The Science of Sex is a column from Broadly exploring the tech behind the complicated and fantastic ways we get off—b__ecause sex is sexy, but science is sexier.

Vanessa* swore off casual sex after an incident at a friend's bachelorette party. She had arranged a Tinder hook-up at 2 AM "while drinking through a penis-shaped straw," eventually meeting up with the guy for some sex she characterizes as just "OK." The sex partner was even less impressive: "I loathed him and everything he stood for with every fiber of my being," she says.


Still, she found herself enthralled with him afterward. "Every fiber of my being was screaming, Never let him go," she says. "It was a head fuck."

It's an all-too-familiar situation for many people: You decide to have sex with someone whose personality you find repugnant, whom you have no interest in dating, only to find yourself bizarrely attached to them in the morning.

"I always want to date people I have sex with," says 25-year-old Lucy, "even if I hate them."

Romantic attachment works in mysterious ways; it's thought to be the result of a complex cocktail of hormones, neurobiological processes, and social conditioning. While many parts of human cognition remain a total enigma, scientists have isolated a few hormones and brain structures that may be responsible for those insane texts you sent the other night.

Much of what we've come to know about love is through prairie voles. The rodents are beloved among scientists attempting to elucidate the mysteries of human love: Unlike 97 percent of mammals, they're monogamous, and vole couples form extremely strong attachments to one another. Given a choice, the animals—which hail from the woodlands of Europe and Asia—will choose to hang out with their partners exclusively, groom each other, and eventually nest together. In studies, researchers isolated two hormones responsible for these enduring bonds: oxytocin and vasopressin, both of which are released during prairie vole sex.


Tests show that when male voles are given a dose of vasopressin—or females of oxytocin—the animals bond on sight with the nearest potential mate, before mating even occurs. For male and female prairie voles, researchers have thus concluded, vasopressin and oxytocin are the magic ingredients for lifelong monogamy, binding the two together, until death do them part.

I always want to date people I have sex with, even if I hate them.

"Male voles produce vasopressin," explains Larry Young, a researcher at Emory University whose research specializes in the social behavior of prairie voles. "The vasopressin system stimulates territorial behavior. It's more of a possessive bond." Studies have shown that when male prairie voles are injected with a chemical that prevents the release of vasopressin, they fail to bond with their female mates.

Meanwhile, female voles depend more on oxytocin (although males release the hormone also). Produced in the hypothalamus, oxytocin is profoundly linked to a range of social behaviors, including maternal bonding, attachment forming, and reading and recognizing social cues. In female voles, oxytocin combines with dopamine to create a strong sense of attachment.

"There's a cocktail of chemicals going on in the [female vole's] brain, and one of them is oxytocin," Young explains. "It makes the brain absorb the social cues of the sexual partner—things like their face, their smell, how they sound." When the voles mate, a part of their brain called the nucleus accumbens makes a connection between the social cues the oxytocin causes them to observe and the sense of pleasure occasioned by a massive dump of dopamine (the pleasure hormone) in their brains.


As dopamine and oxytocin are linked in the brains of the prairie voles post-sex, attachment grows. "It's where the bonding comes from," explains Young. "It takes place in the part of your brain that's involved with addiction, as well."

Prairie voles. Image via Wikipedia.

The human brain, too, contains both oxytocin and vasopressin receptors. And, like prairie voles, humans release massive amounts of oxytocin during sex. Dr. Young explains that breast and cervical stimulation during sex are known to release large amounts of oxytocin into the female brain, which is compounded by a further oxytocin dump post-orgasm. Research from Dr. Helen Fisher of Indiana University has shown that, when you scan the brains of people in love, they exhibit activity in the parts that produce and distribute dopamine—the same regions that become active when you take cocaine.

Young postulates that romantic attachment is an evolutionary hang-up geared to encourage us to pair bond and thus ensure our offspring have the best possible chance of survival. "Human offspring take so long to develop—the mother is nursing the baby for years. Historically, it was beneficial for sexual partners to develop a bond so they could work together to raise healthy offspring," he concludes.

But can this bond be prevented? Since oxytocin and vasopressin are thought to create annoying post-sex attachments, is it possible to manipulate these hormones in order to avoid copious drunk crying after your most recent one-night stand? Dr. Young says it's feasible.


The first step in controlling love hormones, according to him, is avoiding eye contact—it's known that prolonged eye contact increases oxytocin release in the brain. "When you're having sex with someone," Young explains, "you're making an intimate connection with their face and eyes particularly. This is going into your brain, and it's inherently rewarding. Love and attachment are very much like addiction. They have a lot of the same chemicals. So if you can divert that information from coming in by not having that eye contact, that will help."

Read more: Why More Women Are Having Sex on Drugs

On the subject of addiction, it could be helpful to have sex on drugs if you're looking to avoid an emotional bond. "Cocaine and methamphetamine increase dopamine secretion, and dopamine is what is involved in creating pair bonds in the first place. If you exogenously increase this dopamine prior to an intimate moment, then it won't have the same impact later," Young explains. "The specialness of the sex, and the differential caused by the dopamine release won't be so high." In other words, if you get high before getting it on, you'll be less likely to associate the attachment-forming rush of oxytocin with your sex partner.

A caveat: While drugs might be useful in cultivating intentional heartlessness, alcohol may have the reverse effect on women. "When male voles drink alcohol they become promiscuous and it prevents them from bonding," Young says, citing a study he's currently running in which male voles are given alcohol and then allowed to mate with a female. "Normally, if the male vole mated with a female, the next day when we put him in a three-chambered cage containing three female voles, he'll opt to sit with the vole he previously mated with." However, if the male vole was drunk at the time of mating, he'll choose not to sit with a female vole he's already fucked. "He'll prefer the novel females."


Sadly, the same doesn't apply for female voles. "When females drink alcohol, it increases the likelihood they will bond prematurely."

Another way to prevent the intimate association between your fuck buddy and the heightened activity in your brain's reward center is to consciously focus your thoughts on another person during sex. "You're forcing your brain to associate the pleasure you're feeling with someone else," Young explains. "It could be a movie star or someone you're never going to really see. By doing that, you divert the brain's attention onto someone that's not there." This prevents the brain from bonding with the person you're actually having sex with—you're not absorbing the visual cues that are vital to oxytocin release.

When females drink alcohol, it increases the likelihood they will bond prematurely.

Young also suggests avoiding nipple play. Well, OK, he didn't exactly say that—I paraphrase. Here's what he actually said: "Humans are the only species where men have adopted the strategy of breast stimulation during sex to stimulate oxytocin release. The breast has become in humans a point of sexual attraction and foreplay. It's a way to activate the oxytocin system, coaxing the female's brain to become attached to the sexual partner." (Women are conditioned to release oxytocin in response to nipple stimulation; it's how we nurse our babies.)

If you've done all these things and you're still finding yourself inexplicably devoted to the mysterious human lying next to you, don't fret. Sex therapist Nan Wise urges you to remember that we really are, in the words of the Bloodhound Gang, nothing but mammals.

"Those feelings towards a person are a natural, wired-in mammalian reaction. It's like a drug, that sense of infatuation. But you can learn to manage it," says Wise. "Don't regard it as terribly significant. The feelings aren't coming from that person [you've just slept with]; rather, they're coming from your reaction to the stimulation."