Retrieval mediated by hippocampal extracellular signal-regulated kinase/mitogen-activated protein kinase is required for memory strengthening

Established memories can be strengthened by additional learning and rehearsal. However, the brain processes enabling memories to be updated by further information is unclear. We found that blockade of retrieval of a stabilized memory by inhibition of the extracellular signal-regulated kinase/mitogen-activated protein kinase signaling pathway in the hippocampus prevented memory enhancement induced by an additional learning trial in rats. The findings indicate that retrieval is critical for memory strengthening.