Abnormal Growth of Amygdala and its Relation to Autism in Infants

The amygdala is located deep within the brain’s temporal lobe. Shaped like an almond, the amygdala has been found to be enlarged in infants who are later diagnosed with an autism spectrum disorder. The amygdala is actually a collection of nuclei, and though we usually refer to it as one, there are actually two amygdalae in the brain, one in each cerebral hemisphere. Read on to find out more about the abnormal growth of the amygdala and its relation to autism in infants.

The amygdala is an important part of a group of structures in the brain that are collectively known as the limbic system. It is known to play many important roles in emotion, behavior, and memory storage. The amygdala is best known for its role in the processing of fear. It also helps regulate emotions and encode memories, especially when it comes to remembering emotional memories.^{(1, 2, 3)}

Our main understanding of the amygdala and its functions goes back to the 1930s when Heinrich Kluver and Paul Bucy removed the amygdalae of rhesus monkeys and observed the effects on behavior. The researchers observed that the monkeys became more docile and had little sense of fear. Since then, the amygdala has become best known for its role in fear processing in the brain. Today, it is believed that the amygdala sends signals to certain areas of the brain, like the hypothalamus, to trigger the fight or flight response in the body.⁽⁴⁾

Similarly, it is not surprising to learn that the amygdala may also play a role in anxiety. Anxiety is the dread that you feel when thinking or perceiving a potential threat. Several studies have shown that the amygdala is involved in triggering anxiety and that the amygdala may even be overactive in people with anxiety disorders.⁽⁵⁾

Even though the amygdala is most well-known for its role in fear responses, there is now a lot more evidence that shows that there is a lot more contribution of this part of the brain to determining complex behavior. For example, the amygdala is believed to be involved in the formation of positive memories. In fact, studies have shown that any damage to the amygdala can disrupt the ability to form any new positive and negative memories.^{(6, 7, 8)}

New research has revealed that the amygdala might be related to autism. The study showed that the amygdala might grow too fast in infants who develop autism. In fact, it was found that the amygdala was growing too rapidly between 6 to 12 months of age in children who later went on to be diagnosed with autism.

The findings of the study were published in March 2022 in the American Journal of Psychiatry.⁽⁹⁾ The study found that the amygdala grows too fast in babies who were diagnosed with an autism spectrum disorder by the time they turned two years of age. This overgrowth was found to occur between 6 and 12 months of age, much before children are generally diagnosed with autism. The findings of the study suggested therapies for children who were found to be at a high risk of autism judging by the size of the amygdala.

One of the senior authors of the study, Dr. Joseph Piven, who is a professor of Psychiatry and Pediatrics at the University of North Carolina at Chapel Hill, suggested that based on this research, there can be an optimal time to begin interventions and also provide extra support to children who are found to be at the highest risk of developing autism during the first year of life.

Autism spectrum disorder (ASD) is a development disorder that affects thousands of children worldwide, and it affects the way in which a child communicates, interacts socially, behaves, and learns.⁽¹⁰⁾ Though autism can be diagnosed at any age, it is usually known to be a developmental disorder since the symptoms tend to appear most commonly in the first two years of life. Autism is known to be a spectrum disorder because there is a huge variation in the type and severity of symptoms that one may experience.^{(11, 12, 13)}

The research team already knew before starting the study that the amygdala appeared larger in school-aged children who were diagnosed with autism as compared to children who did not have autism. However, what was unknown was precisely when this enlargement of the amygdala began.

In the new study, researchers scanned the brains of over 400 infants, including 270 infants who were known to be at a greater risk of developing autism because they already had an older sibling who had the condition. Out of this, 109 infants had typical development, and there were 29 infants who had Fragile X syndrome, which is a genetic disorder that is known to cause developmental and intellectual disability.^{(14, 15)}

The children all underwent MRI scans at various ages, including six months, 12 months, and at 24 months. By the age of 24 months, it was found that 58 infants or around 21 percent of the children had already been diagnosed with an autism spectrum disorder.

The research team found that at the age of six months, all the children had similar-sized amygdalae. However, by the time the children reached one year of age, the children who went on to later develop autism already had enlarged or overgrown amygdalae as compared to the children who did not develop autism and those with Fragile X syndrome. At the same time, the children who had the fastest rate of amygdala growth experienced the most severe symptoms of autism.

It was found that the faster the amygdala grew in infancy, the more social difficulties the infant showed when they were diagnosed with autism one year later. Based on the results of the study, the researchers hypothesized that early problems with sensory and visual information processing in the infant years might put an added stress on the amygdala, causing it to overgrow.

The amygdala receives signals from the brain’s visual system and other sensory systems in order to perceive and detect potential threats. The study also found that children who were later diagnosed with autism had problems as babies with how they paid attention to visual stimuli or any other type of stimuli. Depending on this, possible interventions in babies who are at a high risk of autism may revolve around focusing on improving visual and other sensory information processing.^{(16, 17)}

At present, early interventions for autism typically begin by the age of two or three years once the child is diagnosed with autism. However, several studies have shown that early interventions in babies who were deemed to be at risk for autism because they already had a sibling who was diagnosed with autism or in babies that showed early symptoms such as visually focusing on certain objects have shown that it can reduce the symptoms of autism by three years of age itself. For example, a small study carried out in 2014 implemented an intervention program in children between the ages of 6 to 15 months. The intervention taught the parents’ new ways of interacting with the babies, including methods to shift the baby’s attention or visual focus away from the object they were fixated on. The study found that this type of intervention therapy reduced the symptoms of autism dramatically by the time the babies reached three years of age.⁽¹⁸⁾

As more research on the amygdala continues, it is hoped that there will be better-informed treatments and management of autism symptoms and more early intervention programs that can help children with autism have a significantly better quality of life.

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• What Happens If Amygdala Is Damaged?