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Your Brain on Love: The Fascinating Biochemical Reactions That Make Sparks Fly

When you and another truly connect, your brain syncs up with the other person’s brain.

Photo Credit: Shutterstock.com/umnola

The following is an excerpt from Love 2.0: How Our Supreme Emotion Affects Everything We Feel, Think, Do, and Become.

 

Love on the Brain

When you and another truly connect, love reverberates between you. In the very moment that you experience positivity resonance, your brain syncs up with the other person’s brain. Within each moment of love, you and the other are on the same wave length. As your respective brainwaves each mirror the other, each of you—moment-by-moment— changes each other’s mind.

At least this is what I’ve been telling you. How do you know it really happens? You can’t see this brain synchrony surface within real-time after all. What you’d need is some way to peer inside two people’s heads while they chatted so that you can tell whether or not their respective brain activity really does march along in time together. This would tell you whether they really “click.” Only with this sort of X-ray vision could you decide whether love is better described as a solo act—an emotion contained within the boundaries of the person feeling it—or a duet or ensemble, performed by a duo or group. That sort of X-ray vision sounds like science fiction.

Yet turning science fiction into science fact is what scientists and engineers love most. Breakthrough work by neuroscientist Uri Hasson, of Princeton University, has done just that. He and his team have found ways to measure multiple brains connecting through conversation. The obstacles they faced to do this were large. First, brain scanners are loud machines—no place to carry on actual conversations. Second, they’re also extraordinarily expensive, both to buy and to use. Almost all brain imaging studies thus scan just one person’s brain at a time. Yet with clever engineering and clever experimental logistics, Hasson’s team cleared both obstacles. They created a custom optic microphone that cancelled out the noise of the scanner without distorting the delicate brain signals his team sought to capture. The logistics feat was to mimic a natural conversation by pulling it apart in time.

Suppose, for a moment, you were stranded at the airport last week. Your plane to Miami was delayed for hours. Bored with your reading and web-browsing, you got to talking to another stranded passenger, a lively young college student on her way home for break. You’d been chatting back-and-forth for a while, every so often, meeting eyes and sharing smiles. The conversation was very natural, like you were friends already. Somehow or another, she got to telling you about her crazy high school prom experience. In great detail, she launched into how she happened to have two dates to the same prom, how she ended up having only five minutes to get dressed and ready for the prom after a full day of scuba-diving; how, on her way to after-prom festivities, she crashed her boyfriend’s car in the wee hours of the morning; and then how she completely lucked out of getting ticketed (or arrested!) by the officer who witnessed her accident. She’s a good story-teller: You hung on her every word. Fifteen minutes melted away as she shared all the twists and turns of her hapless prom night. It’s clear, too, that you both enjoyed the chance to connect, rather than read, while you waited for your plane together.

Okay, now it’s time for a set change: Instead of in an airport terminal, this conversation actually unfolded in a brain imaging lab at Princeton University. And instead of sitting side-by-side with your impromptu friend, Hasson’s team actually invited her to visit the lab weeks ago, and they audio-recorded her entire prom story while scanning her brain’s activity with functional magnetic resonance imaging (fMRI.) You’re here lying in the scanner today, listening to her story over fancy headphones, while Hasson’s team records your own brain activity. After you get out of the scanner, they ask you to report on what you heard in as much detail as possible. This takes a while; hers was a long, circuitous story after all.

Hasson’s team later looked at the extent to which your brain activity mirrored hers. They painstakingly matched up each specific brain area across the two of you, time-locked your respective scans, and looked for “coupling,” or the degree to which your brains lit up in synchrony with one another, matched in both space and time.

It turns out that the brain coupling evident between you two is surprisingly widespread. In other words, speaking with and listening to the human voice appear to activate much of the exact same brain activity at pretty much the same time. Keep in mind that—despite your new friend’s gift for story-telling—this was still a pretty artificial conversation. Isolated inside the brain scanner across different days, you never actually got to see each other’s gestures, meet each other’s eyes, or even take turns speaking. You only listened to her voice over headphones. The brain coupling that would emerge in real-time, with the full and animated dialogue that could well spring up between the two of you if you were in fact seated side-by-side in the airplane terminal is likely to be far more extensive. Yet hearing someone’s voice offers an important channel of sensory and temporal connection, because voice can convey so much emotion. By contrast, consider how little brain coupling would emerge if the connection between the two of you were to be further reduced, for instance, if you only read her story, at your own pacing and presumed intonations, or only heard abouther story, as in my thumbnail depiction of it a few paragraphs back.

Forget the idea of a few isolated mirror neurons. So-called mirror neurons refer to a microscopic brain area that Italian neurophysiologists found to “light up” both when a monkey reaches for a banana, and when that same monkey sees a person reach for a banana. The discovery of mirror neurons was a huge breakthrough because it told us that taking some action and seeing someone else take that same action are far more alike than previously thought. This means that when you know something—like why that person who just walked into your office is smiling—you know it because your brain and body simulate being in that person’s shoes, in their skin. Your knowing is not just abstract and conceptual, it’s embodied and physical. Yet it seems now that the concept of isolated mirror neurons was just the tip of the unseen and enormous iceberg. What Hasson and his team uncovered was far more extensive neuronal coupling than previously imagined. Far from being isolated to one or two brain areas, really “clicking” with someone else appears to be a whole brain dance in a fully-mirrored room. The reflections between the two of you are that penetrating and widespread.

It turns out that you weren’t the only one listening to your new friend’s prom story. Hasson’s team invited ten other people to have their brains scanned while listening to the very same audio-recording of her story that you heard. Whereas you listened attentively to everything she said, others didn’t so much. Those differences showed up clearly when you were each asked to recount her story afterwards. By tallying up the matches between her original, impromptu prom story and each listener’s retelling of it, Hasson’s team rank ordered the whole set of listeners by how well they understood the story. Those differences in comprehension reflect the success or failure of communication— how thoroughly information from her brain was transferred to your brain, and to the brains of the other listeners. Strikingly, Hasson’s team discovered that the degree of success in communication predicted the degree of brain coupling between speaker and listener, and did so in surprising ways.

Most of the time, across most brain areas, listeners’ brains mirrored the speaker’s brain after a short time lag, around one to three seconds later. It only makes sense, after all, that the speaker leads this dance, since the story is hers and she chooses her words before you and the others hear them. In other cases, though, this neural pas-de-deux between speaker and listener showed hardly any lag at all—the respective changes in brain activity were virtually perfectly synchronized. Your particular case was different, however. Recall that you were the one who grasped your new friend’s story better than anybody. You hung on every word and picked up every detail of it, even the seemingly inconsequential ones. Your more complete grasp of her story went hand-in-hand with something truly remarkable: Your brain activity actually anticipatedher brain activity by a few seconds in a several cortical areas. Excellent communication, it thus seems, doesn’t simply involve following along very closely. It also involves forecasting. Once you were in sync and on the same page with your new friend, enjoying her and her story, you could even anticipate what she’d say next, or how she’d say it. Your brain could anticipate her brain’s next move.

Brain coupling, Hasson argues, is the means by which we understand each other. He goes even further to claim that communication— a true meeting of the minds—is a single act, performed by two brains. Considering the positivity resonance of love, what I find most fascinating about these findings is that a key brain area that showed coupling in Hasson’s speaker-listener study was the insula, an area linked with conscious feeling states. Evidence for synchrony in two people’s insulae suggests that in good communication, two individuals come to feel a single, shared emotion as well, one that is distributed across their two brains. Indeed, in other work, Hasson and colleagues have shown that people’s brains come particularly into sync during emotional moments. Neural coupling, then—really understanding someone else—becomes all the more likely when you share the same emotion. Even more so than ordinary communication, a micro-moment of love is a single act, performed by two brains. Shared emotions, brain synchrony, and mutual understanding emerge in step together. And mutual understanding is just steps away from mutual care. Once two people understand each other—really “get” one another in any given moment—the benevolent concerns and actions of mutual care can flow forth unimpeded.

As you move through your day, quite naturally you move in and out different scenes. Each scene, of course, has its own script. For perhaps most of your day, you’re pretty much caught up in your own thoughts and plans, oblivious to the presence or feelings of anyone nearby. Your brain, in such moments, is doing its own thing. But in those rarer moments when you truly connect with someone else over positivity— by sharing a smile, a laugh, a common passion, or an engaging story— you become attuned, with genuine care and concern for the other. You empathize with what they’re going through, as your two brains sync up and act as one, as a unified team.

Neural coupling like this is a biological manifestation of oneness. Laboratory studies have already shown that when positive emotions course through you, your awareness expands from your habitual focus on “me,” to a more generous focus on “we.”9 When you’re feeling bad—afraid, anxious, or angry—even your best friend can seem pretty remote, or separate from you. The same goes for when you’re feeling nothing in particular. Not so, when you’re feeling good. Under the influence of positive emotions, your sense of self actually expands to include others to greater degrees. Your best friend, in these lighthearted moments, simply seems like a bigger part of you.

Hasson’s work suggests that when you share your positive emotions with others, when you experience positivity resonance together with this sense of expansion, it’s also deeply physical, evident in your brain. The emotional understanding of true empathy recruits coinciding brain activity in both you and the person of your focus. Another telling brain imaging study, this one conducted by scientists in Taipei, China, illustrates self-other overlap at the neuronal level. Imagine for a moment being a participant in this study. While you are in the fMRI brain scanner, the researchers show you a number of short, animated scenes and ask you to picture yourself in these scenes. Some of these scenes depict painful events, like dropping something heavy on your toe, or getting

your fingers pinched in a closing door. What the brain images show is that, compared to imagining neutral, non-painful situations, imagining yourself in these painful situations lights up the well-known network

of brain areas associated with pain processing, including the insula, that area linked with conscious feeling states. When you are later asked to imagine these same painful events happening to a loved one—your spouse, your best friend, or your child, for instance—these same brain areas light up. By and large, then, your loved one’s pain isyour pain. By contrast, when you imagine these painful events happening to a complete stranger, a different pattern of activation emerges altogether, one that shows little activation in the insula, and more activation in areas linked with distinguishing and distancing yourself from others, and actively inhibiting or regulating emotions, as if to prevent their pain from becoming your pain. At the level of brain activity during imagined pain, you and your beloved are virtually indistinguishable.

Whereas the Taipei research team defined love to be a lasting loving relationship (what, for clarity’s sake, I call a bond), the work from Hasson’s team at Princeton tells me that neural synchrony and overlap can also unfold between you and a complete stranger—if you let it. Positivity resonance between brains, as it turns out, requires only connection, not the intimacy or shared history that comes with a special bond. Even so, the distinctions revealed in the Taipei study, between imagining your loved one’s pain and imagining a stranger’s pain, underscore that stifled emotions and guarded personal boundaries, while at times necessary and fully appropriate, can also function as obstacle to positivity resonance. As we’ll see in the next section, your attunement to various opportunities for positive connection with others is supported not just by neural synchrony, but by the hormone oxytocin as well.

Biochemistries in Love

Oxytocin, which is nicknamed by some the “cuddle hormone” or the “love hormone” is actually more properly identified as a neuropeptide because it acts not just within your body but also within your brain. Oxytocin has long been known to play a key role within social bonding and attachment. Clear evidence of this first emerged from experiments with a monogamous breed of prairie voles: Oxytocin, when dripped into one animal’s brain in the presence of the opposite sex, creates a long-lasting preference to remain together, cuddled up side-by-side, behavior taken as evidence that oxytocin sparked the formation of a powerful social bond between them. In humans, oxytocin surges during sexual intercourse for both men and women, and, for women, during childbirth and lactation, pivotal interpersonal moments that stand to forge new social bonds or cement existing ones. The natural blasts of oxytocin during such moments are so large and powerful that for many years they all but blinded scientists to the more subtle ebb and flow of oxytocin during more typical day-to-day activities, like playing with your kids, getting to know your new neighbor, or striking a deal with a new business partner. Technical obstacles also needed to be cleared. Decades after oxytocin’s role in monogamous prairie voles had been amply charted, scientists studying human biochemistry still struggled to find ways to reliably and noninvasively measure and manipulate oxytocin during natural behavior. Scientific understanding of oxytocin’s role in your everyday social life could not advance without more practical research tools at hand.

Dramatic new evidence on oxytocin’s power to shape your social life first surfaced in Europe, where laws permitted the use of a synthetic form of oxytocin, available as a nasal spray, for investigational purposes. Among the first of these studies was one in which 128 men from Zurich played the so-called “trust game” with real monetary outcomes on the line. At random, these men were assigned to either the role of “investor” or the role of “trustee,” and each was given an equivalent pot of starting funds. Investors made the first move in the game. They could give some, all, or none of their allocated funds to the trustee. During the transfer of funds, the experimenter tripled their investment while letting the trustee know how much the investor had originally transferred. Trustees made the next move. They could give some, all, or none of their new allotment of funds (the investors’ tripled investment plus their own original allocation) back to investors. The structure of the game puts investors, but not trustees, at risk. If an investor chose to entrust the other guy with their investment, he risked receiving nothing in return if the trustee chose to selfishly keep the entire monetary gain to himself. But if the trustee was fair, they could each double their money.

Prior to playing this trust game, using a double-blind research design, participants received either oxytocin or an inert placebo by nasal spray. The effect of this single intranasal blast of oxytocin on the outcome of the trust game was dramatic: The number of investors who trusted their entire allotment to their trustee more than doubled. Interestingly, related research using this same trust game showed that the mere act of being entrusted with another person’s money raises the trustee’s naturally-occurring levels of oxytocin, and that the greater the trustee’s oxytocin rise, the more of their recent windfall they sacrificed back to the investor. The neuropeptide oxytocin, then, steers the actions of both the investor and the trustee, shaping both trust and reciprocity. These findings suggest that through synchronous oxytocin surges, trust and cooperation can quickly become mutual.

Since the original study on oxytocin and the trust game was published in Naturein 2005, variations on it have abounded. We now know, for instance, that oxytocin doesn’t simply make people more trusting with money, it also makes them far more trusting—a whopping 44% more trusting—with confidential information about themselves. Interestingly, the simple act of sharing an important secret from your life with someone you just met increases your naturally circulating levels of oxytocin, which in turn raises your confidence that you can trust that person to guard your privacy. Thankfully, we also know that oxytocin does not induce trust indiscriminately, making people gullible and therefore open to exploitation. The effects of oxytocin on trust turn out to be quite sensitive to interpersonal cues, like those subtle signs that tip you off that another may be the gambling type, or irresponsible in other ways. Rest assured, then, if oxytocin spray were to be aerated through your workplace ventilation system, you’d still maintain your shrewd attunement to subtle signs that suggest whether someone is worthy of your trust or not.

Researchers have since moved on to examine the effects of oxytocin on people’s sensitivities to the subtle social cues that signal whether or not trust is warranted. From this work, I can tell you that, under the influence of oxytocin, you attend more to people’s eyes and become specifically more attuned to their smiles, especially subtle ones. Perhaps because of the closer attention you pay to peoples’ smiles and eyes, you become a better judge of their feelings, and view people on the whole as more attractive and trustworthy. You also become particularly sensitized to environmental cues linked to positive social connections— for instance, to words like “love” and “kissing.” Researchers who have combined the use of oxytocin nasal spray (versus placebo) with brain imaging have also learned that oxytocin modulates the activity of your amygdala, the subcortical structure deep within your brain linked to emotional processing. Specifically, under the influence of a single blast of oxytocin nasal spray, the parts of your amygdala that tune in to threats are muted, whereas the parts that tune in to positive social opportunities are amplified. Reflecting these negativity-dampening effects, a single shot of oxytocin can also help you glide through stressful social situations, like giving an impromptu speech or discussing a conflict-ridden topic with your spouse. If you were to face these difficulties under the influence of oxytocin, studies suggest, you’d have less cortisol, the so-called “stress hormone,” coursing through you, and you’d behave more positively, both verbally, by disclosing your feelings, and nonverbally, by making more eye contact and friendly gestures. Related research shows that behaving kindly in these ways also raises your naturally-occurring levels of oxytocin, which in turn curbs stress-induced rises in heart rate and blood pressure, reduces feelings of depression, and increases your pain thresholds.

More generally, oxytocin is has been cast as a lead character within the mammalian “calm-and-connect” response, a distinct cascade of brain and body responses best contrasted to the far more familiar “fight-or-flight” response. Let’s face it, meeting new people can be a little scary at times. Think back to what it was like for you on your first day at a new school or in a new job. You’re suddenly thrown in with people you’d never heard of before. Even if a new person seems friendly, it’s hard to know his true motives. Will he help you? Or will he instead take advantage of you in one way or another? Human greed, after all, runs rampant and can yield all manner of exploitation. Oxytocin appears both to calmfears that might steer you away from interacting with strangers and also to sharpen your skills for connection. As I’ve mentioned, though, oxytocin is far from blind. It indeed heightens your attunement to cues that signal whether others are sincere or not. Through eye contact and close attention to all manner of smiles—and the embodied simulations such visual intake triggers—your gut instincts about who to trust and who not to trust become more reliable. Rather than avoid all new people out of fear and suspicion, oxytocin helps you pick up on cues that signal another person’s good will, and guides you to approach them with your own. Because all people need social connections, not just to reproduce, but also to survive and thrive in this world, oxytocin has been dubbed “the great facilitator of life.”

It too can jump the gap between people such that someone else’s oxytocin flow can trigger your own. A biochemical synchrony can then emerge that supports mutual engagement, care and responsiveness.

 The clearest evidence that oxytocin rises and falls in synchrony between people comes from studies of infants and their parents. When an infant and a parent—either mom or dad—interact, sometimes they are truly captivated by one another, and other times not. When an infant and parent do click, their coordinated motions and emotions show lots of mutual positive engagement. Picture moms or dads showering their baby with kisses, tickling their baby’s tiny fingers and toes, smiling at their baby, and speaking to them in that high-pitched, sing-song tone that scientists call “motherese.” These parents are super attentive. As they tickle and coo they’re also closely tracking their baby’s face for signs that their delight is mutual. In step with their parent’s affectionate antics, these attentive babies babble, coo, smile and giggle. Positivity resonates back and forth between them. Micro-moments of love blossom.

Of course, not every infant-parent interaction is so rosy. Some pairs show little mutual engagement. Some moms and dads rarely make eye contact with their infants and emit precious little positivity, either verbally or nonverbally. These pairs are simply less attuned to one other, less connected. And in those rare moments when they are engaged, the vibe that joins them is distinctly more negative. They connect over mutual distress or indifference, rather than over mutual affection.

It turns out that positive behavioral synchrony—the degree to which an infant and a parent, through eye contact and affectionate touch, laugh, smile, and coo together—goes hand-in-hand with oxytocin synchrony. Researchers have measured oxytocin levels in the saliva of dads, moms, and infants both before and after a videotaped, face-to-face parent-infant interaction. For infant-parent pairs who show mutual positive engagement, oxytocin levels also come into sync. Without such engagement, however, no oxytocin synchrony emerges.

Positivity resonance, then, can be viewed as the doorway through which the exquisitely attuned biochemical tendencies of one generation influence those of the next generation to form lasting, often lifelong bonds. Knowing, too, that oxytocin can ebb and flow in unison among non-kin—even among brand-new acquaintances just then learning to trust one another—micro-moments of love, of positivity resonance, can also be viewed as the doorways through which caring and compassionate communities are forged. Love, we know, builds lasting resources. Oxytocin, studies show, swings the hammer.

This core tenet of my broaden-and-build theory—that love builds lasting resources—finds support within a fascinating program of research on . . . rodents. It turns out that rat moms and their newborn pups show an analogous form of positive engagement and synchrony as do human parents with their infants. Sensitive parenting in a rat mom, however, is conveyed by her attentively licking and grooming her newborn pups. When a rat mom licks and grooms her pup it increases the pup’s sensitivity to oxytocin, as indicated, for instance, by the number of oxytocin receptors deep within the pup’s amygdala, as well as within other subcortical brain regions. Sure enough, these well-groomed—or I dare say well-loved—rat pups grow up to have calmer demeanors; they’re less skittish, more curious. The researchers can be certain that it’s the experiences of loving connection that determine the brain and behavioral profiles of the next generation (i.e., their oxytocin receptors and calm demeanors)—and not simply shared genes—because cross fostering studies show the same patterns of results. That is, even when a rat mom raises a newborn pup that is not her own, her maternal attention still forecasts that pup’s brain sensitivity to oxytocin and whether it grows up to be anxious or calm.

Touring Vagus

Who you are today is also shaped by the third biological character that I want you to meet: your 10th cranial nerve. This key conduit connects your brain to your body and is also called your vagus nerve (sounds like Vegas, as in Las Vegas). It emerges from your brainstem deep within your skull and, although it makes multiple stops at your various internal organs, perhaps most significantly it connects your brain to your heart. You already know that your heart rate shoots up when you feel insulted or threatened—registering the ancestral “fight-or-flight” response—but you may not know that it’s your vagus nerve that eventually soothes your racing heart, by orchestrating (together with oxytocin) the equally ancestral “calm-and-connect” response.

Keeping in mind that love isconnection, you should know that your vagus nerve is a biological asset that supports and coordinates your experiences of love. Completely outside of your awareness, your vagus nerve stimulates tiny facial muscles that better enable you to make eye contact and synchronize your facial expressions with another person. It even adjusts the miniscule muscles of your middle ear so you can better track her voice against any background noise. In these exquisitely subtle yet consequential ways, your vagus nerve increases the odds that the two of you will connect, upping your chances for positivity resonance.

Scientists can measure the strength of your vagus nerve—your biological aptitude for love—simply by tracking your heart rate in conjunction with your breathing rate. Specifically, I can look at the degree to which your heart rate, as tracked by tiny sensors placed on your lowest ribs, is patterned by your breathing rate, as revealed by an expandable bellows that encircles your ribcage. This pattern is called vagal tone. Like muscle tone, the higher your vagal tone, the better. In addition to putting the brakes on the big jumps in your heart rate that may be caused by stress, fear, or exertion, your vagus nerve also increases the routine efficiency of your heart, beat-by-beat, or more precisely, breath-by-breath. The human heart rate tends to run fairly high, as if we’re always on guard for the next danger that might be hidden around the corner. When you’re breathing in, a fast heart rate is an efficient heart rate. After all, each successive heartbeat during an inbreath circulates more freshly oxygenated blood throughout your brain and body. Yet when you’re breathing out, a fast heart rate is not all that helpful because your supply of freshly oxygenated blood is waning. Here again, your vagus nerve steps in to help out. It can very gently apply the brake on your heart while you exhale, slowing your heart rate down a small degree. In turn your vagus nerve can gently let up on the brake while in you inhale, letting your naturally high heart rate resume to grab all the oxygenated blood that it can get. This creates a subtle yet healthy pattern of cardiac arrhythmia: Your heart rate speeds up a bit when you inhale, and slows down a bit when you exhale. This is the pattern that reflects your vagal tone, the strength or condition of your vagus nerve.It characterizes the nimbleness with which your primitive, nonconscious brain holds the reins on your galloping heart.

I give you this quick tour of vagus because this conduit within you, between your brain and your heart, has a story to tell about how attuned you are to sources of love in your midst. It even makes a quiet prediction about what illnesses may beset you and how long you’re likely to live. Your biological propensities for love and health, as we shall see, are intimately intertwined. Measured at rest, vagal tone also tends to be extraordinarily stable over time. For most people, it remains roughly the same year after year, rhythmically channeling them toward loneliness or social prosperity, sickness or health.

That’s because people with higher vagal tone, science has shown, are more flexible across a whole host of domains—physical, mental, and social. They simply adapt better to their ever-shifting circumstances, albeit completely at nonconscious levels. Physically, they regulate their internal bodily processes more efficiently, like their glucose levels and inflammation. Mentally, they’re better able to regulate their attention and emotions, even their behavior. Socially, they’re especially skillful in navigating interpersonal interactions and in forging positive connections with others. By definition, then, they experience more micromoments of love. It’s as though the agility of the conduit between their brains and hearts—as reflected in their high vagal tone—allows them to be exquisitely agile, attuned, and flexible as they navigate the ups and downs of day-to-day life and social exchanges. High vagal tone, then, can be taken as high loving potential. Indeed, this is what doctoral student, Bethany Kok and I have found: Compared to people with lower vagal tone, those with higher vagal tone experience more love in their daily lives, more moments of positivity resonance.

You might now be wondering whether you’re one of the lucky ones blessed with high vagal tone. If you are, that’s great. Yet even if you’re not advantaged with high vagal tone today, the latest science gives plenty of reason for hope. Just as you can build muscle tone through regular physical exercises, you can build vagal tone through regular emotional exercises of the kind I share in Part II of this book. The key, once again, is the power of love.

My students and I conducted a longitudinal experiment on the effects of learning the ancient mind-training practice of loving-kindness meditation. Our study participants visited my laboratory at the University of North Carolina one-by-one, and we measured their vagal tone while they sat and relaxed for a few minutes. At the end of this initial laboratory testing session, we instructed participants how to log on to the study website each evening to record their emotions and social connections of the day. A few weeks later, by random chance, we determined which participants would learn loving-kindness meditation, and which would not. All would continue to monitor their day-to-day emotions and social connections using our study website. Months later, weeks after the mediation workshop ended, one-by-one we invited all participants back to my laboratory, where we again measured their vagal tone under the same resting conditions as before.

In May 2010, I had the immense honor of presenting the results of this experiment directly to His Holiness the 14th Dalai Lama. A handful of scientists were invited to a private meeting to brief His Holiness on their latest discoveries about the effects of mind-training. After briefly describing to His Holiness the functions of the vagus nerve and the concept of vagal tone, I shared what my team and I had discovered in this most recent study: That vagal tone—which is commonly taken to be as stable an attribute as your adult height—actually improves significantly with mind-training. Here is your evidence-based reason for hope: No matter what your biological capacity for love is today, you can bolster that capacity by next season.

For it was those study participants who had been assigned at random to learn loving-kindness meditation who changed the most. They devoted scarcely more than an hour of their time each week to the practice. Yet within a matter of months, completely unbeknownst to them, their vagus nerves began to respond more readily to the rhythms of their breathing, emitting more of that healthy arrhythmia that is the fingerprint of high vagal tone. Breath by breath—loving moment by loving moment—their capacity for positivity resonance matured. Moreover, through pain-staking statistical analyses, we pinpointed that those who experienced the most frequent positivity resonance in connection with others showed the biggest increases in vagal tone. Love literally made people healthier.

Upward Spirals Unleashed

It’s time now to step back from isolated scientific findings and take in the big picture. Recall that your body’s positivity resonance operates within a much larger system. Along with love and all the other positive emotions, this system also includes your enduring resources—your physical health, your social bonds, your personality traits, and your resilience. Having assets like these certainly makes life easier, and more satisfying. In addition, though, such resources also serve as booster shots that increase the frequency and intensity of your micro-moments of positivity resonance. Love built those resources in you, and those resources in turn boost your experiences of love. This is not a simple case of cause-and-effect. The causal arrow instead runs in both directions at once, creating the dynamic and reciprocal causality that drives self-sustaining trajectories of growth. Through love, you become a better version of yourself. And as your better self, you experience love more readily. It is within this dance between your enduring resources and your micro-moments of love that life-giving upward spirals are born.

Looking out from this more encompassing vantage point, let’s revisit the scientific findings I shared with His Holiness the Dalai Lama. By learning how to self-generate love, you can raise your vagal tone. And with higher vagal tone, your attention and actions become more agile, more attuned to the people in your midst. You become better able to forge the interpersonal connections that give rise to positivity resonance. Through vagal tone, then, love begets love.

Likewise, evidence suggests that positivity resonance raises your oxytocin levels. And under the influence of oxytocin, you grow calmer, more attuned to others, friendlier, and more open. Here too, your skills for forging connections sharpen, which increases your ability to cultivate positivity resonance. Through oxytocin as well then, love begets love.

Recall, too, that positive connections with others create neural coupling, or synchronous brain activity between people. With repetition, positivity resonance also produces structural changes in the brain, for instance rendering the threat-detecting amygdala more sensitive to the calming influence of oxytocin. While much of the work on neuroplasticity—the brain’s capacity to change with experience—comes from research on nonhuman animals, tantalizing evidence has also recently emerged from studies of humans. Becoming a parent, for instance, not only opens the door for parent-infant positivity resonance, but also appears to usher in structural changes in brain regions that facilitate positivity resonance. This research shows how love reroutes the neural wiring of your brain, making it more likely that you’ll have healthy habits and healthy social bonds in the future. Through brain plasticity, too then, love begets love.

Plasticity, or openness to change, characterizes your body’s cells as well. New cells are born within you all the time. Even now, as you take time to read this book, new cells are coming on-line within you, taking their predetermined place within the massive orchestra of communication and mutual influence that you call your body. Yet not everything about the birth of your new cells is scripted in advance by your DNA. Some aspects are open to contextual influences signaled by the changing biochemicals that course through you. If you feel lonely and disconnected from others, for instance, your circulating levels of the stress hormone cortisol will rise. Your cortisol levels, in turn, signal your immune system to alter the way your genes are expressed in your next-generation white blood cells, specifically making them less sensitive to cortisol. When this happens, studies show, your inflammatory response becomes more chronic, less responsive to cues that a crises situation has subsided. This is how, over time, chronic feelings of loneliness can weaken people’s immune systems and open the door to inflammation-based chronic illnesses, like cardiovascular disease and arthritis. The data go further to suggest that feelingisolated or unconnected to others does more bodily damage than actualisolation, suggesting that painful emotions drive the bodily systems that in turn steer you toward dire health outcomes. By tracking how your emotions—and the biochemical changes they trigger—alter gene expression within your immune system, molecular biology is now showing how a lack of love compromises your immunity and your health.

Even so, there is ample reason for hope. Within countless social exchanges each day, your potential to alleviate loneliness with love is enormous. Your biology, as we have seen in this chapter, enacts your experiences of love. Even so, you have more control over your biology than you realize. Once you grasp the pathways and common obstacles to love, you gain a measure of control over the biochemicals that bathe your cells. To a considerable extent, you orchestrate the messages that your cells hear, the messages that tell your cells whether to grow towards health, or towards illness. My collaborators and I are just beginning to chart the ways that oxytocin and other ingredients within love’s biochemistry trigger healthy changes in gene expression that may foster physical and mental well-being. Also through the plasticity of your cells, we hypothesize, love begets love.

All of love’s unseen biological transformations—within your brain rhythms, your blood stream, your vagus nerve, and your cells—in turn ready you to become even more attuned to love, better equipped, biologically, to cultivate moments of positivity resonance with others. This latent biological upward spiral is a powerful force: Love can affect you so deeply that it reshapes you from the inside out and by doing so alters your destiny for further loving moments. With each micromoment of love, then, as I feature in Chapter 4, you climb another rung on the spiraling ladder that lifts you up to your higher ground, to richer and more compassionate social relationships, to greater resilience and wisdom, and to better physical health.

Love 2.0: The View from Here

Put simply, your body was designed for love, and to benefit from loving. Human bodies become healthier when repeatedly nourished by positivity resonance with others, with the result that human communities become more harmonious and loving. This clear win-win arrangement is written into our DNA.

Everyday micro-moments of positivity resonance add up and ultimately transform your life for the better. You become healthier, happier, and more socially integrated. Your wisdom and resilience grow as well. Having more resources like these, in turn equips you to experience micro-moments of love more readily and more often, with further broaden-and-build benefits. Your body, as biology has it, energizes and sustains this upward spiral. The unseen and heretofore unsung biology of love guides everything you think, do, feel and become. This isn’t all about you, though. Love, as we’ve seen, is not a solo act. The benefits that unfold from love for you, then, also unfold for all those who are party to positivity resonance. Seen from this vantage point, emotional and physical health are contagious. Indeed, studies of actual social networks show that, over time, happiness spreads through whole communities. Your friend’s co-worker’s sister’s happiness actually stands to elevate your wn happiness.

The new science of love makes it clear that your body acts as a verb. Sure enough, some aspects of your body remain relatively constant day in and day out, like your DNA, or your eye color. But your brain continually registers your ever-changing circumstances, and in turn orchestrates the flux of biochemicals that reshape your body and brain from the inside out, at the cellular level. Your body takes action. Most notably, it broadcasts everything you experience—your moments of positivity resonance or their lack—to every part of you, readying you for either health or illness and rendering you either more or less equipped for loving connection.

I hope you’ve found it mind-opening to zoom in on the biology of love in action—the ways positivity resonance can synchronize your brain and oxytocin waves with those of another, and how, over time, it can build the capacity of your vagus nerve, which points you towards physical health, social skill, and overall well-being. Touring love’s biology, I’ve found, can help ground an otherwise nebulous concept, a concept all too often draped in a gauze of rainbows, unicorns and cupids taking aim at cartoon hearts. Even so, a fully upgraded view of love can’t stop with biology. It demands that you zoom out as well, to appreciate the ways that love also infuses all that lies beyond your physical body, its effects on your actions and relationships, your wisdom and your spiritual potential. For it is these more encompassing changes that spring up in love’s path that can motivate you to create a better life for yourself. Before moving on to Part II, then, in which I offer practical guidance on how to seed love more readily, I want to show you what’s new in the bigger picture that is emerging from the science of love—a picture that shows exactly how creating more positivity resonance in your life influences all that you think, do, feel and become.

Copyright © 2013 by Barbara Fredrickson. Reprinted with permission of Penguin Publishing.

Barbara Fredrickson, Ph.D., is the Kenan Distinguished Professor of Psychology and principal investigator of the Positive Emotions and Psychophysiology Lab at the University of North Carolina. She’s the author of "Love 2.0" and "Positivity." Email her at: blf@unc.edu.