Chronic Pain Lowers Motivation, Researchers

Chronic pain reduces motivation to work, a study by researchers at the Stanford University School of Medicine has found.

The study on mice models shows that long-term pain results in lethargy and decrease in motivation to seek rewards. What's worse is that pain-relievers don't help improve motivation or desire to work.

The study might help explain why chronic pain sufferers can't finish daily tasks.

"With chronic pain, your whole life changes in a way that doesn't happen with acute pain," said Robert Malenka, MD, senior author of the study, according to a news release. "Yet this absence of motivation caused by chronic pain, which can continue even when the pain is transiently relieved, has been largely ignored by medical science."

The study is published in the journal Science.                                   

For the study, researchers conducted experiments on mice that had long-term pain. The team found that these animals were less willing to work for rewards even after they were given pain-relievers.

According to the researchers, long-term pain leads to changes in a set of nerve cells located in a deep-brain structure. This area, called the nucleus accumbens, is known to regulate reward-seeking behavior. Malenka and colleagues have been studying this brain region for more than 20 years now.

The team found that a brain chemical called galanin plays a critical role in suppressing activity in the nucleus accumbens.

Galanin has been known for about six decades now. It is a short signaling-protein snippet released by several brain cells. This is the first time that researchers have found that this chemical is involved in causing lethargy in chronic pain sufferers.

Malenka and colleagues are hopeful that someday scientists can develop compounds that can target galanin in nucleus accumbens.

"There's no reason to think this finding won't generalize to people," said Howard Fields, MD, PhD, a professor of neurology at the University of California-San Francisco. "Our brains have galanin, and a nucleus accumbens, just as mouse brains do. However, before jumping from mice to humans it would be wise to test other animal species. If the same things happen in a non-rodent species that happen in mice, then it's probable they happen in humans, too." Fields wasn't part of the research team.