Chronic pain is not caused by a single mechanism, Apkarian noted. Sensory abnormalities in people with chronic pain probably drive this memory abnormality.
About 10 percent of the United States population suffers from chronic pain, of which the majority is back pain.
One of Apkarian’s studies with rats tried to separately measure their emotional suffering and their physical pain after being treated with the drug. (The rats had chronic pain from a healed limb injury.) The results indicated the animals’ emotional suffering decreased much more than their physical pain. While the physical pain appeared to be reduced 30 percent – their emotional suffering completely disappeared.
Rat are nocturnal animals that prefer to be in the dark and are averse to bright light. Researchers placed the rats in a two-compartment chamber –- one side light, one dark. When the rats were in their preferred dark side, scientists mechanically stimulated their sensitive limbs. The rats didn’t like that and bolted into the bright chamber, where they remained. Next scientists took the same rats and treated them with D–Cycloserine. Again, scientists stimulated the rats’ sensitive limbs. This time, however, the rats remained in the dark chamber.
“Their aversive reaction to the stimulation disappeared,” Apkarian said.
Based on the animal results, the next step will be to test the drug in clinical trials, Apkarian said.
“When we do this in a clinical trial, we expect people to say I still have the pain, but it’s not bothering me anymore,” Apkarian said. “We think they will have a physical awareness of the pain, but its emotional consequences will have decreased.”