Rewarding information presented during reactivation attenuates fear memory: Methylphenidate and fear memory updating

In the last decade it became clear that a previously consolidated memory can be modified during the plastic state induced by retrieval. This updating process opens the possibility to adapt undesired memory. Here we investigated whether fear memory could be updated to less-aversive/positive level by inserting hedonic information during retrieval. Considering that methylphenidate has strong rewarding propriety, we injected 3 or 10 mg/kg pre or post-reactivation in rats previously trained in contextual fear conditioning. We found that memory reactivation under effect of methylphenidate attenuates fear memory within-session and in subsequent tests in a drug-free condition, without presenting spontaneous recovery. Interestingly, methylphenidate impaired memory extinction when injected before, but not after a long reactivation session. We also showed that methylphenidate induces place preference and increases motor activity. Thus, this study provides new insights in the memory updating process and suggests that a previously consolidated fear memory can be attenuated by inserting appetitive information during retrieval.