as the one that happens when the rats stimulate their hypothalamus. The more addictive drugs – cocaine and heroin – release more dopamine.
It has now been discovered that even the anticipation of taking a drug can release dopamine. The problem is that in addiction this anticipation is experienced as a craving, which, despite the release of dopamine, isn’t pleasurable. The power of dopamine could explain why addicts will sometimes risk losing their jobs and homes, even their families, in order to get another fix. As the brain adjusts to the new dopamine levels, the drug is needed purely to continue functioning. This is known as the dopamine theory of addiction, but what it can’t explain is why so few people become addicted. Only 10% of people who use cocaine become hooked. Likewise only 10% of the American soldiers who regularly took heroin in Vietnam took it again once they were back home. This implies that a person’s situation plays a big part in addiction.
A Canadian psychologist Bruce Alexander has lent weight to this idea with his creation of a luxury rat park. He trains rats to become addicted to a dopamine pedal, but then instead of placing the pedal in a bare cage, he installed it in the luxury rat park where there are jogger wheels, plants, warm nests, nice food, plenty of space to run around and even mountain scenery and streams painted on the walls. Once rats were in here and were occupied and presumably more contented they barely touched the dopamine pedal, in contrast to the caged rats so desperate to get to the pedal that they would starve themselves in order to reach it. This could provide part of the explanation for the fact that so many people who try drugs don’t get hooked. Provided people have alternative stimulation in life they might not become addicted.
Another possibility is that some individuals have fewer dopamine receptors than others. With fewer receptors you need to take more drugs to derive the same pleasure as someone else. The level of addiction in rats has been successfully altered through manipulation of the number of dopamine receptors.
More radically, there is a suggestion that addicts are born with a gene which stops them from experiencing joy in the same way as other people. The idea is that some people are born with a difference in one particular form of the dopamine receptor gene. The gene controls the way that dopamine is released into the brain and comes in two forms, a common type and a rarer version known as Al. A team from UCLA in the United States led by Ernie Noble found that the same gene seems to be implicated in addiction to cocaine, heroin and nicotine, and even eating disorders. He believes that those with the Al form of this gene don’t feel the same joy from something like sitting on a beach watching a sunset or seeing a live concert, however brilliant. By taking drugs or drinking alcohol they can bring their dopamine up to the same levels as everybody else. This new pleasure leads them to become addicted to the experience. Not all addicts have the gene, but those who do find it harder to overcome their addiction. Even with smoking, people who repeatedly attempted to quit without success were found to be more likely to have the Al form of the gene. With a team in Australia Noble tested his theory during the treatment of alcoholics. Patients were either given a placebo or a drug called bromocryptine which activates your dopamine receptors. They found that with the people possessing the Al form of the gene the bromocryptine reduced their cravings almost completely. Moreover, they felt less anxious and remained in the treatment programme for longer than those who had the more common form of the gene. Once the bromocryptine had rectified their dopamine levels, the desire for alcohol faded. This gene won’t explain all cases of addiction; Noble believes that about half of drug addicts might have it, suggesting that they might benefit from a pharmacological approach to treatment, while others might find counselling more effective. He hopes that in the future treatments for addiction could be targeted according to a person’s genes. According to his theory as many as 30% of the population might have the gene, preventing them from experiencing joy. This, he thinks, might lead some people to seek risky pursuits, in the hope of feeling something.
If this is an accurate assessment then it is cause for some concern, but not everyone agrees with Noble’s theory. Some attempts to replicate his results have ended in failure. It might be an oversimplification to suggest that just one gene is involved; there could be lots of different genes contributing – either in relation to a specific drug or general addictive behaviour.
The curious thing about joy is that if you ask people whether they would like to have the human equivalent of the rats’ joy lever, as the Harvard philosopher Robert Nozick did in a thought experiment in 1989, most people say no. He asked them to imagine a machine which can produce whatever set of feelings you desire. You can experience success, pleasure or friendship in any combination and for as long or as short a time as you want to. The only catch is that although you would remain healthy you would have to spend the rest of your life attached to the machine. Despite the guarantee of feeling good for the rest of their lives, coupled with variety to dispense with boredom, people still say no, believing that however the machine made them feel, they wouldn’t be truly happy.
the joy of exercise
When James was sixteen years old he took part in a crosscountry championship. Near the end of the race he was in fourth place, but knew that he was too tired to make the pace needed for him to win. Then something strange happened. ‘I was feeling really exhausted, but in a space of two minutes I moved into this rhythm and this beat where I felt absolutely invincible. I ran forward, took over first position and sprinted to the finish. I remember at the time I couldn’t talk to anybody; I just had to be on my own. There was just this sense of something in my body rewarding me – almost a chemical-like feeling of power.’
James had experienced something which many athletes find elusive – an exercise high. Some people exercise vigorously for years without achieving even one, but when it happens the theory is that beta-endorphins are key. Endorphin is short for endogenous morphine, i.e. morphine made by your own body. They are the body’s natural tranquillisers, which we release when we are in pain. Like morphine, they can also cause pleasure; the pain remains, but you don’t care anymore.
Is it possible that these endorphins could actually bring feelings of joy? There’s a physiological mechanism called the blood-brain barrier that protects the central nervous system by preventing most substances from crossing from the bloodstream into the brain tissues. The problem is that it’s not known whether the endorphins released into the bloodstream during exercise can actually break through the blood-brain barrier in order to have their effect on the brain. Exercise highs are hard to study systematically because it’s not an effect that can be easily quantified – who is to say what constitutes a high and what doesn’t?
It does seem, however, that exercise can affect the brain, even if the results are somewhat milder than a full-blown high and this might enlighten our understanding of the way both our minds and the rest of our bodies influence our emotions. Two or three short sessions of exercise a week can make people feel demonstrably happier, particularly if they are depressed initially. Some GPs already prescribe exercise for patients with mild depression with some success. There have even been studies showing that exercise can be as effective as anti-depressant medication. As well as the suggestion that this is due to the release of beta-endorphins there is also a theory that, like recreational drugs, exercise might cause the release of dopamine, hence we feel good.
Although research into the effect of exercise on mood might sound straightforward it’s not without its problems. For example, in some studies comparing one group who are prescribed exercise with a group not prescribed exercise, the people taking part were allowed to choose which group to be in. This inevitably introduces a bias – the people choosing exercise are likely to expect to see more positive results than those who avoid exercise. Studies have tended to allow a choice because it would be hard to persuade someone who had always detested exercise to take part in a study which might compel them to join a class. But if exercise could be shown to improve the mood of these people then it would be a powerful tool indeed. Yet another problem for the designers of these comparison studies is that factors other than the exercise itself might affect the group taking the classes. Participants might begin to feel
