Heya, a happy St. Nicholas day to everyone!

After eating too many sweets ☺, I added twelve studies to this website today. Right now, I’m still in the process of uploading – I’ll do a summary later.

I just quickly wanted to point out a new study called “Neural Activation During Mental Rotation in Complete Androgen Insensitivity Syndrome: the Influence of Sex Hormones and Sex Chromosomes” by van Hemmen, Veltman, Hoekzema et al. (Cerebral Cortex, 2014). This study looked at brain activation during mental rotation and compared control groups of men and women against people with male (XY) sex chromosomes and and the CAIS disorder of sex development. CAIS (complete androgen insensitivity syndrome) means that male sex hormones are not being processed by the body, so that testosterone has no effect on people with CAIS.

The findings were: “Previously reported sex differences in neural activation during mental rotation were replicated in the control groups, with control men showing more activation in the inferior parietal lobe than control women. Individuals with CAIS showed a female-like neural activation pattern in the parietal lobe, indicating feminization of the brain in CAIS. Furthermore, this first neuroimaging study in individuals with CAIS provides evidence that sex differences in regional brain function during mental rotation are most likely not directly driven by genetic sex, but rather reflect gonadal hormone exposure.”

This study adds to the body of evidence that some sex differences in the brain are controlled by sex hormones, not by chromosomes. The effects of sex hormones on the brain around birth are the most likely candidate for the main cause of transsexualism.