In one of the largest studies to examine connectivity in the brain, Dr. Ragini Verma and colleagues at the Perelman School of Medicine at the University of Pennsylvania have found major differences in the wiring of men's and women's brains.
Using a relatively new technique called diffusion magnetic resonance imaging (dMRI) on 949 young people, the team was able to track how different regions of their brains wire up with each other, and how large each connection is.
The brain is split into two halves, called hemispheres. Verma’s study found that men have more connections within each hemisphere of the cerebrum, linking the regions for planning and decision-making with the regions for sight and speech.
Women, on the other hand, have more connections between each hemisphere, allowing the two halves of the brain to share information more easily. In the cerebellum, the brain’s physics and motion calculator, the opposite was true—men had more connections between the two hemispheres, and women had more connections within each hemisphere.
The study found minimal gender differences in children under the age of 13, but the differences were much more distinct by age 17. Many brain wiring changes occur during puberty, and men and women seem to develop differently.
Do Brain Differences Mean Differences in Ability?
Verma seems to think these differences are significant. “These maps show us a stark difference in the architecture of the human brain that helps provide a potential neural basis as to why men excel at certain tasks, and women at others,” said Verma in a press release.
According to the study, greater connectivity within hemispheres would make men better at performing single, focused tasks, while women’s connections between hemispheres would make them better at analysis, reasoning, and multitasking.
This notion is supported by a previous study performed on a group of 3500 people ages eight to 21, which included the 949 individuals used for Verma’s study. It found that women performed better at attention, word and facial memory, and social tasks.
Men, on the other hand, performed better at spatial processing and hand-eye coordination tasks. Interestingly, the differences were largest in kids ages 12 to 14, right on the cusp of puberty. By age 21, the differences were smaller.
Gray Matter, White Matter
What other differences are there between the brains of men and women? One is the ratio of gray matter to white matter. Gray matter is found along the surface of the brain's creases and folds, forming the brain’s computing nodes. White matter is found in the interior of the brain, forming the connections between nodes. Verma’s study, using dMRI, tracked the white matter connections.
Another study from some of the same scientists on Verma’s team, led by Dr. Ruben Gur, found that compared with total brain size, women have more gray matter than men, and men have more white matter.
However, a different study, led by Dr. Richard Haier of the University of California, Irvine found that if you compare the brains of men to women, region-by-region, in areas related to IQ, the picture is much more complicated.
Although women had a higher ratio of gray matter to white matter than men, men had 6.5 times as much gray matter in intelligence-related areas, and women had nine times as much white matter.
The differences between men and women were greatest in the frontal lobe, which is responsible for long-term planning, decision-making, and self-control.
A Question of Size
Compared to body size, men's brains are eight to 10 percent larger than those of women. But there are no real differences in IQ between men and women.
Haier thinks the answer is developmental. In order to achieve the same IQ in a smaller space, women’s brains find different wiring solutions for the same tasks that men do.
And none of these differences are enough to explain the massive discrepancy between men and women in STEM (science, technology, engineering, and math) fields. That problem is almost certainly social, not a matter of wiring.