After six weeks, the animals in both exercise groups scored better on memory tests than they had before they trained. But it was what was going on in their bodies and brains that was revelatory. The scientists found that the runners’ brains showed increased levels of a protein known as BDNF, or brain-derived neurotrophic factor, which is known to support the health of existing neurons and coax the creation of new brain cells. The rat weight-trainers’ brains did not show increased levels of BDNF.
The tail trainers, however, did have significantly higher levels of another protein, insulinlike growth factor, in their brains and blood than the runners did. This substance, too, promotes cell division and growth and most likely helps fragile newborn neurons to survive.