Tigers and Pain
I’ve suffered from chronic back pain for five years, the symptoms persisting despite an array of treatments: stomach-wrenching amounts of ibuprofen, prescription painkillers that made me woozy, lengthy ergonomics consultations, and months of physical therapy and acupuncture. My problem is not uncommon. An estimated 50 million Americans suffer from chronic pain, and for a large percentage of those patients, existing therapies are inadequate.
Pain is a complex phenomenon. It depends both on neural signals that are generated during tissue damage, as when you grab a hot pan, and on a higher-level system that interprets those signals to form the pain experience – an interpretation that may be altered by your emotions and level of attention. For example, soldiers wounded on the battlefield often don’t feel the extent of their injuries until they are out of danger. So while pain is an adaptation that evolved to help us avoid bodily injury, our brains have also evolved a sophisticated system for turning it off. “You need to be able to run from a tiger, even if you’re hurt,” says deCharms.
DeCharms chose pain as his first test of real-time fMRI technology, partly because the need is so great and partly because the neurological circuit that underlies pain is well understood. Opioid drugs, such as morphine, target these neurons chemically. Implantable stimulators, which can be an effective treatment for pain, target the circuit with small jolts of electricity. DeCharms, on the other hand, wanted to try to target the system consciously, through cognitive processes.
In last December’s paper in the National Academy journal, deCharms, Mackey, and their collaborators described a study in which participants learned a series of mental exercises derived from strategies used in pain clinics. For example, they might have been asked to imagine the sensation of their brains’ releasing painkilling compounds into the aching area, or to imagine that their painful tissue was as healthy as a pain-free part of their body. Subjects then climbed into the MRI scanner, where they wore special virtual-reality goggles that displayed the activity in a part of the brain involved in feeling pain – the anterior cingulate cortex. They were instructed to try to increase or decrease the activity by performing the exercises. The MRI data gave them direct feedback on how well their mental strategies were working, allowing them to adjust their technique. Some people picked up the knack quickly, while others needed several sessions to learn appropriate control methods.
Eight patients with chronic pain that wasn’t adequately controlled by more conventional means reported a 44 to 64 percent decrease in pain after the training, three times the pain reduction reported by a control group. Those who exercised the greatest control over brain activity showed the greatest benefit.
The researchers also designed an elaborate set of controls to show that the results didn’t simply reflect the placebo effect or an artifact of the experimental process. For example, subjects who did not get fMRI feedback but were instructed to focus attention to and away from their pain did not show as much pain relief. Patients who got fMRI feedback from another part of the brain also did not benefit; nor did patients who got feedback from the cingulate of another person. “If expectation or being in the scanner were contributing … then that group should have seen a similar result,” says deCharms. The researchers also conducted tests in which chronic-pain patients were given more-traditional biofeedback data, such as heart rate or blood pressure. Patients who received fMRI feedback had a significantly greater reduction in pain.
However, some scientists say it’s still not clear what kind of role attention, or even emotion, is playing. “In our experience, people are so engaged in the task, they don’t even know how long they’re in the [MRI],” says Seung-Schik Yoo, a Harvard University neuroscientist who is also studying real-time fMRI. “If someone is so captivated, they could forget to pay attention to the pain.” And success in controlling the activity levels shown on the screens could further distract a patient from the pain. “When it works, time flies,” says Yoo. “When it doesn’t, you get frustrated.” He adds that the best way to determine whether test subjects are permanently affecting their brains will be a long-term clinical trial, like the one deCharms and Mackey have under way. Still, says Yoo, “Their work has paved the way in pain control using this new technique.”