Scientists have noticed that a key brain structure appears to undergo an unusual growth spurt between six and 12 months in babies that go on to develop autism.

Reported in the American Journal of Psychiatry, scientists from the University of North Carolina at Chapel Hill scanned the brains of over 400 kids, including 58 infants with an increased likelihood of developing autism (due to having an older sibling with autism) who were later diagnosed with autism, 212 infants at increased likelihood of autism but who did not develop autism, 109 controls, and 29 infants with “fragile X” syndrome, a genetic condition that causes a range of developmental problems including learning disabilities and cognitive impairment. 

They found that the amygdala underwent an unusual growth spurt in babies between six and 12 months of age that went on to develop autism. This enlargement then continues until the child reaches the age of two, an age where behaviors associated with autism can start to be seen. 

The amygdala is an almond-shaped cluster of cells found buried in the middle of the brain that’s associated with the processing of social behavior, fear, and emotional responses. Researchers have previously known the amygdala is unusually large in children with autism, but this is the first study to highlight how and when that enlargement occurs.

“We also found that the rate of amygdala overgrowth in the first year is linked to the child’s social deficits at age two,” Mark Shen, first study author and Assistant Professor of Psychiatry and Neuroscience at UNC Chapel Hill and faculty of the Carolina Institute for Developmental Disabilities, said in a statement. “The faster the amygdala grew in infancy, the more social difficulties the child showed when diagnosed with autism a year later.”

The question remains: what causes the amygdala to swell and the development of autism? The researchers believe their work can’t answer that yet, but some of their other research may provide some clues. One of their previous studies found that infants who go on to develop autism have problems with visual stimuli in their surroundings. They suspect that early problems with processing visual and sensory information may put strain on the amygdala, forcing it to overgrow.

For the time being, the researchers hope their latest findings might help people reach an autism diagnosis earlier and potentially offer new ways to manage the condition. 

“Our research suggests an optimal time to start interventions and support children who are at highest likelihood of developing autism may be during the first year of life. The focus of a pre-symptomatic intervention might be to improve visual and other sensory processing in babies before social symptoms even appear,” concluded Joseph Piven, senior study author and Professor of Psychiatry and Pediatrics at the University of North Carolina at Chapel Hill.