Abstract
Consolidated memories can persist from a single day to years, and persistence is improved by retraining or retrieval-mediated plasticity. One retrieval-based way to strengthen memory is the reconsolidation process. Strengthening occurs simply by the presentation of specific cues associated with the original learning. This enhancement function has a fundamental role in the maintenance of memory relevance in animals everyday life. In the present study, we made a step forward in the identification of brain correlates imprinted by the reconsolidation process studying the long-term neural consequences when the strengthened memory is stable again. To reach such a goal, we compared the retention of paired-associate memories that went through retraining process or were labilizated-reconsolidated. Using functional magnetic resonance imaging (fMRI), we studied the specific areas activated during retrieval and analyzed the functional connectivity of the whole brain associated with the event-related design. We used Graph Theory tools to analyze the global features of the network. We show that reconsolidated memories imprint a more locally efficient network that is better at exchanging information, compared with memories that were retrained or untreated. For the first time, we report a method to elucidate the neural footprints associated with a relevant function of memory reconsolidation.
Highlights
Consolidated memories can persist from a single day to years, and persistence is improved by retraining or retrieval-mediated plasticity
On day 15, associations that went through the reconsolidation process (Rc) had the best performance while the no reminder condition (Nr) condition presented the lowest retention
The mean correct responses were Rc = 9.5 ± 0.5, Rw = 9.3 ± 0.5 and Nr = 9.3 ± 0.6 for the group that was evaluated five days after training and Rc = 9.3 ± 0.7, Rw = 9.5 ± 0.5 and Nr = 9.2 ± 0.5 for day 15 group. Both Rc and Rw treatments during the reactivation session enhanced memory, making it last longer than memories that were not reactivated. These results showed that it was not possible to differentiate between these conditions in the early test, but when the testing was far away in time from the training, memories that passed through the reconsolidation process (Rc) were more resistant to forgetting compared to Rw and Nr, which led to a better performance
Summary
Consolidated memories can persist from a single day to years, and persistence is improved by retraining or retrieval-mediated plasticity. Strengthening occurs by the presentation of specific cues associated with the original learning This enhancement function has a fundamental role in the maintenance of memory relevance in animals everyday life. We made a step forward in the identification of brain correlates imprinted by the reconsolidation process studying the long-term neural consequences when the strengthened memory is stable again. That is, when consolidated memories are reactivated by the presentation of specific reminders, the retrieved memory enters in a period of labilization followed by a process of restabilization known as reconsolidation[8,9,10]. We demonstrated that only one labilization-reconsolidation process triggered by an incomplete reminder strengthens the original memory, increasing its persistence and making it more resistant to forgetting. The effect, of only one incomplete reminder, was observed seven days after training but not three days after learning, probably due to a ceiling effect[21]
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