In the Nature paper, Emory's Young also noted that nobody knows yet whether drugs used to treat problems such as depression and sexual dysfunction can affect relationships by changing brain chemistry. But, he noted, both the antidepressant Prozac and the erection enhancer Viagra appear to affect the oxytocin system.
In the initial love study at Stony Brook, 10 women and seven men in intense, "early-stage" love were put into a functional MRI brain scanner, which can detect activity in specific parts of the brain. They were then shown pictures of their loved one or a neutral person.
In these lovebirds, one dopamine-rich region in particular -- the ventral tegmental area -- consistently lighted up upon viewing the loved one, but not the neutral person, according to the research, published in 2005. The intensity of the brain's response to falling in love, says co-author Lucy L. Brown, a neuroscientist at Albert Einstein College of Medicine, suggests that it "is not just an emotion but a drive, a real goal like food or water."
In a second experiment, the team found the same brain areas at work in people recently rejected by a loved one. Perhaps loss of love triggers the same kind of craving as withdrawal from cocaine or cigarettes, suggests Helen Fisher, a biological anthropologist at Rutgers University who also worked on the study.
In new data presented at scientific meetings in 2008 and 2009, Bianca Acevedo, now a post-doctoral fellow in social neuroscience at UC Santa Barbara but formerly at Stony Brook, focused on 10 women and seven men still in love after 21 years of marriage. Like the young lovers, when these volunteers were put in scanners and shown pictures of their partners, their dopamine-rich areas lighted up.
"But in contrast to those newly in love," Acevedo says, other brain regions did too, including areas rich in oxytocin, vasopressin (a similar chemical) and serotonin, a brain chemical associated with well-being and calmness.
The link between long-term attachment and oxytocin has long fascinated researchers, among them, Sue Carter, a neuroendocrinologist at the University of Illinois at Chicago.
Carter's work has centered on prairie voles, known for their enduring bonds. Compared with other rodents, prairie voles -- part of the only 3% of mammals that form monogamous bonds -- have more active oxytocin. Moreover, brain cells with receptors that specifically latch onto oxytocin lie in the very brain regions believed to be important in forming attachments, Carter says.
