The role of contextual and discrete conditional stimuli in the retrieval of fear memory
The present work aimed at investigating the extent to which the discrete conditional stimuli used during the acquisition and the contextual elements of the experimental procedure contribute to recalling the fear memory.Twenty-four Hannover Wistar rats were divided into 3 groups according to their conditioning parameters. During the 5 daily acquisition sessions, five mild electric shocks were presented paired with sound and light stimuli, and during the retention sessions, memory retrieval was examined in familiar and new contexts, with or without the associated discrete stimuli. Five of these sessions were conducted next week to the acquisition period and 2 additional sessions were performed after additional 3 weeks. Analysing the intrasession occurrence of freezing response revealed that in the acquisition sessions the freezing time increased in the pre-shock period and decreased immediately thereafter, while in the retention sessions, the freezing reaction showed a bell-shaped curve as a function of repetition of the stimuli. In the retrieval period, the discrete stimuli evoked fear memory in other contexts too, though to a lesser extent than in the original environment. Familiar context without conditional stimuli did not cause a significant increase in freezing, however, after 3 weeks of intermission, the familiar context elicited partial but significant freezing, both with and without conditional stimuli. Conclusions: (1) freezing is an anticipatory response, (2) in the short term, animals anticipate the negative experience based on the conditional stimuli rather than the environment, but in the long-term, the context of the aversive experience is also tagged.