Narrator: This is Science Today. What happens inside the brain of a drug addict? Psychiatry professor, Robert Malenka, of the University of California, San Francisco says parts of the brain responsible for what's called natural reward are altered.
Malenka: There's a cirque in the brain that tells you Athis is good@. This is a rewarding stimulus and the simplest example is when you're hungry, you eat food and that feels good. There are systems in the brain that's saying this is a rewarding thing to do.
Narrator: Malenka says there's evidence heroin and cocaine cause a neurotransmitter related to reward called dopamine, to stay in the system longer, leading to an intense feeling of gratification.
Malenka: If the natural rewards, like eating a good meal, are no longer as effective in activating the reward system, a natural tendency is for the person who's experiencing this lack of reward is they're going to go and find something that gives them that rewarding feeling and that will often be the drug of abuse.
Narrator: By better understanding this process, Malenka hopes researchers can block an unnatural reward process. For Science Today, I'm Larissa Branin.