New research released just in time for World Autism Week (28th March to the 3rd of April) shines a light on the rapid growth of the amygdala during the first two years of life in children who go on to develop autism.
The research, published in the American Journal of Psychology, builds on previous studies showing that the amygdala is enlarged in children with autism and examined the precise onset of this enlargement during infancy, how it relates to later diagnostic behaviours, and whether the timing of enlargement in infancy is specific to the amygdala.[1]
Infants who developed autism had normal amygdala volumes at six months but exhibited significantly faster amygdala growth between six and 24 months, such that by 12 months they had significantly larger amygdala volume compared with all other groups.1
The growth rate between six and 12 months was significantly associated with greater social deficits at 24 months when the children were diagnosed with autism.1
Head of the Autism Research Team at Telethon Kids Institute and Director of CliniKids, Professor Andrew Whitehouse, said that this well conducted study provides very interesting insights into the early emergence of autism.
“We have known for some years that behavioural differences are often observed in the first year of life for babies who are later diagnosed with autism,” Professor Whitehouse said.
“The advance of this study is that it links these very behavioural differences to rapid acceleration in brain growth, specifically in the amygdala. The amygdala is a brain structure that is often thought to be associated with the social differences that are characteristic of autism.”
Past neuroimaging studies have shown amygdala enlargement in two to four-year-old children with autism, however, most neuroimaging studies are cross-sectional and conducted after diagnosis, leaving the developmental timing of amygdala enlargement previously unknown.
Many behaviours characteristic of autism are indistinguishable at six months between infants later diagnosed with ASD and those with typical development.
The defining behavioural features of autism emerge over the latter part of the first and second years of life, and generally do not consolidate into the full syndrome, enabling clinical diagnosis, until 24 to 36 months of age.
The increased growth rate of the amygdala between six and 12 months and the gradual onset of brain and behaviour changes in autism suggests an age and disorder-specific pattern of cascading changes in neurological development.1
This includes a possible link between hyper expansion of cortical surface area in the visual cortex and sensorimotor and attention problems in infants who go on to develop autism, raising the possibility that visual attention deficits in early infancy may lead to discrepancies in activity-dependent synaptic pruning.1
“At the present time, the study does not have any clinical implications. But it could represent an important step to further understand how we can support babies and their families even earlier in life,” Professor Whitehouse said.
[1] Shen et al. (2022). Subcortical Brain Development in Autism and Fragile X Syndrome: Evidence for Dynamic, Age- and Disorder-Specific Trajectories in Infancy. The American Journal of Psychiatry. https://doi.org/10.1176/appi.ajp.21090896