How drugs can hijack the brain

Addiction is a huge problem and it's very difficult to get exact statistics - but estimates from the National Drug Evidence Centre put it in the hundreds of thousands in the UK alone. There's clearly something quite drastic going on in the brain to cause this, and new research from the University of Cambridge might just hold the key, as David Belin explained to Georgia Mills.

David - So addiction is a state. It's a psychiatric disorder characterised by loss of control over habitual drug-seeking behaviour in such a way that people continue searching for drugs, and consuming drugs, despite awareness of negative consequences of doing so.

Georgia - And which drugs do we think of when we think of addiction?

David - Often people tend to think about illegal drugs such as cocaine, heroin but, actually, alcohol and tobacco are highly addictive as well.

Georgia - And how have you been investigating this?

David - We are interested in understanding why only some individuals who are exposed to these drugs will eventually lose control over their consumption. Because clearly, there's an interaction between something in the brain before you start taking drugs and the effects of these drugs that  would eventually make you vulnerable to addiction and you would develop the disorder. And we try to understand it using both clinical and preclinical approaches, and for this we have the help of little   rats that are very clever animals and, interestingly, in humans not all of them if they are given access to drugs would eventually develop addiction.

Connie - So let me get this right Georgia - not everyone forms addiction to these drugs?

Georgia - No - in fact rats, just like humans, have about a 20% chance of become addicted to cocaine.

Connie - So are they giving cocaine to the rats then?

Georgia - Yes they did actually - they allowed them to have small these small amounts they could take freely. But after a while, they would start making them work harder and harder for their next dose. So they'd get them to press a lever once, twice, 10 times, 500 times. And after a certain point most rats decide that actually, the drug is not worth the effort.

But 20%, the 20% that are addicted keep pushing and pushing and pushing the lever, up to 10,000 times to get their next hit.

David - They just can't stop! And they are sweaty, they put everything they've got into pressing this lever to get to the next fix and these rats clearly are addicted.

Georgia - Well that's quite a powerful image there! Did you find out out why some rats were more likely to get addicted than others?

David - We've identified a couple of behavioural traits such as novelty-seeking and impulsivity that predicted this vulnerability to switch from volitional to compulsive cocaine-taking behaviour. So impulsivity, for instance, the example I tend to give my students all the time is, if during one of my lectures - if Chuck Norris is in the room and he stands up and says 'Oh you know I don't really like  your lecture', and I actually engage a fight with him because I'm frustrated, this would be very impulsive, because the consequences would be harmful and then I would regret it. So this is what impulsivity is.

And we've actually identified this trait in cohorts of animals. Three years after we made this discovery, the same vulnerability trait  was identified in humans, so that was a kind of success story.

Georgia - Being more impulsive and novelty-seeking - those are traits identified that makes both rats and humans - you mentioned switched from an adaptive seeking of cocaine to a compulsive one. What is changing in the brain to make this change?

David - Initially volitional drug seeking and taking behaviour depends upon psychological mechanisms which require a pre-existing representation of the outcome. So when you and I work, and we work because we know, for instance, on Friday we may go out to the pub. We have this representation of what we're going to do with the money we've just earnt. When the behaviour become habitual, then the behaviour is subdued, subjected to stimuli in the environment, and stimuli triggers specific behavioural features outside your awareness.

So a good example in your everyday life is, if you go back home tonight and it's dark. What are you going to do? You open your door and then you try to reach the switch and switch on the light. And what if in the morning before you left, the light bulb was broken? When you get back home this is exactly what you would do nevertheless. You would try to switch on the light and then say, oh yes it's broken - this is a habit. And this is exactly what drugs do, they hijack this system and they push the system towards drug seeking becoming habitual. So now every single time you are presented with a cue that you have experienced when you were taking drugs or seeking drugs, all these kinds of cues are going to trigger behavioural repertoire which actually has been designed so that you would get the drug, and you are not aware of what's going on. This is what a habit is. So there is a clear transition psychologically in what's going on.

Connie - So David's arguing that you kind of go into autopilot, trying to get the next hit.

Georgia - Yeah exactly, and they've actually found evidence for this inside the brain. When animals start taking drugs, many parts of the brain are involved, including the pre-frontal cortex which is very closely associated with decision making and control.

But, what happens in addicts is, after a few months the system kind of changes and switches to another area in the brain which we associate with habit, but it completely circumnavigates the prefrontal cortex.

Connie - The area involved in control and decision making?

Georgia - Yes, it forms a kind of backdoor in the brain skipping past your willpower centre implying that it just doesn't come into it.  Which David argues means we should look at addiction in a very different way...

David - Addiction should be considered exactly as schizophrenia or diabetes. It's a chronic disorder and it's not merely a question of willpower. If you suffer from it then there's very little you can do yourself about it and, unfortunately, there are very few effective treatments for drug addiction. There's none for cocaine, for instance, for cocaine addiction.

In terms of social implications, I think it is time to consider drug addicts really as patients and not as criminals. It's not because they want to harm anyone that they may actually go and sell their grandma to get a couple of quid to buy a line. It's because they have to because of their disorder. And, as long as they aren't considered at patients, socially there would be something wrong with the way we handle drug addiction.

Connie - How does this finding correspond to actual therapies ?

Georgia - This work does suggest some new drug candidates and treatment avenues to explore but it's still very much a 'watch this space.'