What Your Brain Looks Like When You Cheat On Your Wife

New fMRI research is beginning to break down the neurology of monogamy and non-monogamy.

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The brains of monogamous men and non-monogamous men respond differently to romantic images, recent neuroscience research suggests. But it’s not all black and white.

“There are some people who are really monogamous and some people who are really non-monogamous,” coauthor on the study Lisa Hamilton of Mount Allison University told Fatherly. “But most people’s desires around monogamy fall somewhere in the middle.”

Hamilton began her works with prairie voles, ostensibly monogamous rodents that are known to occasionally fool around. After a battery of experiments on voles identified neurotransmitters, neuroreceptors, and hormones that likely influence a vole’s decision to remain monogamous or play the field, Hamilton set out to look for similar patterns the brains of sometimes-monogamous men. She showed romantic and sexual images to 20 men—10 monogamous, 10 not so much—and, using fMRI brain scans, found marked neurologic differences. But that’s just the beginning. Fatherly spoke with Hamilton about her plans to conduct far larger studies, and how she hopes to use neuroscience to figure out why some of us stay faithful and others sleep around.

Why Study Men And Not Women?

We had a limited budget and could only run 20 people, and I figured it would be easiest to get men who were open to admitting to being non-monogamous because there’s less social pressure to be monogamous. There’s still pressure, but less of a stigma attached. A big part of it was that we thought we’d be able to find them, but also that the differences between monogamous and non-monogamous men would be greater. With sexual variables in general, you see more sharp distinctions between men, where women tend to be more fluid in their sexuality.

This May Be An Embarrassing Question, But What sort of “romantic” and “sexual” stimuli did the men look at while hooked up the the fMRI machine?

They were images, not video, and all of them essentially showed penetrative sexual intercourse between a man and a woman. People were either naked or mostly naked and you could either see penetration or it was strongly implied. For the romantic stimuli, past studies on love with brain imaging use pictures of people’s partners, but for this we wanted everyone to see the same romantic stimuli. We wanted to see their general response to the concept of romance, so we showed them pictures of couples walking and holding each other’s hands, gazing into each other’s eyes. In all over those pictures, everyone was fully clothed.

What Does Sexual Arousal Look Like In The Brain?

Other studies have found that when people look at sexual videos the occipital lobes, the area of the brain responsible for vision, light up compared to when they’re just looking at scenery. Their visual area is more active looking at sexual imagery. Then there’s the reward pathway of the brain, which is talked about a lot in research about drug addiction, that gets activated as well. But it is very easy to activate that pathway, and this gets overstated when people talk about porn, that because this pathway is “active” it’s “addictive”. Eating a piece of chocolate will activate that same reward system.

So How Did Men’s Brains Differ When You Showed Them These Images?

For the sexual stimuli, monogamous and non-monogamous brains look the same. [But for romantic images, there were differences]. There was some activation in non-monogamous men, but much more in the monogamous guys. But non-monogamous men had more cortex activation, which indicates that instead of responding at a gut level, they’re processing it at a higher level.

What Does Processing Romantic Images “At A Higher Level” Actually Mean?

It just means they’re processing it in a different way. It’s like let’s say you were eating a delicacy from another person’s culture and you didn’t like it. And your brain is processing, “What is this?” “What is this flavor?” You’re processing it on more of a cognitive level, where someone who was raised on it would have automatic reward activation because it’s delicious to them.

Could This Explain Why Monogamous Men Don’t Cheat?

It’s really complicated and we don’t know what’s causing these differences. How our brain reacts to stuff depends on everything we’ve ever experienced in life. It could be that monogamous men have just had really rewarding experiences with love and romance, and that’s why they have more reward activation, because they’ve learned that, not because they’re born that way. Now, all we can say is people who are currently monogamous and people who are currently non-monogamous, their brains respond to different stimuli in different ways, but we don’t know why.

So Personal Experience Makes The Most Difference When It Comes To Fidelity?

People can have a tendency towards monogamy and have rewarding things happen related to monogamy, and then find romance attractive. Or they can be oriented towards monogamy and have very bad experiences and learn to be non-monogamous. I think people have a predisposition one way or the other, but your interactions and the things you experience throughout life can push you in either direction.

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