Ever noticed how older women tend to stay sharper than men? Well, science just uncovered a major clue—it's all in the X chromosome!

A recent study published in Science Advances revealed that the silent X chromosome in females actually reawakens late in life, potentially helping to slow cognitive decline.

Researchers at the University of California, San Francisco discovered that when female mice reached the human equivalent of 65 years old, their silent second X chromosome (aka the Barr body) woke up and started activating genes that strengthen brain connections. This could help explain why women have lower rates of cognitive decline than men.

How did scientists figure this out? Researchers studied female mice by tracking gene activity in the hippocampus—the brain's learning and memory center, which typically weakens with age. Surprisingly, about 20 extra genes from the once-inactive X chromosome suddenly switched on, boosting brain function.

One key player? PLP1, a gene responsible for building myelin, the protective coating around brain cells that helps neurons communicate. The study found that older female mice had more Plp1 than older males, thanks to their extra X chromosome!

The researchers decided to artificially boost Plp1 in both old male and female mice—and the results were mind-blowing! The mice showed better memory, improved learning and stronger brain connections.

So what’s next? Scientists are now digging deeper into how this process works and whether it can be used to develop treatments for brain aging and diseases like dementia.