This Is Your Brain on Sex (35 page)

Several studies have shown that women are more attracted to a masculine face when they are at their most fertile, a period of the menstrual cycle called the follicular phase. The idea here is that female hormones, particularly the raised estrogens, are suggesting that a girl go for a particular mate type, the masculine type. After all, those masculine genes with improved health and extra chutzpah would be beneficial to any potential offspring. If she is not ovulating, well, then a more feminized guy will do, one who is cute but not as strong in the brow and jaw. From an evolutionary perspective, that more feminized guy, without all that raging testosterone, would make a better helpmate; he’d be someone who would stick around, help raise the kids, and do his part in keeping the house tidy. It is a great story, but
it is hard to directly tie these things together. The evidence suggests there is some kind of relationship between hormones and the kind of man a woman is attracted to, but how that effect is mediated is still up in the air.

To look at the underlying neural correlates of this phenomenon, Rupp and her colleagues, including Thomas James, a neuroscientist at Indiana University who studies perception, measured the brain activity in sixteen single female participants as they evaluated photos of male faces that had been slightly masculinized and feminized using computer morphing software. “When we put the two faces side by side, women didn’t consciously see them as masculinized or feminized,” James said. “It’s very difficult to see the difference between the two.”

The task was fairly simple. Each face was presented with the number of the man’s past sexual partners and typical condom use. Study participants were asked to indicate whether they would be likely to have sex with the man based on the information given. Brain activity was measured both while participants were in the follicular phase of their cycle and then again in their luteal phase (the nonfertile half of the menstrual cycle). Their blood was also drawn at both sessions to get a more exact measure of their hormonal state.
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The group found a few interesting results. First, compared with the feminized faces, masculinized faces led to more activity in five specific brain areas: the left superior temporal gyrus, bilateral precentral gyrus, right posterior cingulate cortex, bilateral inferior parietal lobule, and bilateral anterior cingulate cortex. These areas have been implicated in face processing as well as the assessment of risk, suggesting that, consciously or not, masculinized faces are perceived as not only more attractive but also more dangerous. The effect was quite robust considering just how slightly the faces had been morphed.

When the group looked at hormone levels, they found that a woman’s own level of testosterone positively predicted activation in the anterior and posterior cingulate, brain regions implicated in decision making. Yet which phase of the menstrual cycle a participant happened to be in was not correlated with any of the significant brain activations. The authors hypothesized that they had not been specific enough in the timing of testing. With a short
window of fertility, they may have just missed the mark in catching the follicular phase. Still the findings were striking.

These areas were activated in the processing of masculinized faces. Activation in both the anterior and posterior cingulate was correlated with hormonal state.
Illustration by Dorling Kindersley.

Those masculinity cues were fairly subconscious. “Both women and men are good at picking up nonverbal, subconscious cues about a potential sexual partner that tell them all kinds of things they aren’t aware they are receiving,” Rupp told me. “Your hormone level might make them more salient.” But like her former advisor, Kim Wallen, Rupp was quick to point out that seeing a masculine dude during your follicular phase doesn’t mean you are compelled to follow through. “You get these subconscious cues, yes, that may make you more likely to go home with a particular guy,” she said. “But that’s your subconscious. It doesn’t have the only say. The conscious part of your brain can then come on board and help decide whether or not you are actually going to do it.”

Rupp, James, and their colleagues wondered if perhaps hormone levels were changing the way the women appraised male faces. Perhaps the higher estrogen levels seen in the
follicular phase increased motivation to see those masculinized faces, hot but risky, in a more positive light. They decided to test this with a second group of participants who would do the same task as in the previous study, but this time around the women also viewed photos of houses as a control condition.

In this follow-up study the researchers did see altered cerebral blood flow depending on a woman’s cycle phase. When women were most fertile, in the follicular phase, they showed increased activation in the orbitofrontal cortex, an area of the brain implicated in reward and risk evaluation as well as judgments of attractiveness. This was observed when the women viewed both masculinized and feminized faces, leading Rupp to suggest that the follicular phase brings with it not only a lot more estrogen but also increased positive appraisal, or a higher likelihood of wearing rose-colored glasses when a girl interacts with a good-looking dude.
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Like Karremans’s study, these results generated some great headlines, including “Explore Your Dark Side to Win Her Over”
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and my personal favorite, “Why Nice Guys Finish Last.”
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Of course neither topic was really what Rupp, James, and their colleagues were investigating. So when I asked James, “Are girls more attracted to bad boys?” he laughed.

“My answer is that we don’t know enough,” he replied. “I know people want answers, usually a black-and-white answer. But science doesn’t provide those.”

Rupp gave me a similar response. “The verdict is still out. Obviously, for physical reproduction to occur we need these sweeping hormonal changes. And we also know these things affect perception and motivation. But we’re still working with a lot of assumptions here. There are a lot of holes in our understanding that we need to fill.”

Sex and Decision Making

Maybe some of those holes involve decision making itself. That is, are the decisions we make about sex fundamentally different from those we make about what to eat for breakfast or whether to invest in a particular stock? Despite the fact that the brain lights up like crazy for sexual stimuli, Rupp and James argue
that these decision-making processes are not different from any other type.

When the group looked more closely at the anterior cingulate cortex activation during viewing of all male faces, they noticed something interesting. Study participants reported that they paid attention to how many sexual partners a man had and whether he was likely to use condoms; the lower the risk, the more likely the participants would be interested in having sex with the man. Those low-risk men elicited stronger activation in the anterior cingulate cortex, as well as in the midbrain and intraparietal sulcus, which are areas that light up in all manner of decision making, whether the task involves an economic game or whether it involves having to weigh risks and rewards. This, the researchers hypothesized, means that sexual decision making is no different from any other kind.
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“People tend to think of sexual behavior and sexual decision making as something unique that we don’t understand,” Rupp said. “The data, however, suggest otherwise. That makes sense—the brain doesn’t do redundancy. And it would seem sexual motivation and decision making is not unlike any other type of reward-based decision making we do in life.”

Rupp, James, and their colleagues set out to test this directly in a new study. I volunteered to be a pilot subject. Though a bit older than the age range they focused on, I could still assist them. I would do all the things a normal participant would and help them work out any kinks in the study paradigm. I traveled to Indiana University, as part of my pilgrimage to the famous Kinsey Institute, to have my brain scanned during my nonfertile luteal phase—this time to look at my decisions as opposed to my orgasms.

In this study I was shown four different kinds of photos: foods, alcoholic beverages, men, and everyday objects. Each photo, no matter what type, had a number score and the word
Yes
or
No
next to it. For any given food, the number represented the number of calories and the Yes/No told me whether the restaurant preparing the food had been previously cited for health violations. The values next to the drinks indicated the number of alcohol units and whether I had a designated driver on hand to take me home if I overindulged. Those next to the boys? The number of previous sexual partners and whether
the guy typically uses condoms in his liaisons. And for the everyday objects, the number was a price and the Yes/No denoted whether the store that sells a product allows returns. My job was to evaluate the photos and their corresponding values and decide whether I would eat, drink, screw, or buy, respectively—just make a gut decision based on the information given. And I would be doing so using a 4-point scale—extremely unlikely, somewhat unlikely, somewhat likely, or extremely likely—tapping my responses into a keypad that would come with me into the scanner. It was a simple task, yet it took a bit of mental coordination to complete in the few seconds each photo was displayed.

Because I wouldn’t be moving parts of my body to try to elicit orgasm, the fMRI setup was much simpler. To start, it was located not in a hospital but in the psychology building itself, a few doors down from the faculty offices. Very easy access, and no mesh S&M-type mask was required this time. My head was centered and stilled with some soft foam. The noise level was the same—there was no changing the sound of a spinning magnet. But I was infinitely more comfortable than I was in the orgasm study, which was a good thing considering I was going to have to think more. Not to mention press four different buttons, as opposed to just the one located on my nether regions.

Moments after the magnet started to spin, a small plus sign on the monitor let me know where I should be looking. Clank. Click. THUNK! THUNK! THUNK! I was ready. The first photo was of a fruity cocktail, some frozen strawberry concoction in a martini glass, garnished with a sparkling sugared pineapple. Next to it were the number 4 and the word
Yes
. Okay, this drink would be four alcohol units. That seemed like a lot (especially at eight in the morning), but I had a designated driver ready to give me a ride home. Still, I was not really in the mood for an ice cream headache. I clicked “somewhat unlikely” and waited for the next image to appear.

It was a photo of a young man. He was maybe twenty-two years old and straight out of an Abercrombie & Fitch catalog. His hair was too long for my taste, deliberately tousled and gelled to defy gravity. He needed a shave too. His corresponding values told me he had had only one sexual partner in the past month and used
condoms. Obviously he was not a high-risk bed partner. Objectively he was a good-looking guy. But I couldn’t get past the hair. Like some crotchety old lady, I wanted to tell him to get a haircut. The only thing I could do was click “extremely unlikely” and move on to the next photo.

Over the next thirty minutes I was shown images of brownies, Scotch tape, fried shrimp, cheesecake, various mixed drinks, clocks, macaroni and cheese, and a grocery store’s worth of crap light beer brands. And yes, there were plenty of boys too. My use of the term
boys
here is intentional. These sweet young things, like the first one displayed, were all demonstrably handsome. I certainly cannot argue that point. Yet not one was my cup of tea. Between the piercing gazes (à la Zoolander’s Blue Steel) and really stupid hair, I was consistently left cold. I found that no matter how safe they may be as sexual partners, I was wearing out the “extremely unlikely” button each time one appeared. I was beginning to feel like some weird old lady. Some weird old
asexual
lady. This is the age of the cougar, for goodness’ sake—I should have been all over the young dudes. So when a cute boy with a somewhat normal expression on his face popped up, I said that I would be “extremely likely” to go home with him on principle. In truth, if we were in some club or café and he actually did approach me, I’d be more likely to hire him to babysit my kid than to head back to his place to hit the sheets.

During the entire session, aside from that one boy, I clicked the “extremely likely” button a total of five times. That’s out of what must have been close to one hundred photos of various foods, drinks, boys, and objects. I figure I was either very discerning, steeped in my luteal phase, or simply ready for a nunnery thanks to age and my divorce. What was I willing to say I was “extremely likely” to enjoy that fine morning? Some pink Post-it notes (probably because I had just run out at home), a nice-looking rare steak, some absolutely decadent-seeming macaroni and cheese, and a carafe of red wine. Out of all of these photos, including the photo of the one acceptable boy, I have a very strong feeling my brain showed the strongest activation for the steak.