Extinction is typically studied within the Pavlovian fear conditioning framework in which extinction refers to the reduction in a conditioned response (CR; e.g., fear response/freezing) when a conditioned stimulus (CS; e.g., neutral stimulus/light or tone) is repeatedly presented in the absence of the unconditioned stimulus (US; e.g., foot shock/loud noise) with which it has been previously paired.
The simplest explanation of extinction is that as the CS is presented without the aversive US, the animal gradually "unlearns" the CS–US association which is known as the associative loss theory. However, this explanation is complicated by observations where there is some fear restoration, such as reinstatement (restoration of CR in the context where extinction training occurred but not a different context after aversive US is presented again), renewal (restoration of CR in context A but not in B when learning occurred in context A and extinction in context B), and spontaneous recovery (restoration of CR when the retention test occurs after a long but not a short delay after extinction training) and alternative explanations have been offered.
Research on fear extinct indeeded in animal models (typically rats) has clinical implications such as exposure-based therapies for the treatment of phobias and anxiety conditions.
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