According to the study chronic pain can also lead to anxiety and depression as brain inflammation caused by long-term nerve pain alters activity in areas that regulate mood and motivation.

The scientists from University of California have proved this with the research on rodents. The researchers discovered that pain-derived brain inflammation causes the accelerated growth and activation of immune cells called microglia. These cells trigger chemical signals within neurons that restrict the release of dopamine, a neurotransmitter that helps control the brain's reward and pleasure centers. The study also reveals why opioid drugs such as morphine can be ineffective against chronic pain.

Usually Morphine and its derivatives stimulate the release of dopamine, but in research on mice and rats, the researchers learned that these drugs failed to stimulate a dopamine response which results in impaired reward-motivated behaviour.

"Our findings represent a paradigm shift which has broad implications that are not restricted to the problem of pain and may translate to other disorders," said one of the researchers Catherine Cahill, associate professor of anesthesiology & perioperative care at University of California, Irvine in the US.

By Lizitha