This Is Your Brain on Sex: The Science Behind the Search for Love - Softcover

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Kayt Sukel’s work has appeared in myriad publications, including Atlantic Monthly, USA TODAY, The Washington Post, National Geographic Traveler, Continental, American Baby, and Cerebrum. She is a partner in the renowned family travel website, TravelSavvyMom.com, blogs about where neuroscience intersects with life at BigThink, and is also a frequent contributor to the Dana Foundation’s many science publications.

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This Is Your Brain on Sex

Chapter 1

The Neuroscience of Love: A History

(Theirs and Mine)

In 1994 a scientist named Sue Carter submitted a grant application to study a hormone called oxytocin (not to be confused with the narcotic Oxycontin, aka hillbilly heroin) in a small rodent called the prairie vole.



A prairie vole family. Photo by Todd Ahern, University of Massachusetts.

A prairie vole (Microtus ochrogaster) looks a lot like your garden-variety mouse, but scruffier and with a shorter tail. Happily burrowing under gardens and meadows in a large stretch of central North America, these small rodents might completely escape our notice except for one special trait: they are monogamous.

Socially monogamous, that is. Unlike most other rodents—or most other mammals, for that matter—prairie voles form lifelong pair-bonds, or lasting social and sexual relationships with a single member of the opposite sex. Both males and females are also directly involved with the parenting of offspring. Because of the rarity of such habits in the animal kingdom, many animal behaviorists have become exceptionally interested in the prairie vole. One such researcher was Carter.

A professor of psychiatry at the University of Illinois at Chicago, Carter hypothesized that oxytocin, which is linked to childbirth and breastfeeding, could increase social attachment. She had already conducted research to support the idea and hoped that this grant would allow her to continue studying the hormone and its relationship to social behaviors in the prairie vole. In her application she did not mention love, marriage, or even humans. Somehow the grant review committee decided she was studying the little four-letter-word that begins with an l—love, that is—which was considered a serious no-no in the hard science climate of the day.

“I was trying to get federal grant funding to continue my work, and suddenly I was accused of studying love,” she said when I visited her lab in Chicago. Petite, white-haired, and a little bohemian in style, Carter somehow managed the feat of being both incredibly welcoming and intellectually intimidating at the same time. “Honestly, it was a shock to me. I would not have used the word love—I never used the word love. I didn’t think about the work in terms of love. I was simply talking about a preference of one animal for another—not some human construct that seemed to have little to do with what we were actually studying.”

Carter told me she was unsure of how to respond to the review. She conferred with Kerstin Uvnäs-Moberg, a fellow scientist also interested in oxytocin who was working at Stockholm’s Karolinska Institute. Could it be that their work was related to something as messy and indefinable as love? Might there be a neurobiological basis for the future study of love? Looking at newly published research by various labs concerning oxytocin, social attachment, and pair-bonding in prairie voles and other mammal species, the answer seemed to be yes. Carter and Uvnäs-Moberg thought it was time to stop ducking the topic and admit that their work did have implications for human behavior.

“It seemed like the time to really try to articulate and explain the idea that social bonds were critical to human love,” Carter said. While sex was, is, and will be of the utmost importance to propagating our species, Carter and Uvnäs-Moberg were convinced that love needed to be articulated in the context not only of genetic propagation but also of survival—specifically, the ways social bonds can help people thrive in the face of stress and other complexities of life on a daily basis. Perhaps our brains promote social relationships in order to ensure that more than one person is on tap to avoid dangers, to make sure there is enough food around to feed the family, and to help raise the young’uns. Investigating how the neuroscience underlying social bonds might promote these behaviors seemed a pertinent line of study.

Though this line of inquiry seemed very clear to Carter and Uvnäs-Moberg, it was difficult to get respect (and, perhaps more important, funding) to study such ideas experimentally. There was already ample evidence in neuroscience literature to suggest that love was a worthy topic of research. But the scientists never called it such, avoiding it like the dirty word it is. Instead they referred to the related topics of pair-bonding, monogamy, attachment, and mating behaviors. If you read between the lines, there was a lot of information out there, perhaps even enough to make the neuroscientific study of love its own field. Still most professional scientists were afraid to call love by its true name.

There was no sense in talking about the neuroscience of love without a proper working definition—a common standard that scientists across disciplines could use to test and validate hypotheses. Sadly, as fitting (and poignant) as Ted Nugent’s “tire iron” characterization might be as a song lyric, it would be limiting to use as the basis for a credible, replicable scientific study. To that end Carter and Uvnäs-Moberg invited thirty-eight prominent scientists in the field of neurobiology to a meeting at the 1996 Wenner-Gren Symposium in Stockholm titled “Is There a Neurobiology of Love?”

One of the products of that meeting was a definition. Instead of going with Merriam-Webster’s basic statement about love being a case of “strong affection for another,” the group consensus was that love is “a life-long learning process that starts with the relationship of the infant to his or her mother and the gradual withdrawal from the mother with a search for emotional comfort and fulfillment.” This definition was included in the summary report written by the prominent neuroscientist Bruce McEwen.1 It offers more detail than the definition of love as strictly an emotion or a basic mammalian drive, like hunger or thirst—even if it is less romantic than “sweet surrender” or “my first, my last, and my everything.” Though a mouthful, this definition would serve as the standard to which future studies across the neurobiology field could refer.

The meeting also started a renaissance of sorts, a green light for neuroscientists, neurobiologists, and neuroendocrinologists to finally call love, well, love. This allowed them to start studying the nuances of this human phenomenon from the perspectives of brain and biology. Two years later many of the meeting’s prominent attendees published studies in a special issue of the journal Psychoneuroendocrinology on topics ranging from the evolutionary antecedents of love to the physiological consequences of withholding it. With such respected scientists backing the concept, researchers could more easily study the l-word within the space of the brain and neurobiology.

Sexy Baby Banning

Fast-forward ten years. Many great studies concerning neuroscientific aspects of that “life-long learning process” we call love were published in the late 1990s, with a great number appearing in high-profile journals like Nature and Science. Brains, it seemed, have quite a bit to do with love—certainly far more than do our proverbial hearts. While working on a story for a neuroscience website, I accidentally stumbled across McEwen’s...