Abstract
Extinction is the primary mode for the treatment of anxiety disorders. However, extinction memories are prone to relapse. For example, fear is likely to return when a prolonged time period intervenes between extinction and a subsequent encounter with the fear-provoking stimulus (spontaneous recovery). Therefore there is considerable interest in the development of procedures that strengthen extinction and to prevent such recovery of fear. We contrasted two procedures in rats that have been reported to cause such deepened extinction. One where extinction begins before the initial consolidation of fear memory begins (immediate extinction) and another where extinction begins after a brief exposure to the consolidated fear stimulus. The latter is thought to open a period of memory vulnerability similar to that which occurs during initial consolidation (reconsolidation update). We also included a standard extinction treatment and a control procedure that reversed the brief exposure and extinction phases. Spontaneous recovery was only found with the standard extinction treatment. In a separate experiment we tested fear shortly after extinction (i.e., within 6 h). All extinction procedures, except reconsolidation update reduced fear at this short-term test. The findings suggest that strengthened extinction can result from alteration in both retrieval and consolidation processes.
Highlights
Fear extinction creates a new ‘‘safe’’ memory that co-exists with the original fear memory (Bouton, 1993)
All extinction groups showed significant fear during initial stages of extinction session when compared to No extinction (No Ext) group
Following auditory fear conditioning we evaluated the efficacy of several extinction protocols relative to a standard massed training extinction protocol consisting of 53 presentations of the CS spaced 5 s apart
Summary
Fear extinction creates a new ‘‘safe’’ memory that co-exists with the original fear memory (Bouton, 1993). Retrieval of the fear memory leads to an undesired return of fear. Return of fear contributes to relapse following exposure-based therapies (Bruce et al, 2005), establishing a need for methods capable of making extinction robust against fear recovery. Myers et al (2006) hypothesized that beginning extinction soon after fear acquisition might be such a procedure. Memories undergo time-dependent consolidation and they reasoned that if extinction occurred before consolidation of the fear memory, it would be erased and unrecoverable. Supporting this hypothesis, there was less fear recovery if extinction occurred 1 h, rather than 24 h after acquisition. Having acquisition and extinction close in time might result in both memories being encoded into the same episode
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