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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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  • Hilda Sweck

    This is sexist garbage. The differences between female and male brains are tiny, and considering that we force women and men into different social roles, that is equally likely to be the cause of the brain differences. Plus neuroplasticity exists, so structure and brain function may not have that much to do with each other.
    Not to mention, if animals don’t have an ‘internal sense of gender but humans do’ then why would you be able to experiment on animals with this in the first place. Also note that not everyone agrees with the idea of categorizing their personalities into boxes based on their genitalia/actions.
    http://www.amazon.ca/Delusions-Gender…/dp/0393340244

    • Benjamin Wiseman

      Where do societal roles come from if not sexual dimorphism? Furthermore small differences in neurology and hormone levels can still have significant effects on behaviour. Why is it so hard for people to accept that men and women can be different and equal?

      • Estarianne

        Are you implying that heteronormative gender roles are universal throughout humanity? Because that is a path doomed to failure.

        Think about the cultures that existed pre-Christianity, and how many of them were matrilineal/matriarchal, and had female heads of state. Then look at the spread of Christianity via the Roman Empire and missionary activities, and see those cultures replaced by patriarchal/patrilineal cultures. Then explain again how it’s based on sexual dimorphism rather than ideology.

        • memills

          First, understand sexual selection, the process by which sexually dimorphic adaptations evolve.
          Second, take a look at resulting sexual dimorphic neurological adpatations across species, including humans.
          Third, realize that culture does not spontaneously assemble itself de-novo, but rather is based on a foundation of evolved human psychological adaptations, many of which are sexually dimorphic. Cultures reflect underlying human nature rather than determine it.
          Be able to distinguish between science from ideology, and, beware of the moralistic fallacy (i.e., wishing it weren’t so won’t make it so).
          Brain sex differences exist, get used to it.

  • Estarianne

    Wow, how do you announce that sex and gender are internally consistent and not acknowledge the people for whom they are not internally consistent?

    This is a bizarre case of trans invisibility in a science that should be addressing trans issues.

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  • Korosensei’s Wife

    “That boys and girls, men and women, behave differently is so self-evident as to be hardly worth stating”
    Sorry, but this is plain nonsense. I don’t complain, whine or cry like a woman is supposed to do in this society. I’m on the rational side, I like to collect data about things I may like or dislike rather than fueling my subconscious choices.
    Please don’t feed stereotypes…

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