I read that article a few times myself he states in 10% --but not sure why ---if u notice in the article he closes about benefits of exercise.??

Last 15 or 20 yrs science knows the link of serotonin & dopamine and cortisol.

That if cortisol runs high that the serotonin and dopamine levels decrease and exercise has been studied numerous times show the benefit of decreases cortisol and raises serotonin and dopamine levels. Most chronic depression patients are treated with MAOI'S with Prozac for this reason becauses it shown to work increasing serotonin and dopamine --science suggest sometimes something goes wrong like in this article where 10% still show shrinkage ---could it be from cortisol ---its a pretty strong theroy.