You may have heard that your brain stops growing after you are 25 years old, or that adult brains can’t make new neurons.

While this was widely held to be true in the late 20th century, it no longer is. Neuroscientists now embrace a “growth mindset.” Literally.

That’s because they’ve discovered that the brain can develop new neurons in a process called neurogenesis.  In fact, this takes place regularly in the region of the brain that creates memories: the hippocampus. That means that, even as adults, we are capable of growing new neurons to help us form memories, learn new skills, and recognize faces.

But the news gets better. Not only can the brain grow new neurons, this growth can be encouraged.

How?

Not with pills, or injections, or surgery (yet), but with something nearly everyone has access to: exercise.

While exercise has long been known to decrease the risk of cardiovascular disease and promote general health, there is mounting evidence that it also has psychological benefits. Exercise boosts happiness, reduces depression, and even makes us smarter. It appears that the intelligence-boosting effects of exercise owe in part to the creation of new neurons in the hippocampus.

Researchers first saw evidence of this in other animals. Lab rats were put on four different exercise regimens for seven weeks: sedentary, moderate running, resistance training, and high-intensity interval training. The rats that engaged in moderate running showed robust neurogenesis in their hippocampus, and the amount of new neuron growth was directly related to how far the rat had run.

In another study, rats that underwent a short burst of exercise showed enhanced spatial learning. They were able to find an underwater platform faster and with fewer trials than rats that were sedentary.

Scientists have found that exercise increases the synthesis of brain-derived neurotropic factor (BDNF), a protein responsible for stimulating neuron growth. BDNF can cross the blood-brain barrier and activate transcription of molecules that allow new neurons to branch off of existing ones.

Just as in rats, BDNF is produced in humans after exercise, and the positive effect of exercise on cognitive abilities holds true in humans across all ages.

Children who have just a 10 to 20-minute exercise session during the school day show improved math performance. There is also some evidence that exercise increases young adult’s performance on standardized tests.

A review of studies examining the effects of aerobic exercise on older adults found enhanced cognitive abilities, even in those with early signs of Alzheimer’s Disease. Exercise appears most beneficial for activities involving planning, multi-tasking, dealing with ambiguity, and memory.

However, not all exercise is equally beneficial.

For example, rats that underwent high-intensity interval running or weight-based resistance training showed less neurogenesis than those that engaged in moderate running.

Likewise, adult humans who went through a toning and stretching exercise did not show as much improvement in cognitive tests as those who went through a pool-based aerobic regime.

The most effective kind of exercise for neuron growth thus appears to be moderate-intensity aerobic exercise, such as jogging and swimming. High-intensity exercise, particularly when it’s prolonged, may actually be detrimental to neurogenesis because of the high level of stress it can cause.

Research on the link between exercise, brain health, and cognitive functioning is still in its early days, and there is much we still don’t know. What are the best kinds of exercise, and the ideal intensity, frequency, and duration of each? Are these benefits diminished if you start exercising late in life? Can exercise be used to reverse the neurological decay of aging?

In the meantime, if you want to keep your brain healthy, it’s prudent to make sure you are physically active.