Something was wrong with Yamini Karanam. The PhD student had moved from Hyderabad, India, to Indiana to study computer science. But her new life in America was amiss. Once a brilliant student, she now had trouble understanding simple articles. Friends and colleagues would say things to her, only for the sentences to get mixed up in her mind. Because that’s where Karanam’s problem lay: deep within her brain. She went on holiday last fall but returned even more exhausted than when she left. Karanam slept for two weeks straight, missing school. “Then came the headaches. Slips and misses at work...