Reconsolidation of fresh, remote, and extinguished fear memory in medaka: old fears don't die

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Abstract
Long-term fear memory in the medaka fish (Oryzias latipes) regains transient sensitivity to a consolidation blocker immediately after memory reactivation in retrieval ('reconsolidation'). Here we show that reconsolidation occurs in fresh long-term memories but not in remote memories, and that the apparent amnesia induced by blockade of reconsolidation can be reinstated by an unpaired reinforcer, a procedure that has no effect on amnesia induced by blockade of consolidation. Extinction memory also undergoes post-reactivation reconsolidation, the blockade of which exposes the previously acquired fear. Hence in medaka, the process manifested in reconsolidation seems itself to consolidate; moreover, even when the post-reactivation application of the consolidation blocker is still able to disrupt the memory, the conditioned fear does not seem to go away permanently.