Study title

Substance abuse is extremely expensive. This project was motivated by the difficulties of substance abuse treatment. An important piece that is missing is knowledge of drug relevant mechanisms in the healthy human brain. One of the most important neurochemical systems in drug is the opioid system (popularly known as the endorphins). The importance of endorphins has been shown both in animal studies and with molecular imaging of substance abusers. This neurochemical system also has known pain-relieving effect. What was not known at the time this project started was how the endorphins work in the healthy, pain-free human brain. The main aim of the project was therefore to demonstrate what the opioid system is doing in the healthy human brain, and to link the new knowledge with known evidence from animal models and patient studies. Specifically, the goal was to map how the healthy opioid system in humans affects reward behavior such as motivation to win money, as well as how much one appreciates pleasant taste, touch or looking at other people. The results of the project show that the opioid system in healthy people affects reward behavior. A key finding is that the influence follows the same pattern as that reported in rat studies. When stimulating the opioid system with e.g. morphine in rodents - and as we have now proven, in young men - the motivation increases for very valuable rewards, but not for less valuable stimuli. When you block the endorphins with another substance, you see the opposite effect, that is, the motivation drops for very valuable rewards and is unchanged for other stimuli. We have observed this pattern across tasks and stimulus types, such as money, attractive faces and sweet taste. These findings have not been previously demonstrated in humans.