In the initial love study at SUNY-Stony Brook, 10 women and 7 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.

Emory's Young noted in the Nature paper that both Prozac, an antidepressant, and Viagra, an erection enhancer, appear to affect the oxytocin system, though it's not yet known whether such drugs affect relationships by changing brain chemistry.

In fact, a study published this year in Biological Psychiatry supports that idea, showing that oxytocin may help human couples get along better. Swiss researchers gave 47 couples a nasal spray containing either oxytocin or a placebo. The couples then participated in a videotaped "conflict" discussion. Those that got oxytocin exhibited more positive and less negative behavior than those given the placebo. Oxytocin was also linked to lower secretion of cortisol, a stress hormone.

And it's conceivable that, as Emory University neurobiologist Larry J. Young pointed out in the journal Nature earlier this year, once scientists understand the chemistry of love, drugs to manipulate the process "may not be far away."

But they do have a plausible hypothesis: that dopamine plays a big role in the excitement of love, and oxytocin is key for the calmer experience of attachment. Granted, the data are preliminary. But the findings so far are provocative.

It's way too soon - and hopefully, always will be - to say that brain scientists have translated all those warm and fuzzy feelings we call romantic love into a bunch of chemicals and electrical signals in the brain.

In the same lab, older volunteers who claimed to still be intensely in love after two decades of marriage participated in the same experiment. The same brain areas lit up, showing that, at least in some lucky couples, that honeymoon feeling can last. But in these folks, other areas lit up, too -- those rich in oxytocin, the "cuddling" chemical that helps new mothers make milk and bond with their babies, is secreted by both sexes during orgasm, and that, in animals, has been linked to monogamy and long-term attachment.

At a university in Stony Brook, N.Y., a handful of young people who had just fallen madly in love volunteered to have their brains scanned to see what areas were active when they looked at a picture of their sweetheart. The brain areas that "lit up" were precisely those known to be rich in a powerful "feel good" chemical, dopamine -- the substance that brain cells release in response to cocaine and nicotine. Dopamine is the key chemical in the brain's "reward system," a network of cells associated with pleasure -- and addiction.

For centuries, love has been celebrated - and probed - mostly by poets, artists, and balladeers. But now, its mysteries are also yielding to the tools of science, including modern brain scanning machines.

One dopamine-rich region in particular consistently lit up when these lovebirds viewed 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 coauthor 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."

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 this year and last, Bianca Acevedo, formerly at Stony Brook and now a post-doctoral fellow at the University of California-Santa Barbara, focused on 10 women and 7 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 lit up. "But in contrast to those newly in love," says Acevedo, 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 in Chicago.

Carter's work has centered on prairie voles, known for their enduring bonds. Compared with other rodents, prairie voles -- among the only 3 percent 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.

Other researchers have shown that when mice (not known for their monogamous ways) are injected with a gene containing instructions for making the receptor for oxytocin, the mice cozy up to their mates like voles.

Lack of oxytocin is important, too. For instance, if female animals are stressed by being isolated, their oxytocin drops. In humans, Emory University research shows that women who were seriously abused as children have low oxytocin levels as adults.

One question emerging from all this is whether knowing the chemistry of love can help in picking a compatible partner in the first place.

Fisher, the Rutgers anthropologist, who consults for the dating websites Match.com and Chemistry.com, thinks so.

She believes that certain personality types correspond to the preponderance and ratios of specific chemicals in the body; her team is now examining blood, urine, and saliva samples to test her theory.

In a study that involved 28,000 clients using the Chemistry.com dating site, Fisher built personality profiles based on people's answers to a long questionnaire, then sorted them into different "types" and followed their dating experiences to see which types were attracted to which other types.

Creative, risk-taking personalities, which she calls "explorers," may have more active dopamine systems, as well as more activity of another brain chemical, norepinephrine, she says. She found that "explorers" are drawn to other "explorers." People she calls "builders," conventional, calm, conscientious folks, may have more active serotonin and may also be drawn to other "builders."

By contrast, Hillary Clinton types - "directors" - who are analytical and tough-minded, may be high in testosterone and regularly drawn to their opposites, the "negotiators" like Bill Clinton, who may be fueled by estrogen and oxytocin, Fisher says.

Whether this love chemistry will pan out in the new research is still an open question. In the meantime, remember those prairie voles - they get what Fisher calls "life's greatest prize - an enduring mate and partner."

Judy Foreman can be reached at judyforeman@myhealthsense.com.

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