Poster D53, Friday, August 17, 4:45 – 6:30 pm, Room 2000AB

Functional contribution of the arcuate fasciculus to language processing: A tractography study in individuals with stroke

Maria V. Ivanova1,2, Allison Zhong1, And Turken1, Brian Curran1, Nina F. Dronkers1,3,4;1Center for Aphasia and Related Disorders, VA Northern California Health Care System, Martinez, California, USA, 2National Research University Higher School of Economics, Center for Language and Brain, Moscow, Russian Federation, 3University of California, Davis, California, USA, 4University of California, Berkeley, California, USA

Damage to the arcuate fasciculus (AF) has been linked to deficits of various language abilities: speech fluency, informative content of speech, sentence production, naming, repetition and comprehension at the word and sentence level (Breier et al., 2008; Hope et al., 2016; Ivanova et al., 2016; Kümmerer et al., 2013; Marchina et al., 2011; Wilson et al., 2011). Although there are single reports of excellent recovery from aphasia even following complete disruption of the AF (Gyu & Ho, 2011), the bulk of evidence strongly suggests that the AF is critical for language. What remains to be determined is its specific functional contribution to various language capacities. The current study aims to provide a comprehensive evaluation of the functional role of the AF in language, based on different anatomical models of the tract in both ipsilesional and contralesional hemispheres in a large cohort of individuals with chronic aphasia. METHODS: Patients with aphasia (n=33) following left hemisphere stroke participated in the study. Language abilities were tested with the Western Aphasia Battery – Revised (WAB-R, Kertesz, 2007). Diffusion-weighted MR imaging was performed on a 3T scanner (64 directions, 2 mm isovoxel, b = 2000 s/mm2, 10 b0 volumes). After pre-processing in FSL and ExploreDTI, tractography based on the spherical deconvolution model was performed using StarTrack. The AF in the left and right hemispheres were then manually reconstructed in TrackVis using a modified 3-segment model (Catani et al, 2005), with a long segment connecting inferior frontal areas with posterior temporal, and two short segments that connect frontal and temporal areas to inferior parietal cortex, and a modified 2-segment model (Glasser & Rilling, 2008), that includes two long segments originating from the superior temporal gyrus (STG) and the middle temporal gyrus (MTG) and both extending into the frontal lobe. The normalized volumes of the different segments of the AF were correlated with scores on different language subtests of the WAB-R while controlling for age, lesion volume, time post-onset and gender. RESULTS: In the left hemisphere, according to the 3-segment model of the AF, the long segment was strongly associated with all WAB-R subtests, including fluency, spontaneous speech, comprehension, repetition, and naming. The anterior short segment was only associated with fluency, while the posterior short segment was associated with comprehension, repetition and naming. According to the 2-segment model, the AF originating from STG was associated with repetition, while the AF originating from MTG was associated with fluency, spontaneous speech, repetition and naming. No significant relationships were observed between volume of the AF segments in the right hemisphere and residual language deficits. SUMMARY: The current study constitutes a thorough evaluation of the AF after stroke, revealing specific linguistic impairments associated with different segments of the tract. For the first time the 3-segment model of the AF was comprehensively evaluated in both hemispheres. This was also the first study of language deficits in stroke to utilize the 2-segment model by Glasser and Rilling. Results indicate critical contributions of different parts of the AF to language comprehension and production.

Topic Area: Language Disorders