Pitfalls in Sleep and Memory Research and How to Avoid Them: A Consensus Paper

Understanding the complex relationship between sleep and memory is a major challenge in neuroscience. Thousands of studies on memory consolidation in humans suggest that sleep triggers offline memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, an increasing number of contradictory findings reveal potential issues with how research is conducted in this field and call into question the reliability and interpretation of the results. In this consensus paper, we describe four sets of prevalent methodological pitfalls in human sleep and memory research: (i) non-optimal experimental designs, (ii) task complexity, (iii) fatigue effects in repetitive tasks, and (iv) inappropriate data analysis practices. We then offer solutions to each of these pitfalls. We believe that implementing these solutions in future research of sleep and memory will lead to more reliable results and significantly advance our understanding in this field.

Segmentation of semantic and perceptual boundaries affects associative memory and risk of false memories

Temporally structured sequences of experiences, such as narratives or life events, are segmented in memory into discrete situational models. In segmentation, contextual shifts are processed as situational boundaries that temporally cluster items according to the perceived contexts. As such, segmentation enhances associative binding of items within a situational model. One side effect of enhanced associative processing is increased risk of false recollections for not-presented, semantically related items. If so, do boundaries facilitate false recollections, or does segmentation protect against them? In two experiments, we introduced situational shifts in word sequences in the form of semantic and perceptual boundaries, with semantic relatedness between words or the frame color around a word changing on a regular basis. After encoding, we tested participants’ associative memory performance and false recollection rates. In Experiment 1, color boundaries occurred synchronously or asynchronously to semantic boundaries. We found better associative recognition, but also more false recollections, for synchronous than asynchronous boundaries. In Experiment 2, color boundaries occurred synchronous to semantic boundaries or were absent entirely. We found that false recollection rates elicited by semantic boundaries increased when color boundaries were absent. We also tested associative memory performance using a non-semantic, temporal memory task. We found better temporal memory performance for semantic boundaries, as well as a negative correlation between increased false recollection rates and better temporal memory performance for semantic lists, but not for random lists. We discuss implications for false memory theories and segmentation of narrative materials in false memory research.

Spacing, Feedback, and Testing Boost Vocabulary Learning in a Web Application

Information and communication technology (ICT) becomes more prevalent in education but its general efficacy and that of specific learning applications are not fully established yet. One way to further improve learning applications could be to use insights from fundamental memory research. We here assess whether four established learning principles (spacing, corrective feedback, testing, and multimodality) can be translated into an applied ICT context to facilitate vocabulary learning in a self-developed web application. Effects on the amount of newly learned vocabulary were assessed in a mixed factorial design (3×2×2×2) with the independent variables Spacing (between-subjects; one, two, or four sessions), Feedback (within-subjects; with or without), Testing (within-subjects, 70 or 30% retrieval trials), and Multimodality (within-subjects; unimodal or multimodal). Data from 79 participants revealed significant main effects for Spacing [F(2,76) = 8.51, p = 0.0005, ηp2=0.18] and Feedback [F(1,76) = 21.38, p < 0.0001, ηp2=0.22], and a significant interaction between Feedback and Testing [F(1,76) = 14.12, p = 0.0003, ηp2=0.16]. Optimal Spacing and the presence of corrective Feedback in combination with Testing together boost learning by 29% as compared to non-optimal realizations (massed learning, testing with the lack of corrective feedback). Our findings indicate that established learning principles derived from basic memory research can successfully be implemented in web applications to optimize vocabulary learning.

Why Do Some Older Adults Avoid Memory Retrieval When Acquiring a New Skill?

Older adults are slower to acquire new cognitive skills requiring a shift from controlled (algorithmic) processing to automatic responding based on retrieving newly unitized information from memory. Research demonstrates that older adults’ delayed retrieval shift is a strategic avoidance of relying on memory when doing so would be successful, not just a function of age-related slowing in rates of associative learning. Older adults’ retrieval avoidance can be reduced by financial incentives to respond rapidly, recognition probes that demonstrate the accessibility of correct information, and other experimental manipulations. Item-level strategy reports show an exponential rise in retrieval strategy use with practice but not for all participants. A proportion of the older samples are retrieval strategy avoidant across the entire course of skill acquisition task practice. The chapter comments on the motivational nature of retrieval strategy avoidance and the possible practical consequences of a retrieval avoidance mode for older adults.

Using TrackMate to Analyze Drosophila Larval and Adult Locomotion

Drosophila adult and larvae exhibit sophisticated behaviors that are widely used in development, synaptic transmission, sensory physiology, and learning and memory research. Many of these behaviors depend on locomotion, the ability of an animal to move. However, the statistical analysis of locomotion is not trivial. Here we use an open-source Fiji plugin TrackMate to track the locomotion of Drosophila adults and larvae. We build optimal experimental setups to rapidly process recordings by Fiji and analyze by TrackMate. We also provide tips for analyzing non-optimal recordings. TrackMate extracts the X and Y positions of an animal on each frame of an image sequence or a video. This information allows for generating moving trajectories, calculating moving distances, and determining preference indices in two-choice assays. Notably, this free-cost analysis method does not require programming skills.Summary statementThis study uses an open-source Fiji plugin TrackMate to computationally analyze Drosophila adult and larval behavioral assays, which does not require programming skills.

Lesion of the hippocampus selectively enhances LEC’s activity during recognition memory based on familiarity

The sense of familiarity for events is crucial for successful recognition memory. However, the neural substrate and mechanisms supporting familiarity remain unclear. A major controversy in memory research is whether the parahippocampal areas, especially the lateral entorhinal (LEC) and the perirhinal (PER) cortices, support familiarity or whether the hippocampus (HIP) does. In addition, it is unclear if LEC, PER and HIP interact within this frame. Here, we especially investigate if LEC and PER's contribution to familiarity depends on hippocampal integrity. To do so, we compare LEC and PER neural activity between rats with intact hippocampus performing on a human to rat translational task relying on both recollection and familiarity and rats with hippocampal lesions that have been shown to then rely on familiarity to perform the same task. Using high resolution Immediate Early Gene imaging, we report that hippocampal lesions enhance activity in LEC during familiarity judgments but not PER’s. These findings suggest that different mechanisms support familiarity in LEC and PER and led to the hypothesis that HIP might exert a tonic inhibition on LEC during recognition memory that is released when HIP is compromised, possibly constituting a compensatory mechanism in aging and amnesic patients.

The effect of encoding task on the forgetting of object gist and details

One important feature of episodic memory is that it contains fine-grained and vividly recollected details. How to improve and maintain detailed information over time has been one of the central issues in memory research. Previous studies have inconsistent findings on whether detailed memory is forgotten more rapidly than gist memory. In this study, we investigated to what extent different encoding tasks modulated forgetting of gist and detailed information. In three experiments, participants were presented pictures of common objects and were asked to name them (Experiment 1), describe the details about them (Experiment 2) or imagine scenes associated with them (Experiment 3). After intervals of 10 minutes, one day, one week and one month, gist and detailed memories of the pictures were tested and assessed using a remember/know/guess judgement. The results showed that after the naming task, gist and detailed memories were forgotten at a similar rate, but after the description and the imagination tasks, detailed memory was forgotten at a slower rate than gist memory. The forgetting rate of gist memory was the slowest after the naming task, while that of detailed memory was the slowest after the description task. In addition, when three experiments were compared, the naming task enhanced the contributions of recollection and familiarity for gist memory, while the description task enhanced the contribution of familiarity for detailed memory. These results reveal the importance of the encoding task in the forgetting of gist and detailed information, and suggest a possible way to maintain perceptual details of objects at longer intervals.

Spatial Recognition Memory: Differential Brain Strategic Activation According to Sex

Human spatial memory research has significantly progressed since the development of computerized tasks, with many studies examining sex-related performances. However, few studies explore the underlying electrophysiological correlates according to sex. In this study event-related potentials were compared between male and female participants during the performance of an allocentric spatial recognition task. Twenty-nine university students took part in the research. Results showed that while general performance was similar in both sexes, the brain of males and females displayed a differential activation. Males showed increased N200 modulation than females in the three phases of memory process (encoding, maintenance, and retrieval). Meanwhile females showed increased activation of P300 in the three phases of memory process compared to males. In addition, females exhibited more negative slow wave (NSW) activity during the encoding phase. These differences are discussed in terms of attentional control and the allocation of attentional resources during spatial processing. Our findings demonstrate that sex modulates the resources recruited to performed this spatial task.