The Little Man in the Brain
Penfield explored all over the brain and found a handful of other, smaller body maps as well. Even before he zapped the brain of his first patient, he knew that he would find touch and motor maps, since his contemporaries had already found them in cats, dogs, monkeys, and other mammals. By the same token, Penfield also knew of a few other maps he should look for, and found them.
For instance, he was able to locate a region known as the secondary somatosensory cortex, which penorms a slightly higher level of shape, texture, and motion analysis than the primary touch map. Yet he found this secondary map much harder to explore and understand. For one thing, it is quite a bit smaller than the primary map, and its neurons have larger receptive fields that are wired to make more complex sensory discriminations. (Every neuron in a given body map receives information from a specific group of “downstream” neurons, known as that cell’s receptive field. Receptive fields in your primary touch map are made up of receptors in the skin itself. For cells in most other body maps, receptive field inputs come from other, lower-level body maps elsewhere in the cortex.) Penfield’s difficulties were compounded by the fact that the secondary touch map is difficult to access, half-buried where the parietal lobe plunges beneath the temporal lobe like a tucked-in bedsheet.
Penfield had better luck in the frontal lobes. Just in front of the primary motor cortex he found a small, higher-order body map where action plans are made. It is imaginatively known as the premotor cortex. Penfield found that stimulation to this map produced far more complex movements than he could get out of the primary map. While stimulating the hand region of the primary map causes random jerking of the fingers and wrist, stimulating the premotor hand area brings forth more complex and fluid action fragments, such as moving the hand smoothly up to the mouth. To extend Penfield’s piano metaphor, if zaps to the primary motor map are like the discordant din of notes from a palm striking a keyboard, then zaps to the premotor homunculus reel off simple melodies like musical scales or “Chopsticks.”
Higher-order motor maps like those in your premotor cortex also afforded one of the earliest glimpses into the neural mechanisms behind intentionality and free will. Penfield’s patients reported that the movements induced through the primary motor cortex felt involuntary-like something that had been done to them. But the actions produced by stimulation to the premotor cortex were accompanied by an inkling of intention-like something being done by them. Or sometimes Penfield would stimulate a spot and no movement would be produced, but the patient would report a sudden desire to perform some simple gesture or action.
These motor map signals are the basis of modem brain-machine interface systems, by which a paralyzed person can have electrodes implanted in his or her motor cortex and learn to move a cursor or a robot arm through pure thought.
The Homunculus in the Game
Practice Makes Perfect
Alvaro Pascual-Leone is a professor of neurology at Harvard Medical School and director of the Center for Noninvasive Brain Stimulation at Beth Israel Deaconess Medical Center in Boston. Born in Valencia, Spain, he trained in his native country, Germany, and the United States. before joining the Harvard faculty in 1997 with the goal of exploring the brain using powerful electromagnets.
The technique he uses is called transcranial magnetic stimulation, or TMS. The doctor wields a heavy wand with a figure-eight-shaped coil on the end. When he holds the wand over a volunteer’s scalp, the magnet discharges, which induces a weak electrical current an inch or so below, down in the cortex itself. It’s like a magic electrode that can probe and zap the brain remotely. Wilder Penfield would have been green with envy.
What do you think happens when a TMS magnet is used to stimulate, say, the ankle region of a volunteer’s primary motor map? At high power it induces a twitch in the ankle, just as Penfield described in his patients. At low power you may not see a twitch, but it still has an effect. The homunculus is still sending a signal down to the ankle muscles each time the TMS coil goes “pop,” but the signal doesn’t quite reach the threshold required to trigger a full-blown twitch. Still, the muscles respond by tensing ever so slightly, and this tension can be measured by electrodes taped to the skin. By probing around people’s primary motor maps in this way, Pascual-Leone can map out the location and size of their homuncular ankle region, elbow region, neck region, you name it.
Among other things, Pascual-Leone is interested in using TMS to see how the primary motor map changes when the brain learns a new skill. ”The brain changes with anything you do, including any thought you might have,” he says. Any time you learn something new, any time your brain deems an experience worthy of remembering over the long term, new connections sprout between cells and previously existing connections are strengthened. The process is called plasticity.
Imagining Versus Doing
As a weekend athlete, Pascual-Leone says he was curious about mental practice and sports. “Anybody who likes watching sports can see that certain athletes appear to mentally rehearse what they are about to do,” he says. “You can see it when they’re preparing for a free throw or getting ready to bomb down a slope in a ski slalom race. Before they get going, they prime themselves.”
Many famous musicians do the same thing. Vladimir Horowitz practiced mentally before concerts to avoid disturbing his motor skills; feedback from pianos other than his own Steinway was upsetting. Arthur Rubinstein, eager to enjoy life and practice as little as possible, used mental rehearsal to minimize time spent sitting at the piano. A violinist who spent seven years in prison and practiced playing in his mind every day gave a flawless performance the night he got out of jail. Injured ballerinas have been known to lie on the floor running through dance steps with their fingers to retain their skills.
So Pascual-Leone repeated his five-finger exercise with one specific form of mental practice: internally generated motor imagery.
Imagery takes different forms that are important to distinguish. You know what it is like to imagine an object. Close your eyes and picture a hippopotamus. Now imagine a belly dancer. This is visual imagery. You are the spectator. Visual imagery engages parts of your brain involved in visual perception and conjures up pictorial memories of what you have seen with your eyes.
Motor or kinesthetic imagery is the process of imagining a movement. Imagine yourself erasing a blackboard, signing your name, or washing a dish. You are the actor. You perform the movement, virtually, in your mind. You aren’t using your mind’s eye so much as your mind’s body. Motor imagery engages a subset of your body mandala, including maps involved in motor planning and proprioception. It simulates the inner feeling of an action.
Using the same setup as before, Pascual-leone’s new subjects spent two hours a day five days a week imagining the five-finger piano key strokes. They were told to repeat each finger movement mentally, as if they were playing. They could rest their fingers on the keyboard but were not allowed to move them in any way.
The results were astonishing. After one week, motor imagery practice led to nearly the same level of body map reorganization as physical practice. As far as your motor cortex is concerned, executed and imagined movements are almost identical.
The “almost” is fascinating. When you mentally rehearse a movement, all but one of the brain regions that control your movements become active in the absence of movement. You imagine throwing the dart but your body is immobile. You imagine pressing the piano key but your muscles are still. So motor imagery is the off-line operation of your brain’s motor machinery unfolding as if it were happening in real time. It takes you about as long to imagine walking across your bedroom as it would if you actually did the walk. Such a walk takes longer if you imagine yourself carrying a heavy box. If you imagine yourself running, your breathing speeds up and your heart rate increases. If you imagine moving your little finger for ten minutes a day, after four weeks it will be up to one-fifth stronger.
Coaches and athletes of every skill level mustn’t ignore this. While many types of mental practice are undoubtedly helpful, motor imagery is the only technique that alters your body maps in the same way physical practice does. Visual imagery (as from a spectator’s point of view), relaxation, hypnosis, affirmation, prayer, and other techniques may help you in one way or another, but will not alter your motor maps. Remember, the students in Straub’s dart experiment who improved the most were those who carried out motor imagery.
The Bubble Around the Body
Scientists have never been able to detect with advanced instruments the kind of energy field that allegedly gives rise to auras in the paranormal sense. When the philosopher Sir John Eccles talked about a “field of psychons” as creating a unity of subjective experience, he did not base his claims on any experimental evidence or designs for empirical testing. When New Age gurus invoke the mysteries of quantum physics to explain the mysterious nature of energy fields and human consciousness, they are essentially explaining one mystery with another mystery.
But the fact that our body and peripersonal space maps are tremendously flexible provides a new scientific window into understanding many strange experiences. Jet fighter pilots sometimes say they enter an altered state when flying for long periods in monotonous conditions-uniform clouds, engine noise, vibrations. In this condition, they sometimes “leave” the aircraft and float outside the cockpit, looking back in at themselves. Eventually they force themselves to snap to and get back into their bodies. Mountaineers trekking at high altitude and sailors crossing the ocean alone also report losing their bodies.
Michael Murphy tells anecdotes of transcendent experiences in sports in his book In the Zone. Athletes leave their bodies or see other bodies change shape on the playing field. A well-known distance swimmer described how, whenever his physical body was exhausted during a competition, he would relax by floating overhead while his body continued to swim, until he felt refreshed, at which point he would reenter his body. Another swimmer says he can see the entire pool from a larger raised-up perspective and anticipate the moves of the other swimmers.
You can have weird experiences falling into and waking up from sleep. Have you ever awoken to the feeling of an ominous presence in the darkness pressing down on your body? Odds are it wasn’t a dream. People have been reporting these encounters for millennia, which surely lent credence to the existence of otherworldly beings like ghosts and incubi. Or have you ever felt yourself leave your body as you fall asleep? Both phenomena, which are surprisingly common, are created when your brain shifts its state of arousal in the transition from sleep to wakefulness or vice versa. Every night while you’re dreaming, your body is totally paralyzed from the neck down via inhibitory circuits in your brain stem (failures of this system are involved in sleep violence and sleepwalking). Your brain does this to keep your body from jumping out of bed and acting out your dreams. But sometimes you stay paralyzed after you have awoken, and your body mandala’s best-fit interpretation is that a crushing weight is pinning you down. It can be terrifying. But rest assured, when it ends it’s because your brain has reestablished the connection with your muscles, not because the incubus has vanished back to Hell.
When people enter deep meditation or trance, they say that their bodies and minds expand out into space. Body awareness fades, and they are left with a unitary yet diffused and nonlocalized sense of themselves. Along with it come feelings of joy, clarity, and empathy. When Buddhist lamas meditate in brain scanners, activity in their parietal lobes plummets. It can’t be a coincidence that the dissolution of the bodily self accompanies the shutting down of the body and space maps that create it.
Shadowy Illusory Persons
Ever had the creepy feeling, while you are wide awake, that another person is lurking behind your back, only when you turn around, no one is there? What about an out-of-body experience? Have you ever felt yourself floating up near the ceiling, looking down at your corporeal self?
Such experiences, which may be more common than is generally acknowledged, are almost always explained in terms of paranormal forces-an encounter with ghosts or crossing to another realm of reality.
But according to Olaf Blanke, a neurologist at the Ecole Poly technique Federale de Lausanne in Switzerland, the feeling of an illusory shadow person or the sensation of leaving one’s body can be induced, in mentally healthy persons, by delivering a mild electric current to specific spots in the brain.
A zap to one spot, the right angular gyrus, recently gave one woman the palpable sensation that she was hanging from the ceiling, looking down at her body. Current to the left angular gyrus gave another woman the uncanny feeling that a shadowy person was behind her back and that he was intent on interfering with her actions.
Both women were being evaluated for epilepsy surgery at University Hospital in Geneva, Switzerland. Physicians implanted dozens of electrodes directly into their brains to pinpoint the abnormal tissue causing their seizures and to identify adjacent areas involved in language, hearing, or other essential functions, so as not to excise them inadvertently. When each electrode activated a different patch of brain tissue, the women said what, if anything, they experienced.
Despite their epilepsy, both women had normal psychiatric histories, Blanke said. The women were stunned by the bizarre nature of their experiences.
One patient was a twenty-two-year-old pharmacy student who had electrodes implanted into the left side of her brain in 2004. “We were checking language areas,” Blanke said, when the woman turned her head to the right. That made no sense because the electrode was nowhere near areas involved in movement control. It was in a multisensory area where the parietal and temporal lobes meet.
Blanke applied more current. Again, the woman turned her head to the right.
“Why are you doing this?” he asked.
The woman replied that she had the weird sensation that another person was lying directly beneath her body on the bed. It was not in the mattress, but rather stretched out behind. It felt like a “shadow” that did not speak or move; it was young, more like a man than a woman, and it wanted to interfere with her.
When Blanke turned off the current, the woman stopped looking to the right. The strange presence went away. Each time he reapplied the current, she turned her head to try and see it.
The woman sat up, leaned forward, and hugged her knees. Now when the current flowed, she noted that the “man” was also sitting’ and that he was clasping her in his arms. She said it felt unpleasant. When she held a card in her right hand, the person tried to take it from her. “He doesn’t want me to read,” she said.
Because the illusory person closely mimicked the woman’s body posture and position, Blanke concluded that she was experiencing a perception of her own body-a felt double or doppelganger. She did not recognize that the person was an illusion of her own body.
“Heidi” suddenly felt herself lifted out of her body. Floating near the ceiling, she looked down, aghast. Seated around her real body were three people, one of whom held an electrode over the exposed right side of her brain. Blanke was applying small amounts of current to different areas of her cortex to find the locus of her seizures.
When Blanke stimulated Heidi’s right angular gyrus, she felt herself rise up, as if she were the gauzy apparition in a Tim Burton movie.
“I am at the ceiling,” she exclaimed. “I am looking down at my legs.”
This had never happened before. She was stunned.
“What?” Blanke was equally astonished, and removed the electrode. “Wait,” said Heidi.
“I’m back on the table now. What happened?” “I’m not sure,” he said, “Let’s try again.”
Blanke stimulated the same spot in Heidi’s brain for another two seconds. Because the electrode is silent, she had no way of knowing when to expect anything. But while the current flowed, she found herself back at the ceiling, outside her body, floating, with her ghostly legs dangling below her ghostly self. She gasped again.
“What do you see?” Blanke asked Heidi-on-high.
“My back is touching the ceiling. My legs are hanging down a little. I can see the three of you.”
“Do you have arms?”
“I’m not so sure about my arms,” Heidi said. “But I have a head and a body. I see the bed and the side table. I’m lighter than usual, not moving.”
Blanke was fascinated. From the ceiling Heidi saw only the lower part of her body. But why would she tell him that? Why not her whole body? Then it occurred to him to consider the position of her real body propped up in bed, arms straight down at her sides. From her vantage near the ceiling” she saw those same body parts-feet, pajamas, trunk, and legs-that she would see looking at herself from the bed.
Blanke decided that Heidi was not making this up. Given that, he struggled to find an explanation. “Try looking at your limbs,” he said, applying the current for the third time.
“Tell me what you see.”
Again she gasped. Now, when she looked at her outstretched arms, the left arm seemed to shorten to half its normal size. As in a Tom and Jerry cartoon, it grew shorter and shorter, and then, when the current stopped, it popped back out to its normal size.
Heidi had never read a neurology textbook, Blanke says, and had no way of knowing that stimulation to her right brain would affect the left side of her body, specifically her left arm.
Oddly, though, both legs appeared to shorten by a third during the stimulation. Blanke decided to bend her legs in the bed and see what would happen.
Again the current flowed; this time Heidi screamed. Both legs seemed to fly up and were about to hit her in the face, even though her real legs remained motionless. When she closed her eyes, she had the sensation of doing sit-ups, with her upper body approaching her legs.
Heidi’s uncanny adventure, which took place in December 2000, is the first recorded case of an out-of-body experience induced by electrical stimulation of the brain. As long as her body maps were synchronous, her experience and behavior were fluent, holistic, and integrated. But when Heidi’s maps went briefly out of sync, her felt position in space and her seen position in space did not match. Her mind cast about for the best-fit way to turn her confusion into a coherent experience, and concluded that she must be floating up and away with a view downward.
But what if you have an out-of-body experience without someone zapping your right angular gyrus? Plenty of people report briefly perceiving the world from a location outside their bodies, often during a near-death experience. One explanation for the phenomenon is alterations in blood flow. Large arteries converge near the angular gyrus inside your brain. If anything constricts the flow of blood to that area, your felt body sense can become disoriented. You might get the feeling that you are floating above an operating table or the scene of a car accident. At the same time, your field of vision might have what is called a scotoma-a big blank spot, like a black splotch at the bottom of a well-that your brain fills in with images of what it expects or would like to see.
Place cells and grid cells are space-mapping neurons linked to a memory-forming region called the hippocampus. The hippocampus is evolutionarily much older than the cortex. So despite the amazing power and flexibility of our cortical space and body maps, this ancient system of place and grid cells is still very much with us-you could say it was “grandfathered in.” Instead of mapping personal space from an egocentric point of view, as your parietal and premotor circuits do, place cells and grid cells are what scientists call geocentric.
They are different: Place cells are context-sensitive, while grid cells are context-independent. Place cells map the space around your body in terms of whatever environment you happen to be in-a room, a city street, a basketball court. They tell you where you are relative to the specific landmarks around you. They are what enable you to plan your route through a restaurant full of tables, keep track of where you are in a WalMart, and help you decide where to go next while you’re picking your way through a crowded room.
Grid cells are similar, but they do not attune themselves to landmarks. They map space independently from your environment. They are your dead reckoning cells. The point two feet in front of your nose is the point two feet in front of your nose regardless of whether you’re in a cocktail bar or lying in bed or standing in the middle of a featureless plain.
Place cells were discovered in 1971 when two neuroscientists, John O’Keefe and John Dostrovsky, implanted electrodes into the brains of mice in an effort to study memory. Their target was the hippocampus. As the animals moved around their familiar enclosure, the scientists noticed that some cells fired when a mouse was in the southwest region of its home enclosure. Other cells fired when the animal moved to the northwest region. The same thing happened in different areas of the east half of the enclosure. In fact, it was possible to tell where an animal was inside its enclosure simply by looking at which cell!! were active. Each time an animal moved, a different population of hippocampal cells marked its place in space. If the animal moved back to the same location, the same cells became active again.
The researchers named these cells “place cells.” They went on to learn that a rodent has many thousands of place cells, each tuned to a different region of space, called a place field. Even though there are only thousands of cells, a rat can learn many more locations than it has individual place cells through the power of combinatorics-the same principle that allows ten buttons on a telephone to represent all the phone numbers of an entire nation. The place cells can be active in millions of combinations to map all place fields in a given environment, whether it’s a cage, a ship’s hold, a barn, a wide-open pasture, or any other place a rodent might find itself. Moreover, some place cells fire in response to edges in an environment, like walls. And when a mouse or rat enters a new environment, a new place map is formed in minutes.
You have place cells too. When you walk into your kitchen, certain place cells fire when you are standing in front of your refrigerator. As you move toward the sink, a different set of place cells will mark your new position in the room. If you walk into your dining room or living room, another combination of place cells will mark your spot in space.
Your place cells have, in a sense, memorized the contents of each room, helping you know where you are in each zone of space. Thus in the dark you can move around any room in your house or apartment and not bump into things because your place cells have mapped where each piece of furniture is located, where the doorknobs are, and how far the light switch is from the doorframe. You have an internal map of where objects are located in relation to one another and in relation to your body as you move through space. Your place cells also take information from other parts of your self-motion system, including cells that keep track of where your head is turned, and constantly help update you about your balance and your body schema.
Spin yourself around a few times in the middle of a room. Then try to reach a door. You won’t know which direction to go until you locate an object you recognize. Only with this cue can you work out where the door is located. This means that your place fields are calibrated according to fixed reference points-sofa, chair, table, window, door-that do not usually change. If you move your furniture around, your place fields reconfigure to update your map.
As with many big new findings in science, it took a few more years for the research community at large to grasp the significance of Rizzolatti’s findings. But grasp it they did.
In 2001, V. S. Ramachandran, the neurologist who figured out the nature of phantom limbs, declared, “Without a doubt it is one of the most important discoveries ever made about the brain. Mirror neurons will do for psychology what DNA did for biology: They will provide a unifying framework and help explain a host of mental abilities that have hitherto remained mysterious and inaccessible to experiments.”
Using a variety of brain imaging techniques, scientists went on to discover, in humans, many more elaborate mirror circuits that, cognitively speaking, leave monkeys in the dust. You can think of mirror neurons as body maps that run simulations of what others people’s body maps are up to. In this way, they serve to link our body schemas together across the otherwise tremendous gulf that separates one person’s subjective world from another’s. They allow you to grasp the minds of others, not through conceptual reasoning, but by modeling their actions, intentions, and emotions in the matrix of your own body mandala.
For instance, when you watch someone else perform an action-say, using a broom-you automatically simulate the action in your own brain. You understand the sweeper’s action because you have a template for that action in your own motor maps. When you see someone pull back his arm, as if to throw a ball, you have a copy of what he is doing in your brain that helps you understand his goal. You can read his intentions. You know what he is most likely to do next.
“When you see me doing something, you understand because you have a copy of the action in your brain,” says Rizzolatti. “It’s so strange. You become me. When I see you grasping an object, it is as if I, Giacomo, were grasping it.”
The same principle applies to perceiving and understanding other people’s emotions. When you see a friend choke up in emotional distress, your brain automatically simulates that distress. You empathize. Actors, who can make you laugh or cry, are very good at reading the felt states of their own bodies and transmitting those feelings via mirror system communication.
“We are exquisitely social creatures,” says Rizzolatti. “Our survival depends on understanding the actions, intentions, and emotions of others. We simulate these automatically, without logic, thinking, analyzing.”
Luckily, he says, when you observe an action you do not automatically act it out, and when you observe an emotion you do not automatically experience it in full. Your mirror neuron system cordons off the simulations in much the same way it inhibits you from acting out while you scheme or plan an action before you’re ready to execute it.
There may be no such thing as telepathy, but mirror neurons are the next best thing.
Shall We Dance?
How do lowly neurons carry off such a sophisticated feat? How can brain cells, even working together in a circuit, be so incredibly smart? Most sensory neurons are rather pedestrian. They devote themselves to ordinary features of the outside world. For example, some fire when they detect a horizontal line, while others are dedicated to vertical lines. Others detect a single frequency of sound or a direction of movement. Moving to higher levels of the brain, scientists find neurons that detect far more complex features such as specific body parts, or flowers, or letters of the alphabet. As you’ve already seen, you have neurons in your higher motor maps that help your body plan complex movements and postures. For example, some neurons fire when you bring your hand to your mouth from any starting point around your body-that is, they represent the goal of moving hand to mouth.
Mirror neurons make these complex cells look like nincompoops. They seem uncannily smart in the way they link perception, action, and intention. Say you are trying to learn French. You can hear the sounds but you don’t know how to repeat them accurately. Somehow you have to form your mouth into the right shape and right nasal resonance to produce those new sounds. You need to bring two complex properties together: sensory detection and motor planning. This is exactly what mirror neurons do. When you learn French or any new language, they map sounds and, using the same circuitry, produce those sounds.
In trying to understand human behavior, evolutionary psychologists suggest that all through the Stone Age, the human brain evolved modules for language and other uniquely human traits. Just as you have eyes for seeing and ears for hearing, the claim goes, you are born with a hardwired set of specialized brain modules for absorbing language, detecting cheaters of the social contract, calculating sexual attractiveness in others, and so on. In other words, the brain is the computational version of a Swiss Army knife.
Mirror neurons provide an alternative explanation for human brain design. Your brain is unique not because it has evolved highly specialized modules, but because it is parasitic with culture, says Ramachandran. Mirror neurons absorb culture the way a sponge sucks up water. “You can learn much more easily how to shoot an arrow or skin a bear by watching your mom and dad [do it] than by listening to them describe it,” he says.
According to Ramachandran and others, mirror neurons are a major factor in the great leap forward in human evolution one to two hundred thousand years ago, answering the question “What made Homo Sapiens so darned sapient?” Unique human abilities like protolanguage (in which sounds were mapped to lip and tongue movements), empathy, theory of mind (attributing thoughts and motives to other people), and the ability to adopt another person’s point of view arguably arose at this time. Mirror neurons set the stage for the horizontal transmission of culture. As science writer Matt Ridley says, nature occurs via nurture.
Mirror neurons do not negate the fact that there are special areas for language in the human brain, Ramachandran says. But these regions do not have to be performed at the moment of birth to explain how they develop. An alternative theory holds that language areas are shaped by mirror neurons as a baby learns to speak by miming and understanding the lip and tongue movements of others. Think of a mother saying “mama” to her infant son. Mirror neurons are active when the baby sees and hears someone say “mama” and when he utters those twin syllables himself. They are the same neurons. The same brain structures that produce language participate in comprehending it. In other words, mirror neurons serve as a bridge for decoding and internalizing the meanings of other people’s actions by processing them directly within the child’s own body maps.
Language can often seem abstract and transcendent of the body, the world, and even time itself. But language is more closely tied to your body mandala than you may realize, especially where its acquisition during childhood is concerned. If you read the verb “lick,” your tongue area will light up. If you hear someone say “kick,” it activates your leg areas. Christian Keysers, a mirror neuron researcher at the University Medical Center Groningen in the Netherlands, says that mirror neurons may very well be a key precursor to abstract thought and language. For example, he explains, you use the word “break” as a verb as in “I see you break the peanut, I hear you break the peanut, and I break the peanut.” The constant is the mental simulation of breaking even though the context varies in each case. So your body is the foundational source of meaning-not just of words and actions but even the meanings of things you learn about through your eyes, ears, and bodily experience.
Newborns do not talk, but their mirror neurons kick in within minutes of birth. If you stick out your tongue at a newborn infant, he may stick his tongue back out at you. Scientists take this to mean that newborns have an innate sense of a general body plan, but the only muscle they have much control over is the tongue (it is exercised in utero when the fetus sucks its thumb). Newborns cry more when they hear another newborn crying than when they hear white noise, their own cry, the cry of an older baby, or an adult faking a cry. Two-week-old infants sometimes imitate lip protrusion, mouth opening, tongue protrusion, and finger movement.
As the baby matures, his brain receives sensations of touch, proprioception, balance, and the like to build up a model of the world with itself at the center. By the time they are two, children learn quickly and primarily through imitation, which lets them absorb far more knowledge and skill than could ever possibly be explained to them verbally. They then spend years practicing what they have learned. When you realize that children have a system of neurons that is capable of learning by simply seeing, hearing, touching, then you begin to see that the world itself is the teacher, with you, as the parent, in a starring role. Your child’s mirror neurons resonate with your words, intentions, and moods. How you react to adversity or happiness is absorbed by your children through their mirror neuron system as they watch you from moment to moment.
In fact, it has been shown that the imitation instinct in human children is so strong they tend to “overimitate.” Imagine an experiment in which a scientist shows a simple puzzle box to a young child. She watches with interest as the researcher performs a series of simple steps that result in the box opening and a treat being revealed. Some of these steps are mechanically necessary to get the box open, but a few of them are blatantly inessential. He resets the box and hands it to her. As you might expect, it’s monkey see, monkey do: She repeats his actions as faithfully as she can, including the “filler” steps.
Now imagine that the scientist performs the same experiment with a young chimpanzee who is at a roughly comparable stage of cognitive development. The ape wants the treat. He watches and learns how the box is opened. And when he gets hold of it, he opens it in as efficient a manner as possible, omitting the inessential steps. The human child has the same basic ability to analyze and understand the box as the ape child did, but her human mirror system is a much stronger force behind her actions. It may seem counterproductive for her to be such a slavish imitator, but this is only a temporary phase while her mind is immature. Her highly developed mirror system will serve her well as she gets older. She is the one who will go on to absorb the vast array of complex skills and understandings that human culture affords.
Interestingly, says Dr. lriki, even though monkeys have mirror neurons, they don’t actually imitate each other. This may come as a shock, because we tend to imagine monkeys as the quintessential copycat mischief-makers. This isn’t to say monkeys are oblivious to each other. Far from it. They watch each other constantly. Newborns imitate lip smacking and tongue protrusion. Older monkeys take cues from each other, follow each other’s examples, exploit each other’s discoveries. If one monkey sees another lift the lid of a box and pull out a banana, she will quickly run over and take a peek inside the box herself.
You could argue that this qualifies as imitation, but that misses the point. True imitation is of the “aping” variety-mimicking specific gestures that can include arbitrary action sequences. Apes and humans can learn detailed action sequences, like opening a puzzle box to extract a goodie, based on just one viewing. Monkeys can be taught complex action sequences too, but it typically takes a period of patient training in a laboratory setting. In the wild, monkeys imitate each other only at the level of the basic primate repertoire of simple grips and gestures: poking, picking, lifting, pulling, and so on. But for apes and humans, these basic actions can serve as building blocks in long, complicated, and arbitrary action sequences.
Consider a young chimpanzee who watches while an elder snaps a twig off a bush, strips it of leaves and twiglets, pokes it into a termite mound, and comes up with a highly nutritious insect kabob. The young chimp runs off into the bushes to find his own twig and attempts to replicate the same feat. That’s true imitation, and monkeys virtually never approach this level.
So if monkeys don’t use their mirror neurons for imitative learning, what do they use them for? Remember, imitation is not the only function of mirror neurons. They still give monkeys insight into each other’s goals and intentions based on action observation. Even if their mirror neurons aren’t developed enough to generate precise imitation, in the soap opera world of primate society, action understanding and intention reading are essential abilities.
I Feel Your Pain, I Feel Your Pleasure
In the 1962 film Dr. No, James Bond opens his eyes to find a tarantula in bed with him. As it creeps ever so slowly up his arm, you can just feel the hairy, spidery legs, because your mirror neurons are in overdrive.
You have mirror neurons for emotion reading and empathy in two areas folded deep inside your cortex, called the insula and the anterior cingulate cortex. When you see a look of disgust on someone’s face, mirror neurons in your insula give rise to feelings of disgust in your own body. When you see joy, you feel joy. When you see sadness, you feel sadness. When you see pain, you feel pain. When you see someone’s upper arm being jabbed with a needle, the same muscle in your arm tenses up and you start breathing faster.
Tania Singer, a neuroscientist at University College London, illustrated this phenomenon by recruiting lovers and putting one of them (the woman) into a brain scanner and then zapping each person with painful electric shocks. Each woman in the scanner registered a pain response in her anterior cingulate when she received a shock-and also when she witnessed her beloved being shocked. Women who scored higher on an empathy questionnaire showed greater activity in this brain region. This means that when you empathize with someone’s pain, including a stranger’s, at some level you actually feel it. Just as frontal and parietal mirror neurons represent both the observation and execution of actions, these emotional mirror neurons represent both the witnessing and the experience of certain feelings and emotions. (Women tend to have more active mirror neuron responses and to be more empathetic than men, although the reasons for this are not yet clear. It may be that high levels of testosterone limit empathy in some way. In general, women are stronger empathizers, while men are stronger systematizers.)
When someone yawns, you yawn, thanks to mirror activity. When you see someone scratch his chin, you may feel an itch on your own chin. When you see someone afraid, you feel a visceral flutter of fear. This sensation can initiate a fight-or-flight motor preparation in your own body. When danger lurks, fear spreads through the crowd. Everyone gets emotionally aroused and ready to run.
Heart of the Mandala
The greatest evolutionary innovation of mammals was to expand the cortex to tremendous size. The cortex imbues the mammalian mind with the capacity to form highly detailed and versatile representations of sights, sounds, and actions. So a rat, for example, has a rich understanding of the space around its head, thanks to its sensitive whiskers and well developed body and whisker maps. And even though rats don’t have particularly good vision, they can still tell an insect from a wad of used dental floss at a glance, because they have cortical vision maps.
But in the rat-and for that matter, in all other mammals aside from primates-the homeostatic information from the body does not form a rich interoceptive map in the insula. Rats do have insular maps, to be sure, but they are rudimentary. In a rat, pain, itch, sensual touch, and that whole ancient group of somatic senses are primarily integrated in the base of the brain and in subcortical emotional centers. Their interoception, then, is more reminiscent of the frog’s automaton-like vision than the primate’s keen, knowing eye.
The same goes for cats, dogs, horses, and other four-legged animals. Because of this difference in mapping, some experts claim that their sensory experiences must be profoundly different from ours, even though we are often tempted to attribute human emotions and intentions to our pets. While a dog may show “shame” through its body language, it does not feel what you feel when you are ashamed. Dogs are clearly emotional and self-aware, but they are not in the same league with you.
In primates, interoceptive information is elaborated through a rich set of mappings in the insular cortex. And in humans it is richer still. Thus you have a little insula map for sharp pain, another for burning pain, one for itch, one for aching, one for overexerted muscles, and so on, along with visceral homunculi that represent the state of your lungs, heart, and the rest of your innards.
And even that is just the beginning of what your brain does with this information. After reading off the internal state of the body from both the left and right insulas, the human brain-and only the human brain-performs yet another level of integration. The information from both your insulas is routed to the right frontal insula, the same region Critchley found corresponding closely in size and metabolic vigor to a person’s empathic talent.
Your right frontal insula “lights up” when you feel all the quintessential human emotions-love, hate, lust, disgust, gratitude, resentment, self-confidence, embarrassment, trust, distrust, empathy, contempt, approval, disdain, pride, humiliation, truthfulness, deceit, atonement, guilt. It also “lights up” when you feel strong sensations, from physical pain to a fluttery stomach to tingling loins.
If your right insula is damaged by a stroke, you will not be able to detect or feel disgust. If you look at someone who takes a bite of food, spits it out, and makes a retching sound with a disgusted look on his face, you will just smile, take a bite of the same food, and declare it delicious.
This dual physical-emotional sensitivity is not just a coincidence. The right frontal insula is where conscious physical sensation and conscious emotional awareness coemerge. Consider this amazing fact: The right frontal insula is active both when you experience literal physical pain and when you experience the psychic “pain” of rejection or the social exclusion of being shunned. It lights up when you feel someone is treating you unfairly. Scanning experiments have proven all this, and the results are profound. Welcome to one of the most important regions in the human brain.
Reason Runs Hot
Arthur “Bud” Craig is a neuroanatomist at the Barrow Neurological Institute in Phoenix, Arizona, and the first person to figure out how interoception is uniquely wired in the human brain. He is the kind of super-intense scientist who unapologetically spouts rapid-fire jargon-ventrolateral prefrontal cortex, solitary tract nucleus, posterior ventral medial nucleus. But for those who listen and translate, Craig is telling a story that drastically revises our scientific understanding of how bodily sensations are mapped in the human brain and turned into feelings, motivations, pain, and sentience.
The right frontal insula is the focal point of all this, according to Craig, because it literally connects the state of your body to the state of your brain. By “your brain,” in this context, he means the sensory perceptions, abstract thoughts, linguistic processing, and motivations that occur elsewhere throughout your cortex. Your right frontal insula gives rise to the map of “the emotional me” and “the emotional now” by integrating homeostatic information from both your body and your brain. This is a profoundly important insight. You detect the state of your body and the state of your mind together in the right frontal insula. It is here that mind and body unite. It is the foundation for emotional intelligence.
If your mirror neurons are activated by another person’s emotional state, your right frontal insula lights up. If you sense fear in a crowd, crave drugs, or see someone cheat, your right frontal insula lights up. If you are a schizophrenic, your right frontal insula is deformed.
Your right frontal insula integrates your mind and body through strong connections with three other brain regions. One is the amygdala, a lower brain area that plays a key role in linking strong emotions to experiences, people, and things. Another is the orbitofrontal cortex, a region that is critical for self-discipline and for setting plans and priorities in relation to rewards and punishments. And finally it is linked to the anterior cingulate cortex, which allows you to monitor your behavior for mistakes, correct and avoid errors, evaluate context, and plan and carry out actions that have emotional and motivational significance. The anterior cingulate also contains a mapping of your body, with your head at one end and your feet at the other, but so far as is known, the orbitofrontal cortex and amygdala do not.
In every brain imaging study ever done of every human emotion, the right frontal insula and anterior cingulate cortex light up together, Craig says. He takes this to mean that in humans, emotions, feelings, motivations, ideas, and intentions are combined to a unique degree, and that this is a key element of our humanity.
Actually, the idea that we sense our emotions from our bodies has been around for more than a century. Two psychologists, William James and Carl Georg Lange, long ago developed a theory that emotion arises when you perceive changes in your body. When you run from a bear in the woods, you are afraid not because of your rational assessment that you are about to be eaten, but because your heart is racing, your stomach and sphincter are clenched, and you are running as fast as you can. In the wake of an argument, as long as your heart is still racing you still feel angry. There is an aspect of this with bearing on many relationships: In women, according to the Stanford neuroscientist Dr. Robert Sapolsky, the autonomic nervous system ramps down more slowly than in men. As Sapolsky likes to say to his wife after a spat, “Honey, don’t forget the half-life of the autonomic nervous system!”
This theory explains why people with whole-body paralysis often complain that their passions and emotions have become blunted. It is why psychopaths, who often have trouble feeling sensations from their body, feel no guilt, remorse, or anxiety about their actions. It is also why taking a beta blocker-a drug that quiets your sympathetic nervous system can banish the butterflies from your stomach, still your quivering limbs, turn off your drenching stage-fright sweats, and allow you to speak or perform calmly in public. In other words, the fear is more in your body than in your mind. Dampen your interoceptive signals, and you dampen the fear.
Antonio Damasio, a neuroscientist who heads the Brain and Creativity Institute at the University of Southern California at Los Angeles, has updated and revised James and Lange’s idea with his somatic marker hypothesis-the notion that your feelings strongly contribute to even the most “rational” decision making in everyday life. Scientists used to assume that reason and emotion were qualitatively different psychic spheres. Clearly these spheres could influence each other, but most believed that the thinking, knowing, reasoning part of the mind was in some fundamental way distinct from the mind’s feeling, sensing, emotional, and more primitive aspects. But James and Lange, and now Damasio, Craig, and others who follow the neuroscience, argue that it’s just not possible to separate them at a deep level.
Emotion is never truly divorced from decision making, even when it is channeled aside by an effort of will. Even a mathematician pursuing the trail of a new proof is driven by a blend of personal ambition, curiosity, and the sometimes spine-tingling Platonic beauty of the math itself. Even a judge who renders a verdict that the law supports but he finds personally distasteful is being driven by a moral emotion about the principle of the rule of law. Even a terrorist coolly gearing up for a suicide attack on innocents is spurred by an intensely felt motivation inspired by his love of God and God’s favored people, who also happen to be his own.
Interoception, then, is the font of your complex emotionality. It breathes life into your cortex, which is otherwise rather machinelike in character. Interoception is the fire under the kettle of consciousness; remove the heat, and the system settles into tepid equilibrium.
Intutition Cells, aka Von Economo Neurons
In all the talk about what makes humans special, you’ll hear many of the same arguments. We walk upright. We have opposable thumbs. Our brains are enormous. We have language. We’re top predators.
But there is one feature peculiar to humans that you’ve probobly never heard about. You have, tucked into your anterior cingulate cortex and frontal insulas and especially in your right front insula, a special class of cell found in no other species except our cousins in consciousness, the great apes, elephants, and whales. Called Von Economo cells after the scientist who first observed them in 1925, they are big, fat, highly connected neurons that appear to be in the catbird seat for enabling you to make fast, intuitive judgments.
Intuition is your capacity for quick and ready insight. Often you know and understand things instantly, without rational thought or inference. You feel when something’s fishy. You sense it when you have an instant personal bond with a stranger. You are positive that the charismatic politician on television last night is lying through his teeth.
You can make snap judgments because your brain contains Von Economo neurons, but to keep things simple, let’s call them intuition cells. A very small number of intuition cells showed up in your brain a few weeks before you were born. Studies suggest that you probably had about 28,000 such cells at birth and 184,000 by the time you were four years old. By the time you reached adulthood, you had 193,000 intuition cells. An adult ape typically has 7,000.
Intuition cells are more numerous in your right brain. Your right frontal insula has 30 percent more than your left insula. Intuition cells are especially large and seem designed to relay information rapidly to other parts of the brain. They contain receptors for brain chemicals involved in social bonds, the expectation of reward under conditions of uncertainty, and for detecting danger-all ingredients of intuition. When you think your luck is about to change playing blackjack, these cells are active.
John Allman, a neuroscientist at the California Institute of Technology in Pasadena and a leading expert on comparative brain development, says that when you meet someone, you create a mental model of how that person thinks and feels. You have initial, quick intuitions about the person-calling on stereotypes, memories, and subliminal perceptions-which are followed seconds, hours, or years later by slower, more reasoned judgments.
When you make fast decisions, Allman says, your frontal insula and anterior cingulate are active. When you experience pain, guilt, or embarrassment or engage in deception, these areas are active. When you think-something is funny, these same cells fire up, probably to recalibrate your intuitive judgments in changing situations. Humor serves to resolve uncertainty, relieve tension, engender trust, and promote social bonds.
All your social emotions and moral intuitions are processed in this circuit, Allman says. Oddly, they are related to food. Recall that your insulas map your visceral sensations, including gustatory experience. You feel the need to eat or eliminate, rest or run, save energy or expend energy, in this body mapping system. Recall, too, that your right frontal insula re-represents these basic bodily functions as social emotions, which are similarly expressed as polar opposites: love-hate, lust-disgust, gratitude-resentment, self-confidence-embarrassment, trust-distrust, empathy-contempt, approval-disdain, pride-humiliation, truthfulness-deceit, atonement-guilt. These emotions cause you to approach or retreat, favor social bands or disrupt social bonds.
Allman thinks that intuition cells, like mirror neurons, may be defective in autism spectrum disorders, which feature an inability to think and interact intuitively. These cells arose late in evolution, he says, and have not had much time to become integrated with other cell populations. This may make them vulnerable to dysfunction in a manner analogous to our propensity to suffer lower back, hip, and knee disorders from adopting our bipedal posture.