From needle exchanges to diabetes to the aging brain, a look at research out of the Johns Hopkins Bloomberg School of Public Health, one of the busiest places in Baltimore. Can mentoring young people help you stay sharp as you enter your 70s and 80s? A new study by Michelle Carlson might make you want to take up volunteering today. Plus, at a time when more cases of diabetes are being diagnosed, just one in three Americans has their problem under control. Why is that such a challenge? Elizabeth Selvin has the answers. And, we hear from the Hopkins-based president of the International AIDS Society, Chris Beyrer, about the most effective tools in the fight against the spread of HIV. He thinks Congress should lift the ban on federal funding for needle exchanges. Original air date 08/04/15.