Pavlovian fear conditioning is a paradigm in which an initially neutral stimulus such as a tone (conditioned stimulus, CS) acquires aversive properties and comes to elicit fear responses through its pairing with an aversive unconditioned stimulus (US), such as an electrical foot shock. In a typical reconsolidation experiment, a single CS is presented the day after training in the presence of a pharmacological agent aimed at disrupting the cellular machinery involved in reconsolidation processes. Post-reactivation short-term memory (PR-STM) is then tested shortly after the retrieval (within 1-4 hours) and post-reactivation long-term memory (PR-LTM) is tested 24 hours later. Intact performance at PR-STM but impaired at PR-LTM indicates disruption of time-dependent reconsolidation processes. Here we developed a new protocol in which two conditioned stimuli (CS) were used, one to be reactivated (CSr), the other not (CSn).