How does the brain create the experience of joy and desire? That’s the subject of David Linden’s new book, The Compass of Pleasure. A professor of neuroscience at Johns Hopkins University School of Medicine, Linden studies memory. But here, he explores the basis of craving, addiction and satisfaction.
It has kind of a dual role. For example, if you have a person in a brain scanner who is hungry, and you show them a picture of food that they enjoy, you will see dopamine release in part of the pleasure circuit, a part called the striatum. If they actually get a chance to eat that food or any other food that they enjoy while in the scanner, you will also see release of dopamine.
Dopamine actually is what underlies the feeling of pleasure because we also know that if you ask people to report on about how much pleasure they’re getting from eating [or other pleasurable experiences] it matches the [level] of dopamine response.
The role of dopamine is tied up with both liking and wanting, and it’s probably even tied up with something more general called salience. Part of what dopamine does seems to be to say, ‘Here’s something going on that is emotionally relevant and likely important for continued survival or successful procreation, so wake up and pay attention.’
There are some studies in which some dopamine[-producing cells] in the brain are activated by both painful and pleasurable stimulation. Well, how can that be? Both pain and pleasure are salient. They say, ‘Hey this is important.’
In the book, you speculate that that may account for the fact that some people take pleasure in pain.
Certainly, you have to wonder. Even things like chili peppers — lots of people enjoy them and they are a little painful. hy is that? My suspicion, based on no evidence, is that chili peppers engage the brain systems that say, ‘Hey this is important,’ and that aspect adds to the pleasure of eating spicy food.
Some researchers also theorize that dopamine is not so much pleasure but about the expectation or prediction of pleasure.
That’s another complication. We seem to be hard-wired to catch a buzz out of uncertainty. Certainly in other animals and in humans, when you set up a little gambling situation in which someone signals that there’s going to be an outcome in the near future, during the interval when it’s unclear whether or not you are going to get a reward — money for humans, a shot of juice for monkeys — in that five seconds, you see a gradual ramping up of dopamine release.
It really seems to me that that is not saying dopamine isn’t about pleasure. When you talk to people who really like gambling, they like that period of time, perhaps even more than they like winning.
The way to think about this is evolutionary. Evolution is a very slow process and culture and technology change very fast. We’re fairly well adapted for life in a hunter-gatherer society, but evolution has not caught up to the way we live now.
If you’re in a hunter-gatherer society, in a situation where food is scarce and there are frequent famines, you’re served well by being risk-taking and novelty-seeking and enjoying uncertainty. That drives you to greater survival and reproductive success than if you’re very conservative.
If you live in a situation where food is abundant, well maybe you’re better served by being a little more [cautious]. When you live in groups, you’re surviving [together], it’s not an individual battle against others. If you have a group of different people with different proclivities and [everyone] shares, that’s even more adaptive than all people being risk-takers or all risk-averse.
Some say that drug addictions are caused, at least in part, by changes made by drugs to the reward system. But obviously, this system is there to get us to eat food and have sex, so how could those things be “hijacking” the reward system?
My opinion on that is that both food addiction and sex addiction are very real. Food addiction is very common and sex addiction is very rare. If you look at people who are morbidly obese and say, ‘Well, is that because people overeat or because they never exercise or because they have a metabolic disorder?’ The answer is that 90% of severe obesity is a result of overeating.
If you look at the genetics of severe obesity, the same gene variants that turn down the functionality of dopamine signaling that leave you at higher risk for substance addictions also leave you at higher risk for behavioral addictions, including overeating.
One of the most pernicious stereotypes about addiction is that it’s about blind hedonism, where people seek “extra” pleasure all the time.
That’s false on a couple of different levels. On the level of biology, it’s false because we now know that what we see in most addicts’ brains both genetically and developmentally as the arc of addiction progresses is that the dopamine signaling that underlies pleasure is weaker, it’s attenuated.
Addicts seek their pleasure to a greater degree than so-called normal people, not because they want more, but because they’re trying to get the same pleasure others might get with moderate consumption.
I’m always curious about why the pleasure system attaches to a particular activity or experience. Why does one person get obsessed with baseball while another is into butterflies?
That’s a great question. We know that interconnections between the reward circuitry and the parts of the brain involved in emotion, memory and cognition are themselves plastic and experience-modifiable. One’s associations are built up throughout their life history and that guides what your particular pleasure might be at a given moment.
You write about a futuristic “baseball cap” that could one day be used to self-stimulate the brain to create a variety of pleasurable experiences. Would that be the ultimate addiction, or would most people, as they do now, control themselves? After all, the vast majority of drug users — even those who use heroin and cocaine — are not addicts.
I think it’s not entirely clear. If people have the ability to directly stimulate their pleasure centers as strongly as they want, I think it could be really serious. I don’t think there’s a strong prediction about what would happen on a societal level. I wouldn’t be in favor of ‘Just don’t worry, it will be fine, people will use it and still go to work and take care of their children.’
The truth would probably be somewhere between everything’s great and fine and society completely blows up, but the exact ramifications are unclear.
You also describe how researchers in the 1950s did what would now be seen as an extremely unethical study. It was one of the few where humans have been given the ability to stimulate their own pleasure centers: they implanted electrodes in a man’s pleasure regions, in part to try to “cure” his homosexuality. Do we know what happened to him?
He just kind of disappeared after that study. We don’t know what happened to him. He checked in for few months. It really seemed like he was not lastingly heterosexual — that we know — but after that, we really don’t know.
The thing to keep in mind is this guy had huge psychiatric problems. He was profoundly depressed and self-stimulation did not appear to help. It didn’t really have lasting effects.