THE BODY'S MIND: HOW EMOTIONS MATTER FOR HEALTH
In 1974 a finding in a laboratory at the School of Medicine and Dentistry, University of Rochester, rewrote biology's map of the body: Robert Ader, a psychologist, discovered that the immune system, like the brain, could learn. His result was a shock; the prevailing wisdom in medicine had been that only the brain and central nervous system could respond to experience by changing how they behaved. Ader's finding led to the investigation of what are turning out to be myriad ways the central nervous system and the immune system communicate—biological pathways that make the mind, the emotions, and the body not separate, but intimately entwined.
In his experiment white rats had been given a medication that artificially suppressed the quantity of disease-fighting T cells circulating in their blood. Each time they received the medication, they ate it along with saccharin-laced water. But Ader discovered that giving the rats the saccharin-flavored water alone, without the suppressive medication, still resulted in a lowering of the T-cell count—to the point that some of the rats were getting sick and dying. Their immune system had learned to suppress T cells in response to the flavored water. That just should not have happened, according to the best scientific understanding at the time.
The immune system is the "body's brain," as neuroscientist Francisco Varela, at Paris's Ecole Polytechnique, puts it, defining the body's own sense of self—of what belongs within it and what does not.1 Immune cells travel in the bloodstream throughout the entire body, contacting virtually every other cell. Those cells they recognize, they leave alone; those they fail to recognize, they attack. The attack either defends us against viruses, bacteria, and cancer or, if the immune cells misidentify some of the body's own cells, creates an autoimmune disease such as allergy or lupus. Until the day Ader made his serendipitous discovery, every anatomist, every physician, and every biologist believed that the brain (along with its extensions throughout the body via the central nervous system) and the immune system were separate entities, neither able to influence the operation of the other. There was no pathway that could connect the brain centers monitoring what the rat tasted with the areas of bone marrow that manufacture T cells. Or so it had been thought for a century.
Over the years since then, Ader's modest discovery has forced a new look at the links between the immune system and the central nervous system. The field that studies this, psychoneuroimmunology, or PNI, is now a leading-edge medical science. Its very name acknowledges the links: psycho, or "mind"; neuro, for the neuroendocrine system (which subsumes the nervous system and hormone systems); and immunology, for the immune system.
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A network of researchers is finding that the chemical messengers that operate most extensively in both brain and immune system are those that are most dense in neural areas that regulate emotion.2 Some of the strongest evidence for a direct physical pathway allowing emotions to impact the immune system has come from David Felten, a colleague of Ader's. Felten began by noting that emotions have a powerful effect on the autonomic nervous system, which regulates everything from how much insulin is secreted to blood-pressure levels. Felten, working with his wife, Suzanne, and other colleagues, then detected a meeting point where the autonomic nervous system directly talks to lymphocytes and macrophages, cells of the immune system.3
In electron-microscope studies, they found synapse like contacts where the nerve terminals of the autonomic system have endings that directly abut these immune cells. This physical contact point allows the nerve cells to release neurotransmitters to regulate the immune cells; indeed, they signal back and forth. The finding is revolutionary. No one had suspected that immune cells could be targets of messages from the nerves.
To test how important these nerve endings were in the workings of the immune system, Felten went a step further. In experiments with animals he removed some nerves from lymph nodes and spleen—where immune cells are stored or made—and then used viruses to challenge the immune system. The result: a huge drop in immune response to the virus. His conclusion is that without those nerve endings the immune system simply does not respond as it should to the challenge of an invading virus or bacterium. In short, the nervous system not only connects to the immune system, but is essential for proper immune function.
Another key pathway linking emotions and the immune system is via the influence of the hormones released under stress. The catecholamines (epinephrine and norepinephrine—otherwise known as adrenaline and nor-adrenaline), cortisol and prolactin, and the natural opiates beta-endorphin and enkephalin are all released during stress arousal. Each has a strong impact on immune cells. While the relationships are complex, the main influence is that while these hormones surge through the body, the immune cells are hampered in their function: stress suppresses immune resistance, at least temporarily, presumably in a conservation of energy that puts a priority on the more immediate emergency, which is more pressing for survival. But if stress is constant and intense, that suppression may become long-lasting.4
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Microbiologists and other scientists are finding more and more such connections between the brain and the cardiovascular and immune systems—having first had to accept the once-radical notion that they exist at all.5
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