When we get right down to it, what do we human beings do all day long? We read the world, especially the people we encounter. My face in the mirror first thing in the morning doesnt look too good, but the face beside me in the mirror tells me that my lovely wife is off to a good start. One glance at my eleven-year-old daughter at the breakfast table tells me to tread carefully and sip my espresso in silence. When a colleague reaches for a wrench in the laboratory, I know hes going to work on the magnetic stimulation machine, and hes not going to throw his tool against the wall in anger. When another colleague walks in with a grin or a smirk on her face—the line can be fine indeed, the product of tiny differences in the way we set our face muscles—I automatically and almost instantaneously can discern which it is. We all make dozens—hundreds—of such distinctions every day. It is, quite literally, what we do.
Nor do we give any of this a second thought. It all seems so ordinary. However, it is actually extraordinary—and extraordinary that it feels ordinary! For centuries, philosophers scratched their heads over humans ability to understand one another. Their befuddlement was reasonable: they had essentially no science to work with. For the past 150 years or so, psychologists, cognitive scientists, and neuroscientists have had some science to work with—and in the past fifty years, a lot of science—and for a long time they continued to scratch their heads. No one could begin to explain how it is that we know what others are doing, thinking, and feeling.
Now we can. We achieve our very subtle understanding of other people thanks to certain collections of special cells in the brain called mirror neurons. These are the tiny miracles that get us through the day. They are at the heart of how we navigate through our lives. They bind us with each other, mentally and emotionally.
Why do we give ourselves over to emotion during the carefully crafted, heartrending scenes in certain movies? Because mirror neurons in our brains re-create for us the distress we see on the screen. We have empathy for the fictional characters—we know how theyre feeling—because we literally experience the same feelings ourselves. And when we watch the movie stars kiss on-screen? Some of the cells firing in our brain are the same ones that fire when we kiss our lovers. “Vicarious” is not a strong enough word to describe the effect of these mirror neurons. When we see someone else suffering or in pain, mirror neurons help us to read her or his facial expression and actually make us feel the suffering or the pain of the other person. These moments, I will argue, are the foundation of empathy and possibly of morality, a morality that is deeply rooted in our biology. Do you watch sports on television? If so, you must have noticed the many “reaction shots” in the stands: the fan frozen with anticipation, the fan ecstatic over the play. (This is especially true for baseball broadcasts, with all the downtime between pitches.) These shots are effective television because our mirror neurons make sure that by seeing these emotions, we share them. To see the athletes perform is to perform ourselves. Some of the same neurons that fire when we watch a player catch a ball also fire when we catch a ball ourselves. It is as if by watching, we are also playing the game. We understand the players actions because we have a template in our brains for that action, a template based on our own movements. Since different actions share similar movement properties and activate similar muscles, we dont have to be skilled players to “mirror” the athletes in our brain. The mirror neurons of a non-tennis-playing fan will fire when watching a pro smash an overhead, because the non-tennis-playing fan has certainly made other kinds of overhead movements with his arm throughout his life; the equivalent neurons of a fan such as me, who also plays the game, will obviously be activated much more strongly. And if Im watching Roger Federer, I bet my mirror neurons must be firing wildly, because Im a big Federer fan.
Mirror neurons undoubtedly provide, for the first time in history, a plausible neurophysiological explanation for complex forms of social cognition and interaction. By helping us recognize the actions of other people, mirror neurons also help us to recognize and understand the deepest motives behind those actions, the intentions of other individuals. The empirical study of intention has always been considered almost impossible, because intentions were deemed too “mental” to be studied with empirical tools. How do we even know that other people have mental states similar to our own? Philosophers have mulled over this “problem of other minds” for centuries, with very little progress. Now they have some real science to work with. Research on mirror neurons gives them and everyone interested in how we understand one another some remarkable food for thought.
Consider the teacup experiment I dreamed up some years back, which Ill discuss in considerable detail later. The test subjects are shown three video clips involving the same simple action: a hand grasping a teacup. In one, there is no context for the action, just the hand and the cup. In another, the subjects see a messy table, complete with cookie crumbs and dirty napkins—the aftermath of a tea party, clearly. The third video shows a neatly organized tabletop, in apparent preparation for the tea party. In all three video clips, a hand reaches in to pick up the teacup. Nothing else happens, so the grasping action observed by the subjects in the experiment is exactly the same. The only difference is the context.
Do mirror neurons in the brains of our subjects note the difference in the contexts? Yes. When the subject is observing the grasping scene with no context at all, mirror neurons are the least active. They are more active when the subject is watching either of the scenes and most active when watching the neat scene. Why? Because drinking is a much more fundamental intention for us than is cleaning up. The teacup experiment is now well known in the field of neuroscience, but it is not an isolated result: solid empirical evidence suggests that our brains are capable of mirroring the deepest aspects of the minds of others—intention is definitely one such aspect—at the fine-grained level of a single brain cell. This is utterly remarkable. Equally remarkable is the effortlessness of this simulation. We do not have to draw complex inferences or run complicated algorithms. Instead, we use mirror neurons.
Looking at the issue from another perspective, labs around the world are accumulating evidence that social deficits, such as those associated with autism, may be due to a primary dysfunction of mirror neurons. I hypothesize that mirror neurons may also be very important in imitative violence induced by media violence, and we have preliminary evidence suggesting that mirror neurons are important in various forms of social identification, including “branding” and affiliation with a political party. Have you heard of neuroethics, neuromarketing, neuropolitics? You will in the years and decades to come, and research in these fields will be rooted, explicitly or otherwise, in the functions of mirror neurons.
This book tells the story of the serendipitous and groundbreaking discovery of this special class of brain cells, the remarkable advances in the field in just twenty years, and the extremely clever experiments now under way in several labs around the world. Quite simply, I believe this work will force us to rethink radically the deepest aspects of our social relations and our very selves. Some years ago, another researcher suggested that the discovery of mirror neurons promised to do for neuroscience what the discovery of DNA did for biology.1 Thats an extraordinarily bold statement, because essentially everything in biology comes back to DNA. Decades in the future, will everything in neuroscience be seen as coming back to mirror neurons?
For fifteen years I have lived in Los Angeles and worked in my laboratory at UCLA, but as my name suggests, this story should rightly begin in Italy, and Im happy to report that it really does—specifically, in the small and beautiful city of Parma, famous for its fabulous food, particularly prosciutto di Parma and Parmesan cheese, and for its music. Now we can add neuroscience to the list of Parmas world-class exports; it was at the university here that a group of neurophysiologists, led by my friend Giacomo Rizzolatti, first identified mirror neurons.
Rizzolatti and his colleagues work with Macaca nemestrina, a species of monkey often used in neuroscience labs worldwide. These macaque monkeys are very docile animals, unlike their more famous relatives, rhesus monkeys, who are highly competitive alpha-male types (even the females). Research on monkeys in a lab such as Rizzolattis is predicated on its inferential value for understanding the human brain, which is generally considered the most complex entity in the known universe, with good reason. The human brain contains about one hundred billion neurons, each of which can make contact with thousands, even tens of thousands, of other neurons. These contacts, or synapses, are the means by which neurons communicate with one another, and their number is staggering. The distinguishing brain feature in mammals is the neocortex, the most recently evolved of our brain structures. Now heres the key “inferential” point: the macaque brain is only about one-fourth as large as ours, and our neocortex is much larger than the macaques neocortex, but neuroanato-mists typically agree that the structures in the neocortex of macaques and humans correspond relatively well despite these differences.
In Parma, the Rizzolatti teams pertinent area of study was an area of the brain labeled F5, located in a large region called the premotor cortex—that part of the neocortex concerned with planning, selecting, and executing actions. Area F5 contains millions of neurons that specialize in “coding” for one specific motor behavior: actions of the hand, including grasping, holding, tearing, and, most fundamental of all, bringing objects—food—to the mouth. For every macaque, as for every primate, these actions are as basic and essential as they come. We Homo sapiens are grasping and manipulating objects from the moment we fumble for the snooze button on the alarm clock until we adjust our pillows at bedtime, eighteen hours later. All in all, we each perform hundreds, if not thousands, of grasping actions every day. In fact, this is precisely why the Rizzolatti team chose area F5 for the closest possible investigation. All neuroscientists want to understand the brain for understandings sake, but we also have an eye on more practical goals, such as discoveries that may eventually drive new treatments for disease. The discovery of the neurophysiological mechanisms of motor control of the hand in the macaque could eventually help individual humans with brain damage recover at least some degree of hand function.
Through laborious experimentation, the Rizzolatti team had acquired an impressive understanding of the actions of these motor cells during various “grasping” exercises with the monkeys. (They are called motor cells because they are the first in the sequence that controls the muscles that move the body.) Then one day, about twenty years ago, the neurophysiologist Vittorio Gallese was moving around the lab during a lull in the days experiment. A monkey was sitting quietly in the chair, waiting for her next assignment. Sud-denly, just as Vittorio reached for something—he does not remember what—he heard a burst of activity from the computer that was connected to the electrodes that had been surgically implanted in the monkeys brain. To the inexperienced ear, this activity would have sounded like static; to the ear of an expert neuroscientist, it signaled a discharge from the pertinent cell in area F5. Vittorio immediately thought the reaction was strange. The monkey was just sitting quietly, not intending to grasp anything, yet this neuron affiliated with the grasping action had fired nevertheless.
Or so goes one story about the first recorded observation of a mirror neuron. Another involves one of Vittorios colleagues, Leo Fogassi, who picked up a peanut and triggered an excited response in F5. Yet another credits Vittorio Gallese and some ice cream. There are others, all plausible, none confirmed. Years later, when the importance of mirror neurons was clearly understood, the Parma colleagues went back to their lab notes, hoping to put together a fairly accurate timeline of their earliest observations, but they simply couldnt do it. They found references in their lab notes to “complex visual responses” of the monkeys motor cells in area F5. Such notes were unclear, because the scientists did not know what to make of their observations at the time. Neither they nor any neuroscientist in the world could have imagined that motor cells could fire merely at the perception of somebody elses actions, with no motor action involved at all. In light of both knowledge and theory at the time, this made absolutely no sense. Cells in the monkey brain that send signals to other cells that are anatomically connected to muscles have no business firing when the monkey is completely still, hands in lap, watching somebody elses actions. And yet they did.
In the end, it does not matter much that the “Eureka!” moment for mirror neurons stretched over a period of years. What matters is that the team did soon grapple with the odd goings-on in their laboratory. They had a hard time believing these phenomena themselves, but in time they also sensed that the discovery, if confirmed, could be potentially groundbreaking. They were right. Twenty years after that first recording in the laboratory, a cascade of well-controlled experiments with monkeys and later with humans (different kinds of experiments, for the most part; no needles inserted through skulls) have confirmed the remarkable phenomenon. The simple fact that a subset of the cells in our brains—the mirror neurons—fire when an individual kicks a soccer ball, sees a ball being kicked, hears a ball being kicked, and even just says or hears the word “kick” leads to amazing consequences and new understandings.
Excerpted from Mirroring People by Marco Iacoboni. Copyright © 2008 by Marco Iacoboni. Published in April 2008 by Farrar, Straus and Giroux, LLC. All rights reserved.