Memory is not extinguished along with CS presentation but within a few seconds alter CS-offset.

LM PÉREZ-CUESTA; Y HEPP; ME PEDREIRA; H MALDONADO

LEARNING & MEMORY (COLD SPRING HARBOR, N.Y.)

Año: 2006 vol. 14 p. 101 - 108

1072-0502

Despite important progress made in behavioral studies on extinction, our understanding at the phenomenological level still falls short, especially regarding some basic questions related to the dynamic of the extinction phases. Is extinction triggered by the CS retrieval or by the CS-offset? Does extinction level increase over the nonreinforced CS exposure, or is extinction not occurring along with CS presentation? Here we address these questions by using an invertebrate model of contextual memory, which involves an association between the learning context (CS) and a visual danger stimulus (US). We conclude, firstly, that the extinction formation is not synchronous with the presentation of the nonreinforced CS; secondly, that the building up of extinction is triggered by CS-offset but not by retrieval; thirdly, that the extinction memory is formed in not longer than 45 s after CS-offset; and fourthly, that the building of the new memory requires NMDA receptors activity but not protein synthesis. We offer an interpretative scheme of our results and discuss to what extent this scheme, proposed for the case of one-trial extinction would be applicable to that of multi-trial extinction.