Enhancement of long-term memory expression by a single trial during consolidation.

Before the memory trace is stored long term, it must undergo a phase of consolidation during which it remains susceptible to modifications. It has previously been proposed that during consolidation, memories are kept from being stored long term, and can therefore be modified with additional information resulting from ongoing behavior. The Chasmagnathus associative memory model is used here to test whether it is possible during consolidation to modify the long-term expression of a memory generated by a weak training procedure. In this memory model, long-term memory expression is achieved after strong training protocols, a 15-spaced trial procedure. After a weak training protocol (WTP, six spaced trials), crabs do not show memory retention when tested in the long term. Nevertheless, the WTP builds a long-term memory that it is indeed consolidated, but remains unexpressed. Here we show that memory can be modified by experience during this short period after learning: memory expression can be enhanced by a Single Trial Session, on the condition that this session takes place contingent upon the consolidation period. We also found that during this time, the memory built by the WTP is behaviorally expressed, in contrast with what occurs at long term. Our results support the idea that during consolidation memories can be evaluated in the background of concurrent experiences. In particular, we propose that during the consolidation period it is possible for crabs to assess which experiences, among those stored long term, will be expressed long term.