Myth of the male brain vs. the female brain

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Chapter 11 endnote 17, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

...women believe they are more emotional than men, and the men agree. [...] However, when the same people record their emotional experiences as they occur in everyday life, there are no sex differences. [...] Neuroscience evidence suggests that the “male brain” and “female brain” are myths.

A recent meta-analysis of brain imaging studies has documented sex differences in the size of various brain structures,[1] but there are no well-documented structural differences that translate into stable functional differences.[2][3] Brain imaging studies in this area tend to be plagued by very small samples and rarely take account of the fact that some differences (e.g., connectivity) appear to change with ovarian hormone fluctuations in women.

Overall, when sex differences are found in brain structure, it is not clear whether the variation is meaningful in terms of behavior or experience. A very good example is a recent paper published in the Proceedings of the National Academy of Sciences (PNAS) examining differences in structural connectivity between neurons.[4] This study had a decent sample size of 949 youths. The authors conclude that there are “fundamental” differences in connectivity between males and females (men in this sample have stronger connections between neurons within the sample hemisphere of the brain and women have stronger connections between hemispheres), but this makes it sound as if men have one pattern of connectivity and women have another, and this is not true. Men and women, on average, show evidence of both types of connections, and the difference is a matter of degree. Moreover, this paper illustrates three problems that are common in studies like this:

  1. What is the size of these differences when compared to the variation you see when testing a person from one day to the next, one month to the next, and when looking from person to person in general?
  2. How many connections show these differences relative to the number of connections between neurons in the brain?
  3. Does this difference in structure actually predict differences in behavior (i.e., accounting for degeneracy)?[5][6]

When scientists extrapolate from small differences to “his brain, her brain,” they are practicing essentialism. This is because the differences — which are summaries across groups of individuals who vary from one another (not all women are alike, not all men are alike) and whose distributions overlap — are assumed to be present in every single male and female brain and invariant in time and place, due to some fixed, genetic blueprint. It’s unfortunately common for studies (with very small samples) to merely report whatever brain differences they find, speculate on the behavioral consequences without checking, not bother to consider degeneracy or context effects, and leave it at that.[3]

Notes on the Notes

  1. Ruigrok, Amber NV, Gholamreza Salimi-Khorshidi, Meng-Chuan Lai, Simon Baron-Cohen, Michael V. Lombardo, Roger J. Tait, and John Suckling. 2014. "A meta-analysis of sex differences in human brain structure." Neuroscience and Biobehavioral Reviews 39: 34-50.
  2. Fine, Cordelia. 2010. Delusions of Gender: How our Minds, Society, and Neurosexism Create Difference. WW Norton & Company.
  3. 3.0 3.1 Fine, Cordelia. 2013. "Is there neurosexism in functional neuroimaging investigations of sex differences?" Neuroethics 6 (2): 369-409.
  4. Ingalhalikar, Madhura, Alex Smith, Drew Parker, Theodore D. Satterthwaite, Mark A. Elliott, Kosha Ruparel, Hakon Hakonarson, Raquel E. Gur, Ruben C. Gur, and Ragini Verma. 2014. "Sex differences in the structural connectome of the human brain." Proceedings of the National Academy of Sciences 111 (2): 823-828.
  5. Joel, Daphna, and Ricardo Tarrasch. 2014. "On the mis-presentation and misinterpretation of gender-related data: The case of Ingalhalikar’s human connectome study." Proceedings of the National Academy of Sciences 111 (6): E637.
  6. de Vries, Geert J., and Per Södersten. 2009. "Sex differences in the brain: the relation between structure and function." Hormones and Behavior 55 (5): 589-596.