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Brain Sex Differences

By: , Posted on: February 26, 2015

brain mappingYour gender, whether you are a boy or girl, man or woman, is one of the most salient and enduring identifying features one possesses. The term gender is unique to humans as it incorporates both self and societal perceptions of one’s sex, which is either male or female. Thus, studies of animals address sex differences, whereas studies of humans may involve either or both gender and sex. One’s sex is determined on several levels that can be summarized as ‘the three Gs’ – genes, gonads, and genitalia (Joel, 2012).

In the overwhelming majority of cases, these three variables align such that an XX individual will develop ovaries and female genitalia whereas an XY individual will develop testis and male genitalia and this will in turn inform gender. Thus, sex and gender are internally consistent. But is this also true for the sex/gender of the brain? That boys and girls, men and women, behave differently is so self-evident as to be hardly worth stating. But this easy generality is in reality highly nuanced and complex in both its origins and manifestations. In what ways are men and women’s brains really different? And why are they different? Is it biology? Culture? Society? Experience? Or some combination thereof?

Read more: A Beginner’s Guide to Brain Sex Differences

Only in animals can we hope to tease out truly biological sources of variation in male and female brains and the first experimental evidence of this comes from the publication of the now iconic paper of Phoenix, Goy, Gerall, and Young (1959). This study of guinea pigs established that the sensitivity of adult animals to either male (testosterone) or female (estradiol and progesterone) hormones and the induction of sexual behavior were dependent upon the hormonal milieu experienced early in life, with the authors asserting that the neural substrate controlling behavior had been ‘organized’ (Figure 1).

figure 1

This was a heretical idea at the time but in hindsight is entirely consistent with other sensitive periods in brain development that alter adult neural function, as well as newly emerging ideas about early life programming that impacts all manners of adult responding including energy utilization, stress responding, and immune system activation (Bale et al., 2010). The authors made the even further heretical assertion that testosterone and its metabolites alter the structure or function of the neural correlates of sexual behavior. Today, we fully embrace the notion that steroids act on the brain to modify neural structure and function, regardless of whether one accepts this contributes to sex differences in behavior. In fact, the more we look, the more we find. But not all sex differences are made equal, and some may have evolved in order to appear only in response to challenge or to compensate for the costs of reproduction that differ in males and females (McCarthy et al., 2012 and McCarthy and Konkle, 2005).

Read the full article on Brain Sex Differences by M.M. McCarthy here.


Brain Mapping: An Encyclopedic Reference offers foundational knowledge for students and researchers across neuroscience. With over 300 articles and a media rich environment, this resource provides exhaustive coverage of the methods and systems involved in brain mapping. Brain Mapping fully links the data to disease (presenting side by side maps of healthy and diseased brains for direct comparisons), and offers data sets and fully annotated color images. Each entry is built on a layered approach of the content – basic information for those new to the area and more detailed material for experienced readers. Edited and authored by the leading experts in the field, this work offers the most reputable, easily searchable content with cross referencing across articles, a one-stop reference for students, researchers and teaching faculty.

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