Differential Efficacy of Prior Cuing with CS, US, and Context in Enhancing Long-Term Retention of a Conditioned Emotional Response in Rats

Abstract

This study investigates the relative efficacy of the conditioned stimulus (CS), the unconditioned stimulus (US), and a discrete feature of the experimental context to act as retrieval cues on long-term retention of a CS–US association in a conditioned suppression paradigm. Rats pretrained to press a lever for food reward were then given a single session of five trials of classical conditioning in a different chamber. A tone acted as CS and was paired with a footshock as an US. Control rats were given explicitly unpaired tones and footshocks. Conditioning and retention were tested (1 and 50 days later) by presenting the CS alone (extinction procedure) while animals were engaged in the food-motivated lever-pressing task. Long-term retention was measured after an interval of 50 days in independent groups of rats exposed to one of three prior-cuing treatments: the CS, the US, and a specific element of the conditioning context (the pattern of the walls). Noncued rats served as conditioned controls. Conditioned suppression to the CS in noncued rats showed that five CS–US pairings produced reliable conditioning, tested at 1 day, with almost no forgetting after 50 days. Noncued rats demonstrated rapid extinction with repeated presentation of the CS alone. Prior cuing with information related to the CS or the US were ineffective in mediating resistance to extinction, whereas pretest exposure to the context enhanced retention performance, as indicated by the slowing down of the rate of extinction during testing. These results suggest the prevalence of context over the CS and US in promoting retrieval from long-term memory in classical conditioning, even when contextual information is limited to a single discrete feature of the conditioning experience and when no performance deterioration is observed after a long retention interval. They suggest the context may gain control over the CS–US association after a long-term retention interval.