1The Social Brain
It was written in the skies
That the heart and not the eyes shall see.
—AS SUNG BY ELLA FITZGERALD
What happens when you take a typical wedding vow and rewrite it to reflect scientific reality? Darling, from this day forward, I promise to love you with all my brain. In making these words anatomically correct, we have robbed them of romance. The romantic version, the real version, the thing any bride or bridegroom knows to say while clasping hands with their beloved is I promise to love you with all my heart.
The heart is the organ we talk about when we talk about love—not the brain. To reverse these two is to translate the language of love (“you stole my heart”) into something absurd, almost grotesque (“you stole my brain”). Today we know that the brain is chiefly responsible for emotions and cognition and ultimately for our ability to fall and remain in love. So why does our language still not reflect this reality? Why is it that we treat romance and passion as matters of the heart?
I believe that to truly understand love the first thing we must do is relocate it from the place where it has dwelled for most of human history. By that, I mean we must break the ancient bond between love and the heart.
This is no easy task. The Oxford English Dictionary’s entry on “heart” contains an impressive fifteen thousand words, most of them examples of how the term is used to describe love or other kinds of emotions, feelings, and thought processes. To lose someone we love is to be heartbroken. To revise an important decision is to experience a change of heart. To succumb to fear is to lose heart. To be kind is to have a big heart. I confess that despite my line of work, I use many of these expressions myself—maybe I’m a poet at heart?
These idioms aren’t confined to English; versions exist in practically every other human language. And they go back at least as far as the twenty-fourth century BC, when the expression meaning “spreading wide his heart in joy” was carved inside an Egyptian pyramid. Similar expressions appear in the Epic of Gilgamesh (ca. 1800 BC) and Confucian texts (ca. 450 BC). Good luck finding such poetry about the brain in the ancient world.
What most people don’t realize is that these expressions are not really metaphors. They are artifacts, dating from a time when everyone in the world, from Aristotle on, genuinely believed that our feelings originated not in our heads but in our chests. Historians of science have a fancy name for this belief: the cardiocentric hypothesis. And its origins are similar to those of geocentrism, the now-debunked idea that Earth is at the center of the universe and the sun and the planets rotate around it. Such a view may seem silly to us, now that we have telescopes and rocket ships, but in ancient times it conformed to what people experienced as their daily reality: The sun seemed to move in the sky while Earth, by all appearances, stayed put.
The same commonsense thinking led people to believe that our minds were in our chests. Just think about the feeling of being excited. Your heart pumps faster. Your breathing gets heavier. Your stomach tightens. And what does your brain do? As far as people could feel, it just sits there—inert, quiet.
In his search for the locus of the mind, Aristotle noticed that the loss of a heartbeat often accompanied near-death experiences. So Aristotle gave fundamental importance to the heart, blood, and blood vessels. In his cardiocentric view, the heart was responsible for thoughts and feelings. He also noticed that brains, unlike internal organs, were relatively cool to the touch. And so he deduced that our brain served as little more than physiological air-conditioning, tempering “the heat and seething of the heart,” which he regarded as the true “source” of all our senses.
(Interestingly, recent research has shown that Aristotle was not entirely off base. Scientists have discovered that though our hearts might not control our brains, each organ constantly interacts with the other through hormones, electromagnetic fields, and even pressure waves.)
Even though Aristotle’s cardiocentric view dominated in antiquity, there were others in his time and in the centuries that followed—such as the philosopher-scientists Erasistratus, Herophilus, and Galen—who believed that basic emotions, rational thinking, consciousness, and even mysterious phenomena like love originated not in our hearts but in our heads. Yet the exact role that the brain played in our anatomy remained an open question through the Renaissance. As Shakespeare put it in The Merchant of Venice, “Tell me where is fancy bred. Or in the heart or in the head?”
Leonardo da Vinci also wondered about the mystery of the brain. According to Jonathan Pevsner, formerly a psychiatry professor at the Johns Hopkins School of Medicine who has published several papers on Leonardo’s contributions to neuroscience, Leonardo saw the brain as the seat of the mind and the center of all our senses, a “black box” that receives, processes, and translates information. Around 1494, Leonardo drew three sketches hypothesizing the confluence of the senses—or what he called senso comune (common sense) within the brain ventricles. The ventricles are interconnected basins filled with cerebrospinal fluid that protect the brain from physical shocks, distribute nutrients, and remove waste. In his pursuit of knowledge, Leonardo achieved a perfect balance between art and science, and this was also true with his concept of the brain. He believed that visual information—“what you see”—was “processed in the main ventricle to help interpret the world.” Leonardo explored other aspects of the brain, from blood supply to the cranial nerves. Although neuroscientists would later discover that brain matter—rather than ventricles—is the key to mental function, Leonardo’s remarkable intuitive conjectures managed to expand the idea of the brain.
As the centuries progressed, Leonardo’s vision was refined by a succession of pioneering investigators, who built the modern idea of the brain. Their names are revered in the history of neuroscience: Andreas Vesalius, Luigi Galvani, Paul Broca, and Santiago Ramón y Cajal, to mention just a few. Some dissected the brain to understand its constituent parts. Some injected ink stains into blood vessels to reveal connections between brain and body. Some made deductions about the function of different regions of the brain after examining patients who had suffered localized damage. These were the predecessors of modern neuroscientists: the predecessors of people like me.
A Magic Cabbage
For my neuroscience classes at the University of Chicago, I sometimes wheel into the lecture hall a glass jar in which a human brain floats gently in a bath of formaldehyde. I borrow this specimen from the neurobiology department, where a number of brains have been collected over the years, given to the university by generous donors who are enamored with science. Thanks to them, I can offer my students a unique opportunity to show them up close and personal—IRL (in real life), as they would say—the organ they study in such detail in their textbooks. I distribute latex gloves and ask: “Who wants to touch the brain?”
Ninety percent of my students raise their hands. The rest are content just to observe, or they’ve made arrangements with me beforehand to skip this class. Most students are dazzled by the opportunity to come in contact with the brain, to imagine this slippery organ inside their own heads, ruling their bodies and minds in a way that scientists like me are only beginning to fully understand.
But not everyone in the class is equally impressed.
“That’s it?” one girl asks as I extend the brain out to her in my gloved hands. The smile on my face now turns bashful, like a waiter in a Michelin-star restaurant who has just theatrically lifted the cloche off a dish to reveal a tiny tomato. “I thought it would be … I don’t know … somehow more impressive.”
In a way, I can understand her disappointment. I’ve taught her that the brain is the most powerful and complex organ in the universe. And she is now faced with an object that, quite frankly, looks pathetic. It’s a mess of fleshy pink and gray wrinkles, measuring about six inches long, weighing about three pounds, and, having been pickled in formaldehyde, has all the beauty of a boiled cabbage.
But let’s slice this thing in half, separating the left brain from the right. What will we see inside? The wrinkly exterior gives way to a layer of smooth gray tissue. Known as gray matter, this part is richly concentrated with neurons, the nerve cells that are the brain’s building blocks and are responsible for everything from information processing to movement to memory.
We have a lot of neurons—86 billion—yet it is not their sheer number that accounts for much of what we could call intelligence. In fact, as the distinguished neuroscientist Michael Gazzaniga points out, most of the neurons in the brain (about 69 billion) are found in the cerebellum, a small area at the base of the brain that coordinates our balance and motor control. The entire cerebral cortex, the part of our brain that is responsible for complex thinking and other aspects of human nature, contains “only” 17 billion neurons.
Much more important than the total number of neurons in our brain are the connections between our different brain regions. And connectivity is the specialty of the thicker region of nerve filaments packed deep inside our brain, beneath the blanket of gray matter. This is the white matter, the brain’s information superhighway, which links different regions into powerful brain networks that shape both our conscious and unconscious experiences. In recent years, my fellow neuroscientists have identified and precisely mapped brain networks for all kinds of things, from motor skills to visual perception to language. I’ve made my own contribution in discovering the brain network responsible for the uniquely human experience of romantic love.
It’s the volume and quality of those connective nerve fibers between brain cells—and not the size of our brains—that accounts for our incomparable skills as a species. And we have no shortage of them. In fact, if you unraveled all the white matter packed into the average twenty-year-old’s brain, you would find that these microscopic wires extend more than a hundred thousand miles in length—or about four times as long as the circumference of the earth. Right now, in order to design artificial neural networks that many consider to be the future of computing, some of the best computer scientists in the world are studying how such a densely connected and economical biological system works. These scientists marvel at the brain’s power and energy efficiency, how nature evolved a device that can store the equivalent of one million gigabytes of information—which equates to 4.7 billion books or three million hours of your favorite TV shows—while using the same energy as a single twelve-watt lightbulb.
Yet I believe that our neural wiring explains only part of the reason why our brains are so powerful. In addition to the vital connections inside our brain, we also depend on the invisible connections between our brains. By this, I mean our social life, our interactions not only with friends and loved ones but also our interactions with strangers, critics, and competitors. All this social activity, more than any single factor, has influenced the design and function of the brains we have today.
And like so many other stories in this book, the tortuous, mysterious, beautiful process by which our social nature sculpted the brains we have today is, at its core, a love story.
Love Made the Brain
The story begins in Africa, millions of years ago, with two of our earliest primate ancestors. Let’s call them Ethan and Grace. Their romance began as a biological necessity. Yet once their relationship was consummated, Ethan and Grace decided to stay together. Grace had given birth to children that, compared to other mammals, were unusually helpless in their first few years of life. On top of figuring out how to protect them, the couple had to spend hours foraging to meet their dietary requirements. And then, to digest their raw food and store enough energy to live another day, they needed to sleep several hours each night. Juggling these tasks required social coordination. Suddenly, Ethan couldn’t think only about himself; he had to see the world from Grace’s point of view in order to anticipate what she needed.
Ethan and Grace had formed an intense preference for each other, a kind of relationship that biologists call a pair bond. Yet at some point in evolutionary history, their descendants—our human ancestors—took a giant leap, socially speaking. They adapted the skills used to build their own relationship (perspective-taking, planning, cooperation) and generalized them, forming bonds with other primates who were neither their reproductive partners nor their offspring. In other words, they made friends.
And these early humans needed friends because they occupied a vulnerable position in the food chain. They couldn’t fly. They had no camouflage or armor. They lacked the strength, speed, and stealth of other species in the animal kingdom. They spent most of their time scavenging for food and evading predators. All they had, really, was an unusual talent for connection, a special knack for navigating the most complex environment in nature: the social world.
This was quite the superpower—and in the intervening eons, as anthropoid primates evolved, it would prove more decisive than their opposable thumbs, their skills at making tools, or the fact that they walked upright. As war and climate change made life on earth harsher, some species had trouble surviving; but these difficulties actually played to the strengths that early humans were developing.
Their social skills helped them build complex groups and eventually whole societies undergirded by mutual aid. People learned how to sort out friends from foes; to avoid predators; to anticipate the actions of neighbors; to privilege long-term interests over short-term desires; to use language to communicate; to manage mating relationships that were shaped not only by the female’s ovulatory cycle but by different factors like affection and empathy. Finally, they learned how to trust and say “I love you.”
According to the social brain hypothesis proposed by the British anthropologist Robin Dunbar in the 1990s, all these social complexities drove evolutionary changes in the brain that made us smarter. While humans started out with brains that were barely bigger than those of chimpanzees, our neocortex began to grow along with our social skills. Areas for language and abstract thinking blossomed. These higher-order regions did not only grow in size; they also became better connected to other parts of the brain. We can see the legacy of these changes by comparing the number of wrinkles (what neuroscientists call convolutions) in human brains versus those of less sophisticated primates, like baboons, whose brains are smoother and have fewer folds.
About seventy thousand years ago, the distant descendants of Ethan and Grace, our own species, Homo sapiens, moved from East Africa to the Arabian Peninsula and Eurasia. There they met other hominids, most famously the Neanderthals. The Neanderthals were fearsome competition: bigger, stronger, with better vision and brains that may have been slightly larger than those of humans. But the neural architecture of the Neanderthals and Homo sapiens differed in important ways. The Neanderthals had more space dedicated to vision and motor skills—they were ideal physical warriors. But the Homo sapiens were ideal social warriors: they could understand the intentions of others, they could consider a choice from two sides, they learned quickly from their mistakes.
All this allowed them to compensate for their shortcomings in strength. And, as a result, the epic evolutionary matchup between the Neanderthals and the Homo sapiens wasn’t even close. By 11,000 BC, ours was the sole remaining human species. In other words, it was the need to interact with other people—first our significant others, then our friends, then the societies and civilizations that we built—that made us who we are today. And that process began with couples like Ethan and Grace falling in love.
A Neuroscience for a Social Species
Social connections have not only shaped the human brain throughout its evolution; they also continue to shape the brain throughout the course of an individual human’s life. This is a fact that bears repeating because it’s not at all obvious. After all, how many of us grew up thinking of socializing as expanding our minds? Rather we probably thought of it as downtime, something that we did as a break from our studies or creative pursuits, something that was not really important to our intellectual development.
Imagine how different our teenage arguments with our parents could have been if we had been armed with the latest insights from the emerging field of social neuroscience. “Actually, Mom, I don’t have to get off the phone. Studies show that, by building and maintaining salutary social connections, I can literally grow my brain and am better able to focus on cognitively challenging tasks, like school. So Mom, pleeeease! Butt out!”
While it sounds far-fetched, this teenager’s argument is valid. Neuroimaging studies do show that the size of core regions of the brain like the amygdala and the frontal and temporal lobes correlates with the size of our individual social networks. Similar findings reinforcing the value of social connections appear in studies of social species across the animal kingdom. If you raise a fish alone in an aquarium, its brain cells will be less complex than those of the same species of fish raised in a group. A desert locust’s brain, when it’s part of a swarm, grows by an impressive 30 percent, presumably to accommodate the additional information-processing demands of a more complicated social environment. Chimpanzees learn how to use new tools much faster when they are in groups than in isolation.
Yet just as my field reveals the benefits of the social world, it can also show us its dangers. Social pain—the heartache (oops, I mean brain ache!) that follows a bad breakup, for example—activates some of the same brain regions, like the anterior cingulate cortex, that respond to physical pain. People who report feelings of social isolation—what is typically called loneliness—have been shown to have less gray and white matter in key social areas of their brain. If they remain lonely, they are susceptible to a cascade of neurological events that echo throughout their bodies, leading to so many poor health outcomes that some public health experts now consider chronic loneliness on par with smoking as a grave risk to your health.
These are just a few of the insights to come out of social neuroscience, which studies how the connections between different individuals’ brains—our social life—change what goes on inside our heads and our bodies. The discipline originated in the 1990s as a kind of surprising marriage between the so-called soft science of social psychology, in which the researcher must rely on observed external behavior and most likely subjective self-reports, and the so-called hard science of neuroscience, which uses high-tech scanners to peer inside the brain and precisely map its working parts.
Neuroscientists had previously treated the brain in isolation, thinking of it as a kind of solitary computing machine. This tendency to compare the brain to a mechanical device goes all the way back to the seventeenth century. French philosopher-scientist René Descartes, seeing water-powered automatons at work in the Royal Gardens in a suburb near Paris, thought that the human body worked in a similar way to these devices, that it was essentially a complex biological mechanism. And the Danish anatomist Nicolas Steno went even further, declaring that “the brain is a machine” like a clock or a windmill, and that the best way of understanding it was to take it apart and consider what the pieces “can do separately and together.”
As the centuries passed, Steno’s metaphor was updated. In the 1800s, the brain was compared to a telegraph system, sending and receiving signals to and from different parts of the body. In the second half of the twentieth century, it was likened to the personal computer: storing data in memory, processing information, executing commands. We social neuroscientists have further refined the metaphor. We see the brain not as a classic computer but as a smartphone with a wireless, broadband link to other devices. Just imagine how useful an iPhone would be without the ability to access the internet or send a text. Our brain also requires a strong connection to realize its full potential. And, like a smartphone, its connectivity makes it vulnerable. It can be hacked, cluttered with unnecessary apps, bombarded with distracting or anxiety-inducing notifications.
Yet the brain can also do something that smartphone designers can only dream of. It can reprogram itself. Neuroscientists call this neuroplasticity. And neuroplasticity is one of the true wonders of the mind. It refers to the capacity of the brain to grow while pruning inessential neurons when we’re young; to expand and form new connections as we learn new things over the course of our life; and to repair or compensate for damage caused by an injury or the wear and tear of time. And social interaction is often the very thing that drives these vital changes inside the brain.
So, far from being a waste of time or incidental to the human experience, the connections we form with other people are quite literally the reason we exist as a species. Building healthy relationships also builds a healthier brain, one that—as we will discover—can stave off cognitive decline, spur creativity, and speed up our thinking. And there is perhaps no more powerful social activity, no better way of realizing our brain’s full cognitive potential, than by being in love.
Copyright © 2022 by Stephanie Cacioppo
