Yale neuroscientist finds key piece to Pavlov puzzle

Yale psychology professor and neuroscientist Jeansok J. Kim has discovered the brain structure responsible for the "blocking phenomenon" observed in Ivan Pavlov's famous animal experiments and published his results in the Fri., Jan. 23, issue of the journal Science.

MICHAEL ELLIS/YH Psychology Professor Jeansok J. Kim

In a now classic experiment, Pavlov conditioned a dog to salivate at the sound of a bell, even when no food was present. In 1968, Yale psychologist Allan J. Wagner and several colleagues discovered that after a dog, or any animal, has learned a conditional reflex, a blocking phenomenom prevents the animal from being conditioned to a new stimulus.

Kim and his colleagues' research lends credence to the idea that a brain structure called the inferior olive is responsible for this blocking phenomenon. "Our study was the first to show the condition of the blocking paradigm," Kim explained.

Wagner, who is still at Yale, was impressed with Kim's results. Reflecting on his own experiments 30 years ago and on more recent research conducted on blocking, he said, "Kim's article really confirms some speculation about the basis for this blocking phenomenon."

Their results have also strengthened a neuroscience theory which states that the GABA chemical blocks new learning associations between the cerebellum and the inferior olive once previous learning has taken place.

Kim began researching the blocking mechanism in 1992 at the University of Southern California with his colleague Richard F. Thompson, and post-doctoral fellow David J. Krupa. In their experiments, they trained rabbits to associate a tone with a puff of air. The rabbits learned to blink whenever they heard the tone. The researchers then trained the rabbits to connect flashes of light with both the tone and the puff of air. The group of rabbits that lacked the GABA connection showed no blocking, meaning they could have conditioned reflexes to both stimuli simultaneously. According to Kim, "The blocking phenomenon is one way that animals discriminate relevant stimuli from irrelevant stimuli."

Kim believes that their work has larger implications for the scientific community. This latest finding, he said, will help researchers better understand schizophrenia, autism, and other conditions in which patients "cannot filter out irrelevant stimuli."

Former psychology department chair Thomas Carew praised Kim as a "terrific young researcher and a very mature scientist." When Carew hired Kim, the former was struck by Kim's "unique talent." Carew noted, "[Kim] can relate psychological learning theory, things that we know, to actual brain structures and mechanisms."

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