The amygdala is a tiny region located deep within the brain that plays a vital role in understanding the social and emotional meaning of sensory input, from identifying emotion in faces to processing images that make us feel threatened in our environment. Historically, it has been believed that the amygdala is mostly responsible for the social behavior issues at the heart of autism.
The amygdala in school-age autistic children is abnormally large, but when this expansion takes place has long been a mystery to researchers. Now, for the first time, researchers from the Infant Brain Imaging Study (IBIS) Network, used magnetic resonance imaging (MRI) to demonstrate that the amygdala grows too rapidly in infancy.
The earliest identification of this disorder is made possible by the onset of overgrowth between the ages of six and twelve months, which occurs before the age at which the hallmark symptoms of autism fully manifest. The amygdala grew more rapidly in newborns later identified as having autism compared to brain-growth patterns in infants with fragile X syndrome, another neurodevelopmental condition, where no abnormalities in amygdala growth were seen.
Published in the American Journal of Psychiatry, the official journal of the American Psychiatric Association, this research demonstrated that infants with fragile X syndrome already exhibit cognitive delays at six months of age, whereas infants who will later be diagnosed with autism do not show any deficits in cognitive ability at six months of age, but have a gradual decline in cognitive ability between six and 24 months of age, the age when they were diagnosed with Autism Spectrum Disorder in this study.
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.Professor Joseph Piven
At six months, the amygdala of infants who go on to have autism is the same size in all of them. However, between the ages of six and twelve months, their amygdala starts to grow more quickly than that of other infants (including those with fragile X syndrome and those who do not go on to have autism), and by the age of twelve months, it has greatly grown. This amygdala enlargement continues through 24 months, an age when behaviors are often sufficiently evident to warrant a diagnosis of autism.
“We also found that the rate of amygdala overgrowth in the first year is linked to the child’s social deficits at age two,” said first author Mark Shen, PhD, Assistant Professor of Psychiatry and Neuroscience at UNC Chapel Hill and faculty of the Carolina Institute for Developmental Disabilities (CIDD). “The faster the amygdala grew in infancy, the more social difficulties the child showed when diagnosed with autism a year later.”
This research the first to document amygdala overgrowth before symptoms of autism appear was conducted through The Infant Brain Imaging Study (IBIS) Network, a consortium of 10 universities in the United States and Canada funded through a National
Institutes of Health Autism Center of Excellence Network grant.
The researchers enrolled a total of 408 infants, including 58 infants at 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 typically developing controls, and 29 infants with fragile X syndrome. More than 1,000 MRI scans were obtained during natural sleep at six, 12, and 24 months of age.
So, what might be happening in the brains of these children to trigger this overgrowth and then the later development of autism? Scientists are starting to fit the pieces of that puzzle together.
While the social abnormalities that are a hallmark of autism are not present at six months of age, earlier research by the IBIS team and others has shown that children who go on to acquire autism have issues as babies with how they attend to visual stimuli in their surroundings. The amygdala may get overgrown as a result of these early difficulties processing visual and sensory information, according to the scientists’ theory.
Amygdala overgrowth has been linked to chronic stress in studies of other psychiatric conditions (e.g., depression and anxiety) and may provide a clue to understanding this observation in infants who later develop autism.
Senior author Joseph Piven, MD, Professor of Psychiatry and Pediatrics at the University of North Carolina at Chapel Hill added, “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.”
Without the families and kids who took part in the IBIS project, this research would not be possible. Research sites included UNC-Chapel Hill, Washington University in St. Louis, Children’s Hospital of Philadelphia, McGill University, and University of Washington.
This research was supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institute of Environmental Health Sciences, and National Institute of Mental Health (R01-HD055741, R01-HD059854, R01-MH118362-01, R01-MH118362-02S1, T32-HD040127, U54-HD079124, K12-HD001441, R01-EB021391, U54-HD086984; NIH P50 HD103573), along with Autism Speaks and the Simons Foundation.