From the time you were born until you were about two years old, the outermost layer of your brain – the cortex – rapidly thickened in a frenzy of neuron creation. After all that excitement, that dense hedge of nerve cells was pruned back in a process called “cortical thinning.”
Now, a new study has found some important differences in how this process happens in autistic children, depending on their birth gender.
Previous studies have found variations in the way autistic children’s brains experience cortical thinning, but so far the picture has been blurry and inconsistent. This is partly because historically the female gender has been underrepresented in studies of autism spectrum disorders, and this includes research on cortical development.
“It’s clear that these gender biases are partly due to underdiagnosis of autism in women,” says neuroscientist Christine Wu Nordahl of the University of California at Davis. “But this study suggests that differences in diagnosis are not the whole story – biological differences also exist.”
Although the actual ratio is likely much lower, only one woman is diagnosed with autism for about every four men diagnosed, suggesting that sex can influence the development of the condition.
By including both autistic and non-autistic children in the study, the researchers were able to compare differences in cortical thickness associated with autism within each birth sex group (for example, the difference between autistic women and non-autistic women), as well as compare the results. for the autistic groups only on the basis of birth gender.
The study involved brain scans of 290 autistic children (202 men, 88 women) and 139 non-autistic children (79 men, 60 women) with typical development.
These scans were collected up to four times for each child, aged 2 to 13 years, and provide a detailed view of the child’s cortical development from the age when the cortex is thickest to the age when thinning is most rapid. is. , usually around 14 years old.
At age three, certain areas of the cortex – about 9 percent of the total surface area – were thicker in autistic women than in undiagnosed peers of the same age and gender. In the male group, there were few significant differences in cortical thickness between autistic and non-autistic children at age 3.
At age 11, cortical differences between sexes were much more difficult to recognize. The main differences revealed in the study were only visible as changes in the cortex over time.
Compared to their non-autistic counterparts, female children with autism showed faster cortical thinning in certain areas during childhood, while autistic males generally experienced slower thinning than non-autistic males. These changes were not consistent across the brain: only in certain cortical areas that make up less than 5 percent of the whole, including the networks that plan and control motor tasks, maintain attention and problem solve, and the brain’s “radar” which helps us shift our focus when our circumstances change.
In other regions, such as the limbic network, where behavioral and emotional responses arise, cortical thinning occurred more quickly in autistic men compared to non-autistic men, and less rapidly in autistic women compared to non-autistic women.
There are many reasons why a person’s biology may be related to or reflect the sex he or she has at birth, and this is not necessarily fixed: certain traits may be X or Y chromosome linked, while others are influenced by different hormone levels, or even result from cultural attitudes towards assigned sex and gender that lead to different behaviors and lifestyles.
And while this study found observable differences between the male and female groups, more detailed research will be needed to understand exactly how these differences arise, and what this could mean for transgender, non-binary or intersex people with autism.
That nuance is particularly relevant here, given that gender diverse adults are up to six times more likely to be diagnosed as autistic than cisgender adults (those who identify with their sex and sex assigned at birth).
“We typically think of sex differences as being greater after puberty. However, brain development around ages 2 to 4 is very dynamic, so small changes in the timing of development between the sexes can result in large differences that converge later,” says Psychiatrist researcher Derek Andrews of the University of California Davis.
“It is important to learn more about how sex differences in brain development may interact with the development of autistics and lead to different developmental outcomes in boys and girls.”
This research was published in Molecular psychiatry.