Updating of episodic memories depends on the strength of new learning after memory reactivation.

After reactivation, apparently stable memories may reenter an unstable state in which they are modifiable, requiring another phase of stabilization, called reconsolidation. Recent evidence shows that during reconsolidation, reactivated memories may be updated by the incorporation of new information. In the present study, we examined whether the updating of episodic memories depends on the strength of new encoding after reactivation. To this end, healthy participants learned negative and neutral pictures, reactivated them 1 week later, and learned new pictures either once or three times immediately after reactivation. A recognition test was performed another week later. Our results show that the impact of new learning after reactivation depended critically on the strength of new encoding: Whereas learning new pictures only once after reactivation had no effect on subsequent memory, learning new pictures three times after reactivation reduced subsequent memory accuracy, mainly due to intrusions from the newly learned pictures. Our findings indicate that the strength of new encoding after reactivation plays a critical role for the updating of episodic memories and may have important implications for therapeutic interventions that aim to alter unwanted memories after reactivation.