Slide Slam A18
Grammatical parallelism in aphasia revisited: a common lesion substrate for syntactic production and comprehension deficits in the posterior temporal lobe
William Matchin1, Alexandra Basilakos1, Brielle C. Stark2, Dirk den Ouden1, Julius Fridriksson1, Gregory Hickok3; 1University of South Carolina, 2Indiana University Bloomington, 3University of California, Irvine
***INTRODUCTION*** A grammatical parallelism hypothesis in aphasia is commonly espoused: that agrammatism and syntactic comprehension deficits coincide, resulting from common injury to Broca’s area and/or surrounding cortex (Caramazza & Zurif, 1976; Friederici, 2017; Thompson et al., 1997). However, Matchin & Hickok (2020) advocate an alternative hypothesis: that syntactic comprehension deficits coincide with paragrammatism, characterized by the use of complex constructions and functional elements, with syntactic errors rather than overall simplification or reduction (Goodglass, 1993; Kleist, 1914), resulting from common injury to the posterior temporal lobe. Here we test both parallelism hypotheses. ***METHODS*** 220 people with chronic post-stroke aphasia were assessed with the Western Aphasia Battery-Revised (Kertesz, 2007). Subjects’ lesions were manually drawn on their MRI scans and warped to MNI space (Fridriksson et al., 2018).To assess syntactic comprehension, we combined the Sequential Commands subtest with the Auditory Word Recognition subtest as a covariate. Sequential Commands requires subjects to perform increasingly complex sequences of simple actions (e.g. point with the pen to the book), most of which require syntactic parsing to perform correctly. Auditory Word Recognition requires subjects to point to actual or drawn objects, pieces of furniture, shapes, letters, numbers, colors, and body parts (e.g. point to the cup). A subset of 53 subjects were previously assessed for grammatical production deficits using consensus perceptual ratings by four expert raters of elicited speech samples (Cinderella story protocol from AphasiaBank MacWhinney et al., 2011) (Matchin et al., 2020). Agrammatism and paragrammatism ratings were covaried with words per minute to control for speech rate. We first performed one-tailed non-parametric correlations between each grammatical production measure (incorporating lesion volume as a covariate) and the syntactic comprehension measure for the set of 53 subjects. For each of the 220 patients, we calculated proportion damage within each region of interest (ROI), defined as the lesion distributions associated with agrammatism and paragrammatism (voxel-wise p < 0.01), incorporating lesion volume as a covariate, created using NiiStat (https://www.nitrc.org/projects/niistat/). We then performed one-tailed non-parametric correlations between damage to each ROI and syntactic comprehension scores. ***RESULTS*** Agrammatism was not associated with lower syntactic comprehension, (Kendall’s tau B = -0.063, p = 0.255, Figure 1, top left), but paragrammatism was significantly associated with lower syntactic comprehension (Kendall’s tau B = -0.329, p = 0.0002749, Figure 1, top right). Damage to the agrammatism ROI was not associated with lower syntactic comprehension (Kendall’s tau B = 0.009, p = 0.577, Figure 1, bottom left), but damage to the paragrammatism ROI was significantly associated with lower syntactic comprehension (Kendall’s tau B = -0.134, p = 0.002, Figure 1, bottom right). Overlap analyses (including lesion volume, voxel-wise p < 0.01) showed almost no overlap in lesion distributions between agrammatism and syntactic comprehension, whereas there was significant overlap for paragrammatism and syntactic comprehension in posterior superior temporal gyrus and sulcus. ***CONCLUSIONS*** Our results speak against the grammatical parallelism hypothesis rooted in agrammatism and damage to the inferior frontal lobe, and in favor of the grammatical parallelism hypothesis rooted in paragrammatism and damage to the posterior temporal lobe.