Science Interviews

Interview

Sun, 9th Jan 2005

The Brain-science of Addiction

Professor Barry Everitt

Part of the show Addiction & Anti-Nicotine Vaccines

Chris - Does it matter what age you are when you start being exposed to addictive things?

Barry - This is a really hot area of investigation. Most people start taking drugs when they are really young or adolescent, and our brains are continually maturing and developing until the age of about nineteen, twenty and twenty one. Taking drugs early on, especially hard drugs and alcohol, may have long lasting effects as they interact with the developing brain. It's hard to test, but taking drugs when you are young may mould the brain in ways that make it more susceptible to drugs and less able to live without them. Many fundamental developments occur at this stage in life.

Chris - The common pathway to do with addiction in the brain causes a surge of a chemical that gives people pleasure. Why do we have a part of our brain concerned with letting us become addicted to things?

Barry - That is probably the back to front way of putting it. The first assumption is that during evolution, a mechanism has evolved that mediates the pleasure of life survival activities like eating, drinking and sex. That system is a specific neural pathway in the brain that utilises a certain chemical, in this case dopamine. When you take addictive drugs, it short circuits the system that has evolved to reward natural behaviours. It is not only stimulated by drugs, but is stimulated in a particularly intense and non-adaptive way. This provides the basis for the reinforcing effects of drugs and explains why the drugs are taken voluntarily, at least initially. The real issue is how that might change with time.

Kat - If people can get a high from the things they do, like falling in love or exercising, do these use the same pathways in the brain?

Barry - Not really, no. Things related to everyday activities like exercise quite possibly interact with these pathways at some point but they aren't the same. As Mark Griffiths mentioned, it's about how you define addiction. No-one ever died from not exercising. Compulsion to do certain things (such as exercise) might be a large aspect of addiction but they are not the same thing, although the relationship between them is certainly very interesting.

Chris - Why do the effects of drugs wear off over time, so that people have to take more and more to get the same hit, and then have to take it every day just to feel normal?

Barry - When you constantly bombard systems in the brain, the brain fights back and becomes tolerant. Tolerance then gets caught up in withdrawal symptoms because when you give up the drug, it is even easier to see the evidence of the brain's adaptation.

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