By Elisa Gonçalves de Andrade
On the table, there is a cake with pink and blue frosting. Inside the cake, a secret: the colour of the frosting indicates the sex of the new family member. Blue is for a boy, pink for a girl. Depending on the answer, much is at stake. The name of the baby, what they look like, but also a surprising factor: the baby’s brain and mental health.
In the late 90s, studies identified slight brain differences between boys and girls. Scientists found that the development of connections between specific brain areas starts at different points for boys and girls, though it ultimately synchronizes with time. Research looking at brain development, size and composition followed, but with conflicting results.
As it turns out, the differences between boys and girls were more fluid than we expected.
He was a boy, she was a girl. Can it get any more obvious?
As much as it pains me to say, Avril Lavigne was wrong. Studying the biological differences between boys and girls has been anything but obvious. Biology determines the sex one is born with. In more scientific terms, this is known as male, female or intersex, which is somewhere between the two. Every person is assigned one of the sexes when they are born. But for humans, on top of the biological sex, there are the influences of identity and society. This gets us to the concept of gender. According to the way someone sees and expresses themselves, their gender identity is constructed. Within the gender continuum, someone can have no gender, the gender corresponding to their biological sex, or a gender other than their biological sex.
Do biological sex or gender identity drive changes in the brain? The answer is: yes, but we don’t know exactly how. It is practically impossible to isolate gender and sex in humans. Thankfully, animal models can help.
Animal models don’t have gender reveal parties but they can tell us a lot about the female and male sexes
Similarly to us, animal models are assigned one of the three sexes at birth. With identity out of the picture, they have helped us see that, genetically and hormonally, female and male brains are different.
The genetic material, or genes, of males and females differ slightly. In the early 2000s, scientists began to wonder whether this would make any biological difference in the brain. The answer again is yes, although less dramatic than what Avril sings about. For example, the genes of males tend to make them more susceptible to aggressive behaviour when compared to females.
But genes are not everything. Genes provide instructions for cells to work. For instance, they can tell specific cells to produce messenger molecules known as hormones, which help relay information from one part of the body to the other. Different concentrations of hormones between females and males are tied to their different behaviours. Higher testosterone, a hormone driving male-related traits, causes changes in the brains of male but not female birds, making them sing during courtship. Hormones also modulate mood, coordination and even blood pressure. Higher concentrations of estradiol, a hormone driving female-related traits, protects females from the detrimental effects of blood flow interruption in the brain, commonly known as stroke.
Although different hormone concentrations and genetics can separate females and males into somewhat different categories, the distinctions between the two are unclear for other biological processes. Believe it or not, the majority of what we know in the health sciences has only been studied in males. Just recently rigorous funding agencies have started to demand that researchers include both females and males in their studies. And if they don’t, they must have really good reasons that go beyond “females’ menstruation complicates the study”.
Beyond this, animal models are just that: models. They offer only hints, but not exact answers for our very human problems.
Going back to humans: what a gender reveal party says about the baby’s mental health
Neuroscientists like to say that the brain is plastic – meaning it is constantly changing. Every experience sends new information to the brain that, in turn, modulates the connections between our brain cells. Among the numerous experiences that are part of life, the sense of identity is central. Although we are in the early stages of understanding how, it is safe to assume that gender both shapes the brain and is shaped by the brain. Some evidence points out that the concentration of testosterone during fetal development helps direct gender identity later in life. On the other hand, how a feminine identity changes brain connections, has yet to be explored. Moreover, how biologically fluid the transition between each identity is another complete mystery.
At the very least, sex and gender identity are predictors of mental health disorders. For example, autism spectrum disorders and early-onset schizophrenia are four times more prevalent in biological males than females. At the same time, anxiety and panic disorders are almost two times as common in biological females compared with males. Unfortunately, less is known about sex and gender identities outside the binary men-women bias. Research so far shows that youth who identify as transgender are more at risk of depressive and eating disorders than their peers, though the interaction between the societal and biological mechanisms of these risks are still unknown.
Many of our answered questions have their roots in societal problems.
When studying gender diversity in the realm of mental health, biological research often fails to catch up with the humanities. It is not uncommon to find research or medical papers that mistake sex and gender identity, or specific gender identities for a problem. This is evident in the history of the American Psychiatric Association’s Diagnostic and Statistical Manual, frequently used to understand mental health disorders. In the past, the distress that comes from identifying with a gender different from the sex assigned at birth was classified in this manual as a “gender identity disorder”. The manual implied that feeling an identity different from one’s biological sex was a disease or problem, which only contributed to stigma. In the future, understanding how sex and gender play with mental health will need approaches that are more inclusive and just to all.
Is mental health risk caused exclusively by genes, hormones and brain processes regulated by sex and gender? Likely not, but they are part of the answer. A better understanding of how exactly this happens will be fundamental to knowing what populations are more vulnerable and how we can best help them.
Who knew we could learn so much from a gender reveal party?