Opioids control feelings of profit and loss
The joy of winning and the displeasure of losing are regulated by the brains opioid system, according to a British study in which scientists from Karolinska Institutet were involved. The results provide fresh information about the brains reward system and explain how pharmaceutical treatments of gambling addiction work.
The brains reward system is essential to sensations of satisfaction, joy and pleasure, and its keymost chemical agent is thought to be the neurotransmitter dopamine. Now for the first time, however, scientists have linked another class of signal substance the opioids to the human reward system. The involvement of the opioid system in reward processes has only previously been studied in animal models.
"Dopamine plays a vital role when we seek reward, partly in the way it affects motivation and learning," says Predrag Petrovic, who co-conducted the study with a group of researchers in London. "But the reward itself, the sense of joy or pleasure, is controlled by the opioid system."
For the study, subjects were invited to gamble money on a wheel of fortune. Before one of the sessions, they were given a dose of naloxon, which blocks the brains opioid receptors; before the other session they received a placebo.
When the subjects were asked to describe how they felt about the gambling sessions, it turned out that they derived less pleasure from their winnings after having received the naloxon than they did after having been given the placebo. They also experienced greater displeasure on losing during the naloxon session.
High concentration of opioid receptors
Functional MR scans showed that activity in an area of the brain with a high concentration of opioid receptors (the anterior cingulate) increased the more the subjects won and also the more they lost Both these cortical phenomena decreased after treatment with naloxon. This suggests that the anterior cingulate is involved, via the endogenous opioid system, not only in the mediation of the sense of reward but also in the suppression of displeasure when losing.
"Drugs that affect the opioid system are already in clinical use, for treating things like gambling and alcohol addiction," says Dr Petrovic. "e are now in a position to understand better the underlying mechanisms for how these drugs work."
The study was financed by the Swedish Research Council, the Swedish Brain Fund and the Wellcome Trust Centre for Neuroimaging at the University College of London.
Publication
Blocking central opiate function modulates hedonic impact and anterior cingulate response to rewards and losses.
J. Neurosci. 2008 Oct;28(42):10509-16