Histological and magnetic resonance imaging assessment of cortical layering and thickness in autism spectrum disorders.

Background: Qualitative reports of the cerebral cortex in a small number of autism spectrum disorder (ASD) cases have suggested an increase in thickness and disruptions in migration and lamination patterns.

Methods: We examined postmortem ASD individuals and age-matched controls using magnetic resonance imaging (MRI) to evaluate total cortical thickness, and histological samples to evaluate the pattern of cortical layering.

Results: Overall, thickness measures from ASD subjects were equivalent to control cases. Individual regions showed marginal but nonsignificant thickness differences in the temporal lobes. Cortical thickness values in ASD subjects decreased significantly with age. Quantitative examination of proportional layer thickness in histological sections indicated that the pattern of cortical layering was largely undisturbed, while qualitative examination of these same samples revealed evidence of cell clustering and supernumerary cells in layer I and the subplate. These features were not severe and were never found in a majority of cases.

Conclusions: These findings support limited disturbances in cortical cell patterning, but do not indicate a major deficit in the orderly migration of cortical neuroblasts during development, or their subsequent aggregation into the laminar pattern found in typically developing individuals.