Chronic pain may make you lethargic

If you are suffering from chronic pain, it may affect the brain in such a way that it decreases your motivation level even after popping painkillers, says a study.

People with chronic pain report feeling fatigue, depression and decreased motivation, Neil Schwartz from Stanford University in California was quoted as saying.

The brain's rewiring during chronic pain may stem from the way pain prevents people from further injury, researchers said.

"Acute pain is useful because it limits or stops our behaviour to prevent further injury, promote healing and prevent a similar injury in the future," Schwartz added.

In their study, the researchers gave mice a chocolate-flavoured pellet if they poked their noses into a small hole.

But it became more difficult over time, requiring dozens of nose pokes for a pellet.

The injured mice still liked the reward but the pain decreased their motivation, the findings showed.

Even painkillers failed to improve their performance, researcher noted.

A signalling chemical called galanin was found to be the link between changes in the brain's circuits and the decreased level of motivation.

The researchers also found that some of the nerve cells in the nucleus accumbens, an area of the brain associated with pain and motivation, were not responding properly.

The study appeared in the journal Science.