How close is a habit to an addiction?
The New Year is classically a time when we make a resolutions to give things up, usually things we regard as bad for us like some kind of habit. And we tend to think of habits as generally bad things; but actually if we didn't have the ability to form habits, we wouldn't be able to learn anything and life would be a lot more difficult.
Cambridge University addiction researcher Barry Everitt believes that when we get hooked on things this is just as much about the environment triggering us to behave in a certain way as it is about the chemical addiction itself...
Barry - Every day when I was living in my previous house, I would come out of the house in the morning, turn right, turn left, walk along Regent street, through the main gates of Downing College into my department. I would do that every day and I will be thinking about the weather or what I was going to teach when I came in to the department or whatever. On Sundays, I wouldn't be coming in to work. I would be going to buy the Sunday newspaper from the local news agent. So, I come out of the house and turn right and then go to the shop and turn around and come back again with the newspaper. But on numerous occasions, I would find myself somewhere along the route of the department or indeed even in my office in the department, turning on the computer working without ever having had any goal of coming to work. My goal was buying a newspaper, but the automatic elicitation of my sequence of movements that bring me to work was clicked into gear by the stimuli that control our repeated movements.
Chris - Do you know how many people you have made incredibly happy by them knowing that even the professor of psychology at the University of Cambridge does what we all do. I mean, I've driven down a road, got somewhere and then have no recollection whatsoever of going over multiple traffic lights or junctions. It just happens automatically. How is that behaviour established in the brain? What bits of the brain are driving that? How does it work?
Barry - Actually, the key breakthrough here came from experiments in rats. In this department, some years ago, by taking a rat that was hungry and putting it in a little box where it could press a lever to get food. So, imagine looking at that animal, you would attribute goal directedness in the animal's behaviour. Why is it pressing the lever? It's pressing the lever because he learns it delivers food. Why is he working for food? Because he's hungry.
Chris - So, my suggestion would therefore be that as soon as the rat has eaten the food and is no longer hungry, he's going to stop pressing the lever.
Barry - Exactly and you can devalue the outcome. Let's imagine the rat's working for nice tasty chocolate pellets. Instead of just doing that - this hungry rat, you give it access for an hour to unlimited sources of chocolate. So, it eats chocolate until it can't move anymore. So, the last thing it wants is chocolate. That's called devaluation. But if trained for a long time to do this, the animal will carry on lever pressing. It's not pressing the lever for food. It's pressing the lever because through repetition, it's learned that when it goes into the box, the stimuli of the box and the lever causes it to press a lever. The food may not be a desired outcome. Indeed, in this case, the food will be left although the animal continues to respond for it.
Chris - And this is the rat equivalent of you coming out of your house on Sunday and instead of going to the paper shop, end up at your desk in the department. You did want to go to the department to do some work really, didn't you Barry?
Barry - Yes, that's right.
Chris - So, where in the brain is that happening and what circuits are making it possible for the brain to learn and establish these complex behaviours in this way?
Barry - Well, in imaging studies in humans, we can actually see the neural circuitries of that kind of learning. There's a particular part of the brain called the striatum and one particular part of the striatum called the dorsal lateral part of the striatum is crucial for enabling that transition from goal-directed to automatic behaviour. In fact, if you have inactivate temporarily that bit of the brain animals are forever goal-directed.
Chris - So, are you sort of saying in the same way that the rat presses the lever for food in the box because he's in the box, the person who smokes a cigarette isn't just hooked chemically on the cigarette but the environment that goes along with having the cigarette provokes them to also want to seek that drug?
Barry - Well, good question. With smokers, it's an interesting one. Particularly in this new year period, many people will have said, "I am going to stop smoking." But they find themselves after a meal in a bar, with friends, outside their place of work where smokers congregate to smoke. Despite having the firm goal-directed intention not to smoke, suddenly find themselves with a cigarette in their hand and smoking. And drinkers will describe the same thing and many people addicted to drugs like cocaine and heroin will have every intention not to do it. All of their conscious effortful processing is on not lapsing, but the power of the environmental stimuli when they're in drug-taking settings just elicit those behaviours so they find themselves doing it automatically.
Chris - So, that's the sort of habit side of it, but what about the actual physical dependency on the drug? Where is that rooted through the brain or is that all part of the same system?
Barry - There are two sides to addiction. There's the positive incentive pleasure of taking drugs and there's also the negative downside of withdrawal. There are now growing amounts of data in the literature which suggests that the aversive nature of states like withdrawal can more powerfully drive the development of habitual behaviour than even positive incentive states.
Chris - Because lots of people say, "I take drugs not because it's pleasurable anymore, but it's medicine. It stops me feeling bad."
Barry - Yup! And so, in a withdrawal context again, when someone might be trying not to take drugs, the aversive state is able to engage that automatic mechanism more readily than otherwise.