Gay brains similar to straight brains of the opposite sex

Recently, brain scans have provided scientists with some of the best evidence that ‘being gay’ or ‘being straight’ is part of a biologically-fixed genetic trait. The brain scans revealed – that in homosexuals – key brain structures responsible for anxiety, mood, emotion, and aggressiveness are extremely similar to those in straight people of the opposite sex.

To put the findings in simpler terms:

  • homosexual (gay) male brains = heterosexual (straight) female brains
  • homosexual (gay) female brains = heterosexual (straight) male brains

Ivanka Savic, the leader of the study, said that, “Scientists figure that the differences between straight and gay brains of the same sex are likely already set early in the womb or during early infancy.” Ivanka held and carried out this groundbreaking study at the Karolinska Institute in Stockholm, Sweden. Ivanka continues by stating, “This is the most robust measure so far of cerebral differences between homosexual and heterosexual subjects.”

Most previous studies have also discovered differences in brain structure and activity between gay and straight individuals. However, most of these studies relied on individuals’ responses to sexuality driven cues that may have been learned (i.e. rating the attractiveness of male / female faces).

How the study worked

To avoid relying on individuals’ responses to sexuality driven cues, researchers chose to measure brain parameters that were most likely ‘fixed’ at birth. Savic said that the whole point of this study was to show brain parameters that differ; parameters that couldn’t be changed via cognitive processes or learning.

First, the researchers utilized fMRI brain scans to determine the shape / structure of the brains and their overall volume. A group of 90 volunteers that consisted of 25 straight (heterosexual) individuals [of each gender] and 20 gay (homosexual) individuals [of each gender] were scanned.

The results of the “gay brain” study

The results of this “gay brain” vs. “straight brain” study show that straight men tended to have more asymmetric brains, with the right-hemisphere slightly larger than the left. On the other hand, gay men had symmetrical brains just like the brains of straight women.

The research team then used PET scans to determine and measure the amount of blood flow to the amygdalaa part of the brain that regulates aggression and fear. The PET scan images showed how the amygdala – which is connected to other parts of the brain – gave clues as to how it might influence behavior. Researchers learned that patterns of connectivity in the brains of gay men matched those of straight women. In straight women, the connections were mainly into regions of the brain that manifest the emotion “fear” as “intense anxiety.”

The brain connection to mood disorders

Savic, leader of this study added, “The regions involved in phobia, anxiety and depression overlap with the pattern we see from the amygdala.” This is very significant because it correlates with data showing that women are at least 3 times more likely than men to suffer from mood disorders and depression. Gay men tend to have much higher rates of depression too. It’s difficult to know whether the link to mood disorders is due to homophobia, biological traits, or a result of the stigma associated with being gay.

In lesbians and straight men, the amygdala feeds its signals mainly into the straitum and the sensorimotor cortex – 2 regions of the brain associated with generating a “flight or fight” response. Researchers say that it’s more of an “action-determined” response than it is in women.

What the experts had to say

One of the leading researchers in the field of “sexual orientation” at Queen Mary College, London, UK – Qazi Rahman – said, “This study demonstrates that homosexuals of both sexes show strong cross-sex shifts in brain symmetry.” Qazi later added, “The connectivity differences reported in the amygdala are striking.”

Simon LeVay, a prominent United States author who reported in 1991 about finding differences in the hypothalamus (part of the brain) between gay and straight men. After viewing this study, Simon said, “Paradoxically, it’s more informative to look at things that have no direct connection with sexual orientation, and that’s where this study scores.”

Ivanka Savic, the study leader, understands the fact that her study cannot determine whether the homosexual brain differences are inherited or a result from overexposure to certain sex-hormones in the womb (i.e. estrogen and testosterone).

Journal reference: The National Academy of Sciences Proceedings