TERRY GROSS, host:
This is FRESH AIR. I'm Terry Gross.
When you're eating great food or making love, you're probably not thinking about what's happening in your brain, but neuroscientists are investigating that and are discovering the pleasure circuitry of the brain. That's the subject of the new book "The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning and Gambling Feel So Good."
My guest is the author, David Linden. He's a professor of neuroscience at the Johns Hopkins University School of Medicine. He's also the editor-in-chief of the Journal of Neurophysiology. We're going to talk about what happens anatomically and biochemically in the brain when we experience pleasure and why some pleasures can cross the line into addiction.
David Linden, welcome to FRESH AIR. So there's a region of the brain that registers pleasure. Why is it a big deal to know that?
Professor DAVID LINDEN (Author, "The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning and Gambling Feel So Good"): Well, it's a big deal to know that because this is the center of so much of what makes us human. It turns out that this very anatomically and biochemically defined section of the brain, which we call the medial forebrain pleasure circuit, and not to get too technical here, medial just means it's in the middle of the brain, and forebrain means it's in the front of the brain.
And this region of the brain, which is crucially dependent upon the neurotransmitter dopamine, is absolutely essential to our evolutionary survival. Not surprisingly, it's an evolutionarily ancient region, and it exists originally because we want eating food and drinking water and having sex to be pleasurable in order to have children and propagate our genes in the next generation.
GROSS: Now, you say that there's all kinds of pleasure that registers in that part of the brain, ranging from orgasm to eating, shopping, even prayer, meditation, giving to charity.
Prof. LINDEN: Yes, this is entirely true. And so obviously some of these things that we can do in humans - and with humans we do these experiments with people in brain scanners.
So, for example, if we were doing an experiment and we had you in a brain scanner, and you were really hungry, and then we gave you a bite of a food that you found absolutely delicious, we would see these regions in the medial forebrain pleasure circuit light up, meaning that there was neural activity there, as you took that first bite of food.
And just as your subjective experience of pleasure is that the first bite is great and the second bite is a little less, and then as you eat and you become sated, the last bite is okay but not nearly as good as the first bite, that would be reflected in the pattern of brain activation. We would see strong activation in the first bite and subsequently weaker activation as time went on.
What is surprising and what has emerged more recently in a lot of research is that behaviors that societally we consider virtuous also cause activation of the pleasure circuit, and I'm talking about things like exercise and charitable donation and learning.
So a fascinating experiment was done at the University of Oregon, where they gave subjects real money, and they said: Okay, here's your money. You have the choice of giving donations to a food bank, or you can keep the money for yourself, and we've set this up so that no one will ever know what you did. It's all controlled by computers. None of the experimenters will know at all.
And this was the truth. And what they found was that in the majority of the subjects, not all of them, but in the majority of them, even anonymous charitable donation was associated with activation of the pleasure circuit.
And I think it's crucial that this is anonymous because we're deeply social beings, and so one motivation to give to charity is to have others think well of us - and having others think well of us does activate the pleasure circuit - but in this case that was taken out of the equation.
GROSS: Now as you point out, the dark side of pleasure is addiction. Does something different happen in the pleasure circuits of the brain when you're addicted to heroin than when you're, say, giving to charity and getting pleasure out of that or, you know, eating good food and getting pleasure out of that?
Prof. LINDEN: Well, I don't know anyone who has become addicted to giving to charity, although I suppose it's theoretically possible. Almost all things that activate the pleasure circuit, not all, but almost all, are potential substrates for addiction. But some things have a much greater potential for addiction than others.
Nicotine, for example, is extraordinarily addictive. So 80 percent of all people who ever try cigarettes will become nicotine addicts, whereas about 30 percent of all people who inject heroin in their arms will become heroin addicts.
You can become addicted to all kinds of behavioral things. You can become an exercise addict or a gambling addict or a sex addict, as well.
GROSS: So let's look at drugs for a second. Take nicotine. You say it's very addictive. Eighty percent of the people who start smoking become nicotine addicts. Is that what you said?
Prof. LINDEN: That's right. And in a way, this is deeply counterintuitive, right? Because the psychoactive pleasure effect, the pleasure buzz that you get from a puff of a cigarette is very subtle, whereas the pleasure buzz that you get from a shot of heroin is quite profound. So I think it's worthwhile to back up and talk about the pharmacology of the pleasure circuit just a little bit.
GROSS: Yeah, go ahead.
Prof. LINDEN: So not every psychoactive drug activates the pleasure circuit. So alcohol and nicotine and heroin, cocaine and amphetamines and cannabis all do, but the hallucinogens, LSD and mescaline do not, and certain tranquilizers do not. And there is a perfect correlation between those drugs that activate the pleasure circuit and those drugs where there is some risk for addiction.
So LSD and mescaline and certain tranquilizers are not ever addicting, whereas these other drugs have various rates: heroin, 30 percent; nicotine, 80 percent. Why is that? Well...
GROSS: Let me offer you my guess first.
Prof. LINDEN: Yes, please.
GROSS: That people know heroin is really dangerous and it could ruin your life, whereas nicotine, it's dangerous, but you're not going to be a junkie in the streets looking like a toothpick and having sores all over and having to go to horrible neighborhoods to see a drug dealer, spending all your money on heroin. Do you know what I'm saying? It's like there are behavioral reasons. There are social reasons. There are prison reasons why it's easier to smoke than do heroin.
Prof. LINDEN: Well, that's absolutely true. And if heroin is illegal and harder to come by, you're less likely to do it than something that you can just buy at the filling station.
GROSS: But there's more, right?
Prof. LINDEN: But there's more. So there's a neuropharmacological reason. So, addiction is a form of learning. When we, for example, puff on a cigarette or inject heroin in our arm, we are developing associations between the act of puffing or the act of injecting and all the other sensory information that's around, the sights and the smells, the people we're with, the music we're hearing, the room we're in, the situation that surrounds us and the pleasure that is produced as a result of puffing that cigarette or injecting that heroin.
Now, imagine by analogy that we have a dog and we want to train our dog to come when called. And we have a 10-ounce steak that we're holding behind our back and we call: Come, Rover. Come, Rover. And after a little while the dog comes and we give the dog the 10-ounce steak, and the dog eats the steak, and then that steak is gone for the next 12 hours. We don't have another steak to give.
And that's more or less the situation with heroin. It's a very large reward, but even a stone junkie is unlikely to shoot up more than three times a day. So it's very intermittent.
Now, imagine by contrast a pack-a-day cigarette smoker; 20 cigarettes in a pack, about 10 puffs per cigarette. So imagine by analogy you've got your steak and you've cut it into 200 tiny little pieces and you have them in a sack behind your back. Come, Rover. Rover comes, there's a tiny morsel of steak and you repeat that 200 times. Well, by the end of the day, that dog will have learned to come when called.
And consequently, when we smoke cigarettes, and we have extremely reliable small rewards over and over and over again that are associated with the act of puffing the cigarette, we are extraordinarily good trainers of our inner dog, and that is one primary reason why cigarette smoking is so addictive.
GROSS: So could you describe in simple words that we could understand what nicotine is doing to your brain when you smoke?
Prof. LINDEN: Right. Well, so I think there's two parts to the question: What is it doing on the short term, and what is it doing on the long term? So on the short term, nicotine, when you take it into your lungs, it passes into your bloodstream, and it passes from your bloodstream into your brain, and then within the brain, it binds specialized receptor molecules on the surface of neurons within your pleasure circuit.
And through an indirect set of biochemical steps that I'll skip over, it causes dopamine-containing neurons within that circuit, within a brain region called the ventral tegmental area, to fire more strongly and release dopamine, and it is that dopamine release that gives us the pleasure buzz from nicotine.
So there are some drugs, like cocaine and amphetamines, that directly affect the dopamine levels, and there are others, like cannabis and nicotine and alcohol and heroin, that affect it indirectly. But the final common denominator of pleasure on a biochemical level on the brain is dopamine release within this particular pleasure circuit.
GROSS: Now, you write that people assume that drug addicts become addicts because they derive greater reward from getting high than other people do. But you say the biology says no, drug addicts actually seem to want it more, but like it less. Would you explain that?
Prof. LINDEN: Yeah, I mean, I think it's a very compelling notion not just for drug addicts, but also for any kind of addict - a gambling addict or a sex addict. Well, why are you an addict? Well, that person must really love getting high. That person must really love gambling and get so much pleasure out of it. That person must really love sex, more than the rest of us do, and so that's why they're motivated to do it more and more.
And the converging evidence from many different studies, both in humans and in animal model systems, is that it is precisely 180 degrees the opposite. That is to say, there are variants in genes that turn down the function of dopamine signaling within the pleasure circuit, that blunt the pleasures that are felt.
And when you carry these gene variants, and you have a blunted dopamine system, a blunted pleasure circuit, the result of that is that in order to seek the same setpoint of pleasure that so-called normals would be able to achieve with moderate indulgence, you have to, on the other hand, overdo it.
In order to get to that same setpoint of pleasure that others would get to easily, maybe with two drinks at the bar and a laugh with friends, you need six drinks at the bar to get the same thing.
GROSS: Is that why a lot of people describe drinking, smoking, taking drugs as self-medicating?
Prof. LINDEN: I don't know if that is entirely the reason, but it would be a reasonable explanation. In this case - I think when people use the term self-medicating, usually they are referring to something like dealing with stress in their lives.
Prof. LINDEN: Or dealing with depression. And this isn't precisely that. This is something that - this is mostly something that you're born with. That said, a big determinant of the development of addiction is stress. So we know that predisposition for addiction, whether it to be drugs or these behavioral addictions we've mentioned, is roughly speaking, about 40 percent genetic.
And the remainder is a number of life experience factors, but the most important of those life experience factors is stress. And when we talk about stress, you might imagine that we have moved into an airy-fairy realm of psychology, that this biology professor has now taken off his white coat and put on a paisley jacket. But that's not the case at all. Stress is a distinct biological phenomenon.
When you are stressed from having an argument with your sweetheart or with your boss, or you're fighting off an infection, stress hormones are secreted by your adrenal glands that sit on top of your kidneys, and they pass into your brain, and they bind stress hormone receptors on neurons in your pleasure circuit, and they set in motion a series of biochemical steps that end with you having...
GROSS: Ice cream. I'm sorry, go ahead.
(Soundbite of laughter)
Prof. LINDEN: Cravings for ice cream or gambling or cocaine or whatever your particular pleasure might be.
GROSS: So you're saying that stress does something biochemically that makes us crave pleasure more?
Prof. LINDEN: It does. And this is important not only in determining the onset of pleasure-seeking behavior, but in addicts who are trying to stay clean. Anyone who is an addict who is trying to stay clean, or who works with addicts or has one in their family knows that relapse doesn't tend to happen when everything's going great, right? Relapse happens when there's a stressful situation. And we now understand the biology of this.
And we don't need a biologist to tell us that stress is a trigger for relapse, but when we understand the biology of it, this underscores some strategies that we can do. And some of these strategies are simple behavioral things.
So if you're an addict trying to stay clean, you are very well-served by adopting behavioral strategies that reduce stress, whether that is playing with your dog or prayer or meditation or exercise. And what it means is that if you're a drug company trying to develop therapies to help addicts stay clean and reduce their chance of relapse, then one good way to do that is to try to biochemically interfere with the binding of stress hormones to their receptors on the neurons of the pleasure circuit in the brain.
GROSS: So knowing that addictive substances actually arouse the pleasure circuitry of the brain, what implications are there for that, do you think, in how we deal with addiction?
Prof. LINDEN: Well, I think the thing to realize is that there is a common story for all kinds of addictions. So let's imagine a little thought experiment. We have three autobiographies of addicts lying on the table before us, and one is the autobiography of a heroin addict, and one is a gambling addict, and one is a sex addict.
And then we hire research assistants to go through and, before we read these autobiographies, remove all the specific references to the particular addiction, to gambling or heroin or sex. And then we read all these stories. And what we find is that actually there is the same story arc in all of them, and it goes something like this.
Well, I did this particular thing, and it was pleasurable. So I did it some more, and it was really good. And so I started doing it all the time, and as I did it all the time, I found that I developed tolerance so that I needed higher doses or more frequent behavior in order to feel as good, as high, as much pleasure as I did before.
But then what happened, as I started to do it more and more, gradually my liking got transformed into wanting, and in the end, I wasn't doing this thing for pleasure at all. I was just doing it not to feel bad, just to be able to get up in the morning, to fall asleep at night, to have an appetite, to eat food, to face the day, to not have shakes and chills and tremors and anxiety attacks.
And so this transformation of liking to wanting that occurs in all forms of addiction has an underlying biology to it, and not surprisingly, that biology occurs within the pleasure circuit.
GROSS: What's going on?
Prof. LINDEN: Well, so what's going on is that during this process, there are physical changes of neurons within the pleasure circuit. We know that neurons receive chemical signals from their neighboring neurons at structures called synapses. And those synapses can either work with low efficiency or high efficiency.
And we know that the synapses that use the neurotransmitter glutamate, which is excitatory, start to work with much higher efficiency, and we believe that these are some of the changes that underlie the conversion from liking to wanting, that underlie the development of cravings and that make it so that when you're an addict, and even you have stayed clean for months and years, your brain is forever changed. You are never going to be like someone who was never an addict.
And if you should fall off the wagon and take a drink, for example, after three years of sobriety, that first drink is going to feel better to you than it does to anyone else, and that's not just a psychological phenomenon, that's because addiction has physically rewired your brain.
Dr. LINDEN: It physically rewires our brain and I think this is crucial in terms of the way we think about how our attitude towards addicts and our laws and our policies - our public policies about addiction - should be created.
When you understand the biology of the pleasure circuit and when you understand how the contribution of genetics, and stress, and life experience - actually even starting in the womb and going forward - all come together, the end result is that you have to realize that any one of us, any one of us, could be an addict at any time. Addiction is not fundamentally a moral failing. It's not a disease of weak-willed losers. When you look at the biology, the only model of addiction that makes sense is a disease-based model and the only attitude towards addicts that makes sense is one of compassion.
GROSS: So as a neuroscientist, should I presume that you're against imprisonment for drug addiction, for carrying drugs, as opposed to rehab?
Dr. LINDEN: Oh, absolutely. There should be - simple possession should never be dealt with predominately in the penal system. It is a medical phenomenon. Now I think some people might say oh, well, look, you know, you're just a bleeding heart liberal. You are making excuses for antisocial behavior of addicts. And that's not the case at all. I mean, let's look at another disease that also has a heritable component. If you have heart disease, you go into your doctor and you learn that you have heart disease. We don't say well, you have heart disease. You suck. You are morally unfit. You are weak. No. We say well, you have heart disease. But now that you know you have heart disease you have certain responsibilities. You should eat a healthy diet, and you should exercise, and you should see your cardiologist and you should take your meds. And if you don't do those things, it's not society's problem, it is your own darn fault.
And that should be our same attitude towards addicts. We should say okay, well, you're an addict. You have something wrong with your brain the way this other guy had something wrong with his heart. But it's not a free ride. Now that you know you're an addict, you better get in treatment. You should do stress reduction strategies. You should avoid the triggers for your addiction. You should be in a group that can offer you social support. And if you don't do those things, it's your own darn fault.
GROSS: So punish the addict when the addict commits a crime, but not for using or holding.
Dr. LINDEN: That's certainly my view and I would say it is the dominant view in the medical world.
GROSS: Mm-hmm. So, you know, we've talked about drugs. We've talked about nicotine and how they arouse the pleasure circuitry in the brain and what happens chemically when you're addicted to a substance. Let's talk about food. Obesity is such a problem in the United States now, and I think some people feel that they have become food addicts. Food is a necessity. You have to eat to live. You don't need to take heroin or nicotine to live, although some people might feel that they do. But I mean, you must eat to survive. So can you make a chemical argument for food addiction or is it just like food cravings and, you know, that some people maybe are more wired to enjoy food than others. Is it ever an addiction, per se? What can you tell us about that?
Dr. LINDEN: Yeah. So basically speaking, most - about 90 percent cases of severe obesity are food addiction. Now you might imagine well, no, actually it has a lot to do with metabolism. But it turns out that only about 10 percent of the cases of severe obesity have to do with a metabolic defect. And if you look carefully, most severe obesity comes about as a result of overeating. Now you could say well, everybody's got to eat. And so, you know, overeating is somehow fundamentally different than gambling, which is not necessary, or taking cocaine or alcohol, which are not necessary. But what we do know is this: First of all, body weight is about 80 percent heritable. And actually I should say body mass index - that is to say the amount of weight that you have for your height - is about 80 percent heritable. It is one of the very most heritable human traits that there is.
So what we now know is that the same genetic variants we spoke about earlier in drug addicts, that blunt the dopamine pleasure circuit, also give rise to overeating. It is, at its root, the same neurobiological problem.
GROSS: So you're saying overeating actually creates physiological changes in the brain?
Dr. LINDEN: I'm saying two different things. One of them is that there is generic variation in your reward circuit that will make it more likely that you will overeat. The second thing we now know is that if you eat certain classes of food, like very sweet things and very fatty things repeatedly, that this will rewire the pleasure circuit of your brain that, in a way, that down-regulates your pleasure circuit and will compel you to seek those things out more and more. So in that sense, fats and sugars are faintly addictive substances.
GROSS: Faintly addictive.
Dr. LINDEN: Well, they're not addictive in the same way that heroin and nicotine are. But in the sense that they do rewire your brain's pleasure circuitry, at least temporarily, yes.
GROSS: So do you think food marketing people are aware of this neuroscience about the pleasure of high-fat and very sweet and salty foods and are using that?
Dr. LINDEN: Well, I think they are aware of it. But in truth, you don't need to know the neuroscience in order to be an effective corporate food marketer. If you look at the average weight of an American between 1960 and now, it's gone up by an astonishing 26 pounds. And that's not because Americans' genomes have changed significantly in that time. It is entirely a result of 32-ounce sodas and fast food, and food corporations realizing that certain combinations of flavors and textures produce craving.
GROSS: Yeah. Let's talk about a couple of those things. You say the combination of something soft with something crunchy - like say chocolate chip ice cream or cookie crunch ice cream is going to be more appealing than just plain ice cream.
Dr. LINDEN: That's right. And we don't really understand the neuroscience behind this, but one thing is definitely true, we like certain types of contrasting flavors and textures. So ice cream with bits of fruit or nut or candy in it, tends to sell much better and to be much more craveable than an ice cream that just has a single flavor distributed uniformly throughout it.
GROSS: Now another thing that you mention in your book regarding food, you say people will eat more if they don't have to work too hard to chew and swallow. So much of the meat in chain restaurants has been mechanically tenderized and injected with marinade to dissolve in your mouth and it's lubricated for swallowing by high water content. You say, in essence, the factory has done half of your chewing and swallowing for you, so that you can eat more.
Dr. LINDEN: Well, that's right. That's one of the things that the restaurant chains have realized. The other thing they realized is that we tend to finish what's on our plate. So if you put twice as much food on the plate, we're very likely to eat it all up.
GROSS: So what does this lead you to think about how to stop eating a lot for a lot of fatty, sweet foods if you are overweight and if you feel it's having a bad effect on your health?
Dr. LINDEN: Well, I think one of the things to do is to try to take your pleasures broadly. Exercise. Meditate. Learn. Have moderate consumption of alcohol, moderate consumption of your food. Spread your pleasures around and that's the way to not become compulsive in any one realm.
GROSS: What do you think of the new FDA strategy that's going to begin next year - to have cigarette packs feature not only a written warning, but images of the damages cigarettes can cause? For example, perhaps they'll have to show one of nine different pictures. One of them is a picture of a cancerous mouth with brown teeth and big sore on the lower lip, with the caption: cigarette causes cancer.
Another is an image of a corpse with the caption: smoking can kill you. There's one that says smoking during pregnancy can harm your baby. And there's an image of a baby, of a newborn infant in the ICU.
I know you're dealing with the pleasure circuitry and the effects of nicotine on the pleasure circuitry. What about those kind of really negative reinforcement? Do you think that that's helpful?
Dr. LINDEN: It turns out that we already know, in large part, what's going to happen because this experiment has already been done in Europe. And in Europe what happened is that when these gory images were first introduced on cigarette packs, it spurred a lot of people to quit, and it probably dissuaded a lot of people from starting smoking, and that's great. But what happens over time is that we humans can get used to anything. Our entire human cognition and sensory systems are not about detecting what's always there, but about what changes. And so as a consequence, even these gory horrific images we tend to acclimate to them. And so their effectiveness, while not going to zero in Europe, diminishes greatly over time. There's shock value at the beginning and then we get used to them.
GROSS: Let's talk about sex. I think there's still a debate about whether there is such a thing as sex addiction or not. So what's your opinion? You're studying the neuroscience of addiction. Is there sex addiction?
Dr. LINDEN: Well, sex addiction is real. But sex addiction is rare. I think most people are understandably very suspicious of the whole notion of sex addiction. This is, they think oh, well, this is something that philandering celebrities and their publicists make up as some way of excusing their antisocial behavior. And the truth is that, just liking sex a lot, doesn't make you a sex addict. And just cheating or engaging with prostitutes or other antisocial behavior, doesn't make you a sex addict. If you are a sex addict, just like a heroin addict, you have undergone that transformation, from liking to wanting. And so you are at the point where you are having sex, not because you are deriving great pleasure from it, but because you need to do that just to fall asleep at night and wake up in the morning and face the day and not have withdrawal symptoms. And so sex addiction is real, but it's rare. And if you look at someone and they are still enjoying their sex, they're not a sex addict.
GROSS: Why do you think sexually inappropriate behavior seems to be an attribute of men with power - whether it's celebrity power, political power? And I don't want to overgeneralize here, but there has been, lately...
Dr. LINDEN: Mm-hmm.
GROSS: ...a kind of, you know, rash of these stories becoming public.
Dr. LINDEN: Right. I think the thing to keep in mind is that when you have genetic variation that gives you a blunted pleasure circuit, and this drives more pleasure seeking, novelty seeking and impulsive behavior, these are traits that are, to a certain degree, particularly in males, adaptive. These are some of the same traits that make people be innovators and leaders. And they also give rise to impulse control disorders, whether they are in the realm of drug addiction or sexual behavior or gambling. And these things are all comorbid.
So what I would say is that it's not an accident. People tend to say, well, if you're a man of power and you're in this situation and you're surrounded by people paying attention to you, telling you how great you are and eager to cover up for your mistakes, and that's all true. But I think another contributor is that you are likely to have gotten to your position in part because of this novelty-seeking, compulsive personality that also sows the seeds of these particular antisocial behaviors.
GROSS: Risk-taking is a part of that set of...
Dr. LINDEN: Risk-taking is a deep part of that. Risk-taking, novelty-seeking and compulsion all come together in a package, and they all correlate with low dopamine function within the pleasure circuit.
GROSS: Since you have studied pleasure and the pleasure circuitry of the brain, has that affected your own relationship with pleasure and the things that you seek or try not to get pleasure from?
Dr. LINDEN: Well, I try deeply to not let it do that. I certainly, when I'm enjoying a glass of wine, I don't want to be thinking about dopamine levels. And for the most part, fortunately, I've been able to avoid doing that. I'm blessed with not having a particularly addictive personality, although I'm a bit of a hedonist. So it hasn't actually made too much of an impact on my own life.
GROSS: What do you mean when you say you're a bit of a hedonist?
Dr. LINDEN: Well, I enjoy my pleasures. But I am taking my own prescription. I am seeking them widely. I am not compulsively indulging in one to excess. I am spreading them among the vices and virtues.
GROSS: David Linden, thank you so much for talking with us. I wish you pleasure in moderation.
Dr. LINDEN: Thank you. Thanks for having me on.
(Soundbite of laughter)
Dr. LINDEN: It was indeed a pleasure.
GROSS: David Linden is the author of the new book "The Compass of Pleasure." You can read an excerpt on our website: freshair.npr.org.
Coming up, rock critic Ken Tucker reviews Garland Jeffreys' first album of new music in over a decade.
This is FRESH AIR.