Limbic circuitry in patients with autism spectrum disorders studied with positron emission tomography and magnetic resonance imaging

Objective: Cytoarchitectonic changes in the anterior cingulate cortex, hipp ocampus, subiculum, entorhinal cortex, amygdala, mammillary bodies, and sep tum were reported in a postmortem study of autism. Previously, the authors found smaller cingulate volume and decreased metabolism of the cingulate in seven autistic patients. In this study, they measured the volume and gluco se metabolism of the amygdala, hippocampus, and cingulate gyrus in an expan ded group of 17 patients with autism spectrum disorders (autism [N=10] or A sperger's disorder [N=7]) and 17 age- and sex-matched healthy volunteers. Method: Subjects performed a serial verbal learning test during F-18-deoxyg lucose uptake. The amygdala, hippocampus, and cingulate gyrus were outlined on magnetic resonance imaging scans, volumes of the structures were applie d to matching coregistered positron emission tomography scans, and three-di mensional significance probability mapping was performed. Results: Significant metabolic reductions in both the anterior and posterio r cingulate gyri were visualized in the patients with autism spectrum disor ders. Both Asperger's and autism patients had relative glucose hypometaboli sm in the anterior and posterior cingulate as confirmed by analysis of vari ance; regional differences were also found with three-dimensional significa nce probability mapping. No group differences were found in either the meta bolism or the volume of the amygdala or the hippocampus. However, patients with autism spectrum disorders showed reduced volume of the right anterior cingulate gyrus, specifically in Brodmann's area 24'. Conclusions: Compared with age- and sex-matched healthy volunteers, patient s with autism spectrum disorders showed significantly decreased metabolism in both the anterior and posterior cingulate gyri.