MedicalResearch.com Interview with:
Lise Eliot PhD
Associate Professor of Neuroscience
Chicago Medical School
Rosalind Franklin University
North Chicago, IL 60064
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Studies in rats indicate that the amygdala, which is important for many social behaviors including aggression and rough-and-tumble play, is larger in male animals. Early MRI studies also reported that the human amygdala is larger in men, even after correcting for males’ larger overall brain size. Because so many MRI studies are now imaging amygdala volume in matched groups of healthy males and females, we realized that there is a lot of published data that could settle whether the human amygdala is indeed proportionally larger in men. Another rationale for the study is that many psychiatric disorders that involve the amygdala (e.g., depression, anxiety, substance abuse) differ in prevalence between men and women.
MedicalResearch.com: What should readers take away from your report?
Response: Readers can take away that there is far more overlap than difference in amygdala volume between men and women. Based on data collected from nearly 7000 healthy humans, amygdala volume is not specifically enhanced in males. The amygdala is about 10% larger in men than women, in proportion to men’s overall 10-12% larger total brain volume. But in studies that corrected for individuals’ overall brain size, there was no significant difference in amygdala volume between women and men. Thus, the early studies reporting sex difference in the human amygdala appear to be outliers compared to more recent studies and the larger collection of data we meta-analyzed.
Another takeaway is that the term “sexually dimorphic” (literally, “two forms”) does not apply to the human amygdala. Human brains are less sexually-dimorphic than rat brains.
The amygdala is a key structure in our brains’ response to stress. Our finding supports other work that suggests men and women are equally vulnerable to stress-related disorders, but manifest them somewhat differently, with women more vulnerable to anxiety and depression and men more vulnerable to substance abuse and conduct disorders.
The lack of substantial difference between men and women’s brains also impacts efforts to understand the role of the brain in gender transition. Gender-related attributes appear to be arrayed more on a spectrum or in a mosaic than in a binary male/female separation, which may help us understand why gender non-conformity is common across cultures.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: Future studies should look to measures other than overall volume (e.g., activity, connectivity, neurochemistry) to understand statistical male/female differences in amygdala-related behaviors and psychiatric disorders.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
Dhruv Marwha, Meha Halari, Lise Eliot. Meta-analysis reveals a lack of sexual dimorphism in human amygdala volume. NeuroImage, 2017; 147: 282 DOI: 10.1016/j.neuroimage.2016.12.021
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