Episodic memory enhancement versus impairment is determined by contextual similarity across events

For over a century, stability of spatial context across related episodes has been considered a source of memory interference, impairing memory retrieval. However, contemporary memory integration theory generates a diametrically opposite prediction. Here, we aimed to resolve this discrepancy by manipulating local context similarity across temporally disparate but related episodes and testing the direction and underlying mechanisms of memory change. A series of experiments show that contextual stability produces memory integration and marked reciprocal strengthening. Variable context, conversely, seemed to result in competition such that new memories become enhanced at the expense of original memories. Interestingly, these patterns were virtually inverted in an additional experiment where context was reinstated during recall. These observations 1) identify contextual similarity across original and new memories as an important determinant in the volatility of memory, 2) present a challenge to classic and modern theories on episodic memory change, and 3) indicate that the sensitivity of context-induced memory changes to retrieval conditions may reconcile paradoxical predictions of interference and integration theory.

Molecular Mechanisms of Memory Consolidation That Operate During Sleep

The role of sleep for brain function has been in the focus of interest for many years. It is now firmly established that sleep and the corresponding brain activity is of central importance for memory consolidation. Less clear are the underlying molecular mechanisms and their specific contribution to the formation of long-term memory. In this review, we summarize the current knowledge of such mechanisms and we discuss the several unknowns that hinder a deeper appreciation of how molecular mechanisms of memory consolidation during sleep impact synaptic function and engram formation.

Identifying Causal Subsequent Memory Effects

Over 40 years of accumulated research has detailed associations between neuroimaging signals measured during a memory encoding task and later memory performance, across a variety of brain regions, measurement tools, statistical approaches and behavioral tasks. But the interpretation of these Subsequent Memory Effects (SMEs) remains unclear: if the identified signals reflect cognitive and neural mechanisms of memory encoding then the underlying neural activity must be causally related to future memory. However, almost all previous SME analyses do not control for potential confounders of this causal interpretation, such as serial position and item effects. We collect a large fMRI dataset and use a novel experimental design and analysis approach that allows us to statistically adjust for all exogenous confounding variables. We find that, using standard approaches without adjustment, we replicate several univariate and multivariate subsequent memory effects and are able to predict memory performance across people. However, we are unable to identify any signal that reliably predicts subsequent memory after adjusting for confounding variables, bringing into doubt the causal status of these effects. We apply the same approach to subjects' judgments of learning collected during an encoding period, and show that these behavioral measures of encoding quality do predict memory after adjustments, suggesting that it is possible to measure signals at the time of encoding that reflect causal mechanisms but that existing neuroimaging measures may not have the precision and specificity to do so.

Mechanisms of Memory Updating: State Dependency vs. Reconsolidation

Reactivating a memory trace has been argued to put it in a fragile state where it must undergo a stabilization process known as reconsolidation. During this process, memories are thought to be susceptible to interference and can be updated with new information. In the spatial context paradigm, memory updating has been shown to occur when new information is presented in the same spatial context as old information, an effect attributed to a reconsolidation process. However, the integration concept holds that memory change can only occur when reactivation and test states are the same, similar to a state-dependent effect. Thus, in human episodic memory, memory updating should only be found when state is the same across the study, reactivation, and test sessions. We investigated whether memory updating can be attributed to state dependency in two experiments using mood as a state. We found evidence of memory updating only when mood was the same across all sessions of the experiments, lending support to the integration concept and posing a challenge to a reconsolidation explanation.

BehaviorDEPOT: a tool for automated behavior classification and analysis in rodents

Quantitative descriptions of animal behavior are essential to understand the underlying neural substrates. Fear conditioning in rodents is a widely used assay that allows neuroscientists to probe the neural mechanisms of memory. To date, quantification of freezing behavior, a proxy for fear memory strength, is usually performed by hand or with expensive and inflexible commercial software. To overcome these barriers, we developed BehaviorDEPOT (DEcoding behavior based on POsitional Tracking), a MATLAB-based application containing six independent modules. The Experiment Module runs fear conditioning experiments using an Arduino-based design that interfaces with commercial hardware. The Analysis Module classifies freezing and analyzes spatiotemporal behavioral statistics in user-defined ways. The remaining modules can develop custom classifiers. Of note, the Inter-Rater Module establishes reliable ground-truth human labels, making it broadly useful for scientists developing classifiers with any application. BehaviorDEPOT provides a simple, flexible, automated pipeline to move from pose tracking to reliably quantifying task-relevant behaviors.

“The Charm of the PRL”. Memory Culture, (Post)Socialist Nostalgia and Historical Tourism in Poland

The article explores the mechanisms of memory culture and the commercialization of the socialist heritage from the period of the People’s Republic of Poland (PRL) (from 1945 to 1989) as a tourist destination, societal practice and cultural resource in today’s Warsaw. At the intersection of heritage studies, historical tourism and material culture, the ethnographic analysis focuses on three empirical case studies as examples of the commercial popularization of the history of the PRL. These are the communist heritage tours offered by WPT 1313 and the documentation of the socialist heritage at the Museum of Life in the PRL and the Neon Museum. These commodified products of Warsaw’s tourism and entertainment culture fill a gap in the tourist market, based on the prototypical, nostalgic longing of tourists for a sensual and emotional experience of the “authentic past”. This predominantly participant observation-based ethnographic study on the practices, spaces, images and agents filling this touristic niche, illustrates how they create sensual-emotive, aesthetic and performative fields of reifying, discovering and experiencing the socialist past. Finally, the paper focuses on how these polyvalent mechanisms shape the tourist infrastructure of Warsaw oscillating between critical distancing and entertaining appropriation of the socialist heritage.

The Great Patriotic War in People’s memory: potential of personal origin sources and materials of oral history

Developing the problem of the formation and representation of the past, the mechanisms of memory transformation of past events both in individual and collective consciousness, modern researchers are paying more and more attention to the materials of oral history. The article analyzes the importance of oral history materials and documents of personal origin in the study of the Great Patriotic War history. The author believes that proactive documentation is an indispensable source for writing history in the “human dimension” and an excellent opportunity to commemorate memorable events of the war. Reflecting the individuality of storytellers, their cultural values and world outlook / worldview, as well as specific historical conditions that have formed individual views of the world, oral history materials demonstrate images and phenomena of the past that have become socially significant for certain generations, and carry factual and evaluative information. Through indepth interviews with the participants of the events, the researcher actualizes personally significant and socially important memories, transforming them into cultural and historical values. Considering the potential of these sources, the author identifies the main plotlines and themes that resonate with military issues; draws attention to the fact that they illustrate in detail the private world of a person. Due to natural departure of the Great Patriotic War eyewitnesses and contemporaries after the era, the author pays special attention to the accumulation and publication of memoirs that makes it possible to preserve the depth of historical memory horizons. Despite the common and different aspects in the structure and content of the constructed ideas about the war, she concludes that all materials of oral history are an important contribution to the preservation of the collective memory of the nation.