This Is Your Brain on Sex (36 page)

Later I talked to Rupp, the researcher who created the stimulus set for the study. When I mentioned that the boy photos did not really do it for me, she laughed. “I remember when I was choosing
those pictures I felt like I was some old lady picking out boy porn,” she said. “These guys are definitely meant for the younger women. I mean, at the very least they won’t look like boys to them.”

Later I met up with Julia Heiman, director of the Kinsey Institute and a coauthor with Rupp and James on these studies, and she asked what I thought of the stimuli. As I had been honest with everyone else about it, I brought up the stupid hair again. But after having a few hours to think about my experience in the magnet, I felt obligated to try to justify my lack of interest. “I’m in the middle of a divorce right now,” I told her. “I have a feeling my optimal rewarding stimulus is going to remain a steak and a glass of red wine until it’s done.”

She laughed. “That raises an important point. I don’t think how you responded today is how you’ll respond forever. It would be interesting to measure your response today and then again in a year. Who knows, after that much time, you may be in a new relationship or playing the field. You may even kind of like those guys with the stupid hair.”

While Heiman was obviously trying to make me feel better, what she said made me think. Rupp was careful to say that we have a lot of assumptions about sexual decision making. Could it change over time? She and her colleagues have tested women between eighteen and twenty-three. What if the group looked at younger women? Older women? It’s possible our tastes change with time—and our decisions too. It’s also unknown whether those decisions are correlated with hormonal states, which can fluctuate with both age and context. It’s clear that the brain is always changing, with every new thing we learn, with every relationship we have. But we know little about how that occurs, and how it may be mediated by hormone levels, across the life span. Perhaps those “bad boys,” if we can even call them that, are interesting only when we are young.

It is also noteworthy that these kinds of studies have looked only at women’s sexual decision making. What might we see if we studied men? Might their sexual decision making show different effects at different ages? Will they have issues with a woman’s hair? Is the poor decision making mediated by attractive women seen only when men are young and virile?

The answer to all of these questions
is that we just don’t know. Despite those fun headlines, most of these studies offer up a lot more questions than answers. And as for my own lack of appreciation for the bad boys, I can only take Heiman’s advice and suggest that you ask me about them again in a year. Another birthday or a sexy romp with a new fella might make me come to appreciate the stupid hair.

Chapter 15

There’s a Thin Line between Love and Hate

What do a new mother and a soldier have in common
? It almost sounds like a joke, one with a variety of different punch lines, which, in all likelihood, would not be very funny. But as it turns out, both soldiers and mothers exhibit what some call a “tend and defend” response when it comes to protecting their own: their kids or their fellow soldiers. A recent study suggests that this response is linked to oxytocin. Work with animal models has long suggested that oxytocin not only promotes a bond; it can incite a certain type of aggression too.

“Oxytocin helps with the bond, but it doesn’t only bring love,” explained Kerstin Uvnäs-Moberg, the Swedish oxytocin expert and one of the co-organizers of the first neurobiology of love meeting. “New mothers are very defensive, extra protective of their child against their surroundings. So is a man in love. He can be jealous and aggressive. There is a shift in feeling that is extra pleasing and calming, yes, but there seems to be a shift also in how and what we may perceive as threatening when we have made that bond.”

You can see just how aggressive a little love can make us by looking at newly bonded prairie voles. When researchers conduct partner preference tests with the prairie voles, in which a bonded animal is placed in a Plexiglas cage with its mate and a stranger of the opposite sex after a separation, it doesn’t take long for the bonded animals to get aggressive with the interloper. A pair-bonded male will fight another male to the death for his mate. Females, though not quite as aggressive, are also pretty territorial.

“Female prairie voles will not share their
mate with another unfamiliar female,” Sue Carter, that pioneering oxytocin researcher from the University of Illinois at Chicago, said. “We discovered that if you put two unrelated females and one male together, the male would mate with both. However, after mating and by the time the babies were born, there was only one female left. One female died. We could not tell the cause of death, because in most cases there was no obvious fighting. However, we could predict which of the females would die because the one who would live was always sitting between her and the male, apparently guarding the male. We could predict who would survive with a lot of certainty because that female would continually reposition herself so the other female just couldn’t get near the male. It was quite frightening to realize that prairie voles could be ‘stressed to death,’ presumably by being ostracized. We stopped doing these experiments once we realized that one of those females was always going to die if we left them in this kind of situation.”

Ouch. Love, as they say, is fierce. Both in romantic and maternal bonds, along with the union come increased levels of stress and aggression. Carsten De Dreu, a researcher at the University of Amsterdam, wanted to see what role oxytocin might play in that enhanced aggression—and whether it might transcend a love connection and explain in-group affiliation and out-group aggression as you see in wars and other types of human conflict. More specifically, De Dreu hypothesized that oxytocin modulates what he calls “parochial altruism,” or trust and self-sacrifice in order to benefit the in-group with aggression to defend against and attack the out-group.

Parochial Altruism

De Dreu and his colleagues recruited men to participate in a variant of the so-called Prisoner’s Dilemma. In the classic version of this task, two suspects in a crime are offered options for a deal. They are instructed that if one gives up his partner and agrees to testify against him, he will go free while his accomplice receives the full sentence—say, ten years. If both betray each other, then they will both get reduced sentences of five years. If both manage to stay quiet, they will get a veritable slap on the wrist—only six months on a lesser charge. Each must decide
whether to rat out the other suspect or stay quiet. If the suspects are thinking about the group and not just themselves (and trust that their partner will also do the same), the choice is easy: stay quiet. Doing so means both partners will receive the least punishment. Despite this, most individuals simply give up their partner. Fairly quickly too; in individual economic terms, doing so makes the most sense.

In De Dreu’s study, participants were randomly assigned to one of two three-person groups. This variation on the original Prisoner’s Dilemma involved money. Each individual was given ten euros. Participants could then decide to share that money within their own group or between the two groups. If the participant kept the money for himself, each euro was worth exactly that: one euro. If the participant gave a euro to the within-group pool, an extra fifty euro cents would be added to each in-group member—so basically the euro was now worth 1.50. The participants had another option: giving to the between-group pool. If they did that, they not only gave each of their own group an extra fifty euro cents but took away fifty euro cents from each member of the opposing group.

I know it sounds complicated, but by looking at where each participant put his money, the researchers could gauge in-group trust and out-group aggression. For example, contributing to the within-group pool yields the highest benefit to the whole group, representing that in-group love. Contributing to the between-group pool hit the out-group where it hurts, taking away their money while still offering some benefit to the in-group. If the participant decided to keep his money for himself, that suggested he did not identify with his group at all; he was only looking out for himself. Participants snorted some oxytocin or a placebo (they were unaware which they were getting) before sitting down to play the game.
¹

De Dreu and his colleagues found that oxytocin amplified in-group love. That is, participants were more likely to contribute to the within-group pool if they had received a sniff of the neuropeptide instead of the placebo before making their decisions. Oxytocin, however, did not change how they contributed to the between-group pool. It would seem oxytocin did not increase or decrease the desire to stick it to the out-group, just to contribute to the overall common good of the in-group.

Furthermore, when participants were asked, after they made their
allotments, what they thought their fellow group members had done, the researchers found that those who had sniffed oxytocin estimated that the others gave amounts much higher than the estimates of those who hadn’t received the neuropeptide. There was no difference in making judgments about the out-group. This, the researchers suggest, means the oxytocin also increased trust within the group.

Oxytocin administration did not result in any all-out hate or aggression toward the out-group. Would it help foster a defensive state, as seen in mothers and newly bonded animals? To test the idea, De Dreu ran a follow-up experiment. These participants performed the same task, but were also offered an option to cooperate with a member of the out-group to promote intergroup giving—something that would benefit everyone, not just one’s own group. Individuals on oxytocin were much less likely to cooperate with a member of the other group, citing a need to protect the in-group. It would seem that oxytocin does not promote aggression to attack, but does promote aggression to defend a bond from a potential threat.

De Dreu’s study tested only men. Makes you wonder if you would see the same thing in women, doesn’t it? My gut says yes, and any woman who has ever been ostracized by a “mean girl” clique knows what I’m talking about. De Dreu does not have an answer. He claims in the study write-up that “violent intergroup conflict more often involves males rather than females,” so the experiments pertain to the more relevant sex. I’m not so sure. Female prairie voles, it should be noted, are also more aggressive after a pair-bond. Perhaps different situations affect men and women in different ways. In any case I contend that more research needs to be done to see just how separate men and women might be in this respect.

It is clear that oxytocin plays a role in certain types of aggression as well as love and pair-bonds. De Dreu believes this work illustrates oxytocin’s role in soldiers’ ability to work cohesively as a unit against a common hated enemy. Can economic games really tell us about that thin line between love and hate in a more personal context? Though De Dreu’s study illustrates oxytocin’s reach (not to mention its subtlety) and how it might influence both cohesion and defensiveness in certain types of social interaction, it does not tell us much about the neurobiology
of hate. It also does not include all of the other chemicals that may be mediating these effects.

“There is no behavior that is just a mechanism of oxytocin or vasopressin or whatever chemical you have alone,” said Craig Ferris, the aggression researcher from Northeastern University. “The question I always ask is what else is released, what else might the oxytocin be interacting with here. And I venture to guess there are fifty different things released, if not more.”

Neuropeptides are team players—they don’t work alone. Ferris was quick to point out that all aggression is context-dependent, which is going to affect which chemicals are released and, by extension, what kind of brain activation occurs. It is not all about the oxytocin. It’s just not that simple.

Neural Correlates of Hate

What about brain regions? If there is a thin line between love and hate, whether defined by aggression or a more subjective emotional state, shouldn’t we see it in analogous brain activation? As a follow-up study to his work on love, Semir Zeki of University College London decided to use fMRI to look at the brain regions underlying hate. He predicted that there might be some similarity between these two states that could be reflected in neuroimaging results.

“Both love and hate are strong biological sentiments,” he explained. “They are both motivating factors too, that may push people to do great things and sometimes push people to do very evil things. They both can be all-consuming. Hate usually has a negative connotation in people’s minds, but it’s actually a biological phenomenon that serves to keep people together and to achieve things against others. It is just as worthy of study as love.”

When I asked Zeki if he thinks hate is a drive—as many researchers have asserted—he said, yes, it is possible that it falls into the same category. “I think it is a negative drive, but it’s a drive that can help a person achieve things, some of which can be quite useful and others which can be quite harmful. I think you can be driven by hate to pursue lines that are to the detriment of others, but you can also be driven to
pursue lines that are to the benefit of oneself and to others.”