A brief retraining regulates the persistence and lability of a long-term memory.

An experience extending the persistence of a memory after training Aplysia californica with inedible food also allows a consolidated memory to become sensitive to consolidation blockers. Long-term (24 h) memory is initiated by 5 min of training and is dependent on protein synthesis during the first few hours after training. By contrast, a more persistent (48 h) memory is dependent on a longer training session and on a later round of protein synthesis. When presented 24 h after training, a 3-min training that produces no memory alone can cause a memory that would have persisted for only 24 h to persist for 48 h. After a 48 h memory has been consolidated, 3 min of training also makes the memory sensitive to a protein-synthesis inhibitor. These findings suggest that a function of allowing a consolidated memory to become sensitive to blockers of protein synthesis may be to allow the memory to become more persistent.