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Research Team Finds No Biological Sex Differences in the Human Amygdala

Joanna Lawrence
18th January, 2017

A team of researchers analyzed data from a number of studies to determine if the male human amygdala is naturally larger, as sometimes theorized in the past. The team’s meta-analysis revealed no differences between the sexes, adding to evidence that there are few biological differences between male and female brains. The findings were just published in the journal NeuroImage. Past books and articles have often referred to differences between the “male brain” and “female brain.” The theory is that there are several biological differences that partially account for behavioral and psychological differences between the sexes. One such theory is that the human amygdala is larger in males. The amygdala is a part of the brain that helps control emotional reactions and decision-making. Every human brain has two of these nuclei groups (the plural form is amygdalae) and they are also responsible for memory formation and processing. If male humans have larger amygdalae, as the theory goes, they may have differences in emotional responses and memory processes. There hasn’t been much research to support this notion, however. In fact, there had been no hard evidence of sexual dimorphism (differences between males and females) in the human brain. Scientists from the Rosalind Franklin University of Medicine and Science pored over the existing literature on the human amygdala to test the sexual dimorphism theory. The team found a total of 46 studies that met their inclusion requirements and the team analyzed the datasets. The researchers used a statistical technique called meta-regression to control for factors such as size differences between the sexes, sampling methods, and age. After analyzing all of the data, the team found no statistically significant sex differences in human amygdala volume. This is in sharp contrast to texts that claimed the amygdala was larger and “enhanced” in males. The authors acknowledge that there could be more subtle sex differences but that male and female amygdalae appeared the same in all recent MRI studies. The team’s findings provide more evidence that there are few sex differences in human brains. Biologically, male and female brains appear roughly the same in MRI scans and there is no difference between amygdala sizes, as previous literature had incorrectly reported. REFERENCE Marwha et al. Meta-analysis reveals a lack of sexual dimorphism in human amygdala volume. NeuroImage (2017).