Abstract
BackgroundWhile asymmetry in the fusiform gyrus (FFG) has been reported in functional and structural studies in typically developing controls (TDC), few studies have examined FFG asymmetry in autism spectrum disorder (ASD) subjects and those studies are limited by small sample sizes, and confounded by cognitive ability or handedness. No previous work has examined FFG surface area or cortical thickness asymmetry in ASD; nor do we understand the trajectory of FFG asymmetry over time. Finally, it is not known how FFG structural asymmetry relates to ASD symptom severity.MethodsIn this study, we examined FFG volume, surface area, and cortical thickness asymmetry, as well as their cross-sectional trajectories in a large sample of right-handed males aged 7 to 25 years with 128 ASD and 127 TDC subjects using general linear models. In addition, we examined the relationship between FFG asymmetry and ASD severity using the Autism Diagnostic Observation Schedule (ADOS) and Gotham autism severity scores.ResultsFindings revealed that while group differences were evident with mean leftward asymmetry in ASD and mean near symmetry in TDC volume and surface area, asymmetry for both groups existed on a spectrum encompassing leftward and rightward asymmetry. In ASD subjects, volume asymmetry was negatively associated with ADOS and autism severity score symptom measures, with a subset of rightward asymmetric patients being most severely affected. We also observed differential trajectory of surface area asymmetry: ASD subjects exhibited a change from leftward asymmetry toward symmetry from age 7 to 25, whereas TDCs exhibited the reverse trend with a change from near symmetry toward leftward symmetry over the observed age range.ConclusionsAbnormalities in FFG structural asymmetry are related to symptom severity in ASD and show differential developmental trajectory compared to TDC. This study is the first to note these findings. These results may have important implications for understanding the role of FFG asymmetry in ASD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13229-016-0089-5) contains supplementary material, which is available to authorized users.
Highlights
While asymmetry in the fusiform gyrus (FFG) has been reported in functional and structural studies in typically developing controls (TDC), few studies have examined FFG asymmetry in autism spectrum disorder (ASD) subjects and those studies are limited by small sample sizes, and confounded by cognitive ability or handedness
The little research that does exist indicates greater leftward volumetric asymmetry in posterior temporal FFG in ASD compared to TDC (20 vs. 6 %, respectively) [19], and leftward asymmetry in anterior and posterior FFG in both ASD and controls, neither finding was significantly asymmetric after a one-sample t test [1]
In this study, we examined asymmetries in volume, surface area, and cortical thickness in the FFG in a population of individuals diagnosed with ASD and controls (TDC)
Summary
While asymmetry in the fusiform gyrus (FFG) has been reported in functional and structural studies in typically developing controls (TDC), few studies have examined FFG asymmetry in autism spectrum disorder (ASD) subjects and those studies are limited by small sample sizes, and confounded by cognitive ability or handedness. No previous work has examined FFG surface area or cortical thickness asymmetry in ASD; nor do we understand the trajectory of FFG asymmetry over time. Many patients suffering from prosopagnosia—the inability to identify faces—exhibit lesions in the right posterior FFG [8] Consistent with this finding functional studies have largely shown that individuals exhibit a right hemisphere advantage when identifying whole faces, rather than parts [4]. In addition to its proposed role in face processing, research has indicated that the left FFG [9] contains the visual word form area which is thought to be specialized for word recognition [10] and plays a critical role in reading, with lesions in this region resulting in alexia [11]
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