On a recent Wednesday night, Eleanor Phipp spent an hour watching commercial television. Nothing unusual about that — except that Phipp, 30, was in a dark room at a south London medical center, lying inside a loudly whirring Functional Magnetic Resonance Imaging (FMRI) scanner that mapped her brain as video images flickered before her eyes. Brain scanners — which use radio waves and a powerful magnetic field to trace oxygenated blood to areas of neural activity — are mainly used to study or diagnose brain diseases. But Phipp's brain was being scrutinized for decidedly nonmedical reasons. Researchers were monitoring how it...