This Is Your Brain on Sex (18 page)

“Physical attraction, in both men and women, is a big thing. It’s a pretty consistent finding in research studies,” said Cooper. “But there is a ton of variation in what people find physically attractive. People just have different tastes in what they like.”

Even the ancient Greeks knew beauty was in the eye of the beholder. Neuroscience
hasn’t offered us anything more astute than that in the centuries since. People like what they like—cute butts, smoldering eyes, sculpted arms—and what they appreciate in one potential mate may not be so attractive in another. As Cooper said, it’s a tough thing to parse out.

I asked Cooper about the challenges of studying attraction from a neuroscientific perspective. “It’s hard,” he told me. “Social situations are complicated and heterogeneous. There is a lot of variation anytime you make a decision. There’s even more when you involve another person in that decision. You see the same thing in speed dating. Even among the people you match with, you aren’t going to feel the same about all of them. You may say yes to different people for very different reasons.

“It’s a complex situation with a lot of stuff going on,” he continued. “Clearly, the things we have to lump together as ‘interpersonal attraction’ in our work are not always the same things.”

“So is it worth studying? Can we learn anything of value about attraction?” I asked.

“Yes, we can. I think it’s very interesting to know you are using a lot of the same systems in making a decision about a dating partner as you would in an economic game,” he said. “Deciding whether to share five dollars with another person in an economic game overlaps quite a bit at both the computational and neural levels with a person saying, ‘Hey, do you want to go out sometime?’ That’s an interesting thing to learn about humans.”

“So attraction is mostly about weighing a bunch of different variables and calculating some output?”

Cooper laughed and tapped his head. “It’s all numbers up here at some point.”

“Wow, that’s so romantic!” I replied sarcastically.

“I think it’s also important to know that attraction is highly context-dependent, and it’s very fast,” he said. “You don’t receive any kind of social message in a vacuum. You always receive it against the backdrop of who is giving it to you and what you think or feel about them. And we manage to pull out all the information we need and then make our decisions very, very quickly. Like I said, it’s complicated.”

I believe him; it is complicated. But even if neuroscience research can’t offer me a surefire pheromone or a list of qualities I should seek in a hot date, it has demonstrated that
attraction is rewarding, fast, and a little bit different in each and every situation. Knowing, as they say, is half the battle.

“So do you have any advice for the lovelorn? Those who might look to your research and hope for some kind of guidance on how to better attract a mate?”

“Not really,” Cooper said. “Except maybe meet more people.”

“You mean, get a bigger sample size?”

“Yes, up your
N.
” He laughed. In statistics,
N
represents sample size. “I don’t feel like that’s a terribly psychologically inspired answer. But with so much complexity, it certainly can’t hurt to get out and meet more people.”

Chapter 8

Making Love Last

Monogamy is rare in the animal
kingdom; it is estimated that only about 3 percent of mammalian species are monogamous.
¹
Humans fall into that small and exclusive category. We have the ability to form strong, lasting emotional bonds with others—bonds that may even last a lifetime.

Helen Fisher believes love is a drive: the drive to find a preferred mate. The human ideal goes further than this utilitarian way of thinking. According to the common marriage vows, we want someone “to have and to hold.” We want to meet the person who will inspire us to “forsake all others.” We want to promise ourselves to that special someone “until death does us part.” You get the idea. Finding love is not enough; we want our love to last. Which, when you consider the matter, is the tricky bit.

Most of us have fallen in love at least a few times in our lives. And not all of us have managed to hang on to that love. Attraction does not guarantee an attachment. Similarly, an attachment does not guarantee a lifelong bond. Several relationship books have come out in the past few years arguing that a better understanding of the body’s natural neurochemistry can help solidify a monogamous bond with another person. The premise in these tomes is fairly simple: Understand the brain and you’ll understand what it takes to maintain a relationship. They even offer supplements that supposedly provide optimal brain chemistry, whatever that is, and techniques for easy communication to help you in that endeavor. But can neuroscience really present us with any infor
mation about what it takes to transform mutual attraction into a loving bond? Can understanding the brain really help us maintain that bond over time?

Monogamy, Vole Style

Remember our friends, the prairie voles? Oh, cute, cuddly
Microtus ochrogaster
. At first glance, you might not think the prairie vole has much to tell us about making love last. This small rodent seems more likely to elicit a squeal from a nine-year-old girl than provide any insight on lasting monogamous relationships. But this species, along with its close cousins, the montane vole (
Microtus montanus
) and meadow vole (
Microtus pennsylvanicus
), have offered scientists a good look into the chemicals in the brain that may underlie an exclusive bond.

Prairie voles are a monogamous species. The risks inherent in prairie living, with limited food and dangerous predators, make it logical to pair up at an early age and stay bonded for life. It is all the more important, out in the wild, to have someone help gather grub and look after the little ones. Prairie voles make pair-bonds immediately after sexual maturity—in fact after a single sexual encounter. It is just your old-fashioned boy-meets-girl, boy-copulates-with-girl-over-a-twenty-four-hour-period, boy-and-girl-live-happily-ever-after type of tale.

In contrast, the montane and meadow voles are the player types. These species of voles, unlike their prairie cousins, live in places with more food and more cover, making it less important to have a second around. Neither of these species forms lasting attachments; rather both males and females have a love-the-one-you’re-with mentality. Except they don’t really love, more just mate with whoever happens to be nearby and available. Montane and meadow voles are asocial; they do not crave close, personal contact the way prairie voles do. These animals spend only about 5 percent of their time with others. More to the point, they cannot get away quickly enough after mating. Are you familiar with the phrase “coyote ugly,” the feeling you get when you wake up after a night of debauchery to find an ugly stranger in bed and are then compelled to gnaw your own arm off to escape undetected? I think there might be some merit in petitioning
to change the name to “montane ugly.” (Although “meadow ugly” would also apply in this instance, it does not have quite the same ring to it.)

So what might account for these vast differences in mating behaviors in such close species? It all seems to be related to oxytocin and vasopressin. Oxytocin, as discussed in chapter 3, is a hormone produced in the hypothalamus that plays a big part in facilitating labor, birth, and breastfeeding in women. This compound also works as a neurotransmitter, helping to send chemical messages between neurons. It received its nickname, the “cuddle chemical,” because of its role in love, pair-bonding, and orgasm. Vasopressin, which is synthesized in the hypothalamus, has multiple responsibilities in the body, including regulating blood pressure and the retention of water. It also works as a neurotransmitter and has been linked to the formation of memories, aggression, and pair-bonding. Here’s how oxytocin and vasopressin work their magic on the mating habits of our friends, the prairie voles.

Both male and female prairie voles have a high density of oxytocin receptors, the nucleus accumbens in the brain, making them more social and more likely to prefer a mate than a stranger. Several studies have shown that the more receptors there are in this area, the more friendly an animal will be. Scientists hypothesize that when oxytocin binds with these receptors, it lets loose a flood of dopamine, the “feel good” neurotransmitter that strengthens social relationships. Think of it this way: Sex feels pretty good—very good, when you do it right. When you have sex with your pair-bonded partner, additional dopamine is released through this oxytocin system. And that added dopamine gives the sex that little extra oomph that makes you want to go back to that same partner for more. And more. And probably a little more after that. Some social scientists believe that the reason women are more likely to fall in love with a man they have had sex with—as opposed to one they have just spent time with—is due to this oxytocin-induced dopamine rush.

After prairie voles have mated for twenty-four hours, this extra dopamine causes physical changes to the brain: now sex with anyone else will not be as pleasurable. In fact scientists have observed that the approach of another member of the opposite sex may even cue aggressive behavior. After this first mating happens, prairie voles have no reason to go out for a hamburger
when they have steak at home, prepared just the way they like it.
²

An autoradiogram of the male prairie vole brain. The dark areas highlight the density of vasopressin receptors in the ventral pallidum (the two dark areas toward the bottom).
Photo by Sara M. Freeman, Emory University.

An autoradiogram of the male prairie vole brain. The C-shaped black areas show the density of oxytocin receptors in the nucleus accumbens region.
Photo by Sara M. Freeman, Emory University.

Prairie voles have a double whammy of chemicals to help them remain monogamous. Along with oxytocin, vasopressin plays a big role in making vole love last, particularly in males. The boys have vasopressin receptors on the
ventral pallidum, which also triggers a dopamine storm (and, in turn, strengthens pair-bonds in much the same way that oxytocin does, with the chemical incentive to mate with the familiar partner). Both the ventral pallidum and the nucleus accumbens are part of the reward processing pathway and have been implicated in the human brain when it comes to love and attachment.

It may not sound romantic, but researchers hypothesize that prairie vole monogamy can be chalked up to simple conditioning. Prairie voles mate, the neurochemicals oxytocin and vasopressin are released, they bind to receptors on the reward pathway, and that spectacular dopamine flood takes place. Every time a male prairie vole has sex with his pair-bonded partner, he is getting not one but two extra doses of sugar. With that kind of reward, why would he look elsewhere for love?

But prairie voles’ close cousins, the montane and meadow voles, are lacking the density of vasopressin receptors in the ventral pallidum; therefore they do not experience that extra push of dopamine during sex with a particular partner. Without that dopamine, there is no pull for these voles to return to the same female. The only reward is the sex itself—and a montane or meadow vole does not need a specific female for that.