Leave it to science to take all the fun out of something as cosmically pure as love.

Theories about love’s purpose range from the biologically practical to the biologically complicated. Anthropologists have said it helps ensure reproduction of the species; attachment theorists maintain it’s a byproduct of our relationship with our childhood caregivers. And now researchers are exploring what happens physiologically as a romantic relationship progresses.

The more we understand it, they say, the better our chances of making love last and of harnessing its potential to improve our emotional and physical well-being.

Whatever its reason, there can be little doubt -- even from a scientific standpoint -- about the potent feelings that being in love elicits.

Arthur Aron, a social psychologist at Stony Brook University in New York, has done brain scans on people newly in love and found that after that first magical meeting or perfect first date, a complex system in the brain is activated that is essentially “the same thing that happens when a person takes cocaine.”

In one such study, published in 2005, Aron recruited 10 women and seven men who had fallen in love within the last one to 17 months. After taking a brief survey about the relationship (items included statements such as “I melt when looking deeply into ____’s eyes”), participants were put in MRI machines and shown pictures of their beloved, interspersed with pictures of neutral acquaintances. When participants viewed images of their partners, their brains’ ventral tegmental area, which houses the reward and motivation systems, was flooded with the chemical dopamine.

“Dopamine is released when you’re doing something [highly] pleasurable,” like having sex, doing drugs or eating chocolate, says Larry J. Young, a psychiatry professor at the Yerkes National Primate Research Center at Atlanta’s Emory University. Activation of this part of the brain is primarily responsible for causing the sometimes bizarre behavior of new couples, which is linked to motivation and achieving goals: excessive energy, losing sleep, euphoric feelings and, occasionally, anxiety and obsession when they’re separated from their objet d’amour.

According to Helen Fisher, a biological anthropologist and author of “Why Him? Why Her?,” the smitten party is acting out of a motivation to “win life’s greatest prize -- a mating partner for life.”

Bonding

After the dopamine surge, research suggests that two key hormones -- oxytocin and vasopressin -- enter the picture, encouraging couples to form emotional bonds.

Oxytocin is released in humans during intimate moments such as prolonged eye contact, hugging and sex. It’s also the hormone that causes mothers to bond with their infants. And having been proved to be involved in long-term bonding in prairie voles and, most recently, marmosets, researchers speculate that it plays the same role in humans.

Vasopressin -- also linked to bonding in prairie voles -- has similarly been linked to bonding in men. A 2008 study showed that a certain genetic variation of a vasopressin receptor was correlated with marital infidelity and fear of commitment.

All the chemicals and hormones released in new love help ensure that we mate and stay together long enough to reproduce or form partnerships for the long term. But once they’ve subsided, what happens?

Until recently, researchers assumed that most couples eventually settle into what’s called companionate love: relationships that are more intimate, more committed -- and much less thrilling.

A recent study, however, proved this theory (and years of marriage sitcoms) wrong. Bianca Acevedo, postdoctoral researcher at UC Santa Barbara, looked at brain scans of couples claiming to be madly in love after 20 years of marriage. She and her colleagues found that these fortunate folks had the same neural activity observed in newly in love couples, only without the anxiety or obsession.

Acevedo also discovered something that surprised even her: Based on preliminary surveys, this kind of lasting love appears to be present in approximately 30% of married couples in the U.S.

That doesn’t mean, though, that those of us who don’t fall squarely into that group should throw in the towel. Researchers believe that we have a lot to learn from these happy couples, if only we’re willing to do so.

To begin with, a great deal of research shows that doing novel, exciting things together boosts marital happiness. “Take a class together that you know nothing about,” suggests Aron, who has co-written several studies in this area. “See a play, go to a new location, go to a horse race.” The release of dopamine during these activities might remind couples of how it felt to fall in love or even be happily misattributed to the experience of being together.

The love upper

Also, says Acevedo, be thoughtful with your partner.

“We know that things like celebrating the positive is important for a relationship’s well-being, as well as being supportive when [our partners] need us,” she says. Couples that took part in Acevedo’s study also resolved conflict smoothly and quickly, were affectionate and communicated openly with their partners, and spent time bettering themselves as well as the relationship.

“And sex!” she adds. “Sex is always good.”

These types of intimate, loving interactions between couples are all linked, Acevedo says, to bonding hormones. “There’s a connection between being engaged in the relationship -- especially affection, disclosure and intimacy -- and oxytocin.” In fact, in one study, couples that had been administered the hormone were better able to calmly mediate conflict and to empathize with a partner.

Thomas Bradbury, a psychology professor at UCLA and co-director of the university’s Relationship Institute, says that making beneficial relationship changes isn’t as difficult as they may seem.

People -- often men, he says -- “think it’s harder than it really is.” But the basic idea is simple: to listen and respond in a way that is supportive. “When your partner says, ‘I had a funny dream last night,’ you say, ‘Tell me about it,’ ” he says. Or, instead of suggesting that your partner quit his or her job because of a difficult boss, he adds, empathize with their struggle. Saying something as straightforward as, “That must be hard when your boss criticizes you,” can make all the difference.

As cozy and warm as coupledom feels, its benefits extend even further. Healthy, happy marriages have long been linked to lower mortality rates and better immune functioning and, most recently, lower stress. In satisfied couples, says Acevedo, oxytocin and vasopressin have been shown to activate parts of the brain that are associated with calm, and even pain suppression.

“The way that we interpret those findings,” she says, “is that the quality of our relationship bonds has implications for our health.”

Most research in the field of love has been done with married, heterosexual couples. Acevedo suggests, however, that couples that have been living together for a long time but are not married may have comparable experiences. “If they’re living together and almost like marriages, I would predict that they’re highly similar to the married individuals.”

Brain chemistry may not be foremost on most people’s minds when they meet someone new or schedule a date night with their long-term partner. But keeping the spark alive is more than just fun -- it may be vital. And even for those of us who aren’t in love right now, the knowledge may prove useful in the future. After all, says Aron, "[just about] everyone falls in love.”

health@latimes.com