Your new book, “The Compass of Pleasure” argues that most experiences we find pleasurable — shopping, orgasm, learning, highly caloric foods — activate an anatomically-defined circuit in the brain. Why are we hardwired this way? Is there an evolutionary purpose to pleasure?
Basically, we have a pleasure circuit in our brain in order to reward with pleasure those behaviors like eating and sex that are crucial for getting our genes into the next generation. These pleasure circuits are evolutionarily ancient — rudimentary ones can even be found in worms.
What’s interesting, and central to our human experience, is that this pleasure circuit can be hijacked. One way is by taking certain psychoactive drugs: alcohol, nicotine, cocaine and heroin all activate the pleasure circuit artificially. We didn’t evolve to get a pleasure buzz from those substances. Rather, they “short-circuit” our pleasure centers that evolved for those other reasons. The second way is when these connections undergo associative learning as a result of experience. Now, mere ideas and ideologies can be pleasurable — and not just genetically hardwired things like sex and food. A mouse will get pleasure from food or sex, but only a human can get pleasure from fasting or abstaining from sex. This makes our human existence so much more varied and complex (think curling or reality television.)
Where does pleasure fall in the nature/nurture debate? (In other words, is pleasure purely genetic, or is it something we learn?)
Like almost every interesting human experience, both nature and nurture are important. For example, at least in the United States, about 50% of the variation in propensity for addiction (whether to drugs or behaviors like gambling) is accounted for by genes. The remainder is accounted for by experiences, starting in the womb and continuing throughout life. Stress is a huge factor.
While we are hardwired to like food, for example, and generally hardwired to like energy-dense foods (fatty and sweet things), particular food preferences are mostly determined by experience. In studies of identical twins raised apart, it was found that these twins had similar senses of humor but rather different food preferences.
Can you explain the pleasure/pain principle? (Why, for example, do some people derive sexual fulfillment from physical pain?)
It’s worthwhile to remember than the pleasure/pain connection is not just something that occurs in the sexual realm (as any devotee of chili peppers will affirm). As discussed earlier, when associative learning and the pleasure circuit combine, we can take pleasure from all kinds of things that are not evolutionarily hardwired — and some aspects of sexual fulfillment in the BDSM world clearly fall into that realm: They’re less about the pain than the power fantasy. What is becoming clear, however, is that the neural circuits for pain and pleasure do overlap to some degree. There’s a key part of the pleasure circuit called the ventral tegmental area that has neurons that use the neurotransmitter dopamine. In one portion of the ventral tegmental area, these neurons fire only to rewarding/pleasurable stimuli, but in another portion there are neurons that fire to both pleasurable and painful stimuli. The key point here is that both pleasure and pain mark experiences as important (or “salient” as we say in the lab) — and so it is likely that these neurons are salience indicators. They’re saying, in effect “this is important, pay attention and write this down as a memory.”
How do you imagine science will change our notions of pleasure a hundred years from now?
A great question that’s hard to answer. Scientists hate going out on a limb like this. That said, it is very likely that in 100 years there will be technologies that will allow for the fine-scale control of the activity of neurons in the brain without surgery. Then, all bets are off. If everyone stays home and stimulates their pleasure circuits all day in exquisitely variable and interesting ways instead of going to work there could be no end of trouble.
David Linden, Professor of Neuroscience at The Johns Hopkins University School of Medicine, is the author of The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good, just published by Viking. The author of over ninety papers and the award-winning book The Accidental Mind, he serves as the editor-in-chief of the Journal of Neurophysiology.