The Science of Kissing: What Our Lips Are Telling Us

by Sheril Kirshenbaum

  I had hoped for at least fifty responses, a big enough number that I could run some statistics. I’m not sure whom I was kidding. The post got a vast amount of attention and multiple links in from other blogs and websites, and over the following days I received close to a thousand emails about the survey… and that was only the beginning.

  For weeks, they continued pouring in, in vastly greater numbers than I could hope to analyze or process. Some viewers expressed feeling “turned on” by looking at the photos of kissing couples, while a few reported outright disgust. Several suggested ranking each kisser individually, or made recommendations about kissing technique. There were even those who, unsatisfied by the limited options I had provided, went ahead and created new kissing categories separate from my own.

  Meanwhile, countless long threads emerged in discussion forums on the Internet, debating the meanings of erotica and commitment based on the images. It seemed everyone had an opinion about them, and while I didn’t always agree, I certainly felt very encouraged that so many people were interested.

  After spending a day organizing all the survey responses into a spreadsheet, I narrowed the list down to the nine photographs whose interpretation had been most universally agreed upon. At long last, I was ready to take them to New York to show to real live test subjects. The avalanche of responses from the blog survey gave me high hopes for what we might learn in the machine.

  ON JULY 5, 2009, I flew to New York to meet with the Poeppel lab. Before we got started, I wanted to learn more about how the MEG machine worked, so I volunteered to be the first guinea pig in a test run.

  I changed into a pair of scrubs so no aspect of my clothing would interfere with the machine’s magnetic signals. I also had to remove all metallic objects from my body, including jewelry, hairclips, and even my bra. Next, the lab technician, Christine, took digital measurements of my head using a computerized tool shaped like a pencil. I watched as a 3-D image of my head’s shape appeared on the screen of a nearby computer. Once we had my skull’s precise curvature recorded, Christine taped electrodes across my forehead to monitor its position as I was scanned.

  Next, Christine and David led me into the special magnetically shielded room that housed the MEG. By then, with my attire and all the wires on my head, I looked and felt as if I were headed into outer space—but instead, I laid down in the scanner. I asked David about the toilet bowl–like cylinder now surrounding my head, and he explained that liquid helium (a very cold fluid) was circulating through it. I had visions of Mr. Freeze from the Batman comics, but it was too late to back out.

  Over the intercom, David’s assistant, Jeff, instructed me to stay as still as possible, because any movement could change how the magnetic fields from my brain were recorded. At long last, we were ready to begin. Directly above my head I saw a screen where the following message appeared:

  Ready…

  Thank you for participating in this experiment.

  You will now see a series of images of people kissing.

  Please pay close attention. Press the far left button if you find the images Erotic, the middle button if the people in the images seem Committed and the far right button for Friendship.

  Press any button to begin.

  I pushed the button—and watched the nine kissing images I had so carefully selected flash before my eyes in random order, over and over. Each was displayed forty times, for a total of 360 “trials.”

  Inside the machine, I lost my identity and became test subject 0041—the first of the results we would include in the data set. As I watched the images that I already knew so well flash by, it also dawned on me that the process of writing a book about kissing had now, quite unexpectedly, taken me into a world that I’d never before experienced.

  I had been classically trained in the marine sciences; my central scientific experience was in ecology and evolutionary biology. Neuroscience, in practice, was utterly different; and brain imaging was an entirely distinct and new means of understanding human behavior. I felt very much out of my scientific element. But I also felt inspired, and found myself thinking of dozens of questions we could pursue with this new, powerful apparatus. My mind raced with possibilities as kisses flashed before my eyes. I couldn’t help wondering whether my busy thoughts would skew the data collection process.

  Twenty minutes later I emerged into the computer room, curious as to what all the spikes and squiggles on the monitors—my thoughts, my brain’s electrical impulses—really represented. All I had to go on was a “map” of my head, which to me had little more meaning than a hieroglyph.

  It was getting near time to bring in the volunteers who would allow us to run them through the same experiment and continue our scientific study. But first David’s team asked if I would allow them to put me through another brain scanner as well, their functional magnetic resonance imaging (fMRI) machine. One of the most recently developed devices for brain imaging, an fMRI, unlike an MEG, works by measuring blood activity in the brain or spinal cord. Once again, the machine lets scientists and doctors observe brain behavior without risking radiation exposure or other injury to the subject. How could I say no?

  The scientists shoveled me into a tube, which made all sorts of loud banging noises as I stayed as still as possible for thirty minutes. Afterward I got to see my brain onscreen—a pretty surreal experience. I watched as David’s assistant Tobias zoomed in and out, passing through my brain as if it were terrain on Google Earth. It dawned on me that all the experiences of my entire life—every birthday and holiday, every public and private moment, including my very first kiss—took place in that intricate mass of tissue and cells. It was the closest I could ever get to observing my soul. Yet onscreen, while Tobias provided the virtual tour, the image appeared clinical. I felt very fortunate for the opportunity to get such an intimate look at myself, but somehow I also felt it wasn’t a complete image. Surely there was more to me than the maze of dark and light lines I saw.

  At last we returned to the MEG, where our test subjects were now being studied, and I watched the same squiggles dance onscreen for each participant. I wondered why they varied, and which kissing images caused the most intense reactions in each subject (it wasn’t possible to tell yet).

  David and his team spent three days running subjects in the machine, as I watched and took notes. Four men and four women in total were scanned, hailing from different parts of the world (China, Israel, Germany, the United States, and Canada). To me, this seemed like a very small sample size; in my own marine biology research I had studied thousands of sea cucumbers. But in human neuroscience, eight is a reasonable number for an early MEG experiment. The small group allows scientists to evaluate whether there is anything to pursue systematically in the future through more extensive study. If they observe a striking or strong result, the research continues.

  As the work proceeded, my first question was whether the men and women would respond differently to the different images of kissing. From Gordon Gallup’s surveys and Wendy Hill’s blood tests, it seems clear that the sexes experience kissing very differently, but what that meant in terms of brain imaging was yet to be determined.

  Another question was whether there would be a marked difference when the test subjects viewed homosexual versus heterosexual kissing couples. And then there was the matter of sexual arousal. Men are far more sexually responsive, and far more interested in visually arousing images, than women are. Might the erotic photographs in particular trigger a distinct response in each gender?

  I wouldn’t be able to get answers to any of these questions right away—rather, I would have to wait until David and his graduate student Gregory could run statistical analyses on the results the MEG had recorded. For the moment, all I could tell for sure was that our subjects really seemed to get a kick out of participating in this study. Or as one person exiting the machine put it, “Can I go again?” Each subject also expressed interest in hearing about the results when we were finished.

 
; On the final day, we wrapped up our research by heading to a Mets game with the entire lab team. During the seventh inning, the famous “kiss cam” at Citi Field scanned the stands before stopping at Donald Trump and his wife, Melania Knauss-Trump—who happily obliged. The crowd went wild. We weren’t the only ones in New York City that night interested in kissing.

  SO NOW IT’S TIME to turn to the outcome of the experiment—after one critical caveat, anyway. Before going into any further detail, it’s necessary to be completely clear about what this work did, and perhaps, more important, did not, find. In fact, as kissing research proceeds in the future, such qualifications may become increasingly important, due to the sensitive, sexually charged nature of the topic and the strong possibility of popular and media misinterpretations.

  Research on kissing will, from time to time, bring up the matter of differences of sexual orientation, both among study subjects and among kissing couples who are depicted visually (as in our neuroscience experiment). But that does not mean that our work in any way found, proved, or even suggested anything concrete or definitive about the differences between gay and straight people, whether in their behaviors, attitudes, motivations, or preferences.

  The results obtained in both investigations did reveal some interesting, albeit very preliminary, trends. However, scientists are justifiably concerned about publicly reporting these trends, no matter how many caveats they include along with them.

  The problem is that all too often, the news media latch on to a scientific finding to make it sound “sexy” in order to boost ratings or spin the story to suit a particular agenda. Even when researchers are very careful in what they say to the press, the results will frequently be overstated or misstated to make them sound bigger and more definitive, and less nuanced and less uncertain, than they really are. In some cases, very early scientific findings can be spun to the point of ridiculousness or even sheer falsity. When this occurs, it’s no longer science reporting, but entertainment and (quite honestly) dollars to the media industry.

  Moreover, such “journalism” can be particularly damaging when it comes to matters of human sexuality, where many people already have strong biases and preconceived notions. So with all of that said, let me be unequivocal: Our neuroscience experiment does not show that there is something fundamentally different between gay kissing and straight kissing. Instead, it merely opens the door to the next set of questions to explore.

  That said, here’s what happened…

  • • •

  DAVID AND GREGORY tirelessly analyzed the data using a computer program called MEG160, which works by filtering and averaging together all of the results. A few weeks after the scans took place, they called me to discuss the findings. It turns out that they were far more intriguing than any of us had anticipated.

  Two unexpected trends emerged among our volunteer subjects. First, the photographs of same-sex couples kissing resulted in a stronger magnetic field recorded in the MEG than the photographs of opposite-sex couples. What this means is that when a particular same-sex image was displayed, the study subjects generated a greater brain response than they did when looking at opposite-sex couples. This held true regardless of whether the couples in the images were male-male or female-female, and regardless of whether they were engaged in an “erotic,” “friendship,” or “relationship” kiss. Moreover, in statistical terms, the results were highly significant, meaning that some factor must account for the differences we observed.

  But why was everyone showing a stronger response to homosexual kisses, even those among apparent friends? The most plausible explanation could be cultural: Our volunteers probably encounter male-female kissing more often in public and in the media than same-sex kissing. Therefore, the differences we observed in the experiment could be due to the frequency with which we see similar events in our actual lives.

  In neuroscience, there’s even a name for this phenomenon: a “frequency effect.” It means that the more something is encountered, the smaller the response it evokes in our brain. MEG experiments on language recognition, for instance, have demonstrated that rarely used words elicit a much stronger response than common words. For example, because we hear the word “table” so often, a subject hearing it in an MEG machine generates a much smaller magnetic field than when hearing a far less commonly used word, like “ibex.”

  The second result was even more puzzling. The timing of the brain’s first response to each image also varied strongly depending on whether it depicted an opposite- or same-sex kiss. Male-male and female-female kissing alike elicited a much faster brain reaction in the test subjects. While David and Gregory found this fact intriguing, they say it’s very hard to interpret, and is not necessarily evidence of any inherent bias or prejudice. Once again, the quicker reactions may reflect the fact that same-sex kissing was a less ordinary occurrence for our subjects to behold. The difference in responses may also have been due to other factors in the photos, such as lighting and edges, because the MEG response is extremely sensitive. So in sum, we observed an interesting pattern, but more research is required to start developing theories on why it occurred.

  Before we ran the MEG, my hypothesis had been that different kissing types might influence the strength of a subject’s reaction, and that erotic kisses would evoke the strongest ones. I also suspected that male volunteers would show a greater response than women, because they are more sensitive to visual stimuli. I included images of same-sex couples to add more variety to the photographs, not because I wanted to test the difference between reactions to same-sex and opposite-sex kisses.

  And yet when the results came back, there was no difference in responses among male and female test subjects, or based on whether the kisses in the pictures were erotic or not. Rather, the results showed a notable difference in brain response to opposite- and same-sex kissing. It was a classic case of scientific research surprising you and leading you in a very new direction—raising many new questions in the process. In other words the experience was a dramatic example of how science is supposed to work.

  In popular television dramas, science is always portrayed as if mysteries are solvable in an hour or so—or at least within a few episodes. But real science just doesn’t work that way. Our MEG experiment broke new ground by investigating kissing in a way that’s never been done before, at least so far as we can tell. It was a first step in the hope of finding out whether further investigation is worthwhile—which it definitely is. The science of kissing is in its formative years, and there is vastly more to do, both inside MEG machines and elsewhere.

  For precisely this reason, though, scientists cannot go around drawing rash conclusions about human sexuality or behavior based on one preliminary experiment involving a very limited number of participants. Instead, we must use the results as clues to help design the next stage of investigation.

  What’s next? Well, since we now know that small factors in the photographs can affect brain responses, a future study might create a new set of images that more carefully control for differences in background, lighting, contrast, and other attributes, including the people shown. This way, the photographs would be more standardized to make all the conditions as similar as possible, except for the specific factor we’re most interested in examining (i.e., what the response is to an erotic versus a friendship kiss, or to a same-sex versus opposite-sex kiss). Then, if researchers continue to see the same trends in subsequent controlled trials, we might develop much firmer ideas about what’s occurring.

  We might also choose our study participants more carefully in a later test. For example, if the difference between the reaction to opposite- and same-sex kissing was indeed a product of the frequency effect, it’s possible that people who, say, spend hours each week staring at homosexual images (like homosexual pornography) would not show as strong a response to same-sex kisses. That would be a notable finding.

  In short, when we ran the kissing experiment, we saw an interesting pattern that strongl
y suggests more research would be a good idea. One day, we may be able to identify a compelling neurological basis for the different reactions recorded in the MEG scanner—but in the meantime we have already developed some important ideas about how to approach the next set of intriguing questions in brain-kissing research.

  And so, the science of kissing continues. Indeed, it is really just getting started.

  Kissing and the Brain

  Throughout our lives, the physical structure of the brain’s neural network is continuously changing as we experience the world, and the new neural connections formed can be strengthened over time with experience.

  When we kiss another person—especially someone new—there’s a lot of information being processed: his or her scent, taste, movement, touch, and even sound. This information helps the brain interpret the way we think and feel about this individual by associating these sensations with him or her. So as we kiss, we alter our brain. Changes occur on a microscopic scale (as they do with any other activity), but it’s fair to say that in this manner, kissing can literally reshape the mind.

  CHAPTER 11

  The Open Lab

  The neuroscience experiment described in the previous chapter ventured into just one field of many in which scientific research on kissing can evolve. The possibilities of where it may go from here are vast and virtually limitless. At the conclusion of any scientific paper, it is customary to highlight a field’s outstanding questions and potential new directions. So now that we have explored kissing’s history and evolution, its incarnations across species, and its effects on our bodies, let’s try to predict what comes next. Here I will describe some potential experiments worth pursuit that tie together themes across disciplines, building on the most intriguing aspects of what has gone before.