Why repetition works

Thus, the stronger connectivity between the hippocampus and the PPA in L6 than L1 enables the information from different sources to bind together and support the retrieval of scene-related associations after repetition learning. On the other hand, stronger connectivity between the hippocampus and vLPFC in L1 may represent a top-down fashion control involving the MTL in processing the information that is relevant to retrieving associations.

This aspect of our results suggested that the prefrontal cortex is more involved in retrieving associative memory after L1 than L6. The PFC operates on the information delivered to the hippocampus and on the output from it to make memory goal-directed Simons and Spiers, When memories retain more gist or familiarity, they are more likely to become incorporated into a semantic network and acquire its properties Moscovitch et al. Therefore, learning the stimuli once leads to greater demands on the processes of organization and strategic retrieval search Simons and Spiers, Our study also indicated that the connectivity between the PPA and hippocampus was active at four retention intervals, and the connectivity between the left vLPFC and hippocampus was present across four retention intervals except the min interval.

These results suggested that memory information becomes distributed across cortico-hippocampus networks at various stages of consolidation Tambini et al. Once the connectivity is established, it remains stable until the 1-month interval. In this study, we used the imagination task in the L1 group and both the imagination and sentence making tasks in the L6 group.

One may argue that the learning effect was due to the additional task in the L6 group. However, we believe that this should not influence the results and interpretations. First, in the L6 group, the face-scene pairs were presented six times in six rounds.

Thus, variable encoding provides more ways to which the target information can be accessed in a later test for reviews, see Cepeda et al. In other words, the memory representation is strengthened as well LaRocque et al. Therefore, the difference in task types may influence the magnitude of the memory enhancement, but it should not influence the underlying mechanisms. In addition, simply repeating stimuli is not sufficient to enhance memory performance Reagh and Yassa, , partly because the repeatedly presented pairs attract less attentional resources and are more likely transformed into semantic-like representations Yassa and Reagh, Without encoding variability, the difference between L1 and L6 could also be explained as a strong vs.

As suggested by previous studies, subjects likely remember both task-relevant sources in addition to task-irrelevant sources Uncapher et al. Compared to stimulus features e. In contrast, the type of information and type of process are the critical factors in determining the activation in the MTL and PFC Moscovitch et al. There are some potential limitations for this study.

First, although the variable encoding strategy fits our purpose, we could not fully rule out the confound of different encoding tasks, which may bring some uncertainty regarding the data interpretations.

Second, as we did not record the encoding performance, we were unable to analyze the difference in the encoding for the repetition effect. The evidences of the recollection and familiarity processes due to repetition learning were only obtained from previous studies e.

Further studies could adopt the same encoding task and record the encoding performance to avoid the encoding confounds. In addition, when stimuli are learned multiple times, they are more likely to be associated with emotional contexts, inducing different preference to the stimuli.

Previous studies have shown that emotional context enhances memory by increasing the hippocampal activation and its connectivity with the amygdala e. It would be interesting to investigate in future studies whether the activation of the two hippocampo-cortical networks in L1 and L6 is related to the difference in emotional contexts and preference. The current study confirmed that the hippocampus was involved in associative memory retrieval regardless of learning experience and retention interval.

More importantly, the learning experience modulated the associative memory by activating two distinct hippocampus-related brain networks. Multiple learning significantly increased activation in the hippocampus and the connectivity between the hippocampus and posterior regions and led to successful associative memory retrieval. The activation of the hippocampus decreased over time after L1 but remained stable after L6.

These results shed light on how distinct brain networks work in concert to support the retrieval of associative memories and how repetition learning influences subsequent memory over time. LZ designed the experiments, performed the experiments and analyzed the data. DG and GC analyzed the data and wrote the article.

JY conceived and designed the experiments, analyzed the data and wrote the article. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank Dr. Morris Moscovitch and Dr. Zhongxu Liu from University of Toronto for their helpful comments and suggestions on data analysis and the manuscript.

The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. National Center for Biotechnology Information , U. Journal List Front Hum Neurosci v. Front Hum Neurosci.

Published online Jul Author information Article notes Copyright and License information Disclaimer. Received Dec 7; Accepted Jun Government and, as regards Dr. Chen and the US government, is not subject to copyright protection in the United States. Foreign and other copyrights may apply. The use, distribution or reproduction in other forums is permitted, provided the original author s and the copyright owner s are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.

No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract When stimuli are learned by repetition, they are remembered better and retained for a longer time.

Introduction It is well known that after repetition learning, memory performance can be enhanced and maintained for a long time i. Materials and Methods Subjects Thirty-seven right-handed subjects 16 males with a mean age of Materials One within-subjects factor retention interval: min, 1-day, 1-week, 1-month and one between-subjects factor learning: once L1 , 6 times L6 were included in the study.

Open in a separate window. Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Correlation of Hippocampus-vLPFC and Hippocampus-PPA Differed by Learning Experience To explore whether the correlation between the hippocampus and neocortical regions differed when the subjects learned the pairs once or six times, we first chose the bilateral PPA from the localizer as the seed.

Figure 6. Discussion The objective of this study was to explore whether learning experience is associated with different brain activations in the MTL and neocortical regions, and how the activations change over time. Time Effect in the Hippocampus and Other Regions As for time change, our results showed that there were different patterns between L1 and L6. Learning Effect and Task Manipulation In this study, we used the imagination task in the L1 group and both the imagination and sentence making tasks in the L6 group.

Summary The current study confirmed that the hippocampus was involved in associative memory retrieval regardless of learning experience and retention interval. Author Contributions LZ designed the experiments, performed the experiments and analyzed the data. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments We thank Dr. Footnotes Funding. References Achim A. Medial temporal lobe activations during associative memory encoding for arbitrary and semantically related object pairs. Brain Res.

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Memory: organization and control. The medial temporal lobe and recognition memory. A cortical representation of the local visual environment. Brainscape is a web and mobile study platform that helps you learn things faster.

Our mission is to create a smarter world by simplifying and accelerating the learning process. Terms and Conditions. This explanation helps students understand why they should perform the task in the first place Long, Repetition sounds simple enough, but it requires a high level of patience.

It can be challenging to repeatedly say the same thing to a student, but it is necessary to keep calm and maintain a level, assertive tone Hoffman, Showing patience requires the restraint to not outwardly express frustration. An introduction to music theory? A lesson on making a mean cocktail? All this and more is yours for the taking on SpacedEd, a new online learning site that utilizes the benefits of spaced education, a patented methodology developed by B.

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The goal was twofold: could online learning, delivered and repeated in spaced intervals, be used as an effective teaching tool; and could it improve knowledge retention beyond the typical classroom experience? As Kerfoot discovered, the answer was yes on both counts, and he now has a wealth of documented research to prove it.

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