The amygdala, which is enlarged in two-year-old children with autism spectrum disorder (ASD), begins its accelerated growth between 6 and 12 months of age, suggests a study appearing in the American Journal of Psychiatry. The findings indicate that therapies to reduce the symptoms of ASD might have the greatest chance of success if they begin in the first year of life, before the amygdala begins its accelerated growth.
The amygdala, which is involved in processing emotions, such as interpreting facial expression in typically developing children increases substantially in volume from 7.5 to 18.5 years of age. The amygdala in children with autism is initially larger, but does not undergo the age-related increase observed in typically developing children.
The study included 408 infants, 270 of whom with an increased ASD risk from having an older sibling with ASD, 109 typically developing infants, and 29 infants with Fragile X syndrome. The researchers conducted MRI scans of the children at 6, 12 and 24 months of age. They found that the 58 infants who went on to develop ASD had a normal-sized amygdala at 6 months, but an enlarged amygdala at 12 months and 24 months. Moreover, the faster the rate of amygdala overgrowth, the greater the severity of ASD symptoms at 24 months. The infants with Fragile X syndrome had no differences in amygdala growth but enlargement of the caudate, which was linked to increased repetitive behaviours.
The researchers suggested that difficulty in processing sensory information during infancy may stress the amygdala, leading to its overgrowth.
Source: NIH
