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The Brain & the Actions of Cocaine, Opioids, and Marijuana

1: Reward: drug self-administration

Reward: drug self-administration

Introduce the concept of positive reinforcement or reward. Explain that rats will press a lever to self-administer an injection of cocaine or heroin that is inserted into either the peripheral bloodstream (left image) or into specific brain regions (right image). The rat keeps pressing to get more cocaine or heroin because the drugs make the rat feel so good. This is called positive reinforcement, or reward. Natural rewards include food, water, and sex - each is required to maintain survival of our species. Animals and people will continue to exhibit a behavior that is rewarding, and they will cease that behavior when the reward is no longer present. Explain that there is actually a part of the brain that is activated by natural rewards and by artificial rewards such as addictive drugs. This part of the brain is called the reward system. Neuroscientists have been able to pinpoint the exact parts of the brain involved, with the help of the rats. Point to the cartoon on the right and explain that rats will also self-administer addictive drugs directly into their brains, but only into a specific area of the reward system. If the injection needle is moved less than a millimeter away from this crucial area, the rat won't press the lever for more drug. So based on information from working with the rats, scientists have drawn a map of the brain, and located the structures and pathways that are activated when an addictive drug is taken voluntarily. Tell the students that you will show them this "map."

This page was last updated November 2019

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NIDA. (2019, November 19). The Brain & the Actions of Cocaine, Opioids, and Marijuana. Retrieved from https://www.drugabuse.gov/brain-actions-cocaine-opioids-marijuana

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