Brain Sense

Faith Hickman Brynie

• Publisher: AMACOM
• Year: 2009
• ISBN:
  9780814413265
• Topic: Ciencias biológicas
• Subtopic: Biología

Complex and crucially important, the senses collect the massive amount of information we need to navigate daily life, and serve as a filter between our inner selves and the larger world. But the science of how the senses work has been little understood—until now. New research is rapidly uncovering fascinating insights into how the brain processes sensory information. It's not simply a matter of the brain controlling the senses; the senses actually stimulate brain development. For example, the brain's sound-processing centers mature properly only when sound impulses trigger them to do so—which is why cochlear implants are best used before the age of three. Brain Sense reveals this and a wealth of findings on how the brain and senses interact, as it examines each of the five major senses: touch, smell, taste, vision, and hearing. With eloquent writing and gripping stories, the author deploys a rare gift for explaining complex scientific ideas in a way that is clear and comprehensible. She introduces the scientists at the forefront of "brain sense" studies—neurologists, brain mappers, bio­chemists, physicians, cognitive psychologists, and others—as well as real-life people who are contributing to the research and benefiting from its practical applications, such as haptic devices to assist people who have lost limbs or rehabilitative software for those who have suffered impairments to their motion vision. You'll find new research that explains: • Why placebos work by changing the way the brain processes pain • How humans respond to pheromones in the same manner as other animals • How taste is highly influenced by expectations of taste • Why color significantly aids the ability to remember an object • How the capacity for language is already at work in newborn babies • What happens in the brain to produce sensory experiences such as déjà vu and phantom limb pain • And much more Expansive and enlightening, Brain Sense shows us that the brain is both flexible and variable, and the reality that we construct based on inputs gathered from the senses differs from person to person. It sheds a much-needed light on the elusive workings of the extraordinary human brain.

PART ONE

TOUCH

Children are born true scientists. They spontaneously experiment and experience and reexperience again. They ... touch-test for hardness, softness, springiness, roughness, smoothness, coldness, warmness: they heft, shake, punch, squeeze, push, crush, rub, and try to pull things apart.

—R. Buckminster Fuller

“Children Are Born True Scientists”

1978

Chapter 1

Life Without Touch

In many ways, Chuck Aoki is a typical teenager. At seventeen, he’s an avid athlete. His Minnesota Timberwolves basketball team won the national junior championship in 2008. He plays rugby competitively, too. Tennis and baseball are his recreational sports. He likes the history and English courses in his Minneapolis high school, and he is confident that he did well on his SATs, although he hasn’t received his scores yet. He likes Taco Bell food. He finds girls confusing. “Women dance around the bushes. Men get straight to the point,” he says.¹ He and his friends like to ride the bus to downtown Minneapolis to go to a movie, eat at a restaurant, or hang out at the mall. He’s lined up a summer job as a human resources assistant for the Minnesota Twins baseball team, a perfect situation for him since he loves sports. Chuck hopes to go to college on a basketball scholarship. He will major in psychology or sports management.

But for all that, Chuck Aoki isn’t a typical teenager. He was born with no sense of touch in his arms, hands, legs, and feet. With a few spots as exceptions, he feels in his limbs neither heat nor cold nor contact nor pressure nor vibration nor pain, although he experiences normal sensation in his head and trunk. His legs were repeatedly damaged in childhood when he walked, ran, and played baseball. His joints have disintegrated and his bones are crumbling. He’s full-time in a wheelchair now; his athletic teams are wheelchair basketball and quadriplegic rugby. He’s lost eight of his fingers down to the first joint. Text messaging on his cell phone produces bleeding sores on what’s left of his thumbs. Buttoning a shirt is impossible. Cutting lettuce for tacos or taking a pizza from the oven poses a serious risk.

Chuck was born with an extremely rare, inherited disorder called hereditary sensory and autonomic neuropathy (HSAN) type 2. This is his story as he shared it with me in a sidewalk café one sunny afternoon. It’s also the story of his mother, Jennifer Nelson. She’s a librarian for the Minneapolis public library system and the proudest mom I’ve ever met.

GROWING UP

“You young mothers. You worry too much,” the pediatrician told Jennifer when Chuck was a baby. The infant was teething. He’d chewed his fingers to raw and bleeding pulps.

“Is that normal?” Jennifer asked. The doctor wrote a prescription for antibiotics. The baby had an ear infection, he said.

Throughout infancy, Chuck cried intensely and interminably. Only full body contact, his tiny trunk held tight against his mother’s skin, could console him. “Is that normal?” Jennifer asked. The doctor wrote more prescriptions for more antibiotics to treat more ear infections.

Chuck walked at nine months, but he walked on his knees. “Is that normal?” Jennifer asked. More antibiotics. Babies get lots of ear infections.

But by the time Chuck celebrated his first birthday, the fact that something was wrong could no longer be blamed on ear infections. The tentative diagnosis of HSAN type 2 came when a neurologist examined a sensory nerve taken from the boy’s foot. The fiber was smaller than it should have been, and it lacked the dozens of tiny, hairlike projections usually seen on nerves. The fiber also lacked the myelin sheath that surrounds, protects, and insulates normal nerves. In the absence of myelin, nerve impulses could not travel along Chuck’s sensory nerves. The baby’s motor nerves were normal, so his brain could direct his limbs to move, but his sensory nerves were nonfunctional. He could feel nothing past his shoulders and his hips.

Chuck was eighteen months old. None of the doctors knew how to treat his condition; they’d never seen anything like it before. The only model came from diabetic neuropathy, which shares some common features with the inherited neuropathies. Diabetic neuropathy compromises blood flow, leading to infections and the “spontaneous amputations” that have robbed Chuck of his fingers, one by one, over the years. Chuck also developed Charcot joints, in which inflammation and loss of healthy bone lead to the overgrowth of abnormal bone tissue, fragmentation, and instability. Why? Because when he walked, he felt the ground only from his hips. He had no feedback to tell him how much force he was exerting with the muscles of his legs and feet, so he stomped too hard. Similarly, when using his hands, his sensation begins at his shoulders. He pushes too hard when he uses a computer, plays video games, or holds a spoon. As a result, his hands constantly bleed and callus. His mother debrides and bandages his wounds daily.

As a small child, he could grasp with his palm but he never learned to make the finely controlled, pinching movements needed to pick up small objects. Because he felt no pain, everyday activities were hazardous. “We pursued a strategy of avoidance,” Jennifer says. The hot water temperature was lowered so that Chuck would not burn himself. Jennifer was ever vigilant, keeping the boy away from flames, sharp objects, and hot surfaces.

Jennifer recalls a family vacation to Oregon when Chuck was seven. “We played on the beach all day,” Jennifer says, “and that evening Chuck’s left knee was swollen to the size of a grapefruit.” The child had been seeing a rheumatologist, and Jennifer suspected a flare-up. She called the doctor and asked what to do; the family was planning to take a train home the next day. In the absence of an open wound, infection, or any obvious break, the doctor advised merely watching the situation and keeping the boy off the leg as much as possible on the journey home.

Back in Minneapolis, Chuck went for x-rays. Nothing showed up. He went for an MRI. Nothing appeared wrong except for the persistent inflammation, so Jennifer continued icing and wrapping the joint. Weeks passed with no sign of improvement, so the rheumatologist consulted a specialist radiologist. The radiologist examined the images and found a shadow that previous examiners had missed. An orthopedist then decided to open the leg surgically. He found a fracture of the femur, the large bone of the thigh. “Chuck had been walking around for six weeks on a broken leg,” Jennifer says. He was home from school for eight weeks. He had a cast on for twelve weeks. Soon after the cast was removed, he broke his ankle, so he had to be in another cast. He couldn’t use crutches because he couldn’t coordinate the alternating right- and left-arm actions that crutches require.

When Chuck was nine, doctors discovered that the earlier fracture of the left femur had destroyed most of the bone’s growth plate. Subsequent surgery closed the entire growth plate in his right leg and what remained of the growth plate in his left leg to prevent unequal limb growth. “A limb length discrepancy would be dangerous on a daily basis,” Jennifer says, “getting in and out of the shower and that kind of thing.” After that, he snapped his anterior cruciate ligament (ACL). “We don’t know how he did it. We didn’t repair it. What would be the point?” asks Jennifer. “His feet are flat, his ankles have sunk into his heels, and both of his feet are deformed,” she says. Chuck has been using a wheelchair full-time since he was twelve.

DIAGNOSING HSAN

Throughout Chuck’s childhood, his parents remained uncertain about their son’s diagnosis. They took the boy to the Mayo Clinic when he was nine in hopes of getting a definitive answer. A precise diagnosis was important, Jennifer explains, because it would help the family plan for Chuck’s health and care as he grew. His neuropathy was obvious, but the autonomic part of the HSAN description was not. The autonomic nervous system controls those bodily functions outside conscious control. It regulates heart rate, blood pressure, intestinal action, and glandular function. In all those ways, Chuck appeared normal. Did he really have HSAN? If so, was it really type 2? There are several kinds, each with its own symptoms, course, and prognosis.

To look for the autonomic component of the diagnosis, doctors at the Mayo Clinic did a sweat study on Chuck. “They put him on a little gurney, sprinkled him with powder, and put him into a makeshift, plastic covered oven, and heated the space up,” Jennifer explains. “Then they charted where his body turned purple, which is where he sweated. He doesn’t sweat from his fingertips and he doesn’t sweat below his knees. There was the autonomic part of his neuropathy that we hadn’t known about.” The HSAN type 2 diagnosis was confirmed.

The broad category of all hereditary sensory neuropathies (HSNs) includes as few as four and as many as six disorders, depending on which classification system is used. All types are genetic, and all involve loss of feeling in the hands and feet. One HSN that is more common and better known that Chuck’s disorder is familial dysautonomia (FD, HSAN type 3, or Riley-Day syndrome). Children with FD often experience feeding difficulties and fail to produce tears when they cry. Other symptoms may include lung dysfunctions, cardiac irregularities, poor growth, and scoliosis. Children with FD are most often born to parents of Eastern European Jewish heritage, with an incidence of one in every 3,600 live births.² Genetic tests are used to diagnose FD but not the other HSAN types.

Chuck’s HSAN type 2 is inherited as an autosomal recessive. That means both Jennifer and her husband, Andy, carry the gene on chromosome 12. Their chance of having a child with the disorder is one in four. (Chuck’s younger brother, Henry, is unaffected.) Although the inheritance pattern is understood, the reasons why symptoms vary among individuals are not. Some babies with HSAN type 2 feed poorly, exhibit poor muscle tone, and can’t maintain body temperature. Chuck had none of those symptoms, but like most others with the disorder, he suffered numerous fractures of hands, feet, and legs, as well as Charcot joints. Also like most others with the condition, Chuck’s muscular strength is normal.

THE BRAIN WITHOUT TOUCH

As for what happens in the brain when touch signals fail to enter it, Jennifer and Chuck’s doctors can only speculate. The somatosensory (“body sense”) region of the cerebral cortex lies in the parietal lobe at the top of the brain, near the crown of the head. Adjacent to it and forward from it, in the frontal lobe, lies the primary motor cortex, where voluntary actions are triggered. These two long, skinny areas lie sandwiched together, and their nerve fibers are organized in descending rows, like twins lined up side by side. Each nerve and each small area is dedicated to a particular body part—forming side-by-side regions for feeling and movement in the left arm, the right leg, and so on. But the two parallel rows are not identical. In the motor cortex, the amount of “processing power” devoted to a body part varies with the precision of the movements that body part can make. So, for example, the fingers get more space in the motor cortex than the toes do. In the somatosensory cortex, the allocation of space depends on the body part’s sensitivity to heat, cold, pressure, vibration, contact, or pain. Thus, the fingertips and lips get a disproportionate share of the somatosensory cortex. The back gets short shrift.

Touch the Pain Away

Mothers and infants know what the rest of us may forget—a tender touch takes some of the pain away. A pediatrics team in Boston divided mothers and their newborn infants into two groups. Half of the mothers held their babies in whole-body, skin-to-skin contact while a physician performed the standard heel-stick procedure to draw blood samples from the infants. The other half of the babies were wrapped in receiving blankets and placed in bassinets while the blood was drawn. Babies in contact with their mothers grimaced 65 percent less than the bassinet-held babies did, and their crying time was a whopping 82 percent less. The held babies did not experience the same rise in heart rate as the control babies did. The researchers concluded that skin-to-skin contact reduces both stress and pain for infants.³

This basic anatomy suggests (but by no means proves) that Chuck’s somatosensory cortex may have allocated space differently from the way it is allocated in other children. Receiving no sensory impulses from his limbs, the parts of his somatosensory cortex that would have processed touch information from arms, leg, hands, and feet probably failed to develop. Did the sensory nerves from his head and trunk take over the brain’s spare “real estate”? There’s no way to know, but it’s possible. It’s possible, also, that his motor cortex is organized differently, although what happens to the motor cortex if it fails to receive somatosensory feedback is unknown. Still, we can make some guesses in Chuck’s case. Athletes who practice their sport and attain a high level of mastery probably devote larger areas of the motor cortex to the body parts they use most. I suspect Chuck’s practice of basketball skills and his mastery of his sport have modified his motor cortex and probably his cerebellum as well—for that’s where movements that are practiced enough to become automatic are coordinated.

LIVING TO THE FULLEST

Although the brain can reorganize itself to some extent to meet the demands of its owner’s life, major brain regions maintain their own specialized functions. As one expert put it, a brain region steals from its next-door neighbor, not the whole town. So Chuck’s brain regions for hearing, vision, and the other senses probably aren’t any different from anyone else’s. But what he’s learned to do with his senses is another matter. Chuck says that he relies on vision to manage daily living. He dribbles a basketball expertly (an action some doctors think he should be unable to perform), using his peripheral vision to judge where the ball is and how forcibly he is propelling it. When playing video games, he holds the controller in front of his eyes and peers over the top to see the screen. He’s learning to drive a hand-controlled car. He says he uses his peripheral vision to determine where his hands are on the steering wheel, brake, and throttle.

Chuck’s vision, strength, and motivation have helped him achieve in sports. He recently started playing wheelchair rugby on an adult team sponsored by the Courage Center in Minneapolis. He’s getting good at it. He practiced with the U.S. Paralympics team in 2008. “Maybe I can get named to the USQRA [United States Quad Rugby Association] team. ... That would be a step toward a world championship team or the Paralympics team,” he says.

As for touch, “It’s not all it’s cracked up to be,” Chuck jokes, then adds more seriously, “I’ve never had it, so I’ve adapted, and I don’t really get what I’m missing. ... It’s not like it has negatively affected me in any really serious way.”

“He thrives in his life,” Jennifer says. “It is fun to watch him.”

Chapter 2

In...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Preface: Falling in Love with Science
• Acknowledgments
• Part One: Touch
• Part Two: Smell
• Part Three: Taste
• Part Four: Vision
• Part Five: Hearing
• Part Six: Beyond the Big Five
• Appendix: The Brain and the Nervous System—A Primer
• Notes
• Recommended Resources
• Index