Wednesday December 5 5:01 PM ET

Study Finds
Pain and Pleasure
Linked in Brain

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Pain and pleasure may be closer sensations than anyone thought, researchers said on Wednesday.

They found the two often activate the same circuits in the brain -- suggesting that the responses to pain and pleasure are similar.

The findings may open ways to better treat pain and also increase understanding of how the brain works, said Dr. David Borsook of Massachusetts General Hospital, who led the study.

They may also offer an objective way to measure what is now an intensely personal sensation.

"Pain is not just a sensory experience -- 'I feel it here so and just this much' -- but it is also an emotional experience. It is that emotional experience that has been hard to capture or define," Borsook said in a telephone interview.

"By defining this circuitry we believe we now are in a position to understand what in a chronic pain patient is their bigger problem, and this is their emotional reaction to pain. They are anxious, they don't eat as much, they become depressed, even suicidal."

Borsook's team used technology that allows scientists see the brain in action. They took functional MRI images of the brains of eight healthy young men while running various tests.

In one, a small heat pad was attached to the hands of the volunteers. The researchers heated it to either a pleasantly warm 106 degrees F (41 degrees C) or a painful 115 degrees (46 degrees C).

Painfully hot temperatures activated not only areas long associated with pain in the brain, but also areas previously believed to involve "reward" circuitry, the researchers reported in the Dec. 6 issue of the journal Neuron.

In some of the structures associated with reward -- areas known to be activated by cocaine, food and money -- the pattern was different from that caused by pleasurable rewards.

There was also a variation in the response over time. "These are two brain systems that were never associated in the past, and it's the first time that we have seen something aversive activating these reward structures," Lino Becerra, who worked on the study, said in a statement.

Borsook said something more complex than a simple positive or negative response may be going on. "It may be that these circuits previously described as handling reward are actually analyzing stimuli and judging which are important to survival," he said.

"I'm hopeful that these results will help us understand how chronic pain produces changes in the brains of patients. For example, many chronic pain patients report that they cannot enjoy any pleasurable experience... This interaction of brain systems also may explain why patients can take opioid drugs for pain without becoming addicted."

Borsook, who has studied chronic pain for 15 years, said the experiment might also show ways for doctors to use functional MRI to objectively measure pain -- and to measure whether pain drugs are working. "One of the big, big problems in pain treatment is that we don't have the equivalent, for many pain conditions, of an antibiotic -- where you can test for sensitivity and then you give it and the chances are ... that pneumonia or whatever will disappear," he said.

It should also help in the design of better pain drugs. "Current therapies are essentially based on folklore -- opioids and aspirins," he said. "We don't even know how they work."

Borsook said the findings may also explain the unusual response of masochists to pain, although he stressed this was not his particular goal. "Clearly if sadism and masochism represents something in the chemical makeup of a person."