This Is Your Brain on Sex (25 page)

Normal rats would have sex a few times, learn that it caused an icky feeling in their stomach, and stop trying to mate. In fact, Coolen told me, males will actually try to get as far away from females as they can after the association between sex and illness has been made. The animals with damaged PFCs, by contrast, continued trying to mate in spite of the illness-inducing injections. Though they were able to learn and showed normal associative memory in other tasks, this damage to the PFC made them unable to inhibit their sexual behavior even when it resulted in such a negative consequence.
¹⁰

When I asked Coolen what she thought the damage was doing to the reward circuitry, she admitted that she did not know. “It could be some kind of dysfunction in the connections in this circuit or even something that leads to the dysregulation of necessary neurotransmitters. We’re not sure,” she said. “But it’s clear that the prefrontal cortex is important for inhibitory control when it comes to compulsive sexual behavior.”

Risky Business

The mesocortical limbic circuit not only processes reward but also has a hand in weighing risk. Most of the studies looking at love or sex as an addiction examine the reward part of this model. But what about the risk? Might there be some change to this system, perhaps to the dopamine signaling in the circuit, that alters one’s ability to assess the risks involved with a particular behavior? It would seem so.

Any one neurotransmitter may have an arsenal of potential receptor types. Dopamine is no exception. This chemical’s D2 and D1 receptor subtypes have been linked to pair-bond formation and maintenance, respectively, in male prairie voles. However, they have also been linked to addiction. In rat studies stimulating the D2 receptor, the same receptor associated with the formation of a pair-bond, triggers relapse in addicted animals. D1 receptor stimulation, on the other
hand, inhibits those cocaine-seeking behaviors. D2 is linked to connecting with another animal or seeking a drug hit, looking for something to satisfy your longing, if you will. D1 is linked to males’ avoiding any female but the pair-bonded partner as well as steering clear of cocaine. Here perhaps the animal is satisfied and has no need to look for an outside stimulus, be it love or drug. Although there is still a lot of work to be done in this area, the overlaps are hard to ignore. Taken together these studies support the idea that drugs hijack the brain’s natural bonding systems, leading to addiction.
¹¹

Another type of dopamine receptor,
DRD4,
is also considered a receptor of interest when it comes to risky business.
DRD4
has been linked not only to a variety of sensation-seeking behaviors, but also to addiction. A particular polymorphism of the
DRD4
gene called the
DRD4
7R+, denoting seven or more repeats of this variant in the genetic code, is a gene of interest in the study of alcoholism, impulsive behavior, ADHD, and anorexia nervosa. It has also been linked to risky sexual behavior.

Of course, there is a lot of variation in sexual behavior. Some people want to get down and dirty at every opportunity; others can take sex or leave it. Some individuals appreciate novelty and a wide range of partners, and others allow themselves sex only within the context of a committed relationship. Given its association with riskier behaviors, Justin Garcia wondered if some of this diversity might be explained by the
DRD4
gene. Garcia is an evolutionary biologist at the Laboratory of Evolutionary Anthropology and Health at Binghamton University who studies love and sexual behavior. “This gene is important from an evolutionary standpoint,” he said. “It was likely selected for forty or fifty thousand years ago as humans started to push out of Africa and migrate to other parts of the world. It’s a gene that is implicated in novelty-seeking, a general sensation-seeking tendency. And it’s thought that it gave our ancestors the right kind of motivation to forge that valley and see what’s on the other side of the hill.”

Might it also be involved with motivations related to forging sexual hills? To find out, Garcia and his colleagues recruited 181 students (118 females and 63 males) to participate in a study. Participants were asked to fill out an extensive,
confidential questionnaire about their sexual experience, preferences, and behaviors as well as complete measures that looked at nicotine dependence and impulsive behaviors. The participants also provided a DNA sample by buccal wash; that is, they swished ten milliliters of mouthwash around in their mouth and then returned the used liquid to the researchers for genotyping.
¹²

When Garcia and his colleagues compared the genotype of participants, particularly whether they had the 7R+ variety of the
DRD4
gene (24 percent of the overall sample had this particular variation), with their sexual history, they made a few interesting discoveries. First, having 7R+ had no bearing on a person’s overall number of sexual partners; however, those with the 7R+ version of the gene did show a higher rate of promiscuity, or number of uncommitted “one-night stand” sexual experiences—nearly twice the rate of those who did not show the 7R+ variation. Though there was not a significantly higher rate of infidelity in the 7R+ group, those who did report being unfaithful had nearly twice the number of sexual partners outside the marriage.

“We’ve known that dopamine is involved with sexual motivation because of its role in the pleasure and reward circuitry in the brain,” said Garcia. “What was interesting to me is that people with this
DRD4
7R+ type gene did not report having a higher sex drive or higher number of sex partners. It was the context of partners that varied. They went for a more uncommitted, riskier type of sex.”

Garcia was careful to point out that this effect is probabilistic rather than deterministic. That is, a higher proportion of those with the 7R+ are motivated to seek risky behaviors when it comes to sex, but having the 7R+ doesn’t mean they will.

“Can we really attribute these behavioral differences to just one gene?” I asked him.

“No, there are multiple genes involved with motivating behavior. And there are different environmental factors that will change their expression,” said Garcia. “But this is a gene that can explain some of the difference in a behavior that was long thought to be largely culturally defined. That tells us something. That’s important.”

So Is It an Addiction?

Helen Fisher would tell you that love is no simple emotion,
that it is a motivational drive to pursue the greatest of life’s rewards: a preferred mate. Because that drive is associated with the dopamine-rich reward circuitry, as well as cortical areas associated with craving, she maintains it also shares qualities with addiction. Several distinct lines of neurobiological research have consistently supported this hypothesis. When I look at Kristie, an admitted sex addict, I see that love and sex can become an addiction in their own right. Drugs may hijack the brain’s natural reward and risk processing system, but love and sex can be abused too. What is it about addicts—some kind of genetic predisposition, damage to the reward circuitry or dopamine system—that results in nonsubstance addiction? Neuroscientists don’t have a clear answer on that.

It is also important to note that each relationship we have with another person is qualitatively different—often
very
much so. I have had partners I ate, breathed, and slept—I could not get enough of them, despite the fact that we weren’t always well-matched. When we parted, I felt as if someone had died. I craved and grieved them. Those relationships felt a lot like what I imagine an addiction would be. By the same token, I have also been involved with men who were pleasant enough companions but did not exactly rock my world. I’m guessing you can say the same. Each relationship is different. These variations raise a good question: Is all love and sex addictive? Or do certain partners, those who bring with them the right cocktail of internal and external chemistry, provide a more addictive state? The latter, intuitively, seems more accurate.

I asked Fisher about this: “I may break up with someone I once loved without a glance backward. Others shatter my heart. Are there any hypotheses about where there is a difference, how different relationships may be affecting the dopamine systems in different ways?”

She was frank in her response. “No one knows. Some people come along at the right time, they fit well into one’s personal concept of an ideal partner, and the person falls
madly
in love,” she said. “Others aren’t quite right in one way or another, and perhaps the dopamine system isn’t as activated. But no one knows.”

There are many questions left to be answered. Though it would seem
that love uses the same neural substrate as substance addictions, it’s still unknown what makes us love one person madly and another with calm and ease, what changes are occurring in the brain to cause withdrawal, or even how the dopamine system might be regulated in either case. But for those of us who have experienced a love as irresistible (and destructive) as China White, we know that all those love songs referencing addiction have it right, even if the neuroscience hasn’t provided all the details yet.

Chapter 11

Your Cheating Mind

For centuries philosophers, theologians, anthropologists,
physicians, and bored spouses all over the world have pondered the nature of monogamy. Is mating with one person over the course of a lifetime
natural
? If it is, then why do so many people go outside their monogamous relationships to, as my friend John so eloquently puts it, “do dirt”?

Statistics about infidelity vary. Do a Google search and you’ll find a wide range of numbers. The scientific literature has just as much variability. According to Janis Abrahms Spring and Michael Spring, authors of
After the Affair: Healing the Pain and Rebuilding Trust When a Partner Has Been Unfaithful,
a much-cited source in popular magazine articles, infidelity affects one in every 2.7 couples in the United States: that’s 37 percent of couples.
¹
Other self-reported polls say 22 percent of men and 14 percent of women are indulging in activities outside their marriage. Many researchers estimate about 25 percent of all married couples or individuals in committed relationships cheat. For the purposes of this chapter, we’ll just keep things simple and stick with 22 and 14 percent. Because these surveys are self-reported, many researchers generally assume that the numbers are significantly higher; after all, in many cultures cheating is still very much frowned upon. But if everyone was truly as faithful as he or she claimed, the incidence of sexually transmitted diseases (not to mention divorce) would be much lower.

When I asked Helen Fisher about the prevalence of monogamy (or absence of it, as it were), she told me, “There is not a culture on earth where people don’t cheat. I’ve studied forty-two different cultures across
the globe, and you find it in every single one.” The question remains: With so many of these same cultures putting a premium on monogamy, why is “dirt” so widespread?

I am sure it is a question that we have all asked ourselves at one time or another, usually while casting sideways glances at the guys. Maybe it has something to do with all those statistics that suggest men cheat more often, but when the topic of infidelity comes up, we seem to automatically assume it is a primarily male pastime. Could it be that monogamy is not a viable option because there is something about the male brain that predisposes men to cheat? It’s certainly not a new idea.

An acquaintance of mine—I’ll call him Roger—believes that it is his biological imperative to get with as many women as he can. He will tell you straight off the bat that he loves—no, adores—his wife of ten years. In fact he could not live without her. Still he simply cannot resist the siren call of “a little strange” (how he refers to casual sex with strangers) once in a while. To hear Roger talk, usually after a few cocktails, you might think he is bedding a new woman every night. Not so—after all, he has a wife to keep happy. A few times each year Roger uses business trips or boys’ nights out to satisfy his desire for that “strange.”

Ask a random guy who has cheated on his spouse why he did it and he may tell you that his wife does not want sex as often as he does or that he needs a little more sexual variety in his life. Roger says none of those excuses apply in his own situation. He and his wife have an active sex life. Rather, he believes his genes are to blame for his infidelity; as a male, the thrill of the hunt—the desire to chase and catch a new sexual conquest from time to time—is just a part of his biological makeup that he cannot deny.

Some data from the evolutionary biology field may lend credence to his hypothesis, yet a neuroscientific look into the love lives of cuddly prairie voles—and those exquisite neurochemicals, oxytocin and vasopressin—tells us there’s a lot more than just evolution at play when it comes to remaining faithful.