"They also hope in future animal studies to tease out the individual effects of running from those of playing with toys and being otherwise mentally engaged, he

"They also hope in future animal studies to tease out the individual effects of running from those of playing with toys and being otherwise mentally engaged, he says." How can they not have done this yet still draw the conclusion that the exercise was the important factor? I wouldn't be surprised if the "sedentary" individuals would have been diagnosed with depression, had they beem humans. What would make an interesting study is epigenetic effects of depression on human patients.