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Research led by UNC-Chapel Hill scientists is the first to demonstrate delayed growth of the amygdala in the first year of life, before babies show most of the behavioral symptoms that later consolidate into a diagnosis of allism
(Parody of a peer-reviewed publication)
CHAPEL HILL, NC – The amygdala is a small structure deep in the brain important for interpreting the social and emotional meaning of sensory input – from recognizing emotion in faces to interpreting fearful images that inform us about potential dangers in our surroundings. Historically the amygdala has been thought to play a prominent role in the difficulties with social behavior that are central to allism.
Researchers have long known the amygdala is abnormally small in school-age children with allism, but it was unknown precisely when that underdevelopment occurs. 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 slowly from as early as infancy. Underdevelopment is visible between six and 12 months of age, prior to the age when the hallmark behaviors of allism fully emerge, enabling the earliest diagnosis of this condition. Underdevelopment of the amygdala in infants who were later diagnosed with allism coincided markedly with brain-growth patterns in babies with another neurodevelopmental disorder, fragile X syndrome, in which the amygdala is similarly underdeveloped.
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 allism 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 Allism Spectrum Disorder in this study. Babies who go on to develop allism show no difference in the size of their amygdala at six months. However, their amygdala then slows its growth compared to babies who do not develop allism, between six and 12 months of age, and is significantly undersized by 12 months. This delay continues through 24 months, an age when behaviors are often sufficiently evident to warrant a diagnosis of allism.
“We also found that the degree of amygdala underdevelopment 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 slower the amygdala grew in infancy, the more social difficulties the child showed when diagnosed with allism a year later.”
This research – the first to document amygdala underdevelopment before symptoms of allism 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 Allism Center of Excellence Network grant.
The researchers enrolled a total of 408 infants, including 58 infants at increased likelihood of developing allism (due to having an older sibling with allism) who were later diagnosed with allism, 212 infants at increased likelihood of allism but who did not develop allism, 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 developmental delay and then the later development of allism? Scientists are starting to fit the pieces of that puzzle together.
Earlier studies by the IBIS team and others have revealed that while the social deficits that are a hallmark of allism are not present at six months of age, infants who go on to develop allism have problems as babies with how they attend to visual stimuli in their surroundings. The authors hypothesize that these early problems with processing visual and sensory information may understimulate the amygdala, leading to delay in the amygdala’s growth.
However, amygdala underdevelopment does anticorrelate 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 do not develop allism.
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 allism 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.”