According To Science:
The brains of men and women aren’t really that different, study finds
In the mid-19th century, researchers claimed they could tell the sex of an individual just by looking at their disembodied brain. But a new study finds that human brains do not fit neatly into “male” and “female” categories. Indeed, all of our brains seem to share a patchwork of forms; some that are more common in males, others that are more common in females, and some that are common to both. The findings could change how scientists study the brain and even how society defines gender.
So in the new study, researchers led by Daphna Joel, a behavioral neuroscientist at Tel Aviv University in Israel, tried to be as comprehensive as possible. Using existing sets of MRI brain images, they measured the volume of gray matter (the dark, knobby tissue that contains the core of nerve cells) and white matter (the bundles of nerve fibers that transmit signals around the nervous system) in the brains of more than 1400 individuals. They also studied data from diffusion tensor imaging, which shows how tracts of white matter extend throughout the brain, connecting different regions.
The team found a few structural differences between men and women. The left hippocampus, for example, an area of the brain associated with memory, was usually larger in men than in women.
To accommodate this overlap, the researchers created a continuum of “femaleness” to “maleness,” for the entire brain. The male end zone contained features more typical of males, and the female end zone contained the version of the same structures more often seen in females. Then, the team scored every individual region-by-region to find out where they fell on that male-to-female continuum.
The majority of the brains were a mosaic of male and female structures, the team reports online today in the Proceedings of the National Academy of Sciences. Depending on whether the researchers looked at gray matter, white matter, or the diffusion tensor imaging data, between 23% and 53% of brains contained a mix of regions that fell on the male-end and female-end of the spectrum. Very few of the brains—between 0% and 8%—contained all male or all female structures. “There is no one type of male brain or female brain,” Joel says.