Scientists at University College London led by Andreas Bartels recently peered inside the heads of love-obsessed college students. They took 17 young people who claimed to be in love, stuck each of them in an MRI machine, and showed them pictures of their lovers. Blood flow increased to very specific areas of the brain's pleasure center-including some of the same areas that are stimulated when people engage in addictive behaviors. Some of these same areas are also active during sexual arousal, though romantic love and sexual arousal are clearly different: Sex has more to do with hormones like testosterone, which, when given to both men and women, increases sex drive and sexual fantasies. Testosterone, however, doesn't necessarily make people fall in love with, or become attached to, the object of their attraction.