The first study you link to does not appear to address the correlation/causation issue whatsoever. Specifically: "The study acknowledges that people who regularly run marathons, like many of the study's participants, may be genetically predisposed to running long distances."<p>The second link describing neurogenesis stimulation is more interesting due to the fact that they are tracking actual changes in the participants over the course of the study.<p>For the record, I do not doubt for a moment that exercise has numerous positive benefits, both physically and mentally.