels of representation and processing. Speech motor planning is a critical process in speech production taking place after phonological/phonetic encoding and before speech motor execution. Apraxia of speech (AOS) is a disorder that affects speech motor planning that typically co-occurs with aphasia (higher-level language disorder) and dysarthria (motor execution disorder). However, there is no consensus regarding the neural substrates specifically underlying speech motor planning. While post-stroke AOS has been associated with lesions to left precentral gyrus (PrCG) (Basilakos et al, 2015, 2018; Takakura et al., 2019), AOS caused by neurodegeneration was associated with left premotor cortex and supplemental motor cortex (Utianski et al., 2018; Cordella et al., 2019). In addition, the specific processes involved in speech motor planning are often underspecified. In this study, we investigate AOS in Primary Progressive Aphasia (PPA, a neurodegenerative language disorder), a less studied population, to evaluate if the diffuse damage profiles can provide additional insights regarding speech planning processes. We aim to answer the following questions: 1) Which brain areas are uniquely associated with AOS? 2) What speech functions are supported by the identified brain areas? METHODS Participants were 34 right-handed individuals with PPA (12 logopenic, 12 nonfluent, 7 semantic, 3 mixed/unclassifiable; 19 females, mean age = 66.8 years, SD = 7.46). Spoken production was assessed with spoken picture naming (Boston Naming Test, BNT) and single-word repetition (Apraxia Battery for Adults, subtest 2, ABA2). A certified, experienced speech-language pathologist (SLP) rated each PPA participant on the severity of 1) expressive language impairment, 2) AOS and 3) dysarthria, using audio recordings of the two tasks and connected speech. Analysis 1: Whole-brain voxel-based morphometry (VBM) on the T1-weighted images using FSL-VBM (Douaud et al., 2007) was conducted to identify voxels significantly correlated (p < .05) with each of the three SLP ratings, controlling for the other two. Analysis 2: Multiple linear regression analysis was conducted to test if each cluster of significant voxels accounted for unique variance in the SLP ratings of AOS. Analysis 3 (ongoing): Ongoing analyses attempt to identify the speech functions supported by each of the brain areas identified in Analysis 2. First, logistic mixed-effects regressions will identify, for each participant, the characteristics of the spoken words (e.g., phoneme length, lexical frequency, neighborhood density, phonological complexity) associated with accuracy in each behavioral task. Second, multiple linear regression will be used to evaluate if any of the characteristics are uniquely associated with specific brain areas. PRELIMINARY RESULTS Analysis 1: Expressive aphasia was significantly associated with bilateral, left-lateralized regions within the temporal lobes, and AOS was the left PrCG, postcentral gyrus (PoCG), angular gyrus (AG), and supramarginal gyrus (SMG). No voxels were associated with dysarthria ratings, likely due to small number of participants with dysarthria. Analysis 2: The sensorimotor PrCG/PoCG cluster (p = 0.006) and the parietal AG/SMG cluster (p = 0.003) both accounted for unique variance in AOS ratings, indicating that multiple processes contribute to speech motor planning.
Topic Areas: Language Production, Speech Motor Control