Taking cues from what leading neuroscientist Stephen Porges calls the social engagement system, I describe love’s biology as a system, a whole comprised of several interacting parts. You can think of love, or positivity resonance, as one of the more complex and recurrent scenes nested within the act of your day, which is in turn nested within the play of your life. As with any scene in a play, the drama of love has its own cast of characters. Here I turn the spotlight on three main biological characters: your brain; one particular hormone, oxytocin, which circulates throughout your brain and body; and your vagus nerve, the tenth cranial nerve that runs from deep within your brain stem down to your heart, lungs, and other internal organs. Other characters step onto the biological stage to deliver their own lines, to be sure, but these three are primary players in love’s biology.
Although always on stage, these main characters deliver their lines quietly, most often fully outside of your conscious awareness. As you move through your day, these biological characters—your brain, your oxytocin, and your vagus nerve—are ever responsive to set changes. As you interact with one person after another, they gently nudge you to attend to these others more closely and forge connections when possible. They shape your motives and behaviors in subtle ways, yet ultimately, their actions serve to strengthen your relationships and knit you in closer to the social fabric of life. In the sections that follow, I’ll shine the spotlight on each of these three main characters in turn, to help you see how each forges and supports those life-giving moments of positivity resonance for which your body thirsts.
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 wavelength. As your respective brain waves mirror one another, each of you—moment by moment—changes the 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 in real time after all. What you’d need is some way to peer inside two people’s heads while they chatted so that you could tell whether 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 canceled 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 storyteller: 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 you 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 each other, 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 storytelling—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 about her 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 afterward. 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 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 anticipated her brain activity by a few seconds in 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 together. And mutual understanding is just steps away from mutual care. Once two people understand each other—really “get” each other 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 of 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.” 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, Taiwan, 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, nonpainful 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 is your pain. By contrast, when you imagine these painful events happening to complete strangers, 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 obstacles 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 in 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 in that animal a long-lasting preference to remain together with the other, 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. S
cientific understanding of oxytocin’s role in your everyday social life could not advance without more practical research tools at hand.
Dramatic new evidence of 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 investors 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 his investment, he risked receiving nothing in return if the trustee chose to selfishly keep the entire monetary gain for himself. But if the trustee was fair, they could each double their money.
Love 2.0: How Our Supreme Emotion Affects Everything We Feel, Think, Do, and Become Page 5