While they were both in the psychology department of Stony Brook University, Bianca Acevedo and Arthur Aron scanned the brains of long-married couples who described themselves as still "madly in love." Staring at a picture of a spouse lit up their reward centers as expected; the same happened with those newly in love (and also with cocaine users). But, in contrast to new sweethearts and cocaine addicts, long-married couples displayed calm in sites associated with fear and anxiety. Also, in the opiate-rich sites linked to pleasure and pain relief, and those affiliated with maternal love, the home fires glowed brightly.
The Brain on Love (NYT)