Reconsolidation: the samsara of memory consolidation

Abstract

Memory formation is a complex and very dynamic process. After a learning event, the acquired information undergoes a number of changes that eventually result in memory storage. Stored memories are very malleable. Recent rediscoveries show that after reactivation, for example by retrieval, an established memory can become transiently sensitive to disruption and needs to undergo a process of restabilization, known as reconsolidation, to be maintained. The findings that stabilized memories can become labile have challenged the classical view of how memories are consolidated over time and stored. On the other hand, the reconsolidation process is not fully understood, and theories about the nature and function of memory reconsolidation remain controversial. In this paper, I will present my view on some of the controversial issues of memory reconsolidation and propose a hypothetical model for how this process contributes to memory stabilization. The debated issues that will be discussed are: (1) The term reconsolidation; (2) Temporal constraints of memory reconsolidation; (3) Classical theory of memory consolidation versus theory of memory reconsolidation; (4) Procedural constraints: what is it that needs to be reactivated to produce memory fragility? (5) Functions of memory reconsolidation; (6) Disrupting reconsolidation: an impairment of memory stabilization or retrieval?

Pharmacological effects and behavioral interventions on memory consolidation and reconsolidation

“…Temporal constraints on the fragility of memories to post-reactivation interventions, in particular those that lead to amnesia of the original memory (18,53,54) have led some investigators to propose that reconsolidation may be explained as a prolonged phase of consolidation (1,22). Our results may be in accordance with this last interpretation, but further research is necessary in order to elucidate subtle behavioral differences between memory consolidation and reconsolidation.…”

“…In most studies with diverse animal species, memory reconsolidation is demonstrated by pharmacological manipulations of reactivated memories (16,22,44), including those described here. The interferences of reactivated memories through more "physiological" approaches were also described by Walker et al (45), Hupbach et al (46), and more recently by Forcato et al (47).…”

“…Under appropriate experimental conditions, extinguished memories can develop spontaneous recovery, reinstatement, saving and/or renewal (20). In addition, one of the most important findings that should be taken into account when interpreting a "reconsolidation result" is the relationship between the age of the reactivated memory and the susceptibility to be modified (21,22). The precise conditions under which reconsolidation can be manipulated have been conceptualized as "boundary conditions of reconsolidation", and were recently reviewed by Alberini (22) and Tronson and Taylor (16).…”

The role of protein synthesis during the labile phases of memory: Revisiting the skepticism

“…In general, the same principles apply to both consolidation and reconsolidation studies. However, as memory reconsolidation is less well understood, additional questions need to be addressed in relation to the type of proteins involved, the temporal duration and the rate of protein synthesis required (Alberini, 2005;Alberini, 2007;Dudai, 2004;Gold, 2006;Lattal & Abel 2004;Miller & Sweatt 2006;Rudy et al, 2006). Importantly, the effect of protein synthesis inhibition after memory reactivation is likely to be more complex, and, in fact, it needs to take into account other aspects that involve additional phases of protein synthesis, such as the fact that consolidation has in part already occurred and the possible additional implicit nature of reactivation experiences (Anokhin et al, 2002;Alberini, 2007).…”

Temporal requirement of C/EBPβ in the amygdala following reactivation but not acquisition of inhibitory avoidance

“…These studies showed that there is a gradient of protein synthesis dependence after memory reactivation, which is a function of the strength and number of reactivations and can vary with the nature of the reactivation trial (Suzuki et al 2004;Frankland et al 2006). Thus, changes in the protocol of reactivation and/or training seem to reveal differences in the duration of the gradient of protein synthesis required for reconsolidation (Alberini 2007). Moreover, it should be kept in mind that, as seen for memory consolidation (Dudai 2004), the systems and cellular processes underlying reconsolidation are likely to differ among different learning paradigms.…”