Spatial-Memory Formation After Spaced Learning Involves ERKs1/2 Activation Through a Behavioral-Tagging Process

Modulation of memory reconsolidation by adjacent novel tasks: timing defines the nature of change

Reconsolidation turns memories into a responsive state that allows their modulation until they stabilize again. This phenomenon attracted remarkable attention due to its potential impact on therapeutics and education. Recent evidence revealed that different memories undergo reconsolidation via a behavioral tagging process. Thus, their re-stabilization involves setting "reconsolidation-tags" and synthesizing plasticity-related proteins for their capture at the tagged sites. Here, we studied the possibility of affecting these fundamental mechanisms to modulate reconsolidation. Our findings, in laboratory rats, indicate that exploring a novel environment 60 min before or after memory reactivation improves spatial object recognition memory by promoting protein synthesis. Conversely, experiencing novelty immediately after reactivation impairs the reconsolidation by affecting the tags. Similar effects, but with a different optimal time window for improvement, occur in inhibitory avoidance memory. These results highlight the possibility of modulating existing memories using non-invasive interventions that selectively affect the fundamental mechanisms of behavioral tagging during their reconsolidation.

Time-dependent inhibition of Rac1 in the VTA enhances long-term aversive memory: implications in active forgetting mechanisms

The fate of memories depends mainly on two opposing forces: the mechanisms required for the storage and maintenance of memory and the mechanisms underlying forgetting, being the latter much less understood. Here, we show the effect of inhibiting the small Rho GTPase Rac1 on the fate of inhibitory avoidance memory in male rats. The immediate post-training micro-infusion of the specific Rac1 inhibitor NSC23766 (150 ng/0.5 µl/ side) into the ventral tegmental area (VTA) enhanced long-term memory at 1, 7, and 14 days after a single training. Additionally, an opposed effect occurred when the inhibitor was infused at 12 h after training while no effect was observed immediately after testing animals at 1 day. Control experiments ruled out the possibility that post-training memory enhancement was due to facilitation of memory formation since no effect was found when animals were tested at 1 h after acquisition and no memory enhancement was observed after the formation of a weak memory. Immediate post-training micro-infusion of Rac1 inhibitor into the dorsal hippocampus, or the amygdala did not affect memory. Our findings support the idea of a Rac1-dependent time-specific active forgetting mechanism in the VTA controlling the strength of a long-term aversive memory.

A behavioral tagging account of kinase contribution to memory formation after spaced aversive training

Long-term memory (LTM) can be induced by repeated spaced training trials. Using the weak inhibitory avoidance (wIA) task, we showed that one wIA session does not lead to a 24-h LTM, whereas two identical wIA sessions spaced by 15 min to 6 h induce a 24-h LTM. This LTM promotion depends both on hippocampal protein synthesis and the activity of several kinases. In agreement with the behavioral tagging (BT) hypothesis, our results suggest that the two training sessions induce transient learning tags and lead, via a cooperative effect, to the synthesis of plasticity-related proteins (PRPs) that become available and captured by the tag from the second session. Although ERKs1/2 are needed for PRPs synthesis and CaMKs are required for tag setting, PKA participates in both processes. We conclude that the BT mechanism accounts for the molecular constraints underlying the classic effect of spaced learning on LTM formation.

Contributions of extracellular-signal regulated kinase 1/2 activity to the memory trace

The ability to learn from experience and consequently adapt our behavior is one of the most fundamental capacities enabled by complex and plastic nervous systems. Next to cellular and systems-level changes, learning and memory formation crucially depends on molecular signaling mechanisms. In particular, the extracellular-signal regulated kinase 1/2 (ERK), historically studied in the context of tumor growth and proliferation, has been shown to affect synaptic transmission, regulation of neuronal gene expression and protein synthesis leading to structural synaptic changes. However, to what extent the effects of ERK are specifically related to memory formation and stabilization, or merely the result of general neuronal activation, remains unknown. Here, we review the signals leading to ERK activation in the nervous system, the subcellular ERK targets associated with learning-related plasticity, and how neurons with activated ERK signaling may contribute to the formation of the memory trace.

The Spaced Learning Concept in Combination With Halsted and Peyton - A Randomized Controlled Study

BACKGROUND

Several motor learning models have been used to teach highly complex procedural skills in medical education. Two approaches are often employed amongst health care professionals: Halsted's "See one - do one - teach one" concept and Peyton's Four-step approach. Peyton's deconstruction of the learning process into 4 sub-steps was reported to be preferable for learning/acquiring/teaching complex clinical skills. However, a new increasingly popular technique is known as the spaced learning method. In a previous study, we were able to confirm that the spaced learning concept is superior for laparoscopic suturing and knot tying compared to conventional training curricula, this current study aimed to assess the influence of spaced learning in combination with Halsted's and Peyton's tutoring approaches on laparoscopic knot tying of medical students.

METHODS

After randomization, 20 medical students were either assigned to Halsted's or Peyton's teaching approach and trained one-on-one (teacher-student). Additionally, all subjects were trained according to the spaced learning concept, containing 40 minutes of content-blocks, followed by a 20-minute break involving coordinated, standardized physical activity. This was repeated three times. Primary endpoints were time, knot quality, precision, knot strength, as well as overall laparoscopic knotting performance and competency. To evaluate the motivation of the subjects, an 18-item questionnaire was utilized to measure four motivational factors (anxiety, probability of success, interest, and challenge).

RESULTS

All trainees significantly improved after training in all knot attributes. Trainees assigned to Halsted's method were able to significantly outperform the Peyton group in knot quantity within 30 minutes (p = 0.013), time/knot (p = 0.033), performance score (p = 0.009), and precision (p = 0.032). No significant difference between Halsted and Peyton was found for knot strength and quality. Furthermore, no significant difference was identified comparing motivation pre- and post-training. However, subjects in the Peyton appeared to be significantly more anxious after training.

CONCLUSION

Combining spaced learning technique with Halsted's "see one - do one - teach one" appears to be superior to Peyton's Four-step approach in conjunction with spaced learning in surgical naïve students. We recommend further studies evaluating the combination of spaced learning with Halsted and Peyton's instructional methods.

Persistence of spatial memory induced by spaced training involves a behavioral-tagging process

Spaced training, which involves long inter-trial intervals, has positive effects on memories. One of the main attributes of long-term memories (LTM) is persistence. Here, to identify the process that promotes LTM persistence by spaced learning, we used the spatial object recognition (SOR) task. The protocol consisted of a first strong training session that induced LTM formation (tested 1 day after training), but not LTM persistence (tested 7 or 14 days after training); and a second weak training session that promoted memory persistence when applied 1 day, but not 7 days, after the first training. We propose that the promotion of memory persistence is based on the Behavioral Tagging (BT) mechanism operating when the memory trace is retrieved. BT involves the setting of a tag induced by learning which gives rise to input selectivity, and the use of plasticity-related proteins (PRPs) to establish the mnemonic trace. We postulate that retraining will mainly retag the sites initially activated by the original learning, where the PRPs needed for memory expression and/or induced by retrieval would be used to maintain a persistent mnemonic trace. Our results suggest that the mechanism of memory expression, but not those of memory reinforcement or reconsolidation, is necessary to promote memory persistence after retraining. The molecular mechanisms involve ERKs1/2 activity to set the SOR learning tag, and the availability of GluA2-containing AMPA receptor. In conclusion, both the synthesis of PRPs and the setting of a learning tag are key processes triggered by retraining that allow SOR memory persistence.

Behavioral and Cellular Tagging in Young and in Early Cognitive Aging

The ability to maintain relevant information on a daily basis is negatively impacted by aging. However, the neuronal mechanism manifesting memory persistence in young animals and memory decline in early aging is not fully understood. A novel event, when introduced around encoding of an everyday memory task, can facilitate memory persistence in young age but not in early aging. Here, we investigated in male rats how sub-regions of the hippocampus are involved in memory representation in behavioral tagging and how early aging affects such representation by combining behavioral training in appetitive delayed-matching-to-place tasks with the “cellular compartment analysis of temporal activity by fluorescence in situ hybridization” technique. We show that neuronal assemblies activated by memory encoding were also partially activated by novelty, particularly in the distal CA1 and proximal CA3 subregions in young male rats. In early aging, both encoding- and novelty-triggered neuronal populations were significantly reduced with a more profound effect in encoding neurons. Thus, memory persistence through novelty facilitation engages overlapping hippocampal assemblies as a key cellular signature, and cognitive aging is associated with underlying reduction in neuronal activation.

Spatiotemporally resolved protein synthesis as a molecular framework for memory consolidation

De novo protein synthesis is required for long-term memory consolidation. Dynamic regulation of protein synthesis occurs via a complex interplay of translation factors and modulators. Many components of the protein synthesis machinery have been targeted either pharmacologically or genetically to establish its requirement for memory. The combination of ligand/light-gating and genetic strategies, that is, chemogenetics and optogenetics, has begun to reveal the spatiotemporal resolution of protein synthesis in specific cell types during memory consolidation. This review summarizes current knowledge of the macroscopic and microscopic neural substrates for protein synthesis in memory consolidation. In addition, we highlight future directions for determining the localization and timing of de novo protein synthesis for memory consolidation with tools that permit unprecedented spatiotemporal precision.

The Spaced Learning Concept Significantly Improves Acquisition of Laparoscopic Suturing Skills in Students and Residents: A Randomized Control Trial

INTRODUCTION

 Spaced learning consists of blocks with highly condensed content that interrupted by breaks during which distractor activities, such as physical activity, are performed. The concept has been shown to be superior in complex motor skill acquisition like laparoscopic suturing and knot tying. Preliminary studies have solely been conducted with medical students. Therefore, it remained unanswered if the spaced learning concept would also work for pediatric surgery residents.

MATERIALS AND METHODS

 The study aimed to evaluate the effectiveness of spaced learning, students, and residents were asked to perform four surgeons' square knots on a bowel model within 30 minutes prior and post 3 hours of hands-on training. To examine the long-term skills, the same subjects were asked to perform a comparable, but more complex task 12 months later without receiving training in the meantime. Total time, knot stability, suture accuracy, knot quality, and laparoscopic performance were assessed. Additionally, motivation was accessed by using the questionnaire on current motivation. Differences were calculated using mixed analysis of variance, Mann-Whitney U test, and multivariate analysis of covariance.

RESULTS

 A total of 20 medical students and 14 residents participated in the study. After randomization, 18 were trained using the spaced learning concept and 16 via conventional methods. Both groups had comparable baseline characteristics and improved significantly after training in all assessed measures. The spaced learning concept improved procedure performance as well as knot quality and stability in both students and residents. However, residents that trained via spaced learning showed significantly better long-term results regarding knot quality and speed in comparison to students. Although anxiety was significantly reduced in both training groups over time, residents were significantly more interested regarding knot tying than students.

CONCLUSION

 This study dispels any remaining doubt that the spaced learning concept might only work for medical students. It appears that the spaced learning concept is very suitable for residents in acquiring complex motor skills. It is superior to conventional training, resulting in improved procedural performance as well as knot quality and speed. Hence, tailored training programs should not only be integrated early on in students' curricula but also in surgical training programs.

Spaced training enhances memory and prefrontal ensemble stability in mice

It is commonly acknowledged that memory is substantially improved when learning is distributed over time, an effect called the "spacing effect". So far it has not been studied how spaced learning affects the neuronal ensembles presumably underlying memory. In the present study, we investigate whether trial spacing increases the stability or size of neuronal ensembles. Mice were trained in the "everyday memory" task, an appetitive, naturalistic, delayed matching-to-place task. Spacing trials by 60 min produced more robust memories than training with shorter or longer intervals. c-Fos labeling and chemogenetic inactivation established the involvement of the dorsomedial prefrontal cortex (dmPFC) in successful memory storage. In vivo calcium imaging of excitatory dmPFC neurons revealed that longer trial spacing increased the similarity of the population activity pattern on subsequent encoding trials and upon retrieval. Conversely, trial spacing did not affect the size of the total neuronal ensemble or the size of subpopulations dedicated to specific task-related behaviors and events. Thus, spaced learning promotes reactivation of prefrontal neuronal ensembles processing episodic-like memories.