Using sophisticated brain-scanning and a carefully controlled way of inducing muscle pain, the researchers show that the brain's dopamine system is highly active while someone experiences pain – and that this response varies between individuals in a way that relates directly to how the pain makes them feel. It's the first time that dopamine has been linked to pain response in humans.
The finding, published in the October 18 issue of the Journal of Neuroscience, may help explain why people are more likely to acquire a drug addiction during times of intense stress in their lives. It may also yield clues to why some, but not other chronic pain patients may be prone to developing addictions to certain pain medications. And, it gives further evidence that vulnerability to drug addiction is a very individual phenomenon – and one that can't be predicted by current knowledge of genetics and physiology.
"It appears from our study that dopamine acts as an interface between stress, pain and emotions, or between physical and emotional events, and that it's activated with both positive and negative stimuli," says senior author Jon-Kar Zubieta, M.D., Ph.D., professor of psychiatry and radiology at the U-M Medical School and a member of the U-M Molecular and Behavioral Neuroscience Institute and U-M Depression Center. "It appears to act as a mechanism that responds to the salience of a stimuli – the importance of it to the individual – and makes it relevant for them to respond to."