Most of us were taught as kids that you don't get new neurons as an adult. The party line was that by the time you were old enough to care what a neuron was, you had all that you would ever have, and your brain had nothing to look forward to but a slow and beleaguered wasting away. You could, we were also told, help this along by drinking, smoking crack, and huffing glue.
But the juggernaut of science stops for no one, and is also kind enough to correct its mistakes.
A host of research over the last few decades has found that neurons continue to be born throughout our lives. Even better than that, there are actions you can take that will grow more of them and keep them alive for longer.
In a recent article by Tracey Shors, in Current Directions in Psychological Science, she describes how the evidence for adult neurogenesis in the hippocampus is now overwhelming. In humans and other animals this amounts to thousands of new neurons everyday, many of which go on to live happy adult lives as part of your brain.
However, many of them, sadly, also die shortly after birth. The factor that appears to matter most to their longevity is whether or not you have actually done any learning in the meantime. And by learning, the authors say clearly (in different words) that this doesn’t mean learning the plot of a new Glee episode. They mean effortful learning where you try hard, and you might still not get it. This includes things like learning a new language, new tax law, a new musical instrument, or a new route to work.
Effortful learning often involves two key ingredients: 1) spacing the learning out over long periods of time and 2) testing yourself. If you space the learning out, as opposed to cramming all the material into your head during one session, then the material has the opportunity to consolidate and integrate itself with both new and old material. Cramming often skips this consolidation, and leads to more rapid forgetting, because the new material has nothing to cling to but itself.
Spaced learning also allows you to test yourself—the second key ingredient—which is one of the most under-appreciated but powerful forms of learning. By testing yourself you create pathways for retrieving the information in the future, which consistently leads to better learning in the long run. So instead of rereading something you are hoping to remember, it is much better to test yourself on the material and then correct your errors. Indeed, there is good evidence to suggest that getting something wrong is just as good as getting it right with regards to your learning, so don't worry about the errors, just make things difficult on yourself, and you will learn more, faster and keep your shiny new neurons alive for longer--regardless of your age.
Now what controls the rate of neurogensis in the first place? Exercise and good cardiovascular health lead to faster production of new neurons. The evidence also shows some support for spicing this up with sex. Stress and alcohol, on the other hand, decrease cell production. However, just to be clear, exercise doesn't keep the new neurons alive, effortful learning does that. Exercise just gets them born in the first place.
Shors, T. J. (2014). The adult brain makes new neurons, and effortful learning keeps them alive. Current Directions in Psychological Science, 23, 311-318.