A Russian physiologist named Ivan Pavlov discovered classical or respondent conditioning (somewhat accidentally). During 1849-1936, Pavlov was investigating the automatic reflexes of animals. It was during these experiments that he discovered an important learning principle that we now call classical conditioning. Sometimes people also call it Pavlovian conditioning.
Classical conditioning means that a specific stimulus causes a specific response. For instance, if you see food (a stimulus), you will salivate (a response). You didn't need a psychologist to tell you that! Salvation at the sight of food is an unconditioned response. This simply means it is an automatic reflex or response. You don't need to learn to salivate upon seeing food (no conditioning was required). It just happens automatically. Nothing too complicated yet, right?
Now we come to the learning part of classical conditioning (a bit more complicated). In one of Pavlov's experiments, he rang a bell every time he fed some dogs. We could say he paired a bell with the arrival of food. Unlike food, which is an unconditioned stimulus, the bell became a conditioned stimulus. This is because the dogs learned (they were conditioned) that when the bell rang, food would arrive. Pavlov formed a paired association between an unconditioned stimulus (dog food) and a conditioned stimulus (a bell). Eventually, Pavlov's dogs began to salivate at the mere sound of the bell, even when Pavlov did not present the food. The dogs had been conditioned that the bell meant food is on its way. They learned! This learning occurred because of the paired association between an unconditioned stimulus (food) and a conditioned stimulus (a bell). Eventually both the food and the bell elicited the same response, i.e., salivation.
So what do dogs and bells have to do with addiction? Recall that in Pavlov's experiment, the bell served as a cue to the dogs. Food was on its way! Likewise, certain cues (also called relapse triggers) have a powerful effect on addicted persons. These cues can result in a relapse because the brain linked the cues and the addiction. For instance, suppose someone always smokes marijuana in the car on the way home from work. The car and marijuana form a paired association. Thus, the car signals marijuana is on its way, just as the bell signaled to Pavlov's dogs that food was coming. Once the car has become a conditioned stimulus (a cue), the car itself can now trigger powerful cravings. Remember how Pavlov's dogs began to salivate at the sound of the bell? We could say the bell created a craving for food. This is the same for the addict and the car. The car creates powerful cravings. Cravings frequently result in relapse.
Fortunately, this learning principle has some helpful recovery implications. Research has demonstrated that if we ring the bell many times, without food, the paired association ends. Eventually the bell will no longer elicit salivation. Let's return to our previous example of a person who smokes marijuana in a car after work. If this person repeatedly gets into his car after work, and does not smoke marijuana, his cravings will eventually subside. He is not doomed to ride public transportation for the rest of his life!
Cue exposure therapy is one type of addiction treatment that relies on classical conditioning. The "cues" associated with addiction (the sights, smells, locations, people, etc.) are understood as conditional stimuli. With repeated cue exposure, and without engaging in addictive behavior, these cues lose the power to induce craving. Because most people in recovery cannot realistically eliminate every cue associated with their addiction, it becomes critical to reduce the power of these cues. This may occur through specific types of therapy, such as cue exposure therapy. It might also occur simply through practice and the passage of time. People who do not experience a reduction in the power of cues are at significant risk for relapse.
Therapists also use classical conditioning to diminish and/or eliminate many types of unwanted behaviors. This includes addictive behaviors. Aversion therapy is one application of classical conditioning. In aversion therapy, we intentionally form a paired association between an unwanted behavior and an unpleasant experience. For instance, we can administer a drug that causes someone to become horribly nauseous and vomit if s/he ingests even the slightest bit of alcohol. This intentionally forms a paired association between alcohol and vomiting. Prior to the aversion therapy, a person would ordinarily associate alcohol with positive feelings. After aversion therapy, alcohol is associated with nausea and vomiting. For many aversion therapy patients even the thought of drinking elicits feelings of nausea. The effect of aversion therapy can wear off over several months. However, during the period it is effective a person can learn to develop a new manner of healthy living. They can practice coping skills that strengthen their ability to enjoy life without alcohol. To clarify, although drinking is a voluntary behavior, cravings and desire for alcohol are not. Treatment from a classical conditioning approach (aversion therapy) diminishes craving and desire for alcohol by diminishing its appeal.