"Can I hear you say no ifs, ands or buts?" says Dr. Allan Ropper, the Harvard neurologist in charge. The patient tries again. "No ifs, buts, ands or," he says.

Ropper's heard enough. "I think he's probably had a little left temporal, maybe angular gyrus-area stroke," he tells the students and doctors, once they're assembled outside the patient's room. A brain scan confirms his diagnosis.