It's been known for some time that new neurons are produced throughout life, and that exercise can stimulate production of new neurons. Newly-formed cells integrate into existing networks and play an important role in learning and memory. But there is also an age-related decline in formation of new cells. Now scientists at the Max Planck Institute have determined why that may be, at least in mice. They found that within sites in the brain where new neurons are formed, there are two populations of neural stem cells, termed "radial" and "horizontal". The stem cells can either be actively dividing or quiescent (dormant, not growing but in reserve.) In aged mice, there was no decline in the actual numbers of neural stem cells, but there was a shift from active to quiescent. The scientists found more newly-formed neurons in physically active mice than inactive mice. Exercise seemed specifically to activate the dormant radial neural stem cells. Interestingly, other stimuli such as epileptic activity activated the horizontal neural stem cells.

According to one of the authors, Prof. Verdon Taylor:

"Consequently, running promotes the formation of new neurons."

The results are published in the journal Cell Stem Cell