The debate over whether or not men and women have distinctly different brains still rages, regularly making headlines; some claim that differences can be seen, whereas others disagree. Studies have wavered back and forth over the concept, but new research has fallen strongly on one side of the fence: there is essentially no difference, according to the research published in the journal NeuroImage – at least in one section of the brain, the hippocampus.
When a physical aspect of the two sexes of a species physically differ in some way or another, it is known as sexual dimorphism. The obvious example would be the reproductive organs, but there are many variations on the theme: the male species of many animals are far more colorful and flamboyant than their female counterparts – after all, the males tend to be the ones to woo the female.
There are more subtle variations of sexual dimorphism though, and the human brain is often thought to be no exception to this. Adult male brains are somewhat 14 percent more voluminous than female brains, and contain a higher ratio of white-to-gray matter. This also applies to specific structures of the brain, backed up by a wide range of evidence across multiple studies.
The hippocampus is associated with the consolidation of memories from the short-term into the long-term, the regulation of stress, and spatial navigation; it has been previously shown to differ between the sexes, in terms of its anatomy and its ability to persistently strengthen the structural connections (synapses) between nerve cells (neurons). Although the debate over the male/female brain concept has been essentially unsettled for many decades now, this new study, which focuses on the size of the hippocampus, appears to deal a heavy blow to this widely-held theory.
This research, led by the Rosalind Franklin University of Medicine and Science, is a form of meta-study, an investigative technique that analyzes a large number of papers on a particular subject. The team were looking at the strength of the evidence given by 76 independently researched peer-reviewed papers, whilst assessing how well the results did or did not collaborate. These individual studies all used magnetic resonance imaging (MRI) scan data, a non-invasive method of probing the three-dimensional structures of our body, including the complexities of the hippocampus.
The hippocampus has been thought to be disproportionately large in the brains of females, implying that women’s tendency to express themselves more outwardly emotionally than men has a neurological explanation. This new meta-study evaluated the methods and conclusions of the 76 MRI studies looking at the hippocampal volume (HCV) in over 6,000 males and females. No difference was found, after correcting for the overall brain volumes. Not only that, but even when age was taken into account, the HCV volumes did not show any differences between the brains of different sexes.
“Sex differences in the brain are irresistible to those looking to explain stereotypic differences between men and women,” said lead author Lise Eliot, an associate professor of neuroscience at the university’s medical school, in a statement. “They often make a big splash, in spite of being based on small samples. But as we explore multiple datasets and are able to coalesce very large samples of males and females, we find these differences often disappear or are trivial.”