One thing to note is that they find that the increase in hippocampal volume correlates with exercise-induced increases in serological BDNF. Interestingly, previous studies have documented that within the hippocampus, exercise causes a selective upregulation of BDNF expression in the dentate gyrus and CA3. Thus, although Erickson et al. did not assess individual hippocampal subregions, it is plausible to assume that the effect they are seeing is really driven by exercise-induced changes in the dentate gyrus. Indeed, in the discussion section, the authors suggest this as the driving mechanism.

We and others have found that the dentate gyrus is differentially affected by "normal aging" and relatively preserved in AD. This is one reason I think that exercise will be most beneficial for cognitive aging and less so for AD (which more prominently targets other hippocampal subregions).

View all comments by Scott Small