Gender identity leaves imprint on human brains: Study

The society's expectations about gender roles have a very deep impact on human beings even as the subject has not yet made its way to mainstream debates. According to a recent study, it can alter the human brain at the cellular level.

Though the terms 'sex' and 'gender' are often used interchangeably by the average person, for neuroscientists, they mean different things, said Nancy Forger, lead researcher of the study.

"Sex is based on biological factors such as sex chromosomes and gonads [reproductive organs], whereas gender has a social component and involves expectations and behaviours based on an individual's perceived sex," explains Nancy Forger, lead researcher of the study.

"We are just starting to understand and study the ways in which gender identity, rather than sex, may cause the brain to differ in males and females," Forger added.

These behaviors and expectations around gender identity can be seen in "epigenetic marks" in the brain, which drives biological functions and features as diverse as memory, development and disease susceptibility.

Forger explained that epigenetic marks help determine which genes are expressed and are sometimes passed on from cell to cell as they divide. They also can be passed down from one generation to the next, she said.

"While we are accustomed to thinking about differences between the brains of males and females, we are much less used to thinking about the biological implications of gender identity. There is now sufficient evidence to suggest that an epigenetic imprint for gender is a logical conclusion. It would be strange if this were not the case because all environmental influences of any importance can epigenetically change the brain," Forger said.

In one example involving rats, the Georgia State authors cited a study by University of Wisconsin researchers who gave female rat pups extra attention designed to simulate the increased licking that mother rats normally perform on their male offspring. That treatment led to detectible changes in the brains of the female rats that received extra stimulation as compared to those who got the normal level of attention for female pups.

Among the studies involving humans, researchers considered the example of Chinese society during the Great Chinese Famine from 1959-1961, when many families preferred to spend their limited resources on boys, leading to higher rates of disability and illiteracy among female survivors in adulthood. This demonstrates, they said, that early life stress can be a gendered experience as it changes the neural epigenome.