"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." "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. 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 may also yield clues to why some, but not other chronic pain patients may be prone to developing addictions to certain pain medications. 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's the first time that dopamine has been linked to pain response in humans. 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. Now, a new study from the University of Michigan adds a new twist to dopamine's fun-loving reputation: pain. More recently, research has shown that certain drugs like cocaine and heroin amplify this effect – an action that may lie at the heart of drug addiction. For years, the brain chemical dopamine has been thought of as the brain's "pleasure chemical," sending signals between brain cells in a way that rewards a person or animal for one activity or another. However, it is only when that human predisposition is combined with aspects of one’s particular life experience (as influenced by cultural and religious ideas) that the brain’s neural salience circuits are modified to forge the pleasure-pain connection in a sexual context.ANN ARBOR, Mich. This seems to be the case when pain is survivable and doesn’t lead to permanent damage as in both masochistic sexual practice and chili pepper eating. It is likely that there is a human predisposition to learn to find certain forms of pain to be rewarding. Rats and mice, by comparison, cannot be trained to choose chili peppers in their food no matter how their upbringing is manipulated by scientists. If you grow up in a community where chili peppers are readily eaten, you will reject them as an infant, but by about age 5, you will almost certainly develop a taste for these painful foods. Perhaps the best hypothesis for sexual masochism comes by analogy from studies of another painful practice: chili pepper consumption. The end result is that there is an innate rewarding component to both pleasurable and painful experiences. We also know, from different experiments, that protracted physical pain and protracted emotional pain (resulting from social rejection) can cause the release of endorphins, the brain’s own morphine-like molecules and that these endorphins can activate dopamine neurons in the ventral tegmental area. In other words, these latter dopamine-using neurons were salience detectors, releasing dopamine in response to either pleasure or pain. Electrical recordings from single dopamine neurons of the ventral tegmental area revealed that all of these neurons responded to the presentation of a tasty sugar-droplet, yet some of these neurons responded to a brief painful footshock with a decrease in their ongoing rate of activity while others responded with an increase. In rats, one can examine this phenomenon in greater detail. When subjects in a brain scanner received in injection into the jaw muscles that produced a protracted aching type of pain, this triggered dopamine release in the nucleus accumbens and the greatest release was seen in those subjects who rated the pain as most unpleasant. Here are the key findings that help to explain the pleasure-pain connection.
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