The Disordered Mind: What Unusual Brains Tell Us About Ourselves

by Eric R. Kandel

The expectation of reward helps us form habits. A good habit, one that is adaptive, helps us survive by enabling us to perform many important behaviors automatically, without thinking about them. Adaptive habits are promoted by the release of dopamine into the prefrontal cortex and the striatum, the areas of the brain involved with control and with reward and motivation. The release of dopamine not only creates a feeling of pleasure, it also conditions us. Conditioning, as we know, creates a long-term memory that enables us to recognize a stimulus the next time we see it and to respond accordingly. If the stimulus is positive, as in the case of adaptive habits, conditioning motivates us to pursue it. For example, if you eat a banana and find it delicious, the next time you see a banana you will feel motivated to eat it. Addictive drugs, whether legal or illegal—our body doesn’t make a distinction—also stimulate dopamine-producing neurons in the brain’s reward system. In this case, however, the result is greatly increased dopamine concentrations in the prefrontal cortex and the striatum. The excess dopamine generates intense pleasure and creates a conditioned response to the environmental cues that predict pleasure. Such cues—say, the smell of cigarette smoke or the sight of a needle—elicit an intense craving for the drug, which, in turn, elicits drug-seeking behavior.