A new study in mice has revealed one potential mechanism exercise can exert its beneficial effect: ketones. It has long been known that exercise can lead to nearogenesis, especially in the hippocampus, with several theories about the underlying mechanism. In this study, the authors looked at the brains of mice who were given access to a running wheel and those who did not. Not surprisingly, those who had access to the wheel expressed more brain-derived neurotrophic factor (BDNF) than those who did not. What was interesting was the result that ketones (in this case, β-hydroxybutyrate) appeared to disinhibit the production of BDNF by inhibiting histone deacetylases which act as downregulators at the BDNF promoter site. This was confirmed by direct injection of β-hydroxybutyrate into the mice ventricles and observing a rise in BDNF.