Changing memories after reactivation: a one-time opportunity?

After reactivation, apparently stable memories can become sensitive to modifications again, requiring another phase of stabilization, called reconsolidation. Recent evidence shows that repeated reactivations strengthen memories and that stronger memories are more resistant to alterations during reconsolidation. Therefore, we asked whether multiple reactivations make memories less vulnerable to manipulations during reconsolidation and thus serve as boundary condition on memory reconsolidation. In Experiment1, we tested whether new learning after the reactivation of previously learned material alters the subsequent memory for the original material. Participants learned negative and neutral pictures, reactivated them 1week later, and learned new pictures immediately thereafter. Memory for the original pictures was assessed in a recognition test 1day later. We found that new learning after reactivation reduced the subsequent memory of the original pictures; new learning alone or reactivation alone, however, had no effect on memory. Two further experiments investigated the impact of multiple reactivations on this memory impairing effect of new learning after reactivation. These experiments showed that the influence of new learning after reactivation disappeared neither after one (Experiment2) nor after three (Experiment3) additional reactivations completely, indicating that even after multiple reactivations memories remain sensitive to modifications during reconsolidation. These findings may have important implications for novel treatment approaches that aim for modification of unwanted memories during reconsolidation.