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Poster D13, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall

Frontal aslant tract differences in developmental stuttering

Gabriel Cler1, Peter Howell2, Patricia Gough1, Kate Watkins1;1University of Oxford, 2University College London

The frontal aslant tract (FAT) has been identified as a white matter tract related to speech and language function. This tract connects the inferior frontal gyrus pars opercularis (BA44) and the pre-supplementary motor area (pre-SMA) and is considered an association motor pathway. Stimulation of the left FAT interferes with speech initiation and fluency in typically-fluent adults, which suggests that it could be implicated in stuttering. One previous investigation in 15 people who stutter (PWS) and 19 normally fluent controls used diffusion MRI to study the microstructure of the FAT (Kronfeld-Duenias et al, 2016). PWS showed increased mean diffusivity (MD) in the FAT bilaterally, but there were no differences in fractional anisotropy (FA). Here, we aimed to replicate and extend the previous findings by evaluating the FAT in a larger cohort of 29 PWS and 29 matched controls. We hypothesized that there would be differences in the microstructure of the FAT on the left and possibly also on the right. We predicted that FA would be reduced and, based on the previous finding, MD would be increased in PWS. We further hypothesized that in PWS, these abnormalities would correlate with greater disfluency measured with the Stuttering Severity Instrument-3 (SSI-3). We also measured the uncinate fasciculus (UF) as a control cortico-cortical language tract in the ventral pathway that connects anterior temporal pole with orbitofrontal cortex; we predicted that the UF would be unaffected in PWS. Twenty-nine PWS (age range: 14–42 years; mean age: 22.6) and 29 controls (age range 14–45; mean 22.3) were scanned at 1.5T to acquire structural and diffusion-weighted MRI images of the whole head. The PWS ranged in stuttering severity on the SSI-3 from very mild to very severe. Diffusion data were processed using the FMRIB Diffusion Toolbox. Probabilistic tractography (via ProbtrackX) was used to reconstruct fibre tracts for each participant. Average FA and MD were calculated for each tract separately. One-tailed t-tests were used to compare groups, using false discovery rate correction. The PWS had significantly lower FA in the left FAT compared with controls (controls mean=0.359, SD=0.02; PWS mean=0.345, SD=0.01) but did not differ on the right. There was no relationship between FA in the left FAT and stuttering severity in the PWS. MD in the FAT did not differ between the two groups in either hemisphere. As hypothesized, there were no differences between groups in the UF. This analysis in a larger cohort of people who stutter suggests that the microstructure of left FAT is abnormal. However, this was manifest in terms of reduced FA (a measure of white matter integrity) and no differences in MD (as had previously been indicated) were detected. Although these results indicate that there are differences in the microstructure of this tract in people who stutter, it is unknown whether these differences are a cause or consequence of stuttering. Further analyses of additional datasets will be conducted with the aim of replicating the finding in left FAT and to increase power to detect differences in MD should they exist.

Themes: Disorders: Developmental, Speech Motor Control
Method: White Matter Imaging (dMRI, DSI, DKI)

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