In his book The Essential Difference: Male And Female Brains And The Truth About Autism, Simon Baron-Cohen opens with a phrase capable of causing infinite controversy: “The female brain is predominantly hard-wired for empathy. The male brain is hard-wired for understanding and building systems.”

When I first became interested in gender differentation in the brain, after reading about prairie voles and how oxytocin made them more nurturing as parents (in Steven Johnson´s book Mind Wide Open), I started commenting on new findings about the female brain with friends and acquaintances. The response I got was usually rather skeptical. This was especially the case when I tried to bring the subject up with women.

Apparently, after fighting for equal rights for centuries, many women were reluctant to acknowledge significant differences between the male and female brain. The popularization of neuroscience, aided by advances in the research, have conquered only a fraction of that skepticism. But the truth is that none of it is justified.

Vasopressin and Empathy

Structural differences between the male and female brain, most prominently connectivity between the hemispheres, are well known, while many aspects about the way each one of them works are still a mystery.

A recent study focusing on the synthesis of neuropeptides vasopressin (VP) and oxytocin (OT), which are involved in a large number of social behaviors including mate bonding and parental care, concluded that VP and OT systems frequently mediate sex differences in such behaviors.

Another study from earlier this year found that intranasal VP, yet not oxytocin, altered empathic behavior in both men and women. VP systems in male and female brains have shown many differences across different species of rodents, yet the way these differences affect VP release in the brain is still unknown. At any rate, in spite all the uncharted territory, it would seem that when Baron-Cohen attributed empathy to females, he was not too far from the truth.

Creativity in the Male and Female Brain

One of the things scientists observe most frequently when doing fMRIs of the female and male brain executing the same activities is that different areas of the brain tend to “light up.” While one sex seldom outperforms the other, the way men and women solve a problem, recall certain types of memories, or engage in creative processes appears to be quite different.

During a study focusing on creative processes, such as creative conceptual expansion and general divergent thinking, men and women showed indistinguishable performance levels across the different tasks proposed. However, fMRIs revealed profound strategic differences between the genders. For example, while in men, brain areas related to semantic cognition, rule learning, and decision making were primarily engaged during conceptual expansion, in women there was higher activity in regions associated with speech processing and social perception.

Oxytocin and Parenting

More popular than differences in empathic behavior and creativity strategies, oxytocin is the unquestioned star when it comes to making a name for itself in pop culture. Oxytocin is connected with nurturing and caring behaviors towards offspring. Research has shown that besides playing a key role in childbirth and early mother-child bonding, oxytocin release, alongside dopamine release, may also result from rewarding interactions with infants. It has actually been observed that fathers who spend time with their kids may stimulate the oxytocin-dopamine reward system in their brains.

In fact, evidence points to the possibility to “rewire” the male brain to accommodate parenting styles similar to those associated with females. For example, in one study, a vole from a species that is not nurturing with offspring was placed among a group of nurturing voles. The result was that regardless of its neurological predisposition to be less nurturing, the vole learnt from the individuals around it and became a nurturing parent.

When Babies Cry

The question is, if males can acquire characteristics associated with the female brain, why is gender differentiation in the brain still such a big deal?

Well, there is still more functional differentiation to go. Several studies have analyzed the reactions of both mothers and fathers to the crying of their infants. Scans have revealed a greater activation of amygdala and basal ganglia in brand new mothers compared with fathers, which is consistent with mothers being more preoccupied than fathers in these circumstances. Responses to baby stimuli have also been linked to OT pathways, as mothers who give birth through vaginal birth, which stimulates oxytocin release, show greater brain activity in response to the cries of their own babies versus other babies.

Arguably, parenting styles and how they originate in brain function may be the most salient aspect of male-female differentiation in the brain. However, much of the evidence in these respect points to fathers simply being slower learners. For example, when it comes to baby cry stimuli, it may take fathers between 6 to 18 months to match the level of brain activation shown by mothers, but they eventually get there.

The Extreme Male Brain

With as many champions as detractors, Baron-Cohen is still a top expert in the field. His theory of the extreme male brain may be the culprit of the passions his work never fails to excite. Basically, he proposes that the autistic brain is the “full-on” male brain, namely, zero empathy, all systemization.

In a study published earlier this year, Baron-Cohen and his colleagues presented new evidence for the extreme male brain theory in the shape of hemodynamic response measurements during second-order false-belief task and coherent story task performances. Since the measurements revealed “sex difference in the neural basis of Theory of Mind (a cognitive component of empathy) and pragmatic language,” the researchers concluded that this was in line with the extreme male brain hypothesis; a conclusion that seems slightly far-fetched. While the findings do not disprove the extreme male brain theory, they seem to contribute not much more than a grain of sand in the building of a giant castle.

What About the Gay Brain?

An interesting question that surfaces whenever the male and female brain are discussed is what happens with the gay brain? In other words, do homosexual women have a brain more akin to men´s and vice versa?

A research team tried to answer this question by studying functional cerebral lateralization for the processing of facial emotions. The sample comprised 30 heterosexual males, 30 heterosexual females and 40 gay males. Results revealed that while men were right-lateralized when viewing female faces, homosexual men were as left-lateralized as women during the same activity. Thus, researchers concluded that “gay men are feminized in some aspects of functional cerebral lateralization for facial emotion.”

Perhaps the future of male-female brain differentiations studies lies in the understanding of brain formation and development. A study from Beijing University, which appeared in Acta Radiologica earlier this year, attempts to draw conclusions from studying the brains of 400 young adults. The authors observed significant topographical differences between the sexes, including gray matter volume and cortical thickness, both larger in females, and posed a question neuroscientists will bust their own brains – whether male or female – trying to answer in the years to come: Does the difference in the topological architecture represent underlying behavioral and cognitive differences between genders?

As with many areas of neuroscience, when it comes to gender differentiation in the brain, experts today seem to have many more questions than answers, but this is precisely what makes the field so exciting.

Meanwhile, common people continue to devour books about the male and the female brain, in the hopes of understanding the other sex better, a pursuit as likely to be crowned with success anytime soon as the full understanding of the brain itself.

References

Abraham A, Thybusch K, Pieritz K, & Hermann C (2014). Gender differences in creative thinking: behavioral and fMRI findings. Brain imaging and behavior, 8 (1), 39-51 PMID: 23807175

Dumais KM, & Veenema AH (2015). Vasopressin and oxytocin receptor systems in the brain: Sex differences and sex-specific regulation of social behavior. Frontiers in neuroendocrinology PMID: 25951955

Frank CK, Baron-Cohen S, & Ganzel BL (2015). Sex differences in the neural basis of false-belief and pragmatic language comprehension. NeuroImage, 105, 300-11 PMID: 25264229

Hu Y, Xu Q, Shen J, Li K, Zhu H, Zhang Z, & Lu G (2015). Small-worldness and gender differences of large scale brain metabolic covariance networks in young adults: a FDG PET study of 400 subjects. Acta radiologica (Stockholm, Sweden : 1987), 56 (2), 204-13 PMID: 24763919

Nakstad, P. (2015). Gender differences in the human brain Acta Radiologica, 56 (2), 131-132 DOI: 10.1177/0284185114562993

Rahman Q, & Yusuf S (2015). Lateralization for Processing Facial Emotions in Gay Men, Heterosexual Men, and Heterosexual Women. Archives of sexual behavior PMID: 25564038

Swain, J., Kim, P., Spicer, J., Ho, S., Dayton, C., Elmadih, A., & Abel, K. (2014). Approaching the biology of human parental attachment: Brain imaging, oxytocin and coordinated assessments of mothers and fathers Brain Research, 1580, 78-101 DOI: 10.1016/j.brainres.2014.03.007

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