There's no such thing as a "male brain" and a "female brain," and the only discernible difference between the two is that male brains, on average, are 11% larger than female brains. This doesn't mean men are smarter, however.
A massive mega-synthesis, or a study of studies conducted by neuroscientists at Rosalind Franklin University of Medicine and Science in Chicago, Illinois, found brain size is the only clear-cut difference between male and female brains and reveals few male-female differences beyond size.
Although women's brains are some 11% smaller than men's in proportion to their body size, women's brains have a slightly higher ratio of gray matter to white matter and a higher ratio of connections between both cerebral hemispheres.
"Men and women's brains do differ slightly, but the key finding is that these distinctions are due to brain size, not sex or gender," said Dr. Elise Eliot, the study author whose books include "Pink Brain, Blue Brain: How Small Differences Grow Into Troublesome Gaps."
"Sex differences in the brain are tiny and inconsistent, once individuals' head size is accounted for This means that the brain differences between large- and small-headed men are as great as the brain differences between the average man and woman," said Eliot.
"And importantly, none of these size-related differences can account for familiar behavioral differences between men and women, such as empathy or spatial skills."
She said men's and women's brains do differ slightly, but the key finding is these distinctions are due to brain size, not sex or gender
The study also rebuts a stubborn belief men's brains are more lateralized. This means each hemisphere acts independently in contrast to women whose hemispheres are said to be better connected and operate more in sync with each other.
It's been surmised this difference might make males more vulnerable to disabilities following a brain injury such as stroke. In this regard, the new study supports the consensus of many other studies showing the difference is extremely small, accounting for less than 1% of the range of left-right connectivity across the population.
The unusually huge mega-synthesis, "Dump the 'dimorphism': Comprehensive synthesis of human brain studies reveals few male-female differences beyond size," was published in Neuroscience and Biobehavioral Reviews. Its authors are Dr. Eliot and collaborators Adnan Ahmed, Hiba Khan, and Julie Patel (all fourth-year) Chicago Medical School students.
The mega-synthesis included three decades of research, assimilating hundreds of the largest and most highly-cited brain imaging studies addressing 13 distinct measures of alleged sex difference.
The new study is in line with others dismissing the concept of a male brain and a female brain. Northwestern Medicine, a healthcare organization also based in Illinois, also found that while the male brain is larger than the female brain, this size difference does not impact intelligence. Northwestern Medicine also said men's and women's brains are more alike than they are different.
It also agrees with the finding women have more grey matter in their brains. Grey matter contains cell bodies that help us process information in the brain and is located in brain regions involved with muscle control and sensory perception.
Women also use more white matter that connects processing centers. On the other hand, men use more grey matter. This might explain why men tend to excel at task-focused projects. It might also explain why women are more likely to excel at language and multitasking.
