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What Happens to Your Brain When You Fall in Love?

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Falling in love is one of the best feelings in the world—and humans might not be the only creatures who do it. Pair bonding, the two-by-two partnering of creatures, has been seen across the animal kingdom. Whether or not a nesting pair of robins can be said to truly love each other, we're still awfully interested in why animals might pair off. The tools available to biologists have advanced immensely in the last few decades, and some are using that technology to decipher physiology involved in both pair bonding and love.

Getting In-Vole-ved

To unravel the mysteries behind pair bonding, researchers studied not robins, but voles. Prairie voles and montane voles are closely related rodents with a stark difference in mating behavior: prairie voles form lifelong pair bonds after mating, while montane voles are promiscuous. The work of Thomas Insel, director of the National Institute of Mental Health (NIMH), and colleagues showed that the different mating behaviors can be linked to the hormones oxytocin and vasopressin. Oxytocin stimulates childbirth and lactation, while vasopressin regulates the kidneys and constricts blood vessels. More recent research has implicated the two hormones in many different social behaviors, from working cooperatively to selecting mates to inferring the emotions of others. Oxytocin in particular has calming effects and seems to help build trust between people.

The crucial physiological difference between these two species of vole is in the distribution of oxytocin and vasopressin receptors in the voles' brains. Prairie voles have a higher density of both types of receptors in the amygdala, the area of the brain involved in emotion-related memory formation, and in various parts of the dopamine reward system. Both hormones are released when prairie voles mate, prompting pair bonds to form. When the hormone release is blocked, prairie voles become promiscuous. Perhaps more tellingly, when montane voles are genetically modified to have prairie vole-like distributions of vasopressin receptors, they become monogamous.

Dopamine is an important part of the picture as well. The release of dopamine gives a pleasurable feeling, and is used in the brain to reward behaviors such as procreating or eating a hearty meal. Voles that are made more sensitive to dopamine can develop partner preferences without mating—a friendly encounter will do. Voles whose dopamine receptors are blocked do not form partner preferences at all. Many of the dopamine receptors and pathways responsible for pair bonding in voles are also involved in cocaine addiction in rodents. This suggests a possible explanation for the addictive feeling of love.

This is your brain on Love

In humans, Donatella Marazziti, Professor of Psychiatry and Director of the laboratory of Psychopharmacology at the University of Pisa, has found that early stages of romance are linked with diminished levels of the neurotransmitter serotonin and of a serotonin receptor. These two molecules are also depleted in obsessive-compulsive disorder. Since both conditions (to different extents) also give rise to feelings of anxiety and obtrusive thinking, it is tempting to think of early love as a mild, temporary form of obsessive behavior. Early romance is also characterized by higher levels of several different molecules related to stress response. Twelve to 18 months into a relationship, both serotonin and the stress molecules are restored to normal levels.

Researchers like Helen Fisher of the Department of Anthropology at Rutgers University and Semir Zeki of UCL in London have done functional MRI studies to identify the regions of the brain that are activated or deactivated by romantic love. They've found that people in romantic love show increased activity in a number of different regions of the brain that are involved in the dopamine reward system. Parental love activates most of the same regions but not the hypothalamus, suggesting that the hypothalamus may be responsible for the sexual component of romantic love.

Areas that show reduced activity include the amygdala and the frontal and prefrontal cortecies. The amygdala is associated with fear and aversive learning, or learning from one's mistakes. The frontal and prefrontal cortecies are associated with the executive functions of analysis and judgment, delayed gratification, and predicting the outcomes of events. We can speculate that diminished activity in these regions explains why lovestruck persons do not seem to have full grasp of these particular functions. Fisher summarizes some of her findings magnificently in her 2008 TED talk.

The physiology of love is not totally understood, and research is ongoing. Researchers have begun to explain the pair bonding of animals such as voles, and have identified patterns of hormones and brain activity that show up among people in romantic relationships. What physiology tells us about love is what we knew all along—that it is a stressful matter bordering on an addiction or an obsessive disorder, that it muddles one's judgment and leads one to act rashly, and that as it grows, these disturbances fade and give way to calm and joy.

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Big Questions
What is Duck Sauce?
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A plate of Chinese takeout with egg rolls and duck sauce
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We know that our favorite Chinese takeout is not really authentically Chinese, but more of an Americanized series of menu options very loosely derived from overseas inspiration. (Chinese citizens probably wouldn’t recognize chop suey or orange-glazed chicken, and fortune cookies are of Japanese origin.) It would also be unusual for "real" Chinese meals to be accompanied by a generous amount of sauce packets.

Here in the U.S., these condiments are a staple of Chinese takeout. But one in particular—“duck sauce”—doesn’t really offer a lot of information about itself. What exactly is it that we’re pouring over our egg rolls?

Smithsonian.com conducted a sauce-related investigation and made an interesting discovery, particularly if you’re not prone to sampling Chinese takeout when traveling cross-country. On the East Coast, duck sauce is similar to sweet-and-sour sauce, only fruitier; in New England, it’s brown, chunky, and served on tables; and on the West Coast, it’s almost unheard of.

While the name can describe different sauces, associating it with duck probably stems from the fact that the popular Chinese dish Peking duck is typically served with a soybean-based sauce. When dishes began to be imported to the States, the Americanization of the food involved creating a sweeter alternative using apricots that was dubbed duck sauce. (In New England, using applesauce and molasses was more common.)

But why isn’t it easily found on the West Coast? Many sauce companies are based in New York and were in operation after Chinese food had already gained a foothold in California. Attempts to expand didn’t go well, and so Chinese food aficionados will experience slightly different tastes depending on their geography. But regardless of where they are, or whether they're using the condiment as a dipping sauce for their egg rolls or a dressing for their duck, diners can rest assured that no ducks were harmed in the making of their duck sauce.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
Can You Really Go Blind Staring at a Solar Eclipse?
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A total solar eclipse will cut a path of totality across the United States on August 21, and eclipse mania is gripping the country. Should the wide-eyed and unprotected hazard a peek at this rare phenomenon?

NASA doesn't advise it. The truth is, a quick glance at a solar eclipse won't leave you blind. But you're not doing your peepers any favors. As NASA explains, even when 99 percent of the sun's surface is covered, the 1 percent that sneaks out around the edges is enough to damage the rod and cone cells in your retinas. As this light and radiation flood into the eye, the retina becomes trapped in a sort of solar cooker that scorches its tissue. And because your retinas don't have any pain receptors, your eyes have no way of warning you to stop.

The good news for astronomy enthusiasts is that there are ways to safely view a solar eclipse. A pair of NASA-approved eclipse glasses will block the retina-frying rays, but sunglasses or any other kind of smoked lenses cannot. (The editors at MrEclipse.com, an eclipse watchers' fan site, put shades in the "eye suicide" category.) NASA also suggests watching the eclipse indirectly through a pinhole projector, or through binoculars or a telescope fitted with special solar filters.

While it's safe to take a quick, unfiltered peek at the sun in the brief totality of a total solar eclipse, doing so during the partial phases—when the Moon is not completely covering the Sun—is much riskier.

WOULDN'T IT BE EASIER TO JUST TELL YOUR KIDS THEY WILL GO BLIND?

NASA's website tackled this question. Their short answer: that could ruin their lives.

"A student who heeds warnings from teachers and other authorities not to view the eclipse because of the danger to vision, and learns later that other students did see it safely, may feel cheated out of the experience. Having now learned that the authority figure was wrong on one occasion, how is this student going to react when other health-related advice about drugs, alcohol, AIDS, or smoking is given[?]"

This story was originally published in 2012.

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