About one third of Americans, an estimated 100 million people, suffer from chronic pain, making it one of the most common reasons people visit the doctor. Pain can be the side effect of serious medical problems like cancer and rheumatoid arthritis, but it also exists independently of any other medical condition. Despite decades of research and millions of dollars devoted to studying the problem, current therapies provide only marginal relief for many sufferers. But there are glimmers of hope. Among other developments, researchers today are working on novel approaches that focus on controlling activity in the brain's pain centers and on cells previously thought to play only a supporting role in the central nervous system.
Success can't come any too soon. Prescription drugs like Oxycontin, Percocet, and Vicodin, while effective weapons against chronic pain, are under increasing scrutiny because they can be addictive for patients and have also been abused by others who simply take them, without prescriptions, for their euphoria-producing effects. To relieve the widespread overdependence on painkillers, researchers are investigating new ways to attack this most primitive sensation and not merely mask it, as opioid drugs do. But researchers have to tread carefully, as pain can help keep "us out of trouble," as in a warning to draw back from a hot stove, says Sean Mackey, chief of the pain management division at Stanford University School of Medicine. The goal is to lessen or eliminate chronic pain that serves no useful purpose.
Often, pain starts with a physical injury such as a burn or scrape. When tissue is damaged, sensory receptors in the skin or elsewhere in the body send signals in the form of electrical impulses along nerves, or neurons, to the spinal cord. In the spinal cord, chemical neurotransmitters are released that activate other nerves, sending an electrical signal to the brain, where it is processed and interpreted as pain.
Until recently, researchers have focused on the nerves at the site where the pain occurs, like an aching knee joint, and on the spinal cord. But pain is dependent on perception, which occurs in the brain. The sensation is a complex bodily experience incorporating the physical feeling ("That hurts!"), the emotional reaction ("Why did I grab the hot pan?"), and the intellectual response ("I need to be more careful.") "Without perception there is no pain," notes Kenneth Follett, professor and chief of neurosurgery at the University of Nebraska Medical Center. Some soldiers wounded in battle, for example, have said they didn't know they were hurt until after the danger had passed. The reasons for this are unclear, says Follett, but attention likely plays a role. When it is focused elsewhere, the brain may not perceive pain.
At the Stanford Systems Neuroscience & Pain Laboratory, Mackey is trying to better understand the mechanisms involved. In one study, he and colleagues performed brain scans on subjects' anterior cingulate cortices, one of the areas responsible for perceiving and controlling pain. The subjects, whose hands were intermittently heated by a probe, could watch on a screen as their brain activity increased or decreased, depending on the intensity of the pain they were feeling. Researchers suggested ways subjects could control the sensation, such as by focusing on something else or attempting to change their perception of the pain from something frightening and damaging to something neutral. After four 13-minute sessions, healthy subjects, who were included in the study, reduced their sensation of pain by 23 percent. Chronic pain patients, who learned to control their body's own pain sensations, reported an even more dramatic average reduction of 64 percent.
"We thought, maybe we can help people control their own brain activity," Mackey explains. He says researchers hope that, with increased training, patients can "reshape" the circuits responsible for pain. Mackey and his colleagues were recently awarded a $9 million grant from the National Center for Complementary and Alternative Medicine, part of the National Institutes of Health, to study the effectiveness of this neurofeedback technique and other mind-body approaches to treating chronic low back pain.