Many drug users successfully break their habit in rehab, only to resume abusing drugs once they re-enter the real world. In this Science Update, you'll hear about new research in rats that reveals why staying off drugs can be so difficult.
Why drugs make it hard to just say no. I'm Bob Hirshon and this is Science Update.
Many former drug addicts find it hard to stay clean because of the powerful cravings they feel. Now, researchers have discovered exactly how such intense cravings are triggered in the brain: Just thinking about drugs or being reminded of that life may release the same brain chemical that causes a drug high in the first place.
Regina Carelli is a psychologist at the University of North Carolina, Chapel Hill. She and her colleagues continuously measure the brain chemical dopamine in rats that had been trained to press a bar for cocaine.
And what we found is that dopamine increases when animals go over and press that special bar for intravenous infusion of cocaine.
What's more, simply giving the rats a visual reminder of the cocaine also spurred a release of dopamine in the brain.
So for humans, these cues may be simple objects, such as drug-taking paraphernalia. And importantly, this signaling occurs on a sub-second time scale, so it may be responsible for these impulsive urges to take the drugs. And our work is really beginning to understand the biological basis of that process.
Carelli says understanding this process could give counselors new tools to help drug users break the vicious cycle of addiction. For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
Dopamine is one of the most addictive chemicals around. You can't buy it on the street, though: it occurs naturally inside your brain. When something feels good—whether it's a drug, a gooey chocolate brownie, or a kiss from a sweetheart—dopamine plays a big role in creating that satisfying feeling that keeps you coming back for more.
In Carelli's experiment, rats have been trained to press on a bar to get an injection of cocaine. This kind of experiment is common in studies of drug addiction. It's been shown time and time again that rats will learn to give themselves addictive drugs really fast if given the opportunity—in some cases, more easily than they learn to feed themselves.
So, when the rat presses the bar, the cocaine goes in, and the rat's dopamine channels open up the floodgates. But Carelli built other cues into the experiment that signaled when cocaine was on its way: when the rat pressed the bar, they heard a tone and saw a light go on in their little room. Eventually, they found that just flashing the light or playing the tone made the rat's dopamine levels go up—even when no drug was delivered. They also found that artificially inflating the rat's dopamine levels made the rats run over and press the bar again.
The meaning? Well, for one thing, this experiment implies that when someone becomes addicted to a drug, all the environmental cues associated with taking it can become rewarding in and of themselves. In other words, if you usually take a drug in a certain room, or at a certain time, or with certain equipment, just being in that space with all the familiar objects can stimulate your dopamine levels. And that, in turn, can turn up the heat on your craving for the drug.
It's a subtle but powerful process that can be very difficult for recovering addicts to control. Carelli says that understanding this process can make treating addiction more effective, since the counselors will know that access to all the sights, sounds, and smells of drug taking, and not just the drug itself, need to be controlled.
Now try and answer these questions:
- What is dopamine? What role does it play in addiction?
- How does Carelli's experiment compare to real-life drug taking in humans? In other words, how is the experiment designed to create a comparable situation in the rats?
- What are the key findings in the study? Did these findings challenge what you already believed about drug addiction?
- Based on this research, what steps would you take to make addiction therapy more effective?
In Constant Craving, a lesson from the NY Times Learning Network, students investigate the ways that various addictive drugs interact with the human nervous system.
The Addiction Science Research and Education Center, at the University of Texas, is an organization of scientists dedicated to communicating the science of addiction to the general public.
The Brain: Understanding Neurobiology Through the Study of Addiction is a series of interactive, science-based supplements for use by high-school students and teachers (grades 9-12) in the science classroom. The materials are free of charge and can be ordered from the NIH Office of Science Education