As part of the Neuroscience Seminar Series, Mark Bouton, Lawson Professor of Psychology at the University of Vermont, visited St. Mary’s on Nov. 11 to present his lecture, “Context, extinction, and memory: Implications for a biobehavioral understanding of relapse.”
“Forever in my lab at the University of Vermont, we’ve been interested in conditioning on one hand and extinction on the other,” began Bouton. Conditioning and extinction are two of the phases of learning. Classical conditioning, also known as Pavlovian reinforcement, is the process by which a neutral stimulus is paired with a significant stimulus through multiple exposures. For example, if a dog hears a tone every time it is presented with food, it will learn to expect food (its mouth will water) at the sound of the tone.
Extinction, on the other hand, is the process by which a conditioned response is unlearned. The same tone will be presented to the dog over and over again without the food until the dog eventually stops expecting food. Its mouth will stop watering at the sound of the tone.
Bouton discussed the false assumption that extinction rids the learning that took place in the conditioning stage. “Extinction does not involve erasing anything,” said Bouton. “The animal will have two available memories.” This is similar to encountering a word that has an ambiguous meaning; the only way to interpret it correctly is to understand its context. In his experiments, Bouton has discovered that in conditioning and extinction, context is extremely important. This is what makes relapse, reversing extinction and returning to the conditioned response, possible.
In his over 30 years of research, Bouton has done many experiments involving rats and drugs or food. In one context, a rat will be conditioned to press a lever to receive a food pellet. Then, in a second context, the rat will be put through the process of extinction in which the lever no longer produces food for a certain length of time. Then, the rat is placed back into the original context. It is thus observed if the rat will try to press the lever for food again, or if that response has been extinct.
It turns out that learning is context dependent. Bouton changed the visual cues or odors presented in tandem with the lever to alter the context of the rat’s learning. Even though the rat stopped trying to press the lever for food after extinction, when placed back in the original context of learning, the rat again began pressing the lever for food. This is called relapse, also known as the “ABA renewal effect.” Context A is the original context, while B is the new context for extinction.
“Context can be provided not only by rooms and Skinner boxes … but [also] by drug states,” said Bouton. In a different set of experiments, Bouton altered the context of the extinction phase by injecting the rats with drugs like chlordiazepoxide (marketed as Librium) and diazepam (marketed as Valium). In an AAA sequence, the control group with no change in context, extinction was successful. In an ABA sequence, with the extinction phase occurring with a drug injection, a relapse occurred.
This research is very relevant to drug users, like cigarette smokers and heroine addicts. “A person who takes drugs is possibly going to take drugs in one context a lot, but possibly two, three, four, possibly a dozen contexts,” said Bouton. This multitude of contexts associated with conditioning makes it very difficult for a person to go through the process of extinction. Since learning is context dependent, they would have to experience extinction in every context in which they experienced conditioning.
Bouton further studied possible drugs that may improve extinction learning. One of these drugs is called d-cycloserine, which is a drug involved in brain plasticity (the ability of the brain to adapt to change based on experience). He found that though d-cycloserine speeds up learning, it does not change anything else. Another drug, yohimbine, was tested and was found to only increase arousal.
Senior Steven Morris enjoyed the lecture and said, “Dr. Bouton’s lecture was intellectually stimulating and delivered with the grace of a seasoned researcher.”
“I really enjoyed it,” said senior Shelby Jones. “It was nice to hear [Bouton] explain what I learned from his paper in my seminar class, along with the other work he’s done in his lab.”
The next lecture in the Psychology Lecture Series has been canceled. Rebecca Ryan, Assistant Professor of Psychology at Georgetown University, will hopefully return to present her lecture, “Nonmarital Childbirth and Child Development: The Relevance of Marriage Propensity and Family Change,” in the spring.