Pain causes an unexpected brain drain, according to a new study in which the brains of people with chronic backaches were up to 11 percent smaller than those of non-sufferers.

People afflicted with other long-term pain and stress might face similar brain shrinkage, said study leader A. Vania Apkarian of Northwestern University.

The results suggest those with constant pain lose gray matter equal to an oversized pea for each year of pain. Gray matter is an outer layer of the brain rich in nerve cells and crucial to information and memory processing.

The results don't reveal why the brain shrinks, but it might involve degradation of neurons, which are the signal transmitters of the mind and body.

"It is possible it's just the stress of having to live with the condition," Apkarian told LiveScience. "The neurons become overactive or tired of the activity."

Another possibility is that people born with smaller numbers of neurons are predisposed to suffering chronic pain. But some of the differences measured "must be directly related to the condition," Apkarian said.

The research involved a one-time brain scan of 26 people who'd had unrelenting back pain for at least a year (and in one case for up to 35 years), along with a pain-free control group. Pain sufferers had lost 5 to 11 percent of gray matter over and above what normal aging would take away.

"People who have had pain for longer times have had more brain atrophy," Apkarian said.

No attempt was made to correlate brain size to brain function. It is possible that some of the shrinkage involves relatively noncrucial tissue -- other than neurons -- and that some of the effects are reversible if the pain is eliminated, Apkarian and colleagues write in the Nov. 23 issue of the Journal of Neuroscience.

Apkarian said other varieties of pain might cause a similar atrophy of gray matter, and he plans to study that possibility in future studies.

"Suffering of pain is fundamentally an emotional condition," Apkarian said. "Different types of pain will have different types of emotional parameters, which will probably result in different types of atrophy -- different amounts and in different brain regions." (Live Science)