Immediate Extinction Attenuates Spontaneous Recovery and Reinstatement in a Passive Avoidance Paradigm.

Recent research suggests that extinction occurring shortly after fear conditioning attenuates spontaneous recovery and reinstatement of fear. Two experiments investigated whether immediate extinction would prevent spontaneous recovery and reinstatement of fear using a passive avoidance paradigm. In Experiment 1, naive female adult rats (N = 40) received extinction training either immediately or 24 hours (delayed) after fear conditioning. Both extinction groups showed a significant reduction in fear at a 1-day test. At a 15-day test, spontaneous recovery was observed in the delayed extinction group while the immediate extinction group continued to show significant extinction. In Experiment 2, using a naive group of adult female rats (N = 16), the extinction result was replicated in both the immediate and delayed extinction groups at the 1-day interval. Reinstatement of fear, elicited by foot-shock in a neutral environment, was observed for the delayed group but not for the immediate group. By utilizing the passive-avoidance paradigm, these experiments replicate and extend previous findings that immediate extinction attenuates spontaneous recovery and reinstatement of fear.

Mild hypothermia can disrupt extinction learning but not original conditioning.

Using a retrograde amnesia procedure, the susceptibility of the extinction of fear conditioning was assessed in two experiments. Extinction of a passive-avoidance task was impaired by a body-cooling treatment (e.g., hypothermia; [7]) which was too mild to induce amnesia for the avoidance training, suggesting that the memory for extinction is more susceptible to body cooling than the memory for the initial fear conditioning. Decreasing the severity of the treatment decreased its ability to disrupt extinction. Thus, the study demonstrates a difference in the vulnerability to amnesia of fear conditioning vs. extinction of that fear.