Autism is a behaviorally defined disorder with increasing prevalence rates globally. The disorder is characterized by deficits in several domains including social behaviors, restricted and repetitive behaviors, and deficits in communication. Two regions thought to contribute to deficits in social behavior are the posterior cingulate cortex (PCC) and fusiform gyrus (FFG). The PCC is involved in processing emotionally salient stimuli, and also has a role in processing faces. The FFG is the area responsible for object and face recognition. A potential imbalance between excitatory and inhibitory processing in the brain may contribute to some of the abnormal social behaviors observed in autism. This is supported by previous work suggesting reduced GABA receptors in the autistic brain. The present study used thionin stained section to qualitatively assess cortical patterning and quantitatively assess the density of neurons. Furthermore, immunohistochemistry was used to determine the density of a subset of GABAergic interneurons. In the autistic brain, the PCC displayed several abnormal cortical patterns including irregularly distributed neurons in specific cortical layers, and the presence of increased white matter neurons. In marked contrast, the FFG appeared normal and there were no significant differences in the density of neurons or interneurons in either region. The present study highlights the presence of abnormal findings in the PCC, which appear to have developmental origins and could affect local processing of social-emotional behaviors as well as the function of interrelated cortical areas.
Autism is a developmental disorder with prenatal origins, currently estimated to affect 1 in 91 children in the United States. Social-emotional deficits are a hallmark of autism and early neuropathology studies have indicated involvement of the limbic system. Imaging studies demonstrate abnormal activation of the posterior cingulate cortex (PCC), a component of the limbic system. Abnormal activation has also been noted in the fusiform gyrus (FFG), a region important for facial recognition and a key element in social interaction. A potential imbalance between excitatory and inhibitory interneurons in the cortex may contribute to altered information processing in autism. Furthermore, reduced numbers of GABA receptors have previously been reported in the autistic brain. Thionin stained sections were used to qualitatively assess cytoarchitectonic patterning and quantitatively determine the density of neurons and immunohistochemistry was used to determine the densities of a subset of GABAergic interneurons utilizing parvalbumin- and calbindin- immunoreactivity. In autism, the PCC displayed altered cytoarchitecture with irregularly distributed neurons, poorly demarcated layers IV and V, and increased presence of white matter neurons. In contrast, no neuropathology was observed in the FFG. There was no significant difference in the density of thionin, parvalbumin, or calbindin interneurons in either region and there was a trend towards a reduced density of calbindin neurons in the PCC. This study highlights the presence of abnormal findings in the PCC, which appear to be developmental in nature and could affect the local processing of social-emotional behaviors as well as functioning of interrelated areas.