Reconsolidation-Extinction Boundaries in Fear Memory Updating
Marie-H. Monfils, University of Texas at Austin
Associative emotional memories can be formed when an initially neutral stimulus (conditioned stimulus, CS; e.g., a tone) acquires the ability to elicit fear responses after being paired with an unconditioned stimulus (US; e.g., a shock). Two paradigms (blockade of reconsolidation and extinction) have traditionally been used in the to reduce acquired fear (Nader et al., 2000; Wolpe, 1969); however, the clinical efficacy of these techniques has been limited: reconsolidation blockade requires potentially toxic drugs, and extinction is not typically permanent. Fear extinction is generally not enduring, because it generally leads to the weakening of an emotional response not by direct modification of the existing memory, but by formation of a new memory that suppresses activation of the initial trace (Pavlov, 1927). The end results, thus, is that two different memories reside in parallel in the brain, and compete for expression. We recently devised an effective, drug-free paradigm, which capitalizes on the mechanistic differences between reconsolidation and extinction and allows to persistently reduce learned fear (Monfils et al., 2009). Our results show that by simply manipulating the timing of stimulus presentations in extinction learning we can cause memories of the old predictive relationships to be effectively ‘erased’, and/or re-interpreted as safe (Monfils et al., 2009). Boundary conditions defining the limits of our retrieval+extinction paradigm to update memories, as opposed to creating new learning, and the neural mechanisms that set it apart from standard extinction, remain to be examined.