A quarterly publication of the Autism Research Institute

The Autism Research Review International is quarterly publication of the Autism Research Institute

Spring, 2018 | Number 2, Volume 32

Marked differences in the developmental trajectory of the amygdala seen in ASD

A new study indicates that the developmental trajectory of the amygdala, a brain region that plays key roles in anxiety and social interactions, is altered in individuals with autism spectrum disorders (ASD). 

Thomas Avino and colleagues studied postmortem brain tissue samples from 52 individuals—24 neurotypical individuals and 28 individuals with ASD—between 2 and 48 years of age. They found that children with ASD had significantly more neurons in the amygdala than neurotypical controls. However, while the number of neurons in the amygdala increased markedly in neurotypical individuals as they aged into adulthood, it decreased in individuals with ASD. Very young children with ASD had approximately 11% more neurons in the amygdala than controls, while adults with ASD had approximately 20% fewer neurons. 

Senior study author Cynthia Schumann says, “We don’t know if having too many amygdala neurons early in development in ASD is related to the apparent loss later on. It’s possible that having too many neurons early on could contribute to anxiety and challenges with social interactions. However, with time, that constant activity could wear on the system and lead to neuron loss.” 

She notes, “The amygdala is a unique brain structure in that it grows dramatically during adolescence, longer than other brain regions, as we become more socially and emotionally mature. Any deviation from this normal path of development can profoundly influence human behavior.”


“Neuron numbers increase in the human amygdala from birth to adulthood, but not in autism,” Thomas A. Avino, Nicole Barger, Martha V. Vargas, Erin L. Carlson, David G. Amaral, Melissa D. Bauman, and Cynthia M. Schumann,  Proceedings of the National Academy of Sciences, March 20, 2018 (open access). Address: Cynthia Schumann, Department of Psychiatry and Behavioral Sciences, UC Davis MIND Institute, School of Medicine, University of California, Davis, Sacramento, CA 95817, [email protected]


 “Amygdala neurons increase as children become adults—except in autism,” news release, UC Davis MIND Institute, March 20, 2018.