Facilitative Effects of Transcranial Direct Current Stimulation on Semantic Memory Examined by Text-Mining Analysis in Patients With Schizophrenia

Background: Beneficial effects of transcranial direct current stimulation (tDCS) are relevant to cognition and functional capacity, in addition to psychiatric symptoms in patients with schizophrenia. However, whether tDCS would improve higher-order cognition, e.g., semantic memory organization, has remained unclear. Recently, text-mining analyses have been shown to reveal semantic memory. The purpose of the current study was to determine whether tDCS would improve semantic memory, as evaluated by text-mining analyses of category fluency data, in patients with schizophrenia.Methods: Twenty-eight patients entered the study. Cognitive assessment including the category fluency task was conducted at baseline (before tDCS treatment) and 1 month after t administration of tDCS (2 mA × 20 min, twice per day) for 5 days, according to our previous study. The category fluency data were also obtained from 335 healthy control subjects. The verbal outputs (i.e., animal names) from the category fluency task were submitted to singular valued decomposition (SVD) analysis. Semantic memory structures were estimated by calculating inter-item cosines (i.e., similarities) among animal names frequently produced in the category fluency task. Data were analyzed longitudinally and cross-sectionally to compare the semantic structure within the patient group (i.e., baseline vs. follow-up) and between groups (patients vs. healthy controls). In the former, semantic associations for frequent items were compared in the form of cosine profiles, while in the latter, the difference in the magnitude of the correlations for inter-item cosines between healthy controls and patients (baseline, follow-up) was examined.Results: Cosine profiles in the patient group became more cluster-based (i.e., pet, carnivores, and herbivores) at follow-up compared to those at baseline, yielding higher cosines within subcategories. The correlational coefficient of inter-item cosines between healthy controls and patients was significantly greater at follow-up compared to baseline; semantic associations in patients approached the normality status after multi-session tDCS.Conclusions: To our knowledge, this is the first study to demonstrate the facilitative effect of tDCS on semantic memory organization in patients with schizophrenia. Text-mining analysis was indicated to effectively evaluate semantic memory structures in patients with psychiatric disorders.

The Similarity Structure of Real-World Memories

How do we mentally organize our memories of life events? Two episodes may be connected because they share a similar location, time period, activity, spatial environment, or social and emotional content. However, we lack an understanding of how each of these dimensions contributes to the perceived similarity of two life memories. We addressed this question with a data-driven approach, eliciting pairs of real-life memories from participants. Participants annotated the social, purposive, spatial, temporal, and emotional characteristics of their memories. We found that the overall similarity of memories was influenced by all of these factors, but to very different extents. Emotional features were the most consistent single predictor of overall memory similarity. Memories with different emotional tone were reliably perceived to be dissimilar, even when they occurred at similar times and places and involved similar people; conversely, memories with a shared emotional tone were perceived as similar even when they occurred at different times and places, and involved different people. A predictive model explained over half of the variance in memory similarity, using only information about (i) the emotional properties of events and (ii) the primary action or purpose of events. Emotional features may make an outsized contribution to event similarity because they provide compact summaries of an event’s goals and self-related outcomes, which are critical information for future planning and decision making. Thus, in order to understand and improve real-world memory function, we must account for the strong influence of emotional and purposive information on memory organization and memory search.SignificanceOur brains enable us to understand and act within the present, informed by previous, related life experience. But how are our life experiences organized so that one event can be related to another? Theories have suggested that we use spatiotemporal, social, causal, purposive, and emotional dimensions to inter-relate our memories; however, these organizing principles are usually studied using impersonal laboratory stimuli. Here, we mapped and modeled the connections between people’s own annotated life memories. We found that life events are linked by a variety of factors, but are predominantly connected in memory by their primary activity and emotional character. This highlights a need for theories of memory organization and retrieval to better account for the role of high-level actions and emotions.

Revealing the Role of Divergent Thinking and Fluid Intelligence in Children’s Semantic Memory Organization

The current theories suggest the fundamental role of semantic memory in creativity, mediating bottom-up (divergent thinking) and top-down (fluid intelligence) cognitive processes. However, the relationship between creativity, intelligence, and the organization of the semantic memory remains poorly-characterized in children. We investigated the ways in which individual differences in children’s semantic memory structures are influenced by their divergent thinking and fluid intelligence abilities. The participants (mean age 10) were grouped by their levels (high/low) of divergent thinking and fluid intelligence. We applied a recently-developed Network Science approach in order to examine group-based semantic memory graphs. Networks were constructed from a semantic fluency task. The results revealed that divergent thinking abilities are related to a more flexible structure of the semantic network, while fluid intelligence corresponds to a more structured semantic network, in line with the previous findings from the adult sample. Our findings confirm the crucial role of semantic memory organization in creative performance, and demonstrate that this phenomenon can be traced back to childhood. Finally, we also corroborate the network science methodology as a valid approach to the study of creative cognition in the developmental population.

МІНІМІЗАЦІЯ ЛОГІЧНОЇ СХЕМИ ДЛЯ РЕАЛІЗАЦІЇ PSEUDO LRU ШЛЯХОМ МІЖТИПОВОГО ПЕРЕХОДУ У ТРИГЕРНИХ СТРУКТУРАХ

The principle of program control means that the processor core turns to the main memory of the computer for operands or instructions. According to architectural features, operands are stored in data segments, and instructions are stored in code segments of the main memory. The operating system uses both page memory organization and segment memory organization. The page memory organization is always mapped to the segment organization. Due to the cached packet cycles of the processor core, copies of the main memory pages are stored in the internal associative cache memory. The associative cache memory consists of three units: a data unit, a tag unit, and an LRU unit. The data unit stores operands or instructions, the tag unit contains fragments of address information, and the LRU unit contains the logic of policy for replacement of string. The missing event attracts LRU logic to decide for substitution of reliable string in the data unit of associative cache memory. The pseudo-LRU algorithm is a simple and better substitution policy among known substitution policies. Two options for the minimization of the hardware for replacement policy by the pseudo-LRU algorithm in q - directed associative cache memory is implemented. The transition from the trigger structure of the synchronous D-trigger to the trigger structure of the synchronous JK-trigger is carried out reasonably in both options. The first option of minimization is based on the sequence for updating of the by the algorithm pseudo LRU, which allows deleting of the combinational logic for updating bits of LRU unit. The second option of minimization is based on the sequence for changing of the q - index of direction, as the consequence for updating the bits of LRU unit by the algorithm pseudo LRU. It allows additionally reducing the number of memory elements. Both options of the minimization allow improving such characteristics as productivity and reliability of the LRU unit.

Introduction and Overview

In this chapter, a brief overview of autobiographical memory and the general theme of this volume, autobiographical memory organization, is undertaken. In addition, a summary of each of the chapters is provided. The chapter is intended to acquaint the reader with the themes of the volume.