Objectives: We sought to determine if such atypicality is present in the superior temporal gyrus and temporal stem in autism and to quantify its effects on language functioning, if any.
Methods: Thirty high-functioning males with idiopathic autism aged 8-26 years and 30 matched controls participated in a case-control diffusion tensor magnetic resonance imaging study. All autism subjects met full criteria for autism. Convention tensor measures were recorded. A novel tensor asymmetry index, language functioning and psychotropic medication usage were also measured. We also studied an independent replication sample of 12 males with idiopathic autism and 7 matched controls.
Results: In our sample, we observed atypical losses and reversal of leftward asymmetry, atypical reductions in spatial organization and atypical age-related decreases of white matter microstructure in the superior temporal gyrus and temporal stem. Six of these measurements, including the novel tensor asymmetry index, discriminated between control and autism subjects with 91.6% accuracy, 93.6% sensitivity and 89.6% specificity. The classification ability of our method remained equally high with our second sample. Without the novel tensor asymmetry index, results dropped to unacceptably low levels between 66.7 and 71.4%.
Conclusions: Our results suggest that the hemispheric asymmetry, fiber organization and age-related changes in white matter microstructure in the superior temporal gyrus and temporal stem are atypical in autism. These brain circuitry abnormalities could be due to genetic and/or epigenetic dysregulation in brain development and are consistent with a hypothesis of increased proximal connectivity and underdeveloped distal connectivity in the disorder. We also find that six of these atypicalities, including our novel tensor asymmetry index, could serve as useful biological indicators of autism in populations of individuals similar to our own.
Acknowledgements and Disclaimer. The project described was supported in part by grants MH080826 and MH084795 from the National Institute Of Mental Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute Of Mental Health or the National Institutes of Health.