A study, published last year and conducted at the Laboratory of Neuro Imaging at UCLA School of Medicine, explored the extent to which brain anatomy is associated with gender identity. "The degree to which one identifies as male or female has a profound impact on one's life," the authors wrote. "Yet, there is a limited understanding of what contributes to this important characteristic termed gender identity."

Many who live at variance to their birth gender as well as many in the scientific field would heartily agree.

Historical Background

In 1910, German physician Magnus Hirschfeld coined the term "transvestites" to describe individuals who are more comfortable in clothing of the opposite gender. Hirschfeld's interest in this study population was not purely professional; he himself identified as a transvestite in addition to being gay. He believed that sexual orientation was a naturally occurring trait worthy of scientific inquiry, and in his many studies he found that transvestites could be men or women and could identify as any sexual orientation. In fact, most of his participants were heterosexual. Meanwhile, many psychoanalysts during the same period, including Wilhelm Stekel, characterized transvestites as "latent homosexuals" or men who consistently denied their attraction to other men.

Years later in 1948, endocrinologist Harry Benjamin was asked by Alfred Kinsey, the biologist and most famously sexologist who in 1947 founded the Institute for Sex Research, to examine a boy who "assured to be a girl." The mother of the boy had come to him wishing for help that would assist rather than thwart her child, and Kinsey had never encountered such a case. Upon his own examination, Benjamin understood that the boy's condition was markedly different than that of transvestism.

He immediately involved psychiatrists, but they were unable to agree on a strategy for treating the boy. Eventually, Benjamin decided to administer estrogen to the boy; he used Premarin, which had been introduced in 1941. This treatment, he noted, had a calming effect. Next, he helped arrange for the mother and child to go to Germany where surgery could be performed. Hirschfeld supervised the first recorded sex reassignment surgery in Berlin sometime during 1930-1931. The earliest surgeries primarily consisted of the removal of the male sex organs, though unsuccessful uterine transplants were attempted. Although the mother of the boy ceased contact after her departure for Germany, Benjamin continued to refine his understanding of her boy's condition, and in 1954 he reprised the term "transsexualism," which had been coined by Hirschfeld in 1923. Benjamin went on to treat several hundred similar patients in a similar manner, often without accepting payment.

From early on, then, scientists have identified separate communities of people — those who wished to dress as the opposite sex and those who wished to become the opposite sex. Although a much wider spectrum of gender identities currently exists, only now can the original ideas of transvestism and transsexualism be fully explored in a scientific way. And such is the case with the researchers at the UCLA School of Medicine who hoped to pinpoint more concrete factors influencing gender identity.

Brain Science

Specifically, the UCLA researchers chose to investigate potential neuroanatomical variations associated with transsexualism; in particular, they applied a "whole-brain approach" in which they would compare the thickness of the cortex across the lateral and medial brain cortical surfaces at thousands of surface points. "The cerebral cortex contains approximately 80% of the neurons of the central nervous system and contributes largely to factors such as social awareness, attitudes, and decision-making," the authors wrote. Given the relevance of these factors in association with transsexualism, they expected to find alterations in MTF (male to female) transsexuals compared to control men.

To be included in the study, the transsexual participants needed to self-identify as a MTF transsexual, report no history of hormonal treatment, and declare their intention to undergo estrogen replacement therapy. Their ages ranged between 23 and 72. The researchers processed the brain images and examined the regional thickness of the cerebral cortex, comparing the measurements of the 24 MTF transsexuals with those of 24 age-matched control males.

They found the MTF transsexuals, as compared to the control participants, had thicker cortices (outer layers of their cerebellums), both within regions of the left hemisphere and right hemisphere. "Regional gray matter characteristics in MTF transsexuals are more similar to the pattern found in men (i.e., in subjects sharing biological sex) than in women," the authors wrote. "However, we also noticed that brain characteristics in MTF transsexuals and in control men were not fully identical."

The thicker areas within the left hemisphere of MTF transsexuals included the frontal and orbito-frontal cortex (involved in decision-making), central sulcus, perisylvian regions (helps to process language), and paracentral gyrus; and within the right hemisphere included pre-/post-central gyrus (involved in sense of touch), parietal cortex (integrates sensory information), temporal cortex (involved with visual information), precuneus (concerned with reflections upon self and aspects of consciousness), fusiform, lingual, and orbito-frontal gyrus.

"The current study provides evidence that brain anatomy is associated with gender identity, where measures in MTF transsexuals appear to be shifted away from gender-congruent men," wrote the authors.

Scientific corroboration, then, supports what individuals have tried to express for years. Since the time of Hirschfeld and Benjamin, the trans community has expanded to include not just transvestites and transsexuals but also androgynes (individuals who identify as androgynous), genderqueers (individuals who identify as somewhere in between male and female), bigenders (individuals who identify as both male and female), and any other individual who describes gender in a non-binary way. In all likelihood, scientists may soon find distinct features of the brain that correspond with each individual point along this continuum of gender possibility, identification, and expression.

Sources: Luders E, Sánchez F, Tosun D, et al. Increased Cortical Thickness in Male-to-Female Transsexualism. Journal of Behavioral and Brain Science. 2012.

Beemyn G, Rankin S. The Lives of Transgender People. Columbia University Press. 2011.