Learning

Animal studies of these processes have yielded important information about how tolerance develops. A rat that receives morphine injections in one specific environment will develop a strong morphine tolerance in that place but show far less tolerance when injected in a different environment. In fact, a drug concentration that animals have learned to tolerate in the conditioned environment will kill them (from "overdose") if injected in a novel environment. Parallel studies of human heroin addicts who have accidentally overdosed themselves have revealed that most had taken their usual drug dose, but in an unfamiliar setting.

Conditioned drug response to cues of the customary drug-taking situation explains many observations. Addicts who have been detoxified in a hospital nonetheless retain their drug-related conditioning to the cues of home and neighborhood where they learned about and took drugs with acquaintances. Reentering those places typically triggers withdrawal symptoms, such as restlessness, chills, and intense craving. Those adverse reactions, in turn, motivate relapse to drug taking. Similarly, addicts may have earlier associated drug taking with a way to deal with feelings of anxiety, depression, and helplessness. When those feelings recur after detoxification, they could act as conditioned cues to trigger a return of the person's earlier drug craving. Conditioning also helps explain a startling phenomenon: American soldiers used heroin with extraordinary frequency while in Vietnam but had an exceptionally low rate of addiction (7 percent by one estimate) once they were discharged in the United States and thus removed from the situational cues associated with their drug cravings.

Since drug addiction can be conditioned, behavioral techniques can be used to decondition it. Behavioral scientists have successfully used gradual desensitization procedures with detoxified addicts. Addicts are reexposed to the rituals and the handling of drug paraphernalia (e.g., "cooking" equipment, pipes) and observe videotapes of other addicts cooking up cocaine and talking in drug vernacular. However, since no drug is actually given, the addicts' conditioned craving gradually diminishes with repeated exposures to these cues. The addicts can then return to their homes, neighborhoods, and acquaintances armed with specific ways to cope with the recurring temptations, which have now lost their power to trigger relapses to the drug-taking habit.

Instrumental Learning

Animal experiments on "instrumental conditioning," another form of learning, also have important implications for human behavior. In instrumental conditioning, the organism learns that certain environmental events, such as receiving rewards or punishments, depend on their own behavior (such as pressing a lever). Just as classical conditioning underlies many of our involuntary emotional responses to objects and events, instrumental conditioning underlies most voluntary behaviors performed for incentives. Through instrumental conditioning, organisms learn to control events; they learn instrumental responses that obtain rewards and avoid punishments.