When It Hurts So Good

Pain triggers the brain's reward centers, study says

THURSDAY, Dec. 6, 2001 (HealthDayNews) -- Taking a cue from the Marquis de Sade, American researchers have discovered a never-before-seen scientific link between the brain systems for pleasure and pain.

Their study, suggesting that the pleasure centers of the brain react in a unique way to pain, provides the first evidence to closely connect two brain systems which previously were thought to be the opposite ends of the same spectrum, the researcher say.

The researchers, from Massachusetts General Hospital, in Boston, and the National Institute of Drug Abuse, in Baltimore, Md., say the study could point to new ways to diagnose and treat pain. Findings appear in today's issue of Neuron.

More 50 million Americans suffer chronic pain, but only a quarter of them receive proper treatment for it, experts say.

The study involved eight young men who underwent functional magnetic resonance imaging (fMRI) while a heat pad was attached to their hands.

While they were scanned for brain activity, specifically in areas known to be involved in pain and pleasure responses, the heat pad was turned on for 25-second intervals at either 106°F or 115°F.

The heat, comparable to touching the roof of a car on a hot summer day, was painful but not harmful, says lead study author Lino Becerra. On a scale of zero to 10, with zero indicating no pain, the volunteers rated the pain at 2.3 at 106°F and 7.8 at 115°F.

The resulting brain scans surprised the researchers. Not only did the heat stimulate brain areas traditionally linked to pain response, it also activated some areas associated with pleasure. The researchers say the pain triggered brain structures normally activated by reward activities, such as gambling or cocaine use.

"Never has somebody seen these reward-only structures, such as the nucleus accumbens or the sublenticular extended amygdala, involved in pain," says Becerra, chief of imaging and analysis at the Center for Functional Pain Neuroimaging and Therapy Research at Massachusetts General Hospital, in Boston. "There's a continuum between reward and pain … They're not separate aspects."

But the activation patterns in these areas were the opposite of the normal response to a rewarding experience seen in other studies, Becerra says.

Moreover, activity in these reward areas peaked immediately after the hot stimulus started, then returned to normal. In the pain regions, activity started low and peaked towards the end of the 25-second intervals.

Becerra says the early peak in the pleasure center suggests a more primitive response to pain that occurs even before it reaches our consciousness -- before we even recognize the sensation as pain. And the response may be designed to trigger action that prevents damage to our body. "That may have a real survival value," like how rabbits bolt for safety at the sound of rustling before checking if the sound is a snake in the grass, he says.

Min Zhuo, chief of basic research at the Washington University Pain Center, in St. Louis, Mo., says the findings add to the growing body of evidence that specific areas of the brain have multiple functions. "They're more like computer components. Each component actually does multiple jobs," says Zhuo.

"Pain can trigger many, many pathways. For my own thinking, pain and pleasure are so close that it's quite likely that they share many of the same neuronal circuitry," says Zhuo.

Understanding how the brain responds to pain could lead to development of drugs that would soothe pain by targeting the areas stimulated in the study.

Zhuo says while most pain drugs work to block the transmission of pain from the source to the brain, new therapies could tackle what's causing the brain to interpret those signals as pain. For example, he says the drug gabapentin, which works within the brain and was originally designed to treat seizures, appears to help patients with neuropathic pain.

"By understanding how these pathways overlap, maybe we can somehow fool the brain and really treat chronic pain in a very novel and new approach," he says.

Becerra says now that researchers have the tools to understand how the brain might respond to different pain drugs, "within five years, we should be able to have [new pain therapies]."

What To Do

For more information on pain, check the American Society of Anesthesiologists, Pain.com, The National Foundation for the Treatment of Pain, the American Pain Foundation, the American Chronic Pain Association or the North American Chronic Pain Association of Canada.

SOURCES: Interviews with Lino R. Becerra, Ph.D., assistant professor, department of radiology, Massachusetts General Hospital, Boston, Mass.; Min Zhuo, Ph.D., associate professor, departments of anesthesiology, psychiatry, anatomy & neurobiology, chief of basic research, Washington University Pain Center, Washington University School of Medicine, St. Louis, Mo.; Dec. 6, 2001, Neuron
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