Slide Slam C3 Sandbox Series
Anatomical differences in Heschl’s gyrus in dyslexia, and in relation to working memory and phonological skill
Josue Luiz Dalboni da Rocha1, Damien Marie1,3, Sanne Rutten1, Narly Golestani1,2; 1University of Geneva, 2University of Vienna, 3Haute école de santé de Genève
Dyslexia is a learning disorder characterized by reading and phonological processing deficits, but also with deficits in other functions such as working memory (Jeffries & Everatt, 2004), rhythm processing (Dellatolas et al., 2009) and visuo-spatial attention (Vidyasagar & Pammer, 2010). Heschl's gyrus (HG), which includes primary auditory cortex (Hall et al., 2003), displays considerable anatomical variability across individuals and across hemispheres (Penhune et al., 1996). Previous studies on the anatomy of HG and of the adjacent planum temporale have revealed an increased incidence of full posterior duplications (Altarelli et al., 2014; Leonard et al., 2001; Serrallach et al., 2016), as well as evidence for a diminished L>R structural asymmetry and trends for overall smaller HG in this disorder (Altarelli et al., 2014). These studies, however, have relied on manual segmentation of auditory cortex sub-regions based on visual inspection of structural MRI, which is more subject to error and to arbitrary decisions than automated segmentation. Here, in data from 18 dyslexic adults and 27 controls, we used the TASH toolbox (Dalboni da Rocha et al., 2020) to automatically segment HG (including single HG and common stem duplications) in 7T structural MRI, from which we extracted HG gray matter volume, white surface area and gray matter thickness. We tested for group differences using one mixed ANCOVA for each anatomical measure. These 2-way mixed ANCOVAs had group (dyslexic and control) as the between-subjects factor and hemisphere as the within-subjects factor, controlling for the covariates of age, sex and the whole brain respective anatomical measure. Results showed: 1) Volume: only significant main effect of group [F(1,40)=5.65, p=0.022], with smaller bilateral HG in the dyslexic group. The effect of hemisphere and group-by-hemisphere interaction were not significant. 2) Surface area: only significant effect of group [F(1,40)=4.14, p=0.049], with smaller bilateral HG surface areas in the dyslexic group. The effect of hemisphere and group-by-hemisphere interaction were not significant. 3) Cortical thickness: no significant effects for group, hemisphere nor group-by-hemisphere interaction. Additionally, in 34 adults of these participants (17 with dyslexia), we tested for partial correlations between HG anatomical measures (volume, area and thickness) in each hemisphere and behavioral measures of Spoonerisms (Ecla16+) and Backward Digit Span (WAIS-IV), controlling for age, gender, Raven's score, years of education and the respective hemispheric anatomical measure. The partial correlations revealed the following results: 1) Volume: No significance. 2) Surface area: No significance. 3) Cortical thickness: Spoonerism correlates with both left [r(27)=0.348, p(1-tailed)=0.032] and right [r(27)=0.480, p(1-tailed)=0.004] HG. Backward Digit Span correlates with left HG [r(27)=0.508, p(1-tailed)=0.002]. These results are consistent with previous reports of altered auditory cortex anatomy in dyslexia, and extend them to relationships with behavior. As next step, given the previously reported differences in HG gyrification in dyslexia, we will also explore HG anatomical differences using different versions of TASH, ones which select multiple transverse temporal gyri when they are present. We will also relate difference in gross brain anatomy to myelination differences in these same participants, with the aim of a multimodal characterization of risk factors underlying dyslexia.