First comes sex, then comes marriage? Love can grow from lust, study says

Questions about sexual desire and love have plagued humans for eons. While poets, musicians, and artists believe love lives in the heart, scientists know it exists in the brain. And sex? Apparently, that urge resides in the "little brain" or the bed or maybe a barn. It gets a little confusing what with those tired old adages about cows and free milk (or pigs and free sausage).

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He wants you, but does he love you? A new study finds love and sexual desire are controlled by the same part of the brain.

Now a new study has found that the same regions of the brain that control love also control sex -- indicating that sexual desire can actually morph into love. That's right. If a woman has sex with a man, he might not only buy the cow but love the cow, as well.

“Love and sex are clearly overlapping and they are different,” says Jim Pfaus, a professor of psychology at Concordia University in Montreal who's been studying love and libidos for more than a decade. “You can have desire for sex without love.”

But sex can also be the start of a beautiful relationship.

How does all of this work?

The brain's insular cortex (or insula) and the striatum play a role in both sexual desire and love. The insula is nestled deep within the cerebral cortex and influences emotions. While the striatum resides in the forebrain and receives messages from the cortex.

In order to map out the location of sexual desire and love, researchers reviewed 20 studies that used fMRI technology. First, they looked at the regions of the brain that lit up when sparked by love. They then compared the findings of all the papers to see what regions were activated when someone felt aroused or amorous.

What they discovered was a bit surprising -- love and sexual desire both activate the striatum, showing a continuum from sexual desire to love. Each feeling impacts a different area of the striatum.

Sexual desire activates the ventral striatum, the brain’s reward system. When someone enjoys a great dessert or an orgasm, it’s the ventral striatum that flickers with life. Love sparks activity in the dorsal striatum, which is associated with drug addiction.

“You don’t make a connection that love is a drug; it acts just like drug addiction," says Pfaus. "Anyone who has had someone break up with them feels like a drug addict in withdrawal. You end up getting cravings.”

But it doesn't stop there. The researchers also saw an overlap between sexual desire and love in the insula.

“[The insula] translates emotional feelings into meaning,” explains Pfaus. “You take the internal state and give it external meaning.”

The areas of overlap indicate that sexual desire transitions into love in many cases, and the feelings aren’t separate.

“Even love at first sight, can it happen? Of course it can happen," says Pfaus. "And when it does happen, do you want to play Scrabble with each other? When it happens, you normally want to consummate it.”