The amygdala is enlarged in children but not adolescents with autism; the hippocampus is enlarged at all ages Schumann CM, Hamstra J, Goodlin-Jones BL, Lotspeich LJ, Kwon H, Buonocore MH, Lammers CR, Reiss AL, Amaral DG.
Abstract: J Neurosci. 2004 Jul 14;24(28):6392-401 Findings Autism is a lifelong disorder that disrupts the child’s developing nervous system (neurodevelopmental disorder) that includes impairments in social interactions, stereotypical behaviors, and disordered verbal and nonverbal communication. The structural changes to the autistic child’s brain and nervous system are not understood well. Researchers do know that the cerebellum, amygdala, and hippocampus are affected, but there have been no clear results showing how. The cerebellum is the lower back part of the brain responsible for functions such as maintaining balance, and coordinating and controlling voluntary muscle movement. The amygdala is an almond-shaped part the brain structure involved in regulating emotion, and it may also play a role in the association of memories. Finally, the hippocampus is involved in spatial orientation and plays an important role in establishing memories. Dr. Schumann and her colleagues used magnetic resonance imaging (MRI) to measure the size of these structures in children with autism compared with controls. Their two objectives were: (1) to compare volume measurements of the amygdala and hippocampus in children across the autistic spectrum, and (2) to understand contradictory results in previously published MRI studies on the autistic amygdala and hippocampus. Volume of the amygdala, hippocampus, and cerebrum were measured in male children (7.5–18.5 years of age) in four groups: autism with mental retardation, autism without mental retardation, Asperger syndrome, and age-matched typically developing controls. There were no differences between groups in total cerebral volume, but children with autism (7.5-12.5 years of age) had larger right and left amygdala volumes than control children. There were no differences in amygdala volume between the adolescent groups (12.8-18.5 years of age). The amygdala in typically developing children increases substantially in volume from 7.5 to 18.5 years of age. Thus, the amygdala in children with autism is initially larger, but does not undergo the age-related increase that is seen in typically developing children. Children with autism—with and without mental retardation—also had a larger right hippocampal volume than typically developing controls, even when taking into account the total cerebral volume. Children with autism without mental retardation also had a larger left hippocampal volume compared with controls.
Conclusions The findings of this cross-sectional study indicate an abnormal program of early amygdala development in autism and a divergent pattern of hippocampal development that persists through adolescence. The, lack of the age related increase in size of the amygdala in autistic children may reflect the abnormal developmentin social behavior, memory and emotion, and other cognitive processes such as recognition of faces. The enlarged hippocampus may be more related to memory function —some evidence suggests that autistic children may have enhanced memory, a function of the hippocampus. The cause of amygdala and hippocampal abnormalities in autism seen in this study is not known.
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