Wednesday, November 07, 2007

My Insula Made Me Do It

By: Sandra Blakeslee and Matthew Blakeslee

Our bodies and minds interact through a constantly changing network of “body maps” in our brains. As described in Sandra and Matthew Blakeslee’s new book, The Body Has a Mind of Its Own, these maps create our ability to navigate our inner world and the social world of our interactions with other people, as well as the physical world. In Chapter 10, excerpted here, the authors discuss how the abilities to interpret sensations within our bodies and to be emotionally aware of other people are linked.

Our bodies and minds interact through a constantly changing network of “body maps” in our brains. As described in Sandra and Matthew Blakeslee’s new book, The Body Has a Mind of Its Own, these maps create our ability to navigate our inner world and the social world of our interactions with other people, as well as the physical world. Understanding these maps can help answer puzzling questions such as why we still feel fat after losing weight, how we can improve at a sport without moving a muscle, why you can’t tickle yourself, and what causes an out-of-body experience. In Chapter 10, excerpted here, the authors discuss how the abilities to interpret sensations within our bodies and to be emotionally aware of other people are linked. 

 

Excerpted from Chapter 10 of The Body Has a Mind of Its Own: How Body Maps in Your Brain Help You Do (Almost) Everything Better by Sandra Blakeslee and Matthew Blakeslee. © 2007 by Sandra Blakeslee and Matthew Blakeslee. Published by arrangement with Random House, an imprint of Random House Publishing Group, a division of Random House, Inc.  

Do you consider yourself to be emotionally intelligent? Are you empathic, able to read other people’s feelings even when they try to hide or swallow them? Or do friends rib you about your social cluelessness? Do people see you as spiritually grounded, emotionally balanced, a rock? Or do they say you’re repressed, tactless, juvenile? If you weren’t in good touch with your own emotional inner world, how would you ever know?

Several years ago, nine women and eight men came to Dr. Hugo Critchley’s laboratory at the Institute for Cognitive Neuroscience at University College London to explore their level of emotional sensitivity. Critchley, an expert on brain mapping who is now at the University of Sussex, was interested in the relationship between emotional intelligence and a brain function called interoception—your ability to read and interpret sensations arising from within your own body.

Pretend you are a participant in such an experiment You lie down in a brain scanner, put on headphones, and place your left middle finger on a pad that monitors your heart rate. Your right hand rests on another pad with two buttons. As the The more viscerally aware, the more emotionally attuned you are. scanner monitors your brain activity, you listen through the headphone to several series of ten beeps. After each ten-beep sequence there is a pause and you are asked to make a choice: Press one button if you think the beeps were in time with your own heartbeats, or press the other button if you think the beeps were slightly out of sync with your heart. Critchley repeats these sequences, sometimes in sync, sometimes not. Can you tell the difference?

Four of Critchley’s subjects were supremely confident about when the pulse was synchronous or asynchronous with their hearts. They could feel the difference, accurately, every time. Two subjects were veritably heart-blind. They never had a clue about whether the pulses were in or out of sync, and could only guess at random. The others fell in between.

The brain scans revealed significant activity in several brain regions, notably the insula and anterior cingulate cortex. Both these regions are crucial centers of emotional cognition, and as this study makes clear, they are also necessary for attending to feelings that arise from your body.

But the most significant finding in Critchley’s study involved just one brain region, the right frontal insula. This area showed the greatest activity in those who were best at following their heartbeats. Moreover, these were the people who scored highest on a standardized questionnaire to probe their empathy levels. So the better you are at tracking your own heartbeats, Critchley says, the better you are at experiencing the full gamut of human emotions and feelings. The more viscerally aware, the more emotionally attuned you are.

In a follow-up study, Critchley found that people with greater empathy have more gray matter in their right frontal insulas. That is, the thicker this part of your insula, the better you are at reading feelings in yourself and in others. The fact that some people are more emotionally aware than others has a neural, physical basis.

These experiments are a window into some of your most important and fascinating body maps—those that deal in interoception and emotion. Most of this book has been about exteroception, or externally oriented perception. The main Interoception is a separate realm of somatic sensation that is oriented inward.goal of exteroception is to create maps and models of your body, the world around your body, and your body’s relationship to the world. You have read about the many ways your brain creates and maintains maps of your skin surface, limb position, joint movement, and musculoskeletal system so that you can move about and interact with objects and people. You have distinct fibers in your spinal cord that carry such information in both directions: up from your body to your sensory maps, and back down from your motor maps to your muscles.

Interoception is a separate realm of somatic sensation that is oriented inward. It has two sources. The first is the internally mapped state of your body. Bring your attention to the sensations these maps are generating in you right at this moment. Think about your heart, lungs, stomach, intestines, rectum, larynx, throat. Try to feel their activity if you can. All your innards have receptors that send information up to your brain for mapping your “gut” feelings of hunger, thirst, air hunger, and other visceral sensations. In other words, just as your parietal and frontal lobes have a patchwork of sensorimotor homunculi, your insulas contain a quilt of visceral homunculi.

The second source of your interoceptive maps consists of a different class of receptors found on your body’s surface, including your teeth, gums, and tongue. Unlike the touch receptors that deal in pressure and vibration and are tied mainly to deliberate touch and action, these other receptors carry information about the “homeostatic” condition of your body—temperature, pain, itch, muscle ache, sexual arousal, crude touch, and sensual touch. Homeostasis refers to your body’s ability to maintain internal balance. Your spinal cord contains an evolutionarily older set of fibers that carries this information to and from your brain.

This may seem strange at first, since many of your body parts end up being mapped by both systems. If someone pinches your arm, the pressure and pain will be represented in your primary touch map. But the pain will be re-  represented in your insula. Why is pain from one pinch mapped in two places? Because your insular maps serve a different function from your primary touch and motor maps. They are the command center for homeostatic self-regulation. For example, to run your body’s thermostat properly—to keep your body temperature constant—your brain needs to know not just your core temperature but also about air touching your skin. Pain in your muscles, lungs, and joints is important for marshaling your body’s resources during exertion, but so are sensations of strain and movement and resistance in your joints and skin. So the primary brain maps for homeostatic signals from your body surface—about itch, sharp pain, dull pain, burning pain, tickle, sensual touch, heat, and cold—as well as the sensations arising from your body’s interior, are mapped in your insula, not your primary touch cortex. You use these feelings less to deal with the outside world than to seek balance within your body and put your internal sensations in context.

And as Critchley’s results imply, interoception does far more for you than just letting you know you are hungry or exhausted or sexually sated. It is also a crucial ingredient in some of the most important aspects of human beingness: sentiment, sentience, and emotional awareness. 

The Sting of a Bee and the Sting of Rebuke

Like the mirror neuron system, your interoceptive maps are a souped-up version of neural circuitry that had already become highly advanced in the primate line.

In lower vertebrates—a frog, say—sensory information is integrated in the primitive base of the brain. These animals do not have a cortex, the mantle of higher thought and awareness. So a frog’s vision is extremely primitive and robotic in function. It is keyed to buglike motions made by small dark dotlike objects. When the frog “sees” such a stimulus, a targeted tongue attack reflex is triggered. This is just about the only way the frog has to visually identify its food. When a frog is placed in a terrarium and surrounded by dead insects suspended on strings, it will starve to death. Its cortex-free vision just doesn’t have the power to recognize individual features of its prey, like legs or wings.

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 The right frontal insula is where conscious physical sensation and conscious emotional awareness coemerge. 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.

 



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Bill Glovin, editor
Carolyn Asbury, Ph.D., consultant

Scientific Advisory Board
Joseph T. Coyle, M.D., Harvard Medical School
Kay Redfield Jamison, Ph.D., The Johns Hopkins University School of Medicine
Pierre J. Magistretti, M.D., Ph.D., University of Lausanne Medical School and Hospital
Robert Malenka, M.D., Ph.D., Stanford University School of Medicine
Bruce S. McEwen, Ph.D., The Rockefeller University
Donald Price, M.D., The Johns Hopkins University School of Medicine

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