Although male and female brains tend to be different, no single structural feature clearly distinguishes them, scientists have concluded in a new study.





The way it seems to work, they say, is like this: “most brains are comprised of unique ‘mosaics’ of features, some more common in females compared with males, some more common in males compared with females, and some common in both females and males.”





The statement come from a paper published in this week’s edition of the journal Proceedings of the National Academy of Sciences.





To reach the findings, researchers studied more than 1,400 brain scans captured using Magnetic Resonance Imaging, or MRI. The technology uses magnetic fields and radio waves to create detailed images of the organs and tissues. The brain scans fell into four subgroups or “data sets” depending on the precise MRI methodology used.





For each data set, the authors identified brain regions that differed the most between the sexes. For each brain, then, they checked whether the shape of each region was on the end of the distribution where females were more prevalent (“female-end”) or at the end where males were more prevalent (“male-end”).





Depending on the set of MRI data examined, between 23 percent and 53 percent of brains had at least one region with a “male-end” score and one region with a “female-end” score, the investigators said. In contrast, the percentage of brains with all “male-end” or all “female-end” scores was 8 percent or less.





“Our study demonstrates that, although there are sex/gender differences in the brain, human brains do not belong to one of two distinct categories: male brain/female brain,” wrote the researchers, with Tel Aviv University in Israel, the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany and the University of Zurich in Switzerland.



