17.3: Is Extinction Unlearing Or Inhibitory Learning?

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Pavlov was an excellent example of someone who today would be considered a behavioral neuroscientist. In fact, the full title of his classic book (1927) is Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex. Behavioral neuroscientists study behavior in order to infer underlying brain mechanisms. Thus, Pavlov did not perceive himself as converting from a physiologist into a psychologist when he abandoned his study of digestion to explore the intricacies of classical conditioning. As implied by his “psychic secretion” metaphor, he believed he was continuing to study physiology, turning his attention from studying the digestive system to studying the brain.

One question of interest to Pavlov was the nature of the extinction process. Pavlov assumed that acquisition produced a connection between a sensory neuron representing the conditioned stimulus and a motor neuron eliciting salivation. The reduction in responding resulting from the extinction procedure could result from either breaking this bond (i.e., unlearning) or counteracting it with a competing response. The fact that spontaneous recovery occurs indicates that the bond is not broken during the extinction process. Extinction must involve learning an inhibitory response counteracting the conditioned response. The individual appears to learn that one stimulus no longer predicts another. The conclusion that extinction does not permanently eliminate a previously learned association has important practical and clinical implications. It means that someone who has received treatment for a problem and improved is not the same as a person never requiring treatment in the first place (compare with Bouton, 2000; Bouton & Nelson, 1998). For example, even if someone has quit smoking, there is a greater likelihood of that person’s relapsing than a non-smoker’s acquiring the habit.