Scientists have wondered whether boys and girls think differently because their brains are different. A recent paper presents evidence that, indeed, girls do show meaningful differences in their brain circuits that could explain why their cognitive functions differ from those of boys.
Introduction
Men have larger brains than women, on average, but this does not translate into superior intelligence for either sex. In general, women have better verbal skills and perceive things faster, but men have better abilities to visualize and locate things in a spatial sense.
However, girls are also more likely to be diagnosed with various mental health disorders like depression and anxiety, while boys are more likely than girls to suffer attention deficit-hyperactivity disorder (ADHD) or autism spectrum disorder (ASD).
Little is known about why girls show increased cognitive performance as they approach adolescence compared to boys. Traditionally, it has been recognized that physically, intellectually, and emotionally, girls mature ahead of boys at the same age. In the developing brain, white matter builds up over time, faster in girls.
Simultaneously, gray matter is selectively pruned faster in boys during this time. Gray matter density builds up over time in girls, so that a global increase in density is seen by the age of eight years in girls compared to boys. These structural changes are probably linked to functional changes between the sexes.
The current study, published in JAMA Network Open Pediatrics, examined nearly 9000 children between nine and eleven years of age, using neuroimaging tools. The data also included behavioral assessments. All information came from the Adolescent Brain Cognitive Development (ABCD) study carried out between August 2017 and November 2018.
Functional magnetic resonance imaging (fMRI) was carried out in all children whose data was used for the current study. The aim was to assess global functional connectivity density (gFCD) at rest and mean water diffusivity (MD), as well as examining their association with overall cognitive performance.
The gFCD is a data-based method of quantitating the number of neural functional connections per brain voxel. In other words, it helps understand how well brain regions interact.
What did the study show?
Total brain volume was larger in boys, who also had a higher proportion of white matter containing the axons from neurons. Conversely, girls had larger proportions of gray matter, containing the neurons themselves.
The results showed that in girls, distinctively, there was higher global functional connectivity density in multiple regions. It was most obvious in the cortical region of the posterior cingulate gyrus of the brain. This part of the brain is one hub where default mode networks (DMN) meet.
The greater the density in such hub regions, the better was the cognitive performance of the child, other examples being the prefrontal, occipital and parietal cortical regions or the middle temporal gyrus. On the other hand, a lower gFCD in other specific areas associated with better cognition, such as the somatomotor cortex, or the superior temporal gyrus.
These findings agree with earlier research showing higher functional connectivity within DMN hubs for girls and adult women, compared to men or boys. The posterior cingulate cortex is extremely active in metabolic pathways. It is connected to other DMN hubs, while being the site of the greatest differences in functional connectivity between the sexes. In contrast, ASD and ADHD are both common in boys compared to girls by a factor of two- to four-fold, and reduced DMN connectivity has been lined to such disorders.
At the same time, the superior corticostriatal white matter tracts showed lower mean diffusivity in inverse proportion to higher cognitive performance in girls relative to boys. These findings were found to fully explain the difference in cognitive performance between the sexes at this age. Yet they explain that poor childhood brain connectivity is not necessarily linked to better cognitive performance, as earlier researchers have reported to be true of children and male adolescents.
What are the implications?
The scientists suggest that the observed differences between the cognitive performance and the connectivity patterns in a specific brain region between boys and girls, are due to a faster rate of brain maturation in the latter.
Notwithstanding the robustness of the sex differences in brain connectivity and their association with cognition, together they explain a relatively small amount of the overall variance in brain connectivity.” The rest may be partly mediated via different hormones acting on the brain, environmental and sociocultural factors.
The observed patterns could be useful in helping to establish the trajectories of brain development required to identify cognitive or behavioral aberrations, either psychiatric or neurological in origin. Moreover, they could provide a foundation for exploring the origin of differences in the way girls and boys develop, including their biology, as well as the sociocultural factors impacting their lives.