Effects of prediction error on post-retrieval extinction of fear to compound stimuli

Reconsolidation and Fear Extinction: An Update

Fear memories can be updated behaviorally by delivering extinction trials during the reconsolidation window, which results in a persistent attenuation of fear memories (Monfils et al., Science 324:951-955, 2009). This safe and non-invasive paradigm, termed retrieval-extinction (or post-retrieval extinction), has also been found to be successful at preventing the return of fear in healthy fear conditioned humans (Schiller et al., Nature 463:49-53, 2010), and in the time since its discovery, there has been an explosion of research on the use of retrieval-extinction in fear memories in humans and other animals, some of which have found a long-term reduction in conditioned responding, and some who have not. These discrepant findings have raised concerns as to whether retrieval-extinction really results in updating of the original fear memory, or if it simply enhances extinction. We will first review the progress made on elucidating the cellular mechanisms underlying the fear attenuating effects of retrieval-extinction and how they differ from traditional extinction. Special attention will be paid to the molecular events necessary for retrieval-extinction to successfully occur and how these reconsolidated memories are represented in the brain. Next, we will examine the parameters that determine whether or not a memory will be updated via extinction during the reconsolidation window (also known as boundary conditions). These boundary conditions will also be discussed as possible explanations for discrepant findings of the retrieval-extinction effect. Then we will examine the factors that can determine whether an individual's fears will successfully be attenuated by retrieval-extinction. These individual differences include genetics, age, and psychopathology. Finally, we will discuss recent attempts to bring the retrieval-extinction paradigm from the bench to the bedside for the behavioral treatment of anxiety and trauma disorders.

Retrieval-extinction as a reconsolidation-based treatment for emotional disorders:Evidence from an extinction retention test shortly after intervention

The retrieval-extinction paradigm, a non-invasive memory intervention that is methodologically similar to exposure therapy, has significant clinical application prospects for targeting memory reconsolidation. However, it is difficult to distinguish whether the effect of preventing the return of fear by retrieval-extinction depends upon the reconsolidation-based mechanism or extinction-based mechanism. This study tested extinction retention shortly after intervention to determine whether retrieval-extinction is a reconsolidation-based approach or extinction-based approach as well as exploring the effect of sleep. In our experiment, the effects on fear conditional memory of standard extinction, retrieval-extinction, and extinction-retrieval were compared using the fear test at 3 h, 12 h without a night's sleep, and 12 h with a night's sleep after the intervention. The results showed that standard extinction and extinction-retrieval procedures reduce fear 3 h after intervention, while retrieval-extinction procedure reduces fear 12 h with a night's sleep after the intervention. The results suggest that standard extinction and extinction-retrieval create an extinction memory trace that competes with original memory trace, only retrieval-extinction update the original memory trace through memory reconsolidation. These findings provide solid evidence for the reconsolidation mechanism of the retrieval-extinction paradigm and highlight the effect of sleep on memory reconsolidation.

Destabilizing Different Strengths of Fear Memories Requires Different Degrees of Prediction Error During Retrieval

Reactivation of consolidated memories can induce a labile period, in which these reactivated memories might be susceptible to change and need reconsolidation. Prediction error (PE) has been recognized as a necessary boundary condition for memory destabilization. Moreover, memory strength is also widely accepted as an essential boundary condition to destabilize fear memory. This study investigated whether different strengths of conditioned fear memories require different degrees of PE during memory reactivation in order for the memories to become destabilized. Here, we assessed the fear-potentiated startle and skin conductance response, using the post-retrieval extinction procedure. A violation of expectancy (PE) was induced during retrieval to reactivate enhanced (unpredictable-shock) or ordinary (predictable-shock) fear memories that were established the day before. Results showed that a PE retrieval before extinction can prevent the return of predictable-shock fear memory but cannot prevent the return of unpredictable-shock fear memory, indicating that a single PE is insufficient to destabilize enhanced fear memory. Therefore, we further investigated whether increasing the degree of PE could destabilize enhanced fear memory using different retrieval strategies (multiple PE retrieval and unreinforced CS retrieval). We found that spontaneous recovery of enhanced fear memory was prevented in both retrieval strategies, but reinstatement was only prevented in the multiple PE retrieval group, suggesting that a larger amount of PE is needed to destabilize enhanced fear memory. The findings suggest that behavioral updating during destabilization requires PE, and the degree of PE needed to induce memory destabilization during memory retrieval depends on the strength of fear memory. The study indicates that memory reconsolidation inference can be used to destabilize stronger memories, and the findings shed lights on the treatment of posttraumatic stress disorders and anxiety disorders.

Role of prediction error in destabilizing fear memories in retrieval extinction and its neural mechanisms

Memory reconsolidation interference has been shown to be an effective way to neutralize conditioned fear memory and prevent relapse. The critical factor to utilize this paradigm is inducing a labile state of the long-term memory. Novel information is viewed as a driving factor to update memory; however, it is unknown whether different forms of novelty play the same role. In addition, although pharmacological intervention studies have confirmed that prediction error (PE) during reactivation is a necessary condition in memory destabilization, the role of PE in retrieval extinction has remained under debate; furthermore, the neural mechanisms underlying the process are largely unknown. In this study, we isolated two forms of novelty: PE and stimulus novelty without PE during reactivation to compare their role in memory lability. Skin conductance responses (SCR) and functional magnetic resonance imaging (fMRI) were used to clarify their role at the behavioural and neural mechanism levels. A total of 54 healthy adults were tested in a three-day retrieval extinction protocol. The results showed that PE, the novelty of CS-US combinations, was a critical condition to destabilize memory. The novelty of the stimulus itself with the absence of PE was insufficient for retrieving the memory. The neural mechanisms that distinguished standard extinction from retrieval extinction were that the latter was associated with a diminished recruitment of the inferior temporal cortex (IT) and dorsolateral prefrontal cortex (dlPFC) and decreased functional connectivity of the dlPFC-anterior cingulate cortex (ACC) and IT-dlPFC. Possible interpretations were discussed.