Why Your Brain Is Better in Love

The following was originally posted to the Psychology Today blog Neuronarrative.

Here's a quick pop quiz: who makes more money, hookers on birth control or off? During difficult economic conditions, are Playboy Playmates generally older or younger, heavier or thinner? Why are men attracted to larger breasts? And do gentlemen really prefer blondes? (I'll give you the answer to that last one: yes... sort of.)

These and many more questions are discussed in Jena Pincott's candid, evidence-based book, Do Gentlemen Really Prefer Blondes?: Bodies, Behavior, and Brains --The Science Behind Sex, Love, and Attraction. If science could ever be considered sexy, this is the book that shows precisely why. I spent some time talking to Jena about brains in love and lust, the power of dilated pupils, and whether semen has mind control properties, among other topics.

DiSalvo:Do Gentlemen Really Prefer Blondes? is a book that answers a slew of questions people have on their minds all the time but aren't really sure how to ask, or where to ask--or even if they can get away with asking. What inspired you to write it?

Pincott: Do Gentlemen Really Prefer Blondes? is a book about how genes, hormones, and instincts affect our love lives in ways we might not even realize. I've always been fascinated by the things that (mostly) slip under the radar of awareness. Smell is one of them -- at one point, when I was single and dating, I wondered why it is that I like the smell of some men but not others. This led me to do some research on the relationships between body odor preference and genes (more on this below). While I was looking into this, many other love-sex-and-attraction-related questions surfaced -- and I thought the answers would make a fascinating book.

The evolutionary dynamics underlying mating behavior have been discussed for quite a while, and always with the controversy we've come to expect from any subject involving evolutionary explanations for human behavior. Has your foray into this topic brought any controversy your way?

Yes, many of the topics in the book are grounded in evolutionary psychology -- and many evolutionary theories just cannot be proven. Are breasts, long hair, and symmetrical features sexually selected traits? Darwin thought they were. How about creativity, intelligence, humor, and dance and musical ability? There's an argument there, although it's likely that other evolutionary pressures also influenced these traits. To the extent that evolutionary psychology is controversial, so is my book. Then again, as I've recently discovered, a disturbing number of people don't believe in evolution at all!

So let's get into a few of the areas you cover in the book. You say that "Love changes the brain" and that the brain-in-love even "grows." Tell us a little bit about why (and how) this happens.

I love what Einstein said about this: "How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?"

Well, there are a number of studies in which subjects in love were asked to lie inside a fMRI machine and gaze at a picture of their beloved. In brief, here's what researchers found from the brain scans: the ventral tegmental area (VTA) is activated; this produces the "feel-good" hormone dopamine, which targets the reward areas of the caudate nucleus and nucleus accumbens. It's a high, and it's addictive. Bonding is aided and abetted by such hormones as oxytocin and vasopressin. The obsessive fixation many of us get when we first fall in love -- can't stop thinking about him or her -- is due to low serotonin levels.

Meanwhile, the prefrontal cortex, the part of the brain responsible for reasoning, and the amygdala, related to fear, are deactivated—which explains why a lot of us become reckless fools in love. If a woman in love remembers more details than men do, it's because there's more activity in the female hippocampus, the region associated with memory. And it seems true that when it comes to love men are more visual than women are—guys show more activity in their visual cortex.

When two people fall in love, they form a neural pattern of associations and rewards that are strengthened over time and with use. Researchers call this a "love-related" network, and there's some evidence that people in close relationships, when reminded of their love, perform better on mental tasks.

Are there any specific marks of distinction between the brain-in-love and the brain-in-lust?

Yes, researchers such as anthropologist Helen Fisher believe that love and lust are separate yet overlapping neural experiences. That's why you can love your spouse yet be turned on by a stranger. Love and lust are both highly rewarding and addictive -- and affect very similar regions of the brain -- but there are some distinct differences.

For instance, brain scans of people in loving, long-term relationships show increased activity in the ventral pallidum, a region of the brain rich with oxytocin and vasopressin receptors that meditate pair-bonding and attachment.

On the topic of attraction, you say that symmetry is the name of the game. You also talk about the eyes as "the face's most blatant and bewitching feature" -- particularly the pupils. How is it that humans have come to value qualities such as facial symmetry and pupil size so highly when selecting a mate? (and what is it about eyes? Why not lips, or ears?)

Facial symmetry is a cue of health and developmental stability. Interestingly, researchers reviewing medical records found that subjects with the most symmetrical features had fewer infections. As for eyes -- whether or not they're windows to the soul, they do reveal more emotional cues than the ears or nose. (Although the lips are important -- eye contact is most effective when paired with a smile). Dilated pupils signal emotional and sexual arousal, which is why men in particular are attracted to them.

In a nutshell, what do we know about the role smell plays in attraction? Can someone 'scent' him or herself into a meaningful relationship?

There's so much to say about smell and sexuality! I think it's the section of my book that I like the most. In brief, we know smell certainly does mediate attraction. Androstadienone, a testosterone derivative in men's sweat, has been found to make women more attentive and lift their moods. There's no universal aphrodisiac: no cologne, perfume, or spray-on pheromone that will necessarily attract a mate. (But they may boost a person's confidence, and that helps!)

Women are particularly picky about men's body odor smells. It turns out that women prefer the smell of men whose immune system genes (major histocompatibility complex or MHC) are mostly different from their own. There's an evolutionary explanation: children whose parents are genetically dissimilar would inherit a more diverse set of immune system genes. (This was the topic that inspired the book; see question #1 above,)

You say in the book that semen is a sort of "feel good" serum, capable of inducing a temporary form of mind control. What's the deal with this?

Well, it's a provocative theory, and it goes as follows: Semen contains hormones and proteins. Absorbed through the vaginal walls, these hormones and proteins enter the bloodstream and possibly breach the blood-brain barrier. Whether or not this has any psychological affect on a person is unclear and difficult to prove, although a study has found that women who are regularly exposed to their partner's semen are less depressed than women who use condoms most of the time (regardless of the strength of the relationship). There's an evolutionary argument for this: if there's something in semen that makes women happier, they'll come back for more.

Now that you've answered some of the questions on all of our minds, what's next on your radar screen?

What can surpass the science of love, sex, and attraction? I'm always on the lookout for fascinating new research on this topic, which I report on in my blog at www.jenapincott.com.

David DiSalvo is a science, technology and culture writer for Scientific American Mind, Mental Flossand other publications, and the writer behind the blog, Neuronarrative, which reaches 100,000 readers in more than 200 countries every month. He has appeared on CNN’s Headline News, and his work is referenced in news outlets worldwide. David is also an award-winning public outreach and education specialist with nearly 18 years of experience communicating complex technical messages with palatable prose. He has served as a consulting research analyst and communications specialist for the U.S. Environmental Protection Agency and several other public and private organizations in the U.S. and abroad, spanning from Boston to Beijing.He is feverishly working on his first non-fiction book, tentatively titled, What Makes Your Brain Happy, and Why You Should Do the Opposite (Prometheus Books, 2011). He lives in Florida with his wife and three children.