Retrieval and reconsolidation: toward a neurobiology of remembering

Memory involves far more than 'consolidation'

The observation that retrieval returns a stable memory into a labile state cannot be readily explained by any simple version of consolidation theory. This finding has been interpreted as evidence for the need to reconsolidate a memory after reactivating it. However, as we discuss in this commentary, other behavioural observations indicate that even this modification to consolidation theory may be insufficient to describe the dynamic properties of memory.

The labile nature of consolidation theory

'Consolidation' has been used to describe distinct but related processes. In considering the implications of our recent findings on the lability of reactivated fear memories, we view consolidation and reconsolidation in terms of molecular events taking place within neurons as opposed to interactions between brain regions. Our findings open up a new dimension in the study of memory consolidation. We argue that consolidation is not a one-time event, but instead is reiterated with subsequent activation of the memories.

Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval

'New' memories are initially labile and sensitive to disruption before being consolidated into stable long-term memories. Much evidence indicates that this consolidation involves the synthesis of new proteins in neurons. The lateral and basal nuclei of the amygdala (LBA) are believed to be a site of memory storage in fear learning. Infusion of the protein synthesis inhibitor anisomycin into the LBA shortly after training prevents consolidation of fear memories. Here we show that consolidated fear memories, when reactivated during retrieval, return to a labile state in which infusion of anisomycin shortly after memory reactivation produces amnesia on later tests, regardless of whether reactivation was performed 1 or 14 days after conditioning. The same treatment with anisomycin, in the absence of memory reactivation, left memory intact. Consistent with a time-limited role for protein synthesis production in consolidation, delay of the infusion until six hours after memory reactivation produced no amnesia. Our data show that consolidated fear memories, when reactivated, return to a labile state that requires de novo protein synthesis for reconsolidation. These findings are not predicted by traditional theories of memory consolidation.