Instead, children with autism spectrum disorder (ASD) have too many neurons in this part of the brain -- the amygdala -- and lose neurons as they mature, according to researchers at the MIND Institute at the University of California, Davis.
"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," study senior author Cynthia Schumann said in a university news release.
"Any deviation from this normal path of development can profoundly influence human behavior," she said. Schumann is an associate professor of psychiatry and behavioral sciences.
For the study, Schumann's team examined the brains of 52 people who had died, including some with autism. They ranged in age from 2 to 48.
"We don't know if having too many amygdala neurons early in development in ASD is related to the apparent loss later on," Schumann said.
"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 said.