Scientists have found clues in the brains of people with major depression that might help explain why so many depressed people also battle chronic pain, according to a U.S. study published on Monday.
Brain imaging showed people with depression had more activity in brain regions involved in emotions when they anticipated or experienced pain, the researchers found.
Irina Strigo of the University of California San Diego and colleagues told volunteers eight seconds beforehand that a painful experience was coming -- being touched on the arm with a device hot enough to cause brief pain but not injury.
"Not only do you really show this high activation of emotional areas when the pain was not there, but when the pain is there you see this helplessness, not even trying to modulate your experience," Strigo said in a telephone interview.
Her team tested 15 people in their mid-20s diagnosed with major depression but not taking medication to treat it. Their magnetic resonance imaging brain scans were compared to those of 15 similar people who did not have depression.
While anticipating the pain, the people with depression registered increased activation in brain circuitry involved in processing emotions, including structures called the amygdala and insula, compared with the people with no depression.
During the five seconds while their arm was touched with the hot device, their brains continued to show increased emotional activation. But at the same time, brain networks normally involved in mitigating pain were less activated in the depressed people than the others.
More than three quarters of depressed people have recurring or chronic pain, while 30 percent to 60 percent of people with chronic pain report symptoms of depression, the researchers wrote in the Archives of General Psychiatry.
"If a person has chronic pain together with depression, this is a very debilitating condition. This condition is very difficult to treat and the disability is much higher and the cost of treatment is very high," Strigo said.
She said the study's findings may point toward new ways to help patients, either through behavioral therapies or perhaps drugs.