Published: 14:18 EST, June 04, 2007 =

Old memory traces in brain may trigger chronic pain

Why do so many people continue to suffer from = life-altering,=20 chronic pain long after their injuries have actually = healed?

The definitive answer -- and an = effective=20 treatment -- has long eluded scientists. Traditional analgesic drugs, = such as=20 aspirin and morphine derivatives, haven=92t worked very well. =

A Northwestern University researcher = has found a=20 key source of chronic pain appears to be an old memory trace that = essentially=20 gets stuck in the prefrontal cortex, the site of emotion and learning. = The brain=20 seems to remember the injury as if it were fresh and can=92t forget it.=20

With new understanding of the pain source, Vania Apkarian, = professor of=20 physiology, and of anesthesiology, at Northwestern=92s Feinberg School = of=20 Medicine, has identified a drug that controls persistent nerve pain by = targeting=20 the part of the brain that experiences the emotional suffering of pain. = The drug=20 is D-Cycloserine, which has been used to treat phobic behavior over the = past=20 decade.

In animal studies, D-Cycloserine appeared to = significantly=20 diminish the emotional suffering from pain as well as reduce the = sensitivity of=20 the formerly injured site. It also controlled nerve pain resulting from=20 chemotherapy, noted Apkarian, who is a member of the Robert H. Lurie=20 Comprehensive Cancer Center at Northwestern University.

The drug = has=20 long-term benefits. Animals appeared to be pain free 30 days after the = last dose=20 of a 30-day regime of D-Cycloserine.

The study, funded by the = National=20 Institutes of Health, will be published in the journal Pain this = fall.=20 (It has been published on-line.)

=93In some ways, you can think = of chronic=20 pain as the inability to turn off the memory of the pain,=94 Apkarian = said.=20 =93What=92s exciting is that we now may be relieving what has clinically = been the=20 most difficult to treat=97the suffering or the emotional component of = pain.=94=20

Scientists have=20 always tried to understand pain from the viewpoint of sensation, = Apkarian said.=20 =93To control it, they tried to stop the sensory input to the brain. = =94We are=20 saying there=92s a cognitive memory and emotional component in the brain = that=20 seems abnormal. Easing that may have a bigger effect on suffering.=94=20

Chronic pain is not caused by a single mechanism, Apkarian = noted.=20 Sensory abnormalities in people with chronic pain probably drive this = memory=20 abnormality.

About 10 percent of the United States population = suffers=20 from chronic pain, of which the majority is back pain.

One of = Apkarian=92s=20 studies with rats tried to separately measure their emotional suffering = and=20 their physical pain after being treated with the drug. (The rats had = chronic=20 pain from a healed limb injury.) The results indicated the animals=92 = emotional=20 suffering decreased much more than their physical pain. While the = physical pain=20 appeared to be reduced 30 percent =96 their emotional suffering = completely=20 disappeared.

Rat are nocturnal animals that prefer to be in the = dark and=20 are averse to bright light. Researchers placed the rats in a = two-compartment=20 chamber =96- one side light, one dark. When the rats were in their = preferred dark=20 side, scientists mechanically stimulated their sensitive limbs. The rats = didn=92t=20 like that and bolted into the bright chamber, where they remained. Next=20 scientists took the same rats and treated them with D=96Cycloserine. = Again,=20 scientists stimulated the rats=92 sensitive limbs. This time, however, = the rats=20 remained in the dark chamber.

=93Their aversive reaction to the=20 stimulation disappeared,=94 Apkarian said.

Based on the animal = results,=20 the next step will be to test the drug in clinical trials, Apkarian = said.=20

=93When we do this in a clinical trial, we expect people to say = I still=20 have the pain, but it=92s not bothering me anymore,=94 Apkarian said. = =93We think they=20 will have a physical awareness of the pain, but its emotional = consequences will=20 have decreased.=94 He said the drug potentially may lower the amount of = standard=20 analgesics people have to use.

In Apkarian=92s previous study, = published=20 in late 2006, he revealed that chronic back pain appears in a different = part of=20 the brain than the discomfort of burning your finger, for example. With = a=20 functional MRI, he found that chronic back pain shows up in the = prefrontal=20 cortex. By contrast, the acute sensory pain of the burned finger appears = in the=20 sensory part of the thalamus.

Apkarian also found that the = longer a=20 person has been suffering from chronic pain, the more activity in the = prefrontal=20 cortex. He was able to predict the years of their suffering from the = MRI.=20

=93It=92s cumulative memory,=94 he explained. =93I can predict = with 90 percent=20 accuracy how many years they have been living in that pain without even = asking=20 them the question.=94

Source: Northwestern University

=BB Next Article in Medicine & Health - Research: = Brain uses both = neural=20 'teacher' and 'tinkerer' networks in learning

would you recommend this story?

=20