The Believing Brain - Michael Shermer [63]
Dopamine: The Belief Drug
Of all the chemical transmitter substances sloshing around in your brain, it appears that dopamine may be the most directly related to the neural correlates of belief. Dopamine, in fact, is critical in association learning and the reward system of the brain that Skinner discovered through his process of operant conditioning, whereby any behavior that is reinforced tends to be repeated. A reinforcement is, by definition, something that is rewarding to the organism; that is to say, it makes the brain direct the body to repeat the behavior in order to get another positive reward. Here is how it works.
In the divided brain stem—one of the most evolutionarily ancient parts of the brain shared by all vertebrates—there are pockets of roughly fifteen thousand to twenty-five thousand dopamine-producing neurons on each side that shoot out long axons connecting to other parts of the brain. These neurons stimulate the release of dopamine whenever it is determined that a received reward is more than expected, which causes the individual to repeat the behavior. The release of dopamine is a form of information, a message that tells the organism “Do that again.” Dopamine produces the sensation of pleasure that accompanies mastering a task or accomplishing a goal, which makes the organism want to repeat the behavior, whether it is pressing a bar, pecking a key, or pulling a slot machine lever. You get a hit (a reinforcement) and your brain gets a hit of dopamine. Behavior—Reinforcement—Behavior. Repeat sequence.
The dopamine system, however, has its pluses and minuses. On the positive side, dopamine has been linked to a peanut-sized bundle of neurons in the middle of the brain called the nucleus accumbens (NAcc), which is known to be associated with reward and pleasure. In fact, dopamine appears to fuel this so-called pleasure center of the brain that has been implicated in the “high” derived from both cocaine and orgasms. This “pleasure center” was discovered in 1954 by James Olds and Peter Milner of McGill University, when they accidentally implanted an electrode into the NAcc of a rat and discovered that the rodent became very energized. They then set up an apparatus so that whenever a rat pressed a bar it generated a small electrical stimulation to the area. The rats pressed the bar until they collapsed, even to the point of forgoing food and water.4 The effect has since been found in all mammals tested, including people who have undergone brain surgery and had their NAcc stimulated. The word they used to describe the effect was orgasm.5 Now that is the type specimen of a positive reinforcement!
Unfortunately, there’s a downside to the dopamine system, and that is addiction. Addictive drugs take over the role of reward signals that feed into the dopamine neurons. Gambling, pornography, and drugs such as cocaine cause the brain to flood itself with dopamine in response. So, too, do addictive ideas, most notably addictive bad ideas, such as those propagated by cults that lead to mass suicides (think Jonestown and Heaven’s Gate), or those propagated by religions that lead to suicide bombing (think 9/11 and 7/7).
An important caveat about dopamine: neuroscientists make a distinction between “liking” (pleasure) and “wanting” (motivation), and there is a lively debate about whether dopamine acts to stimulate pleasure or to motivate behavior. A positive reinforcement may lead to behavioral repetition because it feels good (liking, or the pure pleasure of getting the reward) or because it will feel bad if the behavior isn’t repeated (wanting, or motivation to avoid the anxiety of not getting the reward). The first reward is related to the pure pleasure of, say, an orgasm, whereas the second is related to the anxiety addicts feel when their next fix is in doubt. The research I cited above supports the pleasure thesis, but new research has scientists leaning toward the motivation position.6 The UCLA neuroscientist Russell