Scans show biology may determine gay/straight brain

William Atkins
Wednesday, 18 June 2008 03:31

Science - Biology

According to a new Swedish study, some physical characteristics within the brains of homosexual people are also found in the brains of heterosexual people of the opposite sex.

The study was performed by Ivanka Savic and Per Lindstöm, both of the Stockholm Brain Institute, Department of Clinical Neuroscience, Karolinska Institutet, in Stockholm, Sweden. The Karolinska Institute one of the largest medical universities in Europe.

In the Savic-Lindstöm study, the two researchers specifically studied brain parameters that are considered very likely present at birth—specifically excluding those that are learned later.

Savic stated, "That was the whole point of the study, to show parameters that differ, but which couldn't be altered by learning or cognitive processes.” [New Scientist (subscription required): “Gay brains structured like those of the opposite sex”]

Based on earlier studies, the two researchers wondered (and stated in the abstract to their paper): “Cerebral responses to putative pheromones and objects of sexual attraction were recently found to differ between homo- and heterosexual subjects. Although this observation may merely mirror perceptional differences, it raises the intriguing question as to whether certain sexually dimorphic features in the brain may differ between individuals of the same sex but different sexual orientation.”

They added, “We addressed this issue by studying hemispheric asymmetry and functional connectivity, two parameters that in previous publications have shown specific sex differences.”

These parameters were measured using magnetic resonance imaging (MRI) scans to find sizes and shapes of brains. Positron emission tomography (PET) scans were also used to measure blood flow to the amygdale.

In all, a group of ninety subjects—participated in the Savic- Lindstöm study.

Specifically, “Ninety subjects [25 heterosexual men (HeM) and women (HeW), and 20 homosexual men (HoM) and women (HoW)] were investigated with magnetic resonance volumetry of cerebral and cerebellar hemispheres. Fifty of them also participated in PET measurements of cerebral blood flow, used for analyses of functional connections from the right and left amygdalae.”

What were the conclusions of the study? Please read on.