Backward excitatory conditioning can determine the role of the CS− in aversion learning

Abstract

The results of Experiment 1 indicated that 16-day-old rats acquired an aversion to a black chamber (CS+) paired with footshock, only if also given exposure to a white chamber (CS−) not paired with footshock. The focus of the present experiments was an effect of the order in which the CS+ and CS− were presented: preconditioning exposure to CS−( CS− CS+ ) enhanced the aversion expressed to CS+, whereas exposure to CS− following CS+( CS+ CS− ) did not facilitate conditioning. In Experiment 2 the CS+ CS− procedure resulted in a reduced preference for CS+, relative to CS−, if a delay was imposed between exposure to CS+ and CS−, suggesting that an aversion was acquired to CS− due to its contiguity with the aversive US. Experiment 3 independently assessed conditioning to CS+ and CS− elements and confirmed that the CS− does become aversive when it is presented following the CS+. Collectively, the results suggest that the CS+ CS− procedure resulted in backward excitatory conditioning of CS−, which interfered with expression of the aversion to CS+. These data are consistent with recent views of Pavlovian conditioning which emphasize contiguity between the CS and US as sufficient in supporting an association between the two events.