Disconnectivity in autistic brain

Abstract

Autism is a life-long neurodevelopmental condition. Autistic individuals have

difficulties in communicative and social ability, and repetitive and stereotypic

behavior. It has proposed that these symptoms are caused by underconnectivity in the

autistic brain. Functional imaging studies have reported functional underconnectivity

in autism. In this thesis, the structural connectivity of the autistic brain was studied.

White matter contains axon fibers, which connect different cortical and subcortical

brain regions. To measure the structural connectivity, Diffusion tensor imaging (DTI)

was applied. Since water diffusion in axons inside the white matter is directional, by

measuring the magnitude and direction of water diffusion in white matter, the

structural integrity of white matter fibers could be estimated.

In this thesis, the background of autism as a genetic, neurological and behavioral

condition is outlined. The methods needed to acquire and analyze DTI data are

illustrated. A meta-analysis on abnormalities found in autistic brain using DTI was

conducted and the most consistently reported regions with DTI differences in autism

compared to typically developing controls are described. The results of the metaanalysis

were localized to white matter tracts likely to be involved, and the possible

associations between anatomy and autistic behavioral features are discussed. Finally,

a DTI tractography study was conducted in a sample but clinically representative

sample of patients with ASD and eighteen major white matter tracts were explored.

Underconnectivity in several tracts was identified. It is hoped that the findings

reported here will enhance our understanding of widespread underconnectivity in

autism.