Gender: Unexpected Sex Differences in Brain Development

A team of researchers from the NIH recently released some of the most comprehensive research yet on sex differences in brain development, as measured by high-resolution MRI scans. They followed a large cohort of kids from age 9 through age 22 (this research actually began back in 1995). So the same kids came in to the lab on multiple occasions to have their brain scanned. That method allows you to distinguish individual differences in brain development from sex differences in brain development.

The group found dramatic and significant sex differences in the structure of the cerebral cortex, which by itself isn't that surprising. Other groups have reported similar differences for more than a decade now. What's particularly interesting about this new report is that the NIH group found that sex differences diminish as a function of age, from age 9 through age 22.

To put it another way: after the onset of puberty - when girls start making lots of estradiol and other ‘female' hormones, while boys start making lots of testosterone and other ‘male' hormones - sex differences in the brain actually decrease. The brains of 9-year-old girls and boys are remarkably different - but they grow more and more alike throughout adolescence and into young adulthood.

For more, see Unexpected Sex Differences in Brain Development by Leonard Sax, MD, PHD, December 11, 2010 at Psychology Today.