title: Toddlers later diagnosed with autism exhibit multiple structural abnormalities in temporal corpus callosum fibers.
abstract: Interhemispheric functional connectivity abnormalities are often reported in autism and it is thus not surprising that structural defects of the corpus callosum (CC) are consistently found using both traditional MRI and DTI techniques. Past DTI studies however, have subdivided the CC into 2 or 3 segments without regard for where fibers may project to within the cortex, thus placing limitations on our ability to understand the nature, timing and neurobehavioral impact of early CC abnormalities in autism. Leveraging a unique cohort of 97 toddlers (68 autism; 29 typical) we utilized a novel technique that identified seven CC tracts according to their cortical projections. Results revealed that younger (<2.5 years old), but not older toddlers with autism exhibited abnormally low mean, radial, and axial diffusivity values in the CC tracts connecting the occipital lobes and the temporal lobes. Fractional anisotropy and the cross sectional area of the temporal CC tract were significantly larger in young toddlers with autism. These findings indicate that water diffusion is more restricted and unidirectional in the temporal CC tract of young toddlers who develop autism. Such results may be explained by a potential overabundance of small caliber axons generated by excessive prenatal neural proliferation as proposed by previous genetic, animal model, and postmortem studies of autism. Furthermore, early diffusion measures in the temporal CC tract of the young toddlers were correlated with outcome measures of autism severity at later ages. These findings regarding the potential nature, timing, and location of early CC abnormalities in autism add to accumulating evidence, which suggests that altered inter-hemispheric connectivity, particularly across the temporal lobes, is a hallmark of the disorder.
authors.affiliation: Department of Brain and Cognitive Sciences, Ben-Gurion University, Israel. Electronic address: noafingher@gmail.com.
authors.forename: Noa
authors.initials: N
authors.lastname: Fingher
authors.affiliation: Department of Brain and Cognitive Sciences, Ben-Gurion University, Israel; Department of Psychology, Ben-Gurion University, Israel.
authors.forename: Ilan
authors.initials: I
authors.lastname: Dinstein
authors.affiliation: Department of English Literature and Linguistics, Bar Ilan University, Israel; The Gonda Multidisciplinary Brain Research Center, Bar Ilan University, Ramat Gan, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Ben-Shachar
authors.affiliation: Department of Brain and Cognitive Sciences, Ben-Gurion University, Israel.
authors.forename: Shlomi
authors.initials: S
authors.lastname: Haar
authors.affiliation: Department of Neurosciences, University of California San Diego, USA; Department of Radiology, University of California San Diego, USA.
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.affiliation: Department of Radiology, University of California San Diego, USA; Desert-Pacific Mental Illness Research, Education, and Clinical Center, VA San Diego Healthcare System, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Eyler
authors.affiliation: Department of Neurosciences, University of California San Diego, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Pierce
authors.affiliation: Department of Neurosciences, University of California San Diego, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Courchesne
mesh_terms: D001321:Autistic Disorder / Q000000981:diagnostic imaging / Q000473:pathology*; D002675:Child, Preschool; D003337:Corpus Callosum / Q000000981:diagnostic imaging / Q000473:pathology*; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D013702:Temporal Lobe / Q000000981:diagnostic imaging / Q000473:pathology*
keywords: Autism; Corpus callosum; DTI; Inter-hemispheric connectivity; White matter