Includes sections: circadian rhythms, eating behavior, sexual response, navigating our environment, learning from the body, the stress response and disease, stress and some common illnesses, mood and health, depression and the heart, depression and stroke, anger, the search for a "mind-body medicine," challenges ahead
If someone you love is gravely ill, you say you are “sick at heart.” You may have a boss who makes your stomach churn. At sixteen, you blush when someone you secretly adore sits next to you in the library. Occasionally, you may be so worried you can’t sleep, feel your head pounding at the end of a frustrating day, or find your heart racing when you spot a police car with its light flashing in your rearview mirror. These feelings show the brain’s power to control your body.
That power flows in the opposite direction, too: eating, sex, exercise, illness, injury, and other physical experiences also affect what you think and feel. As simple an event as the enjoyment of a good meal will likely boost your sense of overall well-being and tranquillity. Jogging, swimming, or even a brisk walk around the block can make you feel energized and upbeat. Having a cold, the flu, or an aching back may make you cranky, perhaps even blue. Even minor everyday physical insults such as a paper cut or a stubbed toe may briefly upset your mood, while small positive physical encounters—a dental assistant’s hand on your arm when you’re getting a tooth drilled—can lessen pain and anxiety.
Most of us are familiar with the idea that our mental states and emotions influence a host of bodily functions and that the opposite is also true, but the ebb and flow of our feelings are just the beginning of the story. As scientists take advantage of ever more refined information about how cells work—the physics and chemistry of both the brain and the body, and how our genes function—the picture of brain and body interactions is beginning to gain detail and become vastly more interesting. Already medical and scientific research to understand how brain and body communicate has provided fascinating clues to the different systems that link brain and body in constant dialogue and feedback. Whole disciplines in brain research are developing around the many ways in which the brain acts as the body’s central command post.
The brain is connected to every part of the human body, and to the outside world, by a communications network dominated by two major components, nerves and messenger chemicals, primarily neurotransmitters and hormones. Nerves form circuits that extend from the brain to the spinal cord and then to both the interior and the farthest reaches of the body. Hormones produced by the body’s glands and internal organs speed messages along these nerve pathways. The brain is able to interpret these hormonal messages with the help of special receptors and then send out messages of its own. These busy communications circuits—and we have quite a few of them, often performing simultaneously—make up, in effect, an intricate “brain-body loop.”
The brain-body loop orchestrates the most familiar routines of our lives: the daily rhythms by which we sleep, wake, and go about our activities, our eating behavior, sex life, and the very act of navigating our environment from minute to minute. The interaction of brain and body managed by this system is also proving to be an important influence on the state of our overall health and mental vitality, often in ways we modify.
The sun rises, and night gives way to day. Light fades, and night returns. The brain uses these daily signals to set the body’s own internal clocks. Researchers estimate that people have more than 100 daily cycles, known as circadian rhythms, circadian meaning “about a day.” Some of our rhythms, such as the menstrual cycle, are much longer than a day, and others, such as the several cycles that make up a night’s sleep, are shorter (or “ultradian”). The best known circadian rhythm is the sleep-wake cycle, but others include the daily rise and fall of body temperature, hormone levels, and urine production. An internal biological clock, or “pacemaker in the brain,” generates and regulates the rhythm of cellular activity. Messages then travel from the pacemaker to the appropriate part of the body. Various genes function as off-and-on switches to keep the clock ticking. External signals—sunlight is by far the most potent—provide time cues to synchronize bodily functions.
The pacemaker is housed in two small clusters of cells in the hypothalamus known as the suprachiasmatic nucleus (SCN). The SCN takes its name from its location, which is “supra,” or above, the optic chiasm, a major junction for nerves that transmit information from the eyes to the brain. The sleep-wake cycle illustrates how the SCN regulates circadian rhythms. Studies of humans living in time-isolation laboratories—research apartments with no windows, clocks, or other time cues—show that people naturally sleep about one-third of the time and remain awake about two-thirds of the time, living on days that are slightly longer than 24 hours. Their schedule thus drifts slowly around a real-time clock. In the outside world, sunlight anchors the sleep-wake cycle to Earth’s 24-hour rotation, programming us to stay awake in the day and to sleep at night. Sunlight enters the eyes, where it is converted to electrical impulses in the retinas, the nerve cells in the back of the eye. Light signals then travel to the SCN.
Once we are awake, the clock begins ticking on the ultradian rhythms that cause fluctuations in our attentiveness throughout the day. The output pathway probably extends from cells in the SCN to other parts of the hypothalamus, the pituitary gland, and the pineal gland, as well as to portions of the brain stem involved in sleep regulation. A number of different hormones act on nerve cells in this circuit, to either induce sleepiness or facilitate wakefulness. For instance, cells in the SCN contain receptors for melatonin, a sleep-inducing chemical produced by the pineal gland that increases in quantity at night and falls after dawn. Other neurotransmitters involved in the sleep-wake cycle include acetylcholine, noradrenaline, serotonin, and histamine; these act in the brain, in the cortex and thalamus, where attention and consciousness are maintained. It is still not clear exactly how all these neural circuits induce sleep or stimulate wakefulness, but there appears to be a seesaw mechanism: in the pons (meaning “bridge”), which connects the medulla, atop the spinal cord, and the midbrain, the activity levels of certain neurons rise and fall, and cells in the thalamus and cortex speed up or slow down in response.
When the body’s daily rhythms fall out of sync with those of the outside world, the result can be physical fatigue and mental sluggishness. A common example of this is jet lag, which occurs after travel across multiple time zones, when our biological clocks take a few days to adapt to the new local time. People who work at night or rotate shifts face similar difficulties.
Until almost the end of the twentieth century, those of us carrying around extra pounds could say only, “I’m naturally big” or “It runs in the family.” The only role in weight control that we ascribed to the brain was a moral one, responsibility for willpower. Brain research beginning in the 1970s, however, began to show that body weight is not that simple. In the early part of that decade scientists began to identify the chemicals the brain uses to direct us to eat and to learn how messages of hunger and fullness sent from the body are processed in the brain. It now seems likely that controls in the brain set a person’s body weight, and if they work properly, we will be healthy, though quite possibly at a point slightly above or below what is fashionable. Metabolism is more clearly a task of the brain, and genes that may contribute to weight problems are active in the brain, too.
The most basic brain-body circuit governing eating behavior consists of the brain’s control through the autonomic nervous system together with blood-borne hormones that carry messages from the body back to the brain. When you taste food, nerves from both your taste and smell receptors activate processing structures in the brain that signal the hypothalamus. The hypothalamus then relays that information to autonomic neurons that control the gastrointestinal tract, to begin the process of secretions that allow food in the stomach to be digested and moved on. As food reaches the stomach, a number of digestive hormones, known collectively as satiety factors, are released. As the stomach fills, levels of these hormones rise, signaling the brain and prompting a decision to stop eating.
Several recent discoveries suggest that other neural pathways may be involved as well. In the past few years, scientists have identified hormones in other parts of the body besides the stomach that also appear to signal the hypothalamus and thereby influence eating behavior. These include leptin, a protein contained in fat cells, and dopamine, a neurotransmitter in the brain involved in the regulation of some hypothalamic eating and drinking circuits. As researchers have studied the traffic in these hormones and neurotransmitters, they have come to believe that body weight is maintained within a narrowly defined “setpoint” as the brain increases or decreases appetite and metabolism to keep the body’s fat stores stable. Enthusiastic publicity for some of these findings has raised high hopes for new weight-loss drugs that may precisely target the brain systems for eating behavior. But many questions remain about how this complicated brain-body system actually works. Research advances in this area will also likely benefit people with disorders such as compulsive eating and anorexia, which may be related to flaws in one of the brain-body loops that govern eating behavior.
We are animals at heart when it comes to sex. What may seem like magic—that first tingle of attraction, the pleasurable muscle contractions of orgasm—actually shares the same chemical and electrical genesis as any other biological event. In fact, animal research has provided some intriguing clues about this particular brain-body connection. In rats, for instance, scientists have found that the hormone estrogen increases the electrical activity of cells in the medial hypothalamus of the female brain. Progesterone enhances the effects of estrogen by increasing sensitivity to touch. An excited female rat, responding to both a male’s touch and her own hormonal flood, will crouch and raise her rump. This posture, which facilitates intercourse and fertilization, results when hormones begin racing along several neural circuits that extend from the medial hypothalamus to the midbrain, and then down to the spinal cord, where motoneurons activate muscle spasms and stretching. At the same time, the medial hypothalamus is sending other signals, which affect heart rate and breathing.
Still, as anyone knows, it’s not all hormones and mechanics. In people, cultural values, personality, and social cues also affect sexual behavior, although scientists do not yet know the biochemical pathways that underlie this influence. But, clearly, the cerebral cortex also plays a role in physical sexual arousal and behavior.
Navigating Our Environment
We see a car coming toward us in the street and step out of the way. We smell some chocolate-chip cookies baking and walk into the kitchen to get some. Every day we use our senses to detect changes in our environment—some good, some not—and then act on them. Our ability to navigate our environment in this way depends on our brain’s ability to detect and interpret signals and then send its own commands to parts of the body that can respond. To figure out how the brain’s command and control systems work, scientists must break things down into almost absurdly small components. For example, a study of how the brain may cause movement may consist of scanning the brain while a volunteer lies perfectly motionless except for tapping a finger. But this kind of careful investigation does pay off, and in recent years scientists have learned more about how our brain guides our body in ordinary ways.
In addition to the five major senses (sight, hearing, touch, taste, and smell), the brain also works with the body to maintain a sense of balance (equilibrium), monitor body and limb positions (proprioception), and keep track of movement (kinesthesis). Additional sensing systems continually track body temperature, blood chemistry, and hormone levels. With all this sensing going on, it’s a wonder our brains don’t collapse from sensory overload. Fortunately, the brain is as skilled at sorting sensory information as it is at detecting it in the first place. Each piece of sensory information is channeled into a specific neural pathway in the brain and then relayed upward through a series of hierarchical circuits. For instance, after you taste something sweet, the information is relayed first to the medulla, in the brain stem, then to the thalamus, and finally to the somatosensory cortex, at which point you decide whether you want to eat more of this substance.
As efficient as the brain is at sensory processing, these complex systems sometimes break down. In an unusual disorder, an agnosia called hemisomatopagnosia, damage to the brain from stroke or trauma can leave a patient adamantly denying the very existence of an arm or a hand or even one whole side of the body (see more on agnosia C72). And many scientists believe flaws in sensory processing may contribute to some of the symptoms of more common disorders, such as autism, schizophrenia, and dyslexia.
Learning from the Body
The remarkable phenomenon that researchers call plasticity is the brain’s power to build new connections among neurons and, under certain conditions, reroute whole pathways. Plasticity underlies all growth and development in the brain, from infancy to the end of life, and is the basis of learning, a process we tend to consider abstract and intellectual. But the brain is a learning machine, and now researchers are discovering ways that it also learns purely from the body’s experiences.
If you are trying to master a new skill or improve one you already have, brain plasticity offers you a distinctly novel way to think about your progress. In the mid-1990s, researchers in Germany conducted brain imaging studies on professional violinists, whose instrument requires intricate finger movements by one hand. The scans showed that in the violinists’ brains the area of the motor cortex that commands finger movement had become larger than the same area in the brains of nonplaying study participants. And in further examining their data, the researchers found that the younger the violinists were when they started playing, the bigger the corresponding area in the motor cortex was. The scientists believe the musicians’ brains responded to the greater and more complex finger use needed for professionallevel skill by producing many times more connections in that area. Thus, if you decide to learn a physical skill, from piano playing to roller-skating, you can talk yourself through the hard times by reminding yourself that you’re making some site in your brain sizzle.
Also mining the brain-body connection are researchers who suspect that this interaction can bring advances in the treatment of physical disabilities. Two fields in which interest is particularly strong are those of stroke treatment and spinal cord injury. In both fields, recent experiments—none yet widely replicated and involving a very small number of patients—have sought evidence for the proposition that messages from the body can stimulate recovery in the brain and spinal cord. These experiments involve long, intensive, and sometimes grueling sessions of coaxing the paralyzed limbs back into use. The theory is that enough stimulation from the moving muscles can induce rewiring in the damaged brain or cord well enough to improve, if not restore, mobility and reduce the patients’ disabilities.
For the most part, brain-body systems are selfdirecting, but we do have a degree of control over them. Thus, most obviously, we can consciously decide whether or not we will do anything about a powerful sexual attraction. We can take steps to reset our Miami- or New York–based body clock if we travel to Los Angeles or London, and we can keep practicing piano or guitar until we play without a hitch. It is unclear whether we can adjust comfortably to a lower body weight than our setpoint if we have an urgent reason, such as damaged knees from playing sports in school. In such circumstances, we can probably get used to reduced food intake, but most studies show that keeping weight down is not a simple set-andforget operation like our circadian clock’s ability to adapt when we visit a different time zone.
Two other areas of brain-body interaction have come under increasing study in recent years and, as a result, present excellent opportunities for patients and physicians to use the brain-body connection to assist in maintaining health and improving healing in illness. These are the stress response and the emotions, two systems that appear to share some neural circuitry and that can do both good and harm.
The Stress Response and Disease
In the early twentieth century, the pioneering physiologist Walter Cannon fed dogs their food mixed with barium and then, using a fluoroscope, watched the progress of that material through the dogs’ intestines. He discovered that whenever a dog perceived a threat, the barium would stop moving. In effect, the dog’s gastrointestinal tract shut down. Eventually, Cannon linked this effect to the secretion of a hormone he called sympathin from the adrenal medulla, a gland in the abdomen closely controlled by the autonomic nerves. He theorized that by halting the digestive system, this hormonal signal freed up more of the dog’s energy to either combat whatever had aroused it or to run away. Cannon termed that response to stress “fight or flight,” and it has become a basic part of how we think about our own brain-body connection.
We all encounter stresses—good and bad—every day. We face deadlines, hit traffic jams, quarrel with spouses, worry about children. We fall in love, hear praise for a job well done, score the winning run. Without such peaks and valleys, our lives would be flat and dull. Any experience may frighten some of us but delight others: consider how you feel about riding a roller coaster or giving a speech. “Strange to say,” Barbara Kingsolver writes in The Poisonwood Bible, “if you do not stamp yourself with the words ‘exhilarated’ or ‘terrified,’ those two things feel exactly the same in a body.”
If you hear footsteps behind you while walking in the dark, you will likely respond much as your ancient ancestors did when they heard a vicious beast crashing through the forest. Your brain alerts your adrenal glands to dispatch stress hormones throughout your body to prepare you to wrestle or run. These hormones, epinephrine (adrenaline) and norepinephrine (noradrenaline), make your heart beat faster, your blood pressure soar, your muscles tense, and the pupils of your eyes open wider. You become more energized and more focused. Blood drains from your stomach and intestines as digestion is put on hold. It goes to the limbs to fortify your muscles. Your awareness of pain falls, distracting you from a sprained ankle or other injuries you might suffer as you act. Like Cannon’s dogs, you are ready for fight or flight.
If those frightening footsteps turn out to come from a passing jogger, you will probably calm down fast. You need to calm down to avoid overtaxing several of your body systems. The next night, you may feel your heart thump as you approach the same spot. That is your brain working, warning you of possible danger.
While this genetically programmed response may help you face an attacker, the stresses we encounter in our daily lives do not often demand intense physical action. Nevertheless, our bodies may still respond that way. According to the National Institute for Occupational Safety and Health, one in four employees views his or her job as the number one stressor in life. Running from or fighting off a saber-toothed tiger may have kept your distant ancestor alive, but facing a snarling boss requires different behavior. Your body’s evolutionary responses can give you the energy to work longer, but they can also make it harder to think or speak clearly in a tense meeting. Either way, you can feel chewed up inside.
Individuals respond to stress in different ways, however. Some people seem to remain unruffled—eating and sleeping normally, remaining physically healthy. Small hassles leave others feeling constantly “stressed out”; Bruce Springsteen describes this state in “For You” when he remembers a woman beset by crises: “Your life was one long emergency.” Our reactions to different types of stresses help define our individual psychologies. Even infants display wide variation in how they respond to novelty and stress, a demonstration of our innate basic temperaments (see more about temperament).
Stress and Some Common Illnesses
To study stress, researchers assess an individual’s responses to a wide variety of challenges and compare them with those of other people in similar circumstances. Emotional stress tests include being asked to do mathematical computations, give a speech, watch scary movies, or perform certain exercises. Researchers may measure levels of epinephrine, norepinephrine, and other biological markers of stress in blood and urine, or assess volunteers’ blood pressure around the clock. They may also use techniques such as functional magnetic resonance imaging (fMRI) to study areas of the brain that become active as people engage in different mental tasks.
In one study of life stress, 276 healthy volunteers completed questionnaires about their life stressors, personality traits, social networks, and health practices. The researchers then gave these men and women nasal drops containing a low dose of a common cold virus. Over the next five days, the research team monitored the volunteers to see whether they developed infections and congestion, runny nose, sneezing, and other symptoms of illness. Blood tests showed 84 percent of the participants had been infected by the virus, but only 40 percent of them developed cold symptoms. What accounted for the difference? The people who reported job stress or problems with family or friends in the previous year that had lasted for a month or more were two to three times more likely to get sick than those without such troubles.
Chronic stress, as well as anger and hostility, may increase the concentration of acid in the stomach, possibly triggering peptic ulcers, stress ulcers, or ulcerative colitis. While a chronic infection of the stomach lining by the bacterium Helicobacter pylori is the prime culprit in nearly all peptic ulcers, many people with this infection do not develop ulcers. Stress may be what makes some individuals more susceptible than others. Air traffic controllers at busy major city airports, who clearly have high-stress jobs, report peptic ulcers more frequently than both controllers working in less-populated areas with lower flight traffic and air industry workers with less stressful jobs.
These findings, in a sampling of diverse diseases, remind us how the brain affects the body at many levels. And the body’s general well-being affects the brain. Everyone knows it’s no fun being sick, and trying to keep up with tasks at home or work while you’re sick can cause stress. Thus, people can enter a cycle in which stress makes them vulnerable to illness, illness causes them stress, and so on. This is the brain-body feedback loop at its most troublesome.
Fortunately, stress management has long been a popular area of concentration in many fields, and good techniques and strategies are easy to find. They are available in every conceivable setting, from business seminars and health clubs to the offices of psychologists and family doctors. If you feel that your stress response is “on” more than it should be, a careful canvass of the stress management approaches that seem appropriate to you should lead you to one that will be helpful. Oftentimes, in the reinforcing company of people with the same goal, you can lower your stress response simply by reforming stress-related bad habits: smoking, too much drinking, careless eating, and staying up too late too many nights.
Chronic, inescapable stress, such as that incurred by taking care of a terminally ill family member or facing a long-term financial crisis, may have serious health consequences. If you or someone you care about is ensnared in a deeply stressful state of affairs that may not be resolved for months or years, confiding in a trusted medical or mental health professional is important. Plans for a respite schedule, guidance to support groups, and many other valuable coping strategies can be the beginning of lightening the load. It is extremely hard for anyone in a chronic stress situation to go it alone.
Mood and Health
When brain scientists refer to “mood” and “emotions,” they are being much more precise than most of us are when we say we “got up on the wrong side of the bed” or are “happy as a clam.” To the scientist, mood—more often called affect—and emotions are the mental states related to specific chemicals and pathways in the brain. And because these brain circuits undeniably communicate with the body, researchers are beginning to look for potentially important connections between mood and health. And in this respect, the likelihood that mood, emotions, and stress all share some pathways seems to offer an especially valuable relationship for study.
Depression and the Heart
Most people know that the stress of sudden shock or fright can trigger heart attacks. News reports of an earthquake, hurricane, or other natural disaster often include the number of people brought to hospitals after suffering heart attacks. For example, immediately after the Northridge, California, earthquake in 1994, the local incidence of sudden death from heart attacks jumped sixfold.
But emotional stress can be comparable in effect to moderate physical stress for people with heart conditions, according to one study. Researchers asked 132 people with heart disease to wear a device that monitored their heart activity for 48 hours. The volunteers also kept diaries in which they noted their activities and emotional states roughly every 20 minutes. Fifty-eight people had episodes in which the blood supply to their hearts fell too low, a condition known as ischemia. Feelings of tension, frustration, and sadness produced changes comparable to moderate or light physical activity. By contrast, participants experienced fewer episodes of ischemia when they reported feeling happy or in control.
In any year, about 7 percent of Americans, 17 million people of all ages, experience mood disorders such as depression. Depression is an independent risk factor for heart disease, many controlled studies show. These include an ongoing study of nearly 1,200 male medical students who enrolled at the Johns Hopkins University School of Medicine between 1948 and 1964. About 12 percent of these students eventually developed depression. These men were more than twice as likely to have heart attacks as peers who were not depressed, even decades after first being diagnosed with the mood disorder.
After suffering a heart attack, people with depression also tend to be sicker than people whose moods remain stable. A group of researchers analyzed data from 8,000 people enrolled in the first National Health and Nutrition Examination Survey (NHANES I). Participants were healthy when they entered the study between 1982 and 1984 and completed a standard test for depres sion. The researchers assessed their health again in 1992 or after they had had a heart attack. Depressed people proved nearly twice as likely to have suffered a heart attack as those who had no depression. Other studies have found that depression also hastens death from heart disease.
But associations, even when they are as clear as these, are not hands-down proof that mood affects health and vice versa. Certainly the studies offer intriguing clues that this might be so, but the nature of this particular brain-body interaction remains sketchy at best. Still, the observed link between depression and heart disease is the strongest evidence so far. Researchers have found that about 65 percent of patients will suffer depression immediately following a heart attack. One in four of them will develop severe and recurrent clinical depression. At the same time, other studies have suggested that depressed people are more likely to develop heart disease. In one large population study, 18 percent of depressed people had coronary artery disease, compared with only 5 percent of those who were not depressed. Other intriguing clues come from reports that regular aerobic exercise—which improves cardiovascular health—can also improve mood. In fact, one recent study found that moderate exercise might be as effective as medication in treating depression.
But which comes first, depression or heart disease? The fact that the two appear together so often suggests the existence of a distinct brain-body circuit. Scientists do not yet know what such a circuit might consist of, but they have identified several chemical messengers that may be involved. It has been reported that specific neurotransmitters—serotonin and the catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline)—are found in reduced levels in the cerebral spinal fluid of people with depression or anxiety. These same substances, acting as hormones in the body, also have a role in cardiac function by increasing heart rate, raising blood pressure, and strengthening the contractions of the heart. Catecholamines also increase the “stickiness” of blood platelets, which help to form clots, and decrease anticlotting compounds in the bloodstream. The brain’s mood-regulating systems and the heart clearly share some chemicals. Whether this constitutes a bona fide brain-body link remains to be seen.
Depression and Stroke
The same NHANES data also showed that people with depression are nearly twice as likely to suffer strokes as their nondepressed counterparts. On the other side of the brain-body loop, almost everyone who suffers a stroke experiences some feelings of depression, either soon after the event or some months later. About half suffer what doctors call clinical depression, mood changes serious enough to require medication or other treatment. Most of these people did not experience depression before suffering a stroke, suggesting that the mood disorder arises from both biological factors provoked by their brain injury and their response to being impaired.
In one large study, researchers followed nearly 13,000 healthy participants for six years. These people completed a self-test by responding to statements such as “I am a hotheaded person” and “When I get angry, I say nasty things,” ranking their experience with anger on a scale from “almost never” to “almost always.” Those who identified themselves as highly prone to rage proved nearly three times more likely to have a heart attack in the following years than people with even tempers. A high propensity for anger, the researchers found, put people at higher risk of heart attacks regardless of whether they also smoked, were obese, or had high blood pressure.
Given findings about anger as a trigger for heart attacks, researchers wondered about its impact on strokes (see more about ischemic stroke and hemorrhagic stroke), so one group analyzed findings from an eight-year study of some 2,100 middle-aged men in eastern Finland. The men had completed a questionnaire similar to the one used in the heart study to describe their usual ways of dealing with anger. Men prone to outbursts proved almost twice as likely to have a stroke as those who were more easygoing.
Researchers offer several hunches about how and why stress and anger boost the risk of heart disease and stroke. We know these states raise blood pressure and that sustained high blood pressure weakens the heart and blood vessel walls. In addition, long exposure to stress-related hormones such as epinephrine, norepinephrine, and dopamine may damage the arteries and heart muscle and disrupt the electrical rhythms that keep the heart beating regularly. These hormones may also promote platelet “stickiness,” leading to clots that block arteries that feed the heart muscles. In addition, they prompt fat to accumulate in the abdomen and in the arteries, where it may block the passage of blood or break off in globs that circulate until they plug smaller blood vessels.
You should be careful to remember, however, that indications such as these still leave plenty of room for debate: If people who have experienced clinical depression are more vulnerable to certain diseases, is that because of hormonal or immune system changes in their bodies, or because their depression has made them less likely to take care of their bodies? People under chronic stress are more apt to smoke, overeat, and skip regular exercise than people with less emotionally charged lives. So is the stress itself the cause of their increased health problems, or are their unhealthy behaviors at fault? Some studies have tried to isolate one factor from another by identifying people who smoke, overeat, and so on. The evidence may lean toward an independent health effect for stress and emotions, but the case is still far from open-and-shut.
With that warning in mind, however, if you are of an activist inclination when it comes to your health, the very nature of the brain-body loop suggests all sorts of ways to encourage that interaction to keep working for you. Strategies that favor biochemical harmony in these systems range from cognitive to nutritional to medicinal.
We can choose many different ways to respond to the stressors in our daily lives. Many people find relief in exercise, hobbies, volunteer activities, and their families. Others respond by eating too fast or too much, missing sleep, skipping exercise, and drinking or smoking or using other drugs. People in the first group usually report better health and overall quality of life. People in the second group more often report such symptoms as tension headaches and other muscle aches; nausea, diarrhea, or other digestive problems; rapid heartbeat; and shortness of breath. When stress persists, normal bodily care and repair activities get short shrift. This condition can make us more vulnerable to colds, flu, herpes, and other infections, and to more serious illnesses, including obesity, heart disease, and cancer.
The Search for a “Mind-Body Medicine”
When you think of “mind-body medicine,” you might think of meditation, relaxation techniques, guided imagery, and other approaches that are said to harness the body’s natural healing power. These are often lumped together with thousands of other unconventional treatments. In 1998 the National Institutes of Health set up an office of Complementary and Alternative Medicine to evaluate such approaches. So far there have been few studies as large and rigorous as have been done for most standard treatments.
Consider the connection between stroke and depression that we described earlier. One research team studied 50 people admitted to the hospital after suffering strokes and followed them for the next two years. People who reported having a difficult relationship with their “closest other” before their stroke and a limited social life proved most likely to be depressed both right after their stroke and many months later. To lessen the chance of entering a depression, the researchers concluded, survivors need social support and contact most in the first few weeks after a stroke. One to two years after a stroke, another study showed, depression alone limits how well people have recovered physically regardless of their social functioning. The study also found that people who suffer depression after a stroke are three times more likely to die earlier than stroke survivors who are not depressed.
Futhermore, for many stroke patients, relief of their depression actually restores lost mental function. Researchers randomly assigned 21 people who had had strokes to take an antidepressant and gave 26 other stroke survivors a placebo. Those taking the antidepressant showed significantly greater improvement in both mood and mental function over the next 6 to 12 weeks. Nearly three fourths of people with strokes who took an antidepressant drug in this study improved their orientation, memory, language, and hand-eye coordination.
Similarly, most people who have cancer suffer distress and a depressed mood after hearing their diagnosis. One in four becomes clinically depressed. Improving their mood lowers pain, curbs anxiety, and improves the quality of their lives. It improves various markers of immune system functioning, and, some studies suggest, may even increase longevity.
One of the underpinnings of belief in the mind’s healing power is the “placebo effect,” a concept with decades-long standing in medical research. This doctrine holds that if we expect our health to improve, it often does. With that assumption, the best medical studies are designed to cancel out the placebo effect.
The term placebo is Latin for “I shall please.” It found its way into medical dictionaries in the early nineteenth century, when treatments often involved much more art than science. Doctors began to believe that their patients’ expectations affected how they responded to treatment. For instance, at that time people often sought medicines that made them vomit or defecate quickly so they would know the drugs were effective. (Today we generally view such reactions as side effects, and drug manufacturers strive to minimize them.) Every patient wanted to receive some medication, so physicians often prescribed harmless substances that would please the people who took them—hence the name placebo. But these prescriptions seemed to benefit some patients’ health, and not just in their own perceptions. So with this in mind, as research grew more sophisticated and bent on accuracy, scientists began making sure they measured all sorts of apparent placebo effects.
Scientists account for placebo effects by trying to make sure that all volunteers for treatment studies believe that the medication or procedure they receive has the same chance of being effective as that which every other subject gets. Researchers typically assign subjects randomly to receive an active or inactive treatment. They instruct all subjects the same way, not telling them whether they will get the study treatment or the placebo. To avoid subtly influencing the results, the people who dispense the treatments are often also kept in the dark as to which treatment is active; such a study is termed double-blind. The randomized, double-blind, placebo-comparison study has long been the gold standard for research on how well treatments work: To be deemed effective by the U.S. Food and Drug Administration, a new drug or procedure must significantly outperform placebos. That is why when you hear or read news of a finding about a drug, the results are explained in comparison with “a sugar pill” or a “sham treatment.” This is good research trying to screen out the placebo effect.
However, the venerable placebo-controlled research concept took a blow in 2001 when the New England Journal of Medicine published a careful study suggesting that the placebo effect may be overblown, if not nonexistent. The study analyzed a large number of clinical trials and looked at the differences between placebo and no treatment. The conclusion the study offered was that perhaps the effect researchers were reporting was actually a disease or problem retreating according to its normal ebb and flow. The report looked for instances in which studies had adjusted for this possibility and they found none. Some news reports raised fears that this revelation might mean that drugs tested against placebos are not as good as thought, but while that may be possible in some cases, a drug that works better than waiting out a disease is probably an effective drug. However, the placebo report did underscore the need for caution in turning mind-body clues too hastily into mind-body medicine. The leap from placebo to assumptions about the power of the mind has always been a long one, and the study questioning the placebo’s reality suggests it may be a false one.
Some forms of brain-body interaction have become entwined in the idea of the placebo effect. For example, most doctors believe the placebo effect is part of every doctor-patient interaction, but many base this assumption not on a positive but a negative effect. Specifically, some research has estimated that one in four individuals experiences higher blood pressure during a visit to the doctor, a condition called white coat hypertension. Many people with this reaction relax after a few minutes, and their blood pressure falls to its usual level. For this reason, physicians who see an initial high reading usually take further readings before the visit is over. Some people don’t settle down until after they leave, however, and are mistakenly diagnosed as having chronic high blood pressure. Thus, it bears considering whether too easily crediting the placebo effect interferes with more constructive medical thinking—for example, wondering if a patient is prone to stress that should be discussed and perhaps treated.
Expect more to come on the question of placebos, because the challenge to them calls for an answer, and surprisingly few studies have ever focused directly on how placebos work or if they do. While the new doubt raised by the report is being explored in follow-up studies, placebos will remain an important standard in clinical trials of new drugs. Some experts think that the use of a placebo may lower a patient’s stress and anxiety over symptoms, thus easing stress-related changes in hormones, blood pressure, and other body systems and perhaps letting the immune system resume its normal functioning. Studies show that people who believe a placebo will ease pain secrete the natural pain-killing substances called endorphins that block pain signals to the brain. Still, for many conditions, from the common cold to well-set broken bones, healing occurs naturally with time.
While many mainstream researchers distrust studies that claim the power of the mind acting by itself to heal, even people on the distant opposite sides of the mind-body question do respect well-designed research that takes both body and mind carefully into account. Mind-body medicine is an attractive goal, as the tantalizing brain-body links suggest. Such research with modern methods is still in its infancy, so an open mind is important. The hope is that the National Institutes of Health’s Office of Complementary and Alternative Medicine will produce much more, and much better, science in this area.
Physicians still have a hard time defining, assessing, and treating such subjective or “invisible” symptoms as fatigue and pain. Anyone can see a rash, a broken bone, or the reading on a thermometer. But how do we measure a person’s pain from one day to the next except through what he or she reports? As the pathways in body and brain for such symptoms become better understood, the opportunities to devise tests to detect their chemical markers and to intervene in their operations are increasing, and the outlook, particularly for the treatment of pain, is very promising.
Another challenge is that in most countries, including the United States, some medical-practice trends march in the opposite direction from the highly individualized treatments to which the mapping of brain-body connections would lead. The average doctor visit has shrunk to only a few minutes, while health insurers seek to standardize care and minimize costs by treating all patients with particular diagnoses as similarly as possible—even though individuals can respond to the same condition and treatment in very different ways. Many health insurance plans also reimburse people for care of so-called mental illnesses at lower rates than they provide for illnesses classified as medical. This practice works as a disincentive to seeking combined brain and body treatment. The more that is learned about the brain-body loop, the harder it becomes to make such distinctions.
Although a viable mind-body medicine is very much a work in progress, already hard science on brain-body interaction, sparse as it is, has given mainstream medicine more ability to recognize and respond to both emotional and physical dimensions in the diseases doctors treat. A back-to-the-future component has even popped up, as a few doctors around the country adopt the old-fashioned practice of making house calls. While the difficult work of defining and explaining the brain-body loop goes on, such a desire to focus not just on a particular disease but on our total experience of an illness—what neurologist Oliver Sacks calls a patient’s “predicament”—can only improve our confidence in medicine and add optimism to the quality of our health.
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