Memory Retrieval and the Passage of Time: From Reconsolidation and Strengthening to Extinction

Abstract

An established memory can be made transiently labile if retrieved or reactivated. Over time, it becomes again resistant to disruption and this process that renders the memory stable is termed reconsolidation. The reasons why a memory becomes labile after retrieval and reconsolidates still remains debated. Here, using inhibitory avoidance learning in rats, we provide evidence that retrievals of a young memory, which are accompanied by its reconsolidation, result in memory strengthening and contribute to its overall consolidation. This function associated to reconsolidation is temporally limited. With the passage of time, the stored memory undergoes important changes, as revealed by the behavioral outcomes of its retrieval. Over time, without explicit retrievals, memory first strengthens and becomes refractory to both retrieval-dependent interference and strengthening. At later times, the same retrievals that lead to reconsolidation of a young memory extinguish an older memory. We conclude that the storage of information is very dynamic and that its temporal evolution regulates behavioral outcomes. These results are important for potential clinical applications.

Memory reconsolidation and its maintenance depend on L-voltage-dependent calcium channels and CaMKII functions regulating protein turnover in the hippocampus

“…It is likely that mechanisms other than reconsolidation secure retrieval shortly after reconsolidation (3,10). The present findings attest to the long-lasting nature of reconsolidation effects (17).…”

“…An important factor in memory maintenance is reconsolidation (14)(15)(16), which originates in the labilization of memories caused by nonreinforced retrieval. Reconsolidation is a protein synthesis-dependent mechanism without which traces become progressively weaker (5,(14)(15)(16)(17)(18)(19). In most cases, it occurs more readily the first few times that memories are retrieved (3).…”

Extinction learning, which consists of the inhibition of retrieval, can be learned without retrieval

“…Reconsolidation is viewed as a consequence of the labilization of consolidated memories at the time of the unreinforced retrieval, which renders them open to strengthening and updating (3)(4)(5)(6)(7)(14)(15)(16)(17)(18)(19)(20), whereas extinction is viewed as a form of learning to inhibit retrieval of original memory (8)(9)(10)(11)(12). Pavlov observed more than a century ago (8) that extinguished responses can recover spontaneously with the passage of time, which indicates that extinction does not erase memories.…”

The curriculum prerequisite network: Modeling the curriculum as a complex system

“…In a CPN, where arcs represent prerequisite relationships, one link or step typically denotes the passage of at least one semester. The more steps there are separating two courses, the more opportunity there is for a student to forget material learned in the earlier course, unless there are opportunities later in the curriculum for reinforcement [47,48]. Thus, as one moves across the CPN through time, one can think in terms of an extinction time for concepts.…”

“…It is possible that a course could serve as a prerequisite in name only if it does not sufficiently use and build upon prior knowledge. Opportunities for reinforcement legitimized by prerequisite bindings should be used to strengthen retention [47,48], which does not necessarily happen if prior topics are treated as already covered, rather than incorporating new topics into this already established knowledge framework [59].…”