Men’s and women’s brains really work in different ways, genetic study reveals

STANFORD, Calif. — Men’s and women’s brains really work differently, and scientists say it all comes down to their genes. A team from Stanford Medicine has discovered more than 1,000 genes that are much more active in the brain gray matter of either sex.

According to the researchers, these genes are responsible for programming “appraisal, dating, mating, and hate.” The findings have implications for a host of diseases, including Alzheimer’s disease, autism and multiple sclerosis.

“Using these genes as entry points, we have identified specific groups of brain cells that orchestrate specific gender-specific behaviors,” lead author Professor Nirao Shah explains in an academic statement.

The relationship guide “Men are from Mars, Women are from Venus” is famous for bringing this gender phenomenon to light. In the international bestseller, American author and advisor John Gray claimed that men and women are so incompatible that they could literally be from different planets.

Experiments on mice now suggest that Gray was right. Male and female brains vary significantly. The study authors believe their findings will also apply to humans, pointing to important gender differences.

“Mice are not humans,” Shah notes. “But it’s reasonable to expect analogous brain cell types to play a role in our sex-typical social behaviors.”

Women’s reproductive cycles also result in hundreds of differences

The study analyzed four tiny structures that help animals reproduce and offspring survive. Other mammals, including humans, also share these structures. They program males’ rapid determination of a stranger’s sex, females’ receptivity to mating, and maternal protection.

The researchers extracted tissue from the animals that contained neurons enriched in sex hormones. Genes are the blueprints for proteins, which do virtually all of a cell’s work. Activation levels – the speed at which genes copy and convert information – determine its functions.

The team also identified more than 600 differences between female mice in different phases of their estrous cycle, equivalent to a woman’s menstrual cycle.

“Finding, within these four tiny brain structures, several hundred genes whose levels of activity depend only on the stage of a woman’s cycle was quite surprising,” says Professor Shah.

Estrogen levels in women and levels of another hormone, progesterone, rise and fall about every month, like the phases of the moon.

The link between these genes and diseases

Certain cataloged genes are risk factors for brain disorders that are more common in men or women, depending on the particular gene. Autism spectrum disorders are four times more common in men. Of 207 genes that confer high risk, 29 are more active in men, compared to only 10 in women.

Scientists have found genes linked to Alzheimer’s disease and multiple sclerosis, which affect more women, in an overexcited state in female mice. Researchers assume that men and women need different genes to work harder. A mutation in a gene that requires high activation can do more damage than a mutation that just sits around.

“The frequency of migraines, seizures, and psychiatric disorders can vary across the menstrual cycle,” Shah continues, “and our findings about differences in gene activation across the cycle suggest a biological basis for this. variation”.

Social behaviors typical of sex have developed in the brains of animals over millions of years of evolution. Male mice, for example, quickly distinguish the sex of strangers encroaching on what they consider their territory.

If an intruder is another male, they attack him immediately. If it is a female, they initiate a “swirling courtship display”. Female mice, on the other hand, exhibit maternal rather than territorial aggression, attacking anything that threatens their young. They are much more likely to guard their young and retrieve those that stray. Their willingness to mate varies powerfully depending on the stage of their cycle.

“These primary behaviors are essential for survival and reproduction,” explains the professor, “and they are largely instinctive. If you need to learn how to mate or fight once the situation arises, it’s probably already too late. The evidence is pretty clear that the brain is not purely a blank slate simply waiting to be shaped by environmental influences.

“Finding Needles Within Needles”

Previous attempts to find genetic differences in the brain cells of male and female rodents have found only about 100, apparently too few for many deep instinctive behaviors.

“We ended up finding about 10 times more,” Shah reports, “not to mention the 600 genes whose levels of activity in women vary by cycle stage. In total, this represents a solid 6% of a mouse’s genes that are regulated by sex or cycle stage.

Professor Shah compares the team’s process to “finding needles in needles in a haystack”.

“The cells that we identified as mission critical for these typical rating, dating, mating, or hating behaviors likely represent less than 0.0005% of all brain cells in a mouse,” he said. author of the study.

Determining what drives the mice also required separating surrounding cells and examining their genetic content, one at a time.

“This is probably just the tip of the iceberg,” Professor Shah concludes. “It’s likely that there are a lot more sex-differentiated features in these and other brain structures, if you know how to look for them.”

The study is published in the journal Cell.

South West News Service writer Mark Waghorn contributed to this report.

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