Recovery of the US representation over time during extinction

Four experiments used a conditioned suppression procedure in rats to explore changes in the US representation over time during the course of extinction. They employed two previously reported effects: reinstatement of responding to an extinguished CS by separate US presentation, and the erasure of that effect by interposed nonreinforcement of a second excitatory CS. These effects have been interpreted as enhancing and depressing the US representation, respectively. Experiment 1 found the erasing effect to decrease but still to remain substantial after over a 4-day period, suggesting a partial recovery with time of a deliberately depressed US representation. Experiment 2 implicated this change as a contributor to the phenomenon of spontaneous recovery by showing that recovery to be sensitive to erasure effects. Experiments 3 and 4 found evidence for an interaction between the state of the US representation and the amount of associative change which results from nonreinforcement of an excitatory CS. When the US representation was strong, either because of reinstatement or the passage of time, nonreinforcement of a CS was especially effective in producing associative change. When the US representation had been depressed by erasure, those nonreinforcements produced relatively less associative loss. Moreover, these effects upon associations were reasonably stable in the sense that they left asymptotic differences in the strength of associations after extinction. Together with previous findings, these results point to an important role for the US representation in the performance and learning which occurs during extinction.