Just keep learning

 “It is no longer believed that neurons in the brain are incapable of being regenerated. It was once wildly believed that we are born with our full conpletement of neurons and that new neurons are not gerneated. This idea is now untenable, at least in a region called the dentate gyrus.” ~ Jamie Ward (2015) Student’s guide to cognitive neuroscience.  

This means you need to work your brain out to keep it healthy just like your heart. You do this by learning something that’s just beyond the reach of what you think you can do.