Diffusion tensor imaging in autism and Asperger Syndrome: evidence for impairment of long range white matter integrity

Background: Recently, many studies concerning neural connectivity in autism have been published, leading to hypotheses that entail impaired neural information integration and long distance disconnection. However, little is known about the structural integrity of the white matter tracts that are involved in neural connectivity.

Objectives: To investigate the structural integrity of white matter tracts in autism and Asperger Syndrome. Methods: Diffusion tensor imaging was performed on 12-18-year old participants with high functioning autism, Asperger Syndrome and typically developing children matched for age, IQ, handedness, head circumference, and gender. Scans included the cerebrum and cerebellum and fractional anisotropy and mean diffusivity measures were analyzed in a voxel based morphology manner. 

Results: Participants with autism had lower fractional anisotropy in long distance white matter tracts including inferior and superior fronto-occipitial fasciculus and the inferior and superior longitudinal fasciculus bilaterally as well as the cerebello-pontine tract bilaterally. Fractional anisotropy in Asperger Syndrome was intermediate between that of participants with autism and controls, but non-significant.

Conclusions: The findings suggest that there is a generalized reduction of structural integrity of long distance white matter tracts in autism that connect the frontal cortex to other systems. The reductions may contribute to the behavioral pattern observed in autism. The preliminary fractional anisotropy results in the Asperger group suggest that although the same neurobiological causes may underlie autism and Asperger syndrome, the severity and distribution of affected cortical areas differ.