DULUTH, Minn.—Shadab Rahman's business is sleep, but it wasn't his dream job. "I needed a summer research project," the Harvard Medical School instructor said. "The only available lab was in Toronto. ... They studied sleep." That was when Rahman, now 36, was an undergraduate with an interest in cardiovascular medicine. His summer in Toronto led to a second summer as a research associate at the same lab and then work at another Toronto lab with the same mentor as he achieved his doctorate degree.