By Florence Williams

We all know that when love is good, it’s really good. Research shows that romantic attachments, when they’re healthy and supportive, can be immensely beneficial for our health. Married people tend to live longer than single people and seem to fare better when seriously sick.

But as poets and pop singers have long told us, when love goes awry, it hurts like nothing else. After my marriage ended—not by my choice—I found some comfort in art, but what I really wanted was science. I wanted to know why we feel so operatically sad when a romantic attachment dissolves. What I discovered is that love changes us so deeply—at a physiological level—that when it’s lost, we hurt more than if we had never loved at all.

“One of the most painful experiences that a human being can suffer is to lose a life partner,” says Helen Fisher, the author of Anatomy of Love: A Natural History of Mating, Marriage, and Why We Stray and a biological anthropologist who studies the neurochemistry of love as a research fellow at the Kinsey Institute. Despite that, she told me, it’s been vastly underexamined as a topic of study. Many scientists, she believes, simply underestimate the power of heartbreak, but they also find the excitatory state of falling in love more alluring. Fisher herself has done plenty of that. But after years of tracking the brains of the suckers who fall in love, she thought it would be interesting to see what happened to them once they’ve tumbled out the other side. She herself has been there, and so have most people.

For a paper published in 2010, Fisher and her colleagues put 15 people who hadn’t gotten over their breakups in a brain scanner. Researchers took images of each subject’s brain as the person viewed a photo of their rejecter and as they viewed a photo of a neutral, familiar person. While viewing rejecters, their brains showed activation in some of the same regions as those still happily in love. It reminded me of a passage from Rachel Cusk’s divorce memoir, Aftermath: “Grief is not love but it is like love. This is romance’s estranged cousin, a cruel character, all sleeplessness and adrenaline unsweetened by hope.”

In the study, brain regions that are associated with cravings and emotional regulation lit up, including the ventral tegmental area (VTA) bilaterally, ventral striatum, and cingulate gyrus. Many of the activated regions are necessary for feeling romantic love—and, Fisher added, for fostering cocaine addiction.

If love is an addiction, it can be a constructive one, compelling us toward one another. But when love is not returned, the physical effects can be ugly. In addition to finding activity in parts of the brain linked to craving and addiction, Fisher’s team also saw activation in parts of the insular cortex and the anterior cingulate that are linked to physical pain. These regions also light up when you have a toothache, said Fisher. The difference is that with heartbreak, the pain can last and last.

In Fisher’s study, all subjects said that they thought about their rejecting beloveds for more than 85 percent of their waking hours. They also reported “signs of lack of emotion control on a regular basis since the initial break up, in all cases occurring regularly for weeks or months,” the researchers wrote. When it comes to heartbreak, many of us become uncharacteristically tempestuous.

Sometimes we become suicidal. One paper found that among adolescents experiencing suicidal ideation in the U.S., breaking up is one of the largest risk factors for a first suicide attempt, and according to one study, among adults who died by suicide, intimate-partner problems are a factor 27 percent of the time, more than any other the study asked about, including poor physical health, financial trouble, and eviction. “I think nature has overdone it,” Fisher told me.

She explained there are two basic neurological stages of getting dumped: protest and resignation. During the protest stage, many people try to win their beloved back. This behavior, she said, seems to be based on a cocktail of extra dopamine and norepinephrine flooding your brain. You’re searching for what you’re missing, and you’re scared. I could relate: I felt like I’d been plugged into an amplifier in the months after my split. This was, Fisher told me, hypervigilance in response to one’s new threat-filled state. That helps explain the sleeplessness, weight loss, and general agitation that can occur among the newly dumped.

During the resignation stage, Fisher said, people largely give up the protests and the bargaining. This is when the dopamine drops off, and so does serotonin, a neurotransmitter often linked to feelings of well-being. “Yeah, I’m there,” I said, although I wasn’t completely convinced about the resignation. “You sound like you’re there,” she said. “Once you’re there, it’s lethargy and, of course, a lot of tears. Now some people will drink too much, drive too fast, or hole up and watch TV. Other people will talk their heads off about it. [None of those are] very good.”

Zoe Donaldson, a behavioral neuroscientist, is also interested in seeing the signature of heartbreak in our brains. But her ambition is to map it on an absurdly granular level, at the scale of neurons. You can’t really go around sticking mini-​microscopes in the heads of heartbroken people, so her subjects are prairie voles.

Prairie voles may not get divorced, but they know partner loss. Like us, some prefer to play the field, but they tend to be socially monogamous (meaning they shack up with a partner and raise their young together). They are even a bit more loyal to the idea of coupledom than we are these days. Once paired up, about 75 percent will stay together until one dies, even when the female isn’t reproducing. (By comparison, a little more than 30 percent of adults older than 20 in the U.S. who’ve been married have also gotten divorced—and that’s not even counting all the couples that never get married.) Prairie voles are inveterate snugglers with their mates and their pups. Males even seem to console stressed female partners by grooming and licking them. Within a few days of their first mating encounter in a lab, males and females will almost always prefer to spend time with their lover over all others, even when sexy newcomers are dangled like taffy before them.

rief is often characterized by stress and depression, along with yearning. Although it’s tricky to compare these emotions across species, scientists have tried to study them in prairie voles who lose their partners. A former colleague of Donaldson’s, Oliver Bosch, split up half of his vole couples in an experiment. He also paired some male voles with their male siblings, and then split half of those pairs as well. He then subjected the males to various tribulations: He either dropped them into steep beakers of cool water (the so-called Forced Swim Test); suspended them by their tails, which were duct-taped to an aluminum stick that was hung in a black box (aptly named the Tail Suspension Test); or placed them in a maze suspended high above the ground (the Elevated Plus-​Maze). The latter creates a conflict situation: Will the voles indulge their exploratory nature by venturing into the exposed open corridors of the maze or stay in the closed corridors?

Compared with males who were still enjoying time with their mate, the partner-​separated voles spent less time flailing and fighting their way out of the swim beaker and the black box. They essentially threw up their paws. Scientists call this listlessness “passive coping,” and many believe it resembles depression, though that label is somewhat controversial. Bosch’s study found some increase in anxious behaviors among those separated from any pairing (male or female) in the maze, and similar research conducted elsewhere showed that newly bereft voles spent less time venturing out into the open and more time in the enclosed corridors (behavior likened to anxiety).

It wasn’t only the voles’ behavior that changed; so did their neurochemistry. Partner-​separated voles produced more corticosterone, a stress hormone, than voles separated from their siblings, and, according to Bosch’s study, their adrenal glands—​which manufacture these hormones—​also weighed more. Their high stress levels seemed to be linked to their behaviors in the tests. When Bosch and his team shut down the voles’ corticotropin-​releasing factor (CRF, a major generator of the stress hormones), they spent about the same amount of time passively floating or hanging immobile as their happier brethren.

But here’s where things get really interesting. In all partnered males in Bosch’s study, regardless of whether they were later split up or not, their brains made more of the stress-generating machinery, CRF, than the never-partnered. At first, Bosch and his team were surprised by this. Why would the brains of those in love rev up all that ammunition just to sit idly by? But then they learned that in coupled-up prairie voles, CRF largely doesn’t lead to stress activation. Unless, that is, the bonds of love are broken. Then the enhanced stress machines are prepared to respond to heartbreak quickly. As much as it hurts, the misery may be adaptive: It drives us to reconnect with our lost partners after brief separations, and it keeps us coming back home.

We are built for heartbreak just as we are built for love. To paraphrase the French philosopher Paul Virilio, the invention of the ship is also the invention of the shipwreck. Or, as Helen Fisher put it, “almost nobody gets out of love alive.” It may sound grim, but I found it comforting. My pain wasn’t singular, although heartbreak often feels that way. There was a reason for it after all.

Pair ​bonding, love—call it what you will—changes us. It changes the brain in some permanent ways that make us more sensitive to both joy and woe; it gives us a sense of something to lose. Falling in love puts a loaded gun to our head.

This is an excerpt from Florence Williams’ new book, Heartbreak: A Personal and Scientific Journey.