Extinction of conditioned defensive burying.

Rats were shocked once through a wire-wrapped dowel when they contacted it in a bedding-lined test chamber. Then the amount of conditioned defensive burying was measured for several days under extinction conditions; each of the rats was placed in the chamber for 15 min every 24 hr but no more shock was administered. The frequent bursts of burying directed at the dowel on the first test were almost totally absent by the fifth or sixth. Repeated exposure to the dowel conditioned stimulus was necessary for this extinction; neither the passage of time per se nor repeated exposure to the chamber in the absence of the dowel was sufficient to produce any significant decline in the tendency for the rats to push bedding at it. Making it impossible for the subjects to engage in burying behaviour during the extinction trials by removing the bedding from the test chamber did not affect the rate of extinction.