Why do we know about being male, female or any other type? Why does that identity correspond to the genitals in the vast majority of cases? Until recently, it all seemed clear: Just as there are males and females in nature, there are males and females in our species.
Is it always like this? Can a male-female binomial be transferred to a man-female? It seems that no, there are individuals whose consciousness of being male or female does not match their genitalia. We are talking about transgender people who, in this respect, differ from the vast majority that make up congruent or cisgender people.
Is trans identity correlated with specific features of brain structure and function? Is there a psychological basis? According to our research, yes.
after the rats
When we studied sex differences in the rodent olfactory system and reproductive behavior in the 1980s, we did not imagine that this would prompt us to investigate gender identity.
It all started with the work of Dutch neurobiologist Dick Swab of the Netherlands Institute for Neurosciences. The swabs compared the volumes of different regions of the preoptic area and hypothalamus in the brains of deceased cisgender men, women and transgender women, and found that the volume of the nucleus in an area called the stria terminalis was feminized in the trans women.
Swab based his study on previous findings from our group: he showed that, in rats, this nucleus is sexually dimorphic (it varies physiologically depending on sex) and participates in sexual behavior. It was also described as containing receptors for sex hormones. Everything related to sex and gender can be best understood from the gender discrimination perspective of the mind.
Today, neuroimaging technology allows us to study in vivo The anatomical and functional structure of the brain of cis and transgender people. Initially, interest was focused on the hypothalamus, and researchers found that its response to odors related to male pheromones is similar in cis and trans females. These results supported the feminization of the brain in recent years, as the swab had already progressed.
differences in the cerebral cortex
The hypothalamus is a region that controls autonomic and neurohormonal responses, but gender identity is a behavioral trait that requires interactions between body perception and social stimuli and models. This fact prompted us to focus our study on the cerebral cortex, where this complex process is managed.
It is known that the cortex of cis and trans women and trans men is thicker than that of cisgender men. Interestingly, although cis women and trans men and women did not differ in the overall thickness of that part of the brain, each of the three groups differed from cis men in the thickness of the different regions. Consequently, we proposed the existence of four phenotypes or cortical modalities associated with binary gender identity.
Throughout life, the cortex undergoes a thin process that depends on the functionality of androgen receptors, proteins to which sex hormones bind to DNA and exert their effect. Furthermore, after examining a large population of cis and transgender people, we observed the existence of genetic variations for androgen, estrogen and aromatase receptors associated with trans individuals. These findings suggest that the cortex develops differently depending on hormones.
connection under magnifying glass
When we get closer to the connectivity of the cortex, we observe a difference between the four identities with respect to the microscopic structure of the brain’s fascias or connecting pathways involved in cognition and emotion. In addition to distinguishing between cis men and women, some of these follicles are masculinized and defined in transgender men and feminized and demasculinized in trans women.
Structural studies and the role of androgen and estrogen receptors in sex differentiation of the brain set the framework for us to offer an explanatory theory that bases the various identities on the differential development of the cerebral cortex.
Through a technique called Functional Connectivity at Rest (rfMRI), we managed to visualize neuronal activity in different areas of the brain by the degree of oxygenation of hemoglobin. Together with the received signals, complex communication networks are defined, which allow us to trace how different areas of the brain communicate and information is managed. That is, how does the thinking organ work.
Are there gender differences in these neural networks as well? The group’s work of neuroscientist Ivanka Savic points to a frontal-parietal connection related to body perception. In particular, connectivity is weaker in trans men.
To form a body image, the basis of identity is not enough to represent its parts in sensory areas (somato-perception) of the cortex: a complex reconstruction is also needed that includes feelings and attitudes towards one’s own body. are (somato-perception). -Representation).
itself is not neutral, its gender is
Our strategy consisted of advancing the hypotheses and seeing whether networks emerged in which the four phenotypes differed. Thus, we observed differences in the strength of connections related to the identity of cis and trans men and women, and in the interconnectedness of so-called attention networks, the neural, fronto-parietal and sensorimotor networks by default.
In this respect, the attention network appears to perform an on/off function in relation to others, a finding that added complexity to the network. That this architecture was associated with different gender identities led us to propose that the self is not neutral, but is a gender: it is a gender-self,
fMRI studies provide a picture of connections, but these are constantly changing in response to internal and external stimuli. Movies of connectivity, how it changes over time, is provided by dynamic rMRI. With this technique we have described several patterns of association associated with different gender identities. Four brain phenotypes are also identified when studying how neural activity spreads in the brain and how it spreads over time.
The fact that the four phenotypes are linked to genetic variations at the level of structure and function of the brain and in receptors for hormones related to sex differentiation suggests that it prepares brains to adapt to social models of males or females. Is. , regardless of the genitals.