Chronic pain affects brain circuitry and increases chances of physical exhaustion, a new research by the Stanford University School of Medicine shows.

People suffering from chronic pain often complain about fatigue, depression and reduced motivation. The study conducted on mice showed that constant pain leads to changes in a set of nerve cells in a deep-brain structure that is known for reward-seeking behavior.

"We showed that those brain changes don't go away when you transiently relieve the mice's pain," senior study author Robert Malenka, MD, PhD, said in a press release. He explained that the rewiring of brain during chronic pain does not crop up due to the pain, but is more psychological.

For the study, researchers gave the mice a chocolate-flavored pellet if they poked their noses into a small hole. The mice were trained for the activity. At first, a single nose poke earned a pellet. However, the researchers increased the number of nose pokes required for a reward.

Researchers found that over time it became difficult for the mice to poke their noses into the holes at least dozens of time for a single pellet. Although the mice enjoyed the reward, the pain did not motivate them. Moreover, painkillers were of no help.

The team stated that a chemical known as galanin was found to be the connection between changes in the brain's circuits and the decreased level of motivation.

Furthermore, the researchers observed that certain nerve cells in the nucleus accumbens, an area of the brain associated with pain and motivation, did not respond properly.

The study was published in the journal Science.