Evidence for a cerebellar role in reduced exploration and stereotyped behavior in autism

Background: Although limited environmental exploration in autism is an obvious behavioral feature and may be a manifestation of "restricted interests" as described in DSM-IV criteria, there have been no behavioral or neurobiological studies of this important aspect of the disorder. Given consistent reports of cerebellar abnormality in autism, combined with animal research showing a relationship between exploration and the cerebellum, this study aimed to test the possible link between cerebellar abnormality and exploration in autism. Methods: The relationship between visuospatial exploration, stereotyped motor movements, and magnetic resonance imaging measures of the cerebellar vermis, whole brain volume, and frontal lobes in 14 autistic and 14 normal children was investigated. Children were exposed to a large room with several exploration containers and instructed to play. Exploration behavior was videotaped and scored for percentage of time engaged in exploration, number of containers explored, as well as stereotyped movements. Results: Children with autism spent significantly less rime in active exploration and explored fewer containers overall than normal children. Measures of decreased exploration were significantly correlated with the magnitude of cerebellar hypoplasia of vermal lobules VI-VII in the autistic children, but no relationship to vermis size was found with normal control children. Further measures of rates of stereotyped behavior were significantly negatively correlated with area measures of cerebellar vermis lobules VI-VII and positively correlated with frontal lobe volume in the autism sample. Conclusions: Reduced environmental exploration and repetitive behavior may have particularly important developmental consequences for children with autism be cause it may lead them to miss learning opportunities that fall outside their scope of interest. Our findings represent the first documented link between the restricted range of interests and stereotyped behaviors pathognomonic of autism and particular neuroanatomic sires. (C) 2001 Society of Biological Psychiatry.