THURSDAY, June 21 (HealthDay News) -- Even after their injuries have healed, some people continue to suffer chronic pain that can't be totally relieved through traditional analgesic drugs, such as aspirin and morphine derivatives.

Scientists have long tried to uncover the reasons for this kind of serious pain and to find effective treatments for it.

Now, a new study by a researcher at Northwestern University School of Medicine suggests that a main cause of this form of chronic pain may be old "memory traces" that get stuck in the brain's prefrontal cortex, which controls emotion and learning. As a result, the brain seems to remember the injury as if it were fresh, even long after it's healed.

Vania Apkarian, a professor of physiology and anesthesiology, says his findings from research with rats indicates there may be an abnormal cognitive memory and emotional component in the brain that causes the chronic pain.

He also identified a drug -- D-Cycloserine -- that controls persistent nerve pain by targeting the area of the brain that experiences the emotional suffering of pain. Over the past decade, the drug has been used to treat phobic behavior.

In rats, the drug appeared to greatly reduce pain-related emotional suffering and sensitivity of injury sites that had healed.

The next step will be to test the drug in clinical trials, Apkarian said.

The findings appear online in the journal Pain and will be published in print this fall.

The study was funded by the U.S. National Institutes of Health.

More information

The American Academy of Family Physicians has more about chronic pain.