Extinction learning, which consists of the inhibition of retrieval, can be learned without retrieval

Abstract

In the present study we test the hypothesis that extinction is not a consequence of retrieval in unreinforced conditioned stimulus (CS) presentation but the mere perception of the CS in the absence of a conditioned response. Animals with cannulae implanted in the CA1 region of hippocampus were subjected to extinction of contextual fear conditioning. Muscimol infused intra-CA1 before an extinction training session of contextual fear conditioning (CFC) blocks retrieval but not consolidation of extinction measured 24 h later. Additionally, this inhibition of retrieval does not affect early persistence of extinction when tested 7 d later or its spontaneous recovery after 2 wk. Furthermore, both anisomycin, an inhibitor of ribosomal protein synthesis, and rapamycin, an inhibitor of extraribosomal protein synthesis, given into the CA1, impair extinction of CFC regardless of whether its retrieval was blocked by muscimol. Therefore, retrieval performance in the first unreinforced session is not necessary for the installation, maintenance, or spontaneous recovery of extinction of CFC.contextual fear conditioning | fear extinction | hippocampus | retrieval | unreinforced conditioned stimulus

Facilitation of fear extinction by novelty depends on dopamine acting on D1-subtype dopamine receptors in hippocampus

“…4B). The interval between the novelty and extinction was established in pilot experiments and was found to be shorter than that described as optimum by de Carvalho Myskiw et al (15)(16)(17) in another task, the CFC. In an alimentary spatial task, Morris and coworkers found an enhancement by exposure to novelty 30 min before the task (35).…”

“…Many memories rely on hippocampal LTP and LTD (1,2,(6)(7)(8)(9)(10)(11), and the "synaptic tagging-and-capture" process has been applied to the explanation of interactions between concurrent memories (11)(12)(13), among which are novelty and fear acquisition (12,14) and novelty and fear extinction (15,16). Exposure to novelty [an open field (OF) in which they had never been before] involves two consecutive processes: its detection, which is very brief (seconds), and the immediately ensuing habituation (17), which lasts much longer; both rely on hippocampal LTD (18). With a relatively restricted time window before and/or after an extinction trial, novelty can enhance the extinction of contextual fear conditioning (CFC) lastingly (15,16).…”

“…To test the generality of the novelty effect [attributable to hippocampal LTD (15)(16)(17)(18) during the time of exposure to the OF],…”

Can an aversive, extinction-resistant memory trigger impairments in walking adaptability? An experimental study using adult rats

“…In the first part of the experiment, to assess extinction-resistance of the aversive memory [5,13,17], we randomly assigned rats into two groups: shock (N=7) and sham (N=9). Twenty-four (S1) and 48 hours (S2) after the exposure to IF, the rats were placed back in the same apparatus for ten minutes of extinction training (no footshocks were given).…”

“…The chamber was cleaned with 70% ethanol before and after each use. This protocol was adapted from previous studies [5,13,17] .…”