Diffusion Tensor Imaging in Autism Spectrum Disorder: A Review

Abstract

White matter tracts of the brain allow neurons and neuronal networks to communicate and function with high efficiency. The aim of this review is to briefly introduce diffusion tensor imaging methods that examine white matter tracts and then to give an overview of the studies that have investigated white matter integrity in the brains of individuals with autism spectrum disorder (ASD). From the 48 studies we reviewed, persons with ASD tended to have decreased fractional anisotropy and increased mean diffusivity in white matter tracts spanning many regions of the brain but most consistently in regions such as the corpus callosum, cingulum, and aspects of the temporal lobe. This decrease in fractional anisotropy was often accompanied by increased radial diffusivity. Additionally, the review suggests possible atypical lateralization in some white matter tracts of the brain and a possible atypical developmental trajectory of white matter microstructure in persons with ASD. Clinical implications and future research directions are discussed. Autism Res 2012, 5: 289–313. © 2012 International Society for Autism Research, Wiley Periodicals, Inc.

Reduced Gyrification Is Related to Reduced Interhemispheric Connectivity in Autism Spectrum Disorders

“…Schaer et al 18 interestingly showed a relationship between reduced gyrification index (GI) and reduced white matter connectivity in a small group of low-functioning children with ASD, where right prefrontal gyrification was positively correlated with the number of white matter fibers in ASD. This ties in with an evergrowing body of literature reporting development changes in (interhemispheric) connectivity in ASD, especially in prefrontal tracts such as the forceps minor (reviewed in 21,22 ).…”

“…In contrast with inconsistent findings of reduced gyrification in ASD, reduced interhemispheric connectivity-and specifically decreased forceps minor connectivity-has been reported consistently (for reviews see 21,22 . On the behavioral level, reduced forceps minor connectivity has indeed been related to restricted and stereotyped behavior 18,42 .…”

Differences in the right inferior longitudinal fasciculus but no general disruption of white matter tracts in children with autism spectrum disorder

“…One of the most widely claimed brain signatures of autism spectrum disorder (ASD), reported in dozens of papers that used diffusion-weighted imaging (DWI), is reduced integrity of long-range fiber tracts (1). This finding has been taken as evidence that autism is fundamentally a "disconnection" syndrome, in which the core cognitive deficits result from reduced integration of information at the neural and cognitive levels (2)(3)(4)(5).…”

“…However, the literature reveals little actual agreement on the existence and direction of group differences in diffusion parameters (reviewed in ref. 1). White-matter differences have been reported in various brain regions in positive and negative directions.…”

Contralateral targeting of the corpus callosum

“…However, the extent of callosal malformations is largely obscured by differences in cohort selection criteria and/or methodological approaches between studies (see meta-analyses summarising these data for autism (Frazier and Hardan, 2009), schizophrenia (Arnone et al, 2008), ADHD (Valera et al, 2007), and a review for dyslexia ). Diffusion MRI (dMRI) studies have shown a somewhat more consistent, although still variable, decrease in functional anisotropy (FA; a measure of tract organisation) of the corpus callosum or its sub-regions in autism (Alexander et al, 2007;Travers et al, 2012;Aoki et al, 2013), schizophrenia (Patel et al, 2011), ADHD (Cao et al, 2010) and developmental language disorder (Kim et al, 2006). Symptom severity and callosal abnormalities are also correlated in a number of these disorders, suggesting that callosal defects may predict functional outcome (see examples for autism (Alexander et al, 2007;Hardan et al, 2009;Pryweller et al, 2014;Hahamy et al, 2015), schizophrenia (Innocenti et al, 2003;Whitford et al, 2010;Nakamura et al, 2012), ADHD (Giedd et al, 1994) and dyslexia (Odegard et al, 2009)).…”