Exercise increases hippocampal neurogenesis to high levels but does not improve spatial learning in mice bred for increased voluntary wheel running.

The hippocampus is important for the acquisition of new memories. It is also one of the few regions in the adult mammalian brain that can generate new nerve cells. The authors tested the hypothesis that voluntary exercise increases neurogenesis and enhances spatial learning in mice selectively bred for high levels of wheel running (S mice). Female S mice and outbred control (C) mice were housed with and without running wheels for 40 days. 5-Bromodeoxyuridine was used to label dividing cells. The Morris water maze was used to measure spatial learning. C runners showed a strong positive correlation between running distance and new cell number, as well as improved learning. In S runners, neurogenesis increased to high levels that reached a plateau, but no improvement in learning occurred. This is the first evidence that neurogenesis can occur without learning enhancement. The authors propose an alternative function of neurogenesis in the control of motor behavior.