Reconsolidation: maintaining memory relevance

Abstract

The retrieval of a memory places it into a plastic state, the result of which is that the memory can be disrupted or even enhanced by experimental treatment. This phenomenon has been conceptualised within a framework of memories being reactivated and then reconsolidated in repeated rounds of cellular processing. The reconsolidation phase has been seized upon as crucial for the understanding of memory stability and, more recently, as a potential therapeutic target in the treatment of disorders such as post-traumatic stress and drug addiction. However, little is known about the reactivation process, or what might be the adaptive function of retrieval-induced plasticity. Reconsolidation has long been proposed to mediate memory updating, but only recently has this hypothesis been supported experimentally. Here, the adaptive function of memory reconsolidation is explored in more detail, with a strong emphasis on its role in updating memories to maintain their relevance.

Fig. 1

Schematic representation of the different hypotheses regarding the function of memory reconsolidation. Filled circles connected by solid lines depict idealised data points on a learning curve (i.e. behaviour observed). Dotted lines represent the hypothesised action of reconsolidation, with the lowest edge showing the impact of disrupting the reconsolidation process. A, reconsolidation may serve progressively to stabilise an acquired memory. As part of a longer consolidation process, memory reactivation and reconsolidation likely occur repeatedly in order to stabilise further the memory, with no necessity for qualitative or quantitative change to the memory. What the figure does not depict is the temporal limitation on this process, in that reconsolidation only occurs for a certain period following acquisition. This hypothesis presumably does not distinguish between memories acquired through a single trial (as shown), or over several trials, and does not propose a specific role for reconsolidation in memory strengthening/modification. B, reconsolidation may be a consolidation of updating information. A major purpose of reconsolidation is to enable the integration of updating information without suffering the deleterious impact of interference. Reconsolidation does not invoke the complete destabilisation of the previously-consolidated memory, and so disruption of reconsolidation entails little or no loss to the existing memory (for clarity, the figure shows only the theorised reconsolidation process on the 2^nd & 3^rd trials; reconsolidation itself mediates the strengthening of the memory [curved dotted lines], in the absence of which the memory remains relatively constant in strength [straight dotted lines]). C, memory updating involves destabilisation and reconsolidation. In order to strengthen a memory, that memory must be fully destabilised such that the updating information can be added or integrated into a modified unitary memory trace. Thus each updating of the memory involves destabilisation that places the memory at risk of disruption if the reconsolidation process is impaired. Equally, memories only reconsolidate when the memory is being updated (i.e. not when fully learned).