Brain development disturbed in autism.

Two inner-brain structures show signs of unusual development in autistic children and teenagers, according to a new brain-scan investigation.

The imagery reveals that boys between ages 7 and 12 diagnosed with autism have larger amygdalas than neurologically healthy boys do, say David G. Amaral of the University of California, Davis and his coworkers. The amygdala is associated with emotional responses to social situations.

This finding held regardless of whether autism was accompanied by mental retardation, as often occurs. However, amygdala volume expanded markedly by age 18 in the healthy youths while remaining the same in those with autism. As a result, amygdala size ultimately wound up about equal for both groups, Amaral's team reports in the July 14 Journal of Neuro-science.

All boys with autism also displayed a larger right hippocampus than healthy boys did. Only boys whose autism was accompanied by good intellectual functioning possessed a larger left hippocampus as well. These neural differences remained during adolescence.

An enlarged hippocampus in autism may aid memory for spatial and factual information, the scientists suggest.

They used magnetic resonance imaging to study the brains of 98 participants, ages 7 to 18, who met criteria for autism with retardation, autism without retardation, Asperger syndrome (a mild form of autism), or typical development. For boys with Asperger syndrome, amygdala and hippocampus development was disturbed to a lesser extent than it was in boys with autism.--B.B.