Physical activity has long been celebrated for keeping the mind sharp and guarding against cognitive decline, but how working out actually alters brain structure has remained a puzzle. A new study in mice offers a surprising answer: exercise creates a novel physical force inside the brain by causing star-shaped support cells to contract, which directly prompts the growth of new neurons.
Researchers have known that exercise stimulates neurogenesis—the formation of new brain cells—within the hippocampus, the key region responsible for learning and memory. While physical activity releases various hormones and signaling molecules into the bloodstream, how these compounds trigger brain changes was poorly understood. Researchers at the University of Illinois Urbana-Champaign focused on astrocytes, central nervous system cells that act as early detectors of circulating chemicals and supply vital nutrients to developing neurons.
By monitoring mice placed in cages with running wheels, scientists discovered that astrocytes in the hippocampus began contracting within just one to two minutes of running. To uncover the trigger, the team exposed mouse astrocytes to substances released by contracting muscle cells. The muscle chemicals significantly amplified the mechanical force exerted by the astrocytes, proving that contracting muscles actively signal brain cells to shrink.
The team then applied the liquid harvested from contracting astrocytes to hippocampal neurons. Astrocytes that contracted with the greatest force stimulated the greatest number of immature neurons, confirming a clear link between astrocyte contraction and neurogenesis. Scientists suspect this physical shrinking might alter cell membrane permeability or facilitate the release of microscopic vesicles carrying essential growth factors to surrounding cells.
Independent neuroscientists call the discovery a novel insight into brain plasticity. Because humans share similar cell types and machinery with rodents, experts believe the biological mechanism likely operates in human brains as well. Understanding this pathway could eventually lead to medical treatments that mimic the cognitive benefits of exercise for individuals unable to stay physically active.