Different requirements for protein synthesis in acquisition and extinction of spatial preferences and context-evoked fear.

Many molecular accounts of long-term memory storage postulate that the synthesis of new proteins is necessary for long-term changes in neuronal function. These experiments generally have examined the learning that occurs as associations are acquired between neutral and biologically important stimuli. Little is known about the importance of protein synthesis in the establishment of memories for extinction, which occurs as the relations established during acquisition are severed. Extinction appears to be an active learning process that results in the formation of new memories rather than in the simple erasure or forgetting of memories from acquisition. Furthermore, under certain circumstances, extinction can result in long-term changes in behavior lasting for days to weeks. Here we show that although memories for the acquisition of spatial and contextual learning required protein synthesis, memories for extinction formed in the absence of protein synthesis. These results suggest that acquisition and extinction are mediated by distinct molecular mechanisms and that long-term memories can form in the absence of protein synthesis.