Mismatch between what is expected and what actually occurs triggers memory reconsolidation or extinction

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

Nyborg Dinamarca

Congreso; VII International Congress of Neuroethology; 2004

When learned associations are recalled from long-term memory stores by presentation of an un-reinforced conditioned stimulus (CS), two processes are initiated. One, termed reconsolidation, re-activates the association between the conditioned and unconditioned stimuli and transfers it from a stable state to a more labile protein-dependent one.  The other is an extinction process in which presentation of the CS alone degrades the association between CS and US. To address the mechanistic relationship between reconsolidation and extinction, we have used an invertebrate model of contextual memory which involves an association between the learning context and a visual danger stimulus. We proposed that re-exposure duration to the learning context acts as a switch guiding the memory course towards reconsolidation or extinction, both depending on protein synthesis. This proposal implies that the system computes the total exposure time to the context, from CS-onset to CS-offset, and therefore, that the reminder presentation requires to be terminated for the switching mechanism to become operative. Here we investigate to what extent such requirement is necessary and besides, we explore the relation between diverse phases in the reconsolidation and extinction processes.. Results show that two factors, unreinforcement during the reminder and CS-offset, are the necessary conditions for both processes to occur.. Either process could only be triggered once the definitive mismatch between CS and US is confirmed by CS termination without the expected reinforcement.