From similar sets of neuroimaging data, researchers are reaching different conclusions about whether brain wiring differs between men and women.

In a brain-imaging study published in PNAS in December 2013, scientists reported significant differences in brain connectivity patterns between men and women. If confirmed, their finding would overturn the widespread assumption among neuroscientists that sex doesn’t matter when it comes to brain anatomy and function. What’s more, the authors—a group co-led by Ruben Gur at the University of Pennsylvania—suggested that such wiring differences could give rise to behavioral differences between the sexes.

“Detailed connectome maps of the brain will not only help us understand the differences between how men and women think, but it will also give us more insight into the roots of neurological disorders, which are often sex-related,” Gur said in a statement.

But it wasn’t long before the results were called into question. Several researchers pointed out that the authors failed to include data on effect size, making it difficult to verify claims about “fundamental” differences in brain wiring between the sexes. Some critics also argued that Gur and colleagues had ignored other factors that could have accounted for the results—gendered experiences like hobbies or study subjects, say, or brain size. Still others accused the authors of having served up untested stereotype-based speculation on how such wiring differences could affect behavior.

Then, in November 2014, Jürgen Hänggi at the University of Zurich and his colleagues published a study in Frontiers of Human Neuroscience demonstrating that the wiring differences observed by Gur’s team were driven by differences in brain size rather than sex.

To further muddy the waters, researchers who were not involved in either study offer conflicting views on the links among sex, brain size, and the human connectome.

To neurobiologist Larry Cahill’s mind, sex is the biggest factor driving brain size, so even if connectivity differs according to brain size, there is still a strong sex influence, on average, on connectivity patterns. “While we can and should debate what these findings mean,” said Cahill, a professor at the University of California, Irvine, “the findings leave little doubt that there exist striking differences in the ways in which the brains of women, on average, and men, on average, are wired.”…Read more
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