Biological meaning of reconsolidation and extinction in an invertebrate model of memory

M.E. PEDREIRA; Y HEPP; LM PÉREZ-CUESTA; H MALDONADO

Magdalen College. Oxford, Inglaterra

Congreso; Gordon Research Conferences: Neuroethology: Behavior, Evolution & Neurobiology; 2005

Title: Biological meaning of reconsolidation and extinction in an invertebrate model of memory. Pedreira ME1, Pérez-Cuesta LM, Hepp Y and Maldonado H2. mpedreira@fbmc.fcen.uba.ar                                           hector@fbmc.fcen.uba.ar Laboratorio de Neurobiología de la Memoria, FCEyN, Universidad de Buenos Aires, Argentina. The idea that memories retrieved into the active state are vulnerable to disruption has reemerged as a major hypothesis in contemporary research on the neurobiology of memory. The reactivation of learned associations (unconditioned stimulus, US - conditioned stimulus, CS) by the presentation of a reminder returns memory to a labile state and starts a process of memory stabilization, termed reconsolidation, which involves a new round of protein synthesis.  Experiments with invertebrates support the view that intracellular events subserving the consolidation phase of memory are preserved across evolution. We investigated whether such evolutionary persistence extends to reconsolidation mechanisms, and the mechanistic relationship between reconsolidation and extinction. For these purposes, we used the contextual memory model of the crab Chasmagnathus which involves an association between the learning context (CS) and a visual danger stimulus (US). We showed that re-exposure duration to the learning context acts as a switch guiding the memory course to reconsolidation or extinction each depending on protein synthesis. Regardless of the reminder duration, memory retrieved by unreinforced CS re-exposure emerges intact and consolidated when tested before CS offset, suggesting that neither reconsolidation nor extinction is concomitant with CS-re-exposure. Either process could only be triggered once the definitive mismatch between CS and US is confirmed by CS termination without expected reinforcement. Here, we offer a probable biological meaning of the labilization-reconsolidation phase after the offset of the unreinforced CS. We assume that a mismatch between what was expected and what actually occurred should result from a failed prediction. A wide variety of memory flaws, ranging from outdated to faulty or incomplete information, might account for such failure. Therefore, the labilization-reconsolidation process plays a repair role by enabling the system to integrate new information on the background of the past. In addition, we investigated to what extent extinction represents a real learning process, dependent on the violation of the CS-US contingency established during acquisition. We performed different experimental manipulations after the extinction of memory, some of them causing the old memory to re-appear. Our findings support the hypothesis that extinction involves the acquisition of a new memory that coexists with the old one, so that CS becomes endowed with two different meanings. The actual performance depends on which of the two associations is controlling the behaviour.