Working memory as an emergent property of the mind and brain

Supramodal and cross-modal representations of working memory in higher-order cortex

Working memory is essential for guiding our behaviors in daily life, where sensory information continuously flows from the external environment. While numerous studies have shown the involvement of sensory areas in maintaining working memory in a feature-specific manner, the challenge of utilizing retained sensory representations without interference from incoming stimuli of the same feature remains unresolved. To overcome this, essential information needs to be maintained dually in a form distinct from sensory representations. Here, using working memory tasks to retain braille patterns presented tactually or visually during fMRI scanning, we discovered two distinct forms of high-level working memory representations in the parietal and prefrontal cortex, together with modality-dependent sensory representations. First, we found supramodal representations in the superior parietal cortex that encoded braille identity in a consistent form, regardless of the involved sensory modality. Second, we observed that the prefrontal cortex and inferior parietal cortex specifically encoded cross-modal representations, which emerged during tasks requiring the association of information across sensory modalities, indicating a different high-level representation for integrating a broad range of sensory information. These findings suggest a framework for working memory maintenance that incorporates two distinct types of high-level representations-supramodal and cross-modal-operating alongside sensory representations.

Signal Intrusion Explains Divergent Effects of Visual Distraction on Working Memory

Perceptual distraction distorts visual working memories. Recent research has shown divergent effects of distraction on memory performance, including attractive biases, impairment of memory precision, and an increase in the guess rate, indicating multiple mechanisms of distraction interference. Here we propose a novel signal-intrusion model based on the TCC (target-confusability-competition) framework to reconcile those discrepant results. We hypothesized that sensory interference is driven by the integration of a target signal and an intrusive distractor signal. Model comparisons showed that this TCC-intrusion model had a superior fit to memory error distributions across three delayed-estimation tasks with distraction (N = 220 adults) compared with other candidate models. According to the model, distractor intrusions decreased along with target-distractor dissimilarity, in accordance with the sensory-recruitment hypothesis. Moreover, TCC-intrusion successfully replicated divergent effects of distraction on memory bias, precision, and guess rate using this one intrusion mechanism. Together, these results suggest that perceptual distractors affect working memories through a unified mechanism of signal intrusion.

The serial order system in word production and working memory: A case series approach

Serial order is important in verbal behavior, such as sequencing words in working memory (WM) or arranging phonemes during speech. In both WM and word production, distinct processes are found for item identity and their serial order. In the current study, we investigated whether a shared system supports the serial order of verbal items (phonemes or words) across cognitive functions (WM and production) and tasks (repetition and naming). We recruited 30 participants with chronic stroke-induced aphasia. We examined WM abilities to recall item and serial order information using immediate serial recall tasks of words. We also assessed the ability to accurately sequence phonemes in word repetition and naming tasks, with its impairment indexed by the proportion of misordered phonemes among all incorrect phonemes compared to chance in phonologically related word and nonword responses. We examined how variability of this index of serial order impairment in repetition and naming relates to item and serial order WM capacities. Our findings reveal that serial order WM capacity, but not item WM capacity, was associated with the severity of serial order impairment in repetition, indicating a shared serial order system for WM and repetition. We also found that item WM, but not serial order WM, was associated with serial order impairment in naming, implying an item WM buffer for phonemic sequencing in naming. These results suggest distinct sequencing processes for repetition and naming, each linked to different WM mechanisms. Implications for word production models and the relationship between WM and word production are discussed.

The emergent property of inhibitory control: implications of intermittent network-based fNIRS neurofeedback training

Background

Studies have shown that inhibitory control is supported by frontal cortex and small-world brain networks. However, it remains unclear how regulating the topology changes the inhibitory control. We investigated the effects of small-worldness upregulation training on resting-state networks via fNIRS neurofeedback training, which will contribute to a deeper insight of inhibitory control.

Methods

A five-day training session was used to regulate the small-worldness of the frontal cortex, and the color-word Stroop task was tested before and after training. Fifty healthy adults were recruited and randomly assigned to the sham feedback group (sham group), or intermittent fNIRS-based brain network feedback group (fNIRS-NF group). On the basis of the exclusion of incomplete data, 45 valid data sets were retained and analyzed (sham: 21, fNIRS-NF: 24).

Results

Training increased resting-state small-worldness and improved Stroop task performance, with a significant correlation between these changes (r = -0.32, p = 0.032). The fNIRS-NF group exhibited reduced hemodynamic activation (βvalue decreased, indicating lower cognitive load) during posttest and follow-up. Notably, the right dorsolateral prefrontal cortex (dlPFC) showed greater intra-regional connectivity increases than the left dlPFC, suggesting asymmetric plasticity.

Conclusion

Intermittent fNIRS neurofeedback effectively modulates resting-state small-world networks and enhances inhibitory control, with effects sustained for at least one week. These findings highlight small-worldness as a novel target for cognitive interventions.

Working memory needs pointers

Cognitive neuroscience has converged on a definition of working memory (WM) as a capacity-limited system that maintains highly accessible representations via stimulus-specific neural patterns. We argue that this standard definition may be incomplete. We highlight the fundamental need to recognize specific instances or tokens and to bind those tokens to the surrounding context. We propose that contextual binding is supported by spatiotemporal 'pointers' and that pointers are the source of neural signals that track the number of stored items, independent of their content. These content-independent pointers may provide a productive perspective for understanding item-based capacity limits in WM and the role of WM as a gateway for long-term storage.

Behaviorally Irrelevant Feature Matching Increases Neural and Behavioral Working Memory Readout

There is an ongoing debate about whether working memory (WM) maintenance relies on persistent activity and/or short-term synaptic plasticity. This is a challenging question, because neuroimaging techniques in cognitive neuroscience measure activity only. Recently, neural perturbation techniques have been developed to tackle this issue, such as visual impulse perturbation or "pinging," which reveals (un)attended WM content during maintenance. There are contrasting explanations of how pinging reveals WM content, which is central to the debate. Pinging could reveal mnemonic representations by perturbing content-specific networks or by increasing the neural signal-to-noise ratio of active neural states. Here we tested the extent to which the neural impulse response is patterned by the WM network, by presenting two different impulse stimuli. If the impulse interacts with WM networks, the WM-specific impulse response should be enhanced by physical overlap between the initial memory item and the subsequent external perturbation stimulus. This prediction was tested in a working memory task by matching or mismatching task-irrelevant spatial frequencies between memory items and impulse stimuli, as well as probes. Matching probe spatial frequency with memory items resulted in faster behavioral response times and matching impulse spatial frequency with memory items increased the specificity of the neural impulse response as measured from EEG. Matching spatial frequencies did neither result in globally stronger neural responses nor in a larger decrease in trial-to-trial variability compared to mismatching spatial frequencies. The improved neural and behavioral readout of irrelevant feature matching provide evidence that impulse perturbation interacts directly with the memory representations.

Separate orexigenic hippocampal ensembles shape dietary choice by enhancing contextual memory and motivation

The hippocampus (HPC) has emerged as a critical player in the control of food intake, beyond its well-known role in memory. While previous studies have primarily associated the HPC with food intake inhibition, recent research suggests a role in appetitive processes. Here we identified spatially distinct neuronal populations within the dorsal HPC (dHPC) that respond to either fats or sugars, potent natural reinforcers that contribute to obesity development. Using activity-dependent genetic capture of nutrient-responsive dHPC neurons, we demonstrate a causal role of both populations in promoting nutrient-specific intake through different mechanisms. Sugar-responsive neurons encoded spatial memory for sugar location, whereas fat-responsive neurons selectively enhanced the preference and motivation for fat intake. Importantly, stimulation of either nutrient-responsive dHPC neurons increased food intake, while ablation differentially impacted obesogenic diet consumption and prevented diet-induced weight gain. Collectively, these findings uncover previously unknown orexigenic circuits underlying macronutrient-specific consumption and provide a foundation for developing potential obesity treatments.

A tale of two algorithms: Structured slots explain prefrontal sequence memory and are unified with hippocampal cognitive maps

Remembering events is crucial to intelligent behavior. Flexible memory retrieval requires a cognitive map and is supported by two key brain systems: hippocampal episodic memory (EM) and prefrontal working memory (WM). Although an understanding of EM is emerging, little is understood of WM beyond simple memory retrieval. We develop a mathematical theory relating the algorithms and representations of EM and WM by unveiling a duality between storing memories in synapses versus neural activity. This results in a formalism of prefrontal WM as structured, controllable neural subspaces (activity slots) representing dynamic cognitive maps without synaptic plasticity. Using neural networks, we elucidate differences, similarities, and trade-offs between the hippocampal and prefrontal algorithms. Lastly, we show that prefrontal representations in tasks from list learning to cue-dependent recall are unified as controllable activity slots. Our results unify frontal and temporal representations of memory and offer a new understanding for dynamic prefrontal representations of WM.

Eye movements follow the dynamic shifts of attention through serial order in verbal working memory

How are arbitrary sequences of verbal information retained and manipulated in working memory? Increasing evidence suggests that serial order in verbal WM is spatially coded and that spatial attention is involved in access and retrieval. Based on the idea that brain areas controlling spatial attention are also involved in oculomotor control, we used eye tracking to reveal how the spatial structure of serial order information is accessed in verbal working memory. In two experiments, participants memorized a sequence of auditory words in the correct order. While their eye movements were being measured, they named the memorized items in a self-determined order in Experiment 1 and in a cued order in Experiment 2. We tested the hypothesis that serial order in verbal working memory interacts with the spatial attention system whereby gaze patterns in visual space closely follow attentional shifts in the internal space of working memory. In both experiments, we found that the gaze shifts in visual space correlated with the spatial shifts of attention along the left-to-right one-dimensional mapping of serial order positions in verbal WM. These findings suggest that spatial attention is employed for dynamically searching through verbal WM and that eye movements reflect the spontaneous association of order and space even in the absence of visuospatial input.

A shared serial order system for verbal working memory and language production: evidence from aphasia

Many aspects of human performance require producing sequences of items in serial order. The current study takes a multiple-case approach to investigate whether the system responsible for serial order is shared across cognitive domains, focusing on working memory (WM) and word production. Serial order performance in three individuals with post-stroke language and verbal WM disorders (hereafter persons with aphasia, PWAs) were assessed using recognition and recall tasks for verbal and visuospatial WM, as well as error analyses in spoken and written production tasks to assess whether there was a tendency to produce the correct phonemes/letters in the wrong order. One PWA exhibited domain-specific serial order deficits in verbal and visuospatial WM. The PWA with verbal serial order WM deficit made more serial order errors than expected by chance in both repetition and writing-to-dictation tasks, whereas the other two PWAs showed no serial order deficits in verbal WM and production tasks. These findings suggest separable serial order systems for verbal and visuospatial WM and a shared system for serial order processing in verbal WM and word production. Implications for the domain-generality of WM, its connection to language production, and serial order processing across cognitive functionssc are discussed.

Verbal Encoding Strategies in Visuo-Spatial Working Memory

Visual working memory and verbal storage are often investigated independently of one another. However, a growing body of evidence suggests that naming visual stimuli can provide an advantage in performance during visual working memory tasks. On the other hand, there is also evidence that labeling could lead to biases in recall. Here, we present an exploratory investigation of verbal labels associated with the memorization of simple visuo-spatial stimuli, and how the use of these labels informs recall behavior of the same stimuli in a separate working memory task. English-speaking participants performed a working memory task with orientation and location stimuli, followed by a separate naming task featuring the same stimuli. We found a diverse set of labels employed frequently and with a consistent distribution across stimulus types, the stimulus space, and among participants. The use of individual spatial words, predicted class 1 cardinal biases in memory (i.e. the observation that cardinal stimuli are more accurately recalled than non-cardinal ones). Conversely, words expressing uncertainty (e.g. 'slightly', 'near') predicted class 2 cardinal bias (i.e. recall biases away from the cardinal planes). This relationship between word use and recall biases is consistent with shared representational resources that are used for both visuo-spatial and verbal working memory.

Congruent Prosody Reduces Cognitive Effort in Memory for Spoken Sentences: A Pupillometric Study with Young and Older Adults

BACKGROUND

In spite of declines in working memory and other processes, older adults generally maintain good ability to understand and remember spoken sentences. In part this is due to preserved knowledge of linguistic rules and their implementation. Largely overlooked, however, is the support older adults may gain from the presence of sentence prosody (pitch contour, lexical stress, intra-and inter-word timing) as an aid to detecting the structure of a heard sentence.

METHODS

Twenty-four young and 24 older adults recalled recorded sentences in which the sentence prosody corresponded to the clausal structure of the sentence, when the prosody was in conflict with this structure, or when there was reduced prosody uninformative with regard to the clausal structure. Pupil size was concurrently recorded as a measure of processing effort.

RESULTS

Both young and older adults' recall accuracy was superior for sentences heard with supportive prosody than for sentences with uninformative prosody or for sentences in which the prosodic marking and causal structure were in conflict. The measurement of pupil dilation suggested that the task was generally more effortful for the older adults, but with both groups showing a similar pattern of effort-reducing effects of supportive prosody.

CONCLUSIONS

Results demonstrate the influence of prosody on young and older adults' ability to recall accurately multi-clause sentences, and the significant role effective prosody may play in preserving processing effort.

Working Memory Is as Working Memory Does: A Pluralist Take on the Center of the Mind

Working memory is thought to be the psychological capacity that enables us to maintain or manipulate information no longer in our environment for goal-directed action. Recent work argues that working memory is not a so-called natural kind and in turn cannot explain the cognitive processes attributed to it. This paper first clarifies the scope of this earlier critique and argues for a pluralist account of working memory. Under this account, working memory is variously realized by many mechanisms that contribute to the maintenance and manipulation of information across tasks. This view in effect updates one of the earliest pluralist formulations of working memory. Juxtaposing this view against deflationary descriptions allows us to delineate two gradients that help us chart various accounts of working memory and identify their respective theoretical commitments. In turn, we can isolate those accounts that fail to accord with the evidence supporting a pluralist view, and we can begin to rehabilitate working memory as a pluralist, and ultimately more informative, construct.

A domain-general process for theta-rhythmic sampling of either environmental information or internally stored information

Many everyday tasks, such as shopping for groceries, require the sampling of both environmental information and internally stored information. Selective attention involves the preferential processing and sampling of behaviorally important information from the external environment, while working memory involves the preferential processing and sampling of behaviorally important, internally stored information. These essential cognitive processes share neural resources within a large-scale network that includes frontal, parietal, and sensory cortices, and these shared neural resources can lead to between-domain interactions. Previous research has linked external sampling during selective attention and internal sampling during working memory to theta-rhythmic (3-8 Hz) neural activity in higher-order (e.g., frontal cortices) and sensory regions (e.g., visual cortices). Such theta-rhythmic neural activity might help to resolve the competition for shared neural resources by isolating neural activity associated with different functions over time. Here, we used EEG and a dual-task design (i.e., a task that required both external and internal sampling) to directly compare (i) theta-dependent fluctuations in behavioral performance during external sampling with (ii) theta-dependent fluctuations in behavioral performance during internal sampling. Our findings are consistent with a domain-general, theta-rhythmic process for sampling either external information or internal information. We further demonstrate that interactions between external and internal information-specifically, when to-be-detected information matches to-be-remembered information-are not dependent on theta-band activity (i.e., theta phase). Given that these theta-independent 'match effects' occur during early processing stages (peaking at 75 ms), we propose that theta-rhythmic sampling modulates external and internal information during later processing stages.

Sequential syntactic knowledge supports item but not order recall in verbal working memory

Previous studies have shown that psycholinguistic effects such as lexico-semantic knowledge effects mainly determine item recall in verbal working memory (WM). However, we may expect that syntactic knowledge, involving knowledge about word-level sequential aspects of language, should also impact serial-order aspects of recall in WM. Evidence for this assumption is scarce and inconsistent and has been conducted in language with deterministic syntactic rules. In languages such as French, word position is determined in a probabilistic manner: an adjective is placed before or after a noun, depending on its lexico-semantic properties. We exploited this specificity of the French language for examining the impact of syntactic positional knowledge on both item and serial order recall in verbal WM. We presented lists with adjective-noun pairs for immediate serial recall, the adjectives being in regular or irregular position relative to the nouns. We observed increased recall performance when adjectives occurred in regular position; this effect was observed for item recall but not order recall scores. We propose an integration of verbal WM and syntactic processing models to account for this finding by assuming that the impact of syntactic knowledge on serial-order WM recall is indirect and mediated via syntax-dependent item-retrieval processes.

The strength of anticipated distractors shapes EEG alpha and theta oscillations in a Working Memory task

Working Memory (WM) requires maintenance of task-relevant information and suppression of task-irrelevant/distracting information. Alpha and theta oscillations have been extensively investigated in relation to WM. However, studies that examine both theta and alpha bands in relation to distractors, encompassing not only power modulation but also connectivity modulation, remain scarce. Here, we depicted, at the EEG-source level, the increase in power and connectivity in theta and alpha bands induced by strong relative to weak distractors during a visual Sternberg-like WM task involving the encoding of verbal items. During retention, a strong or weak distractor was presented, predictable in time and nature. Analysis focused on the encoding and retention phases before distractor presentation. Theta and alpha power were computed in cortical regions of interest, and connectivity networks estimated via spectral Granger causality and synthetized using in/out degree indices. The following modulations were observed for strong vs. weak distractors. In theta band during encoding, the power in frontal regions increased, together with frontal-to-frontal and bottom-up occipital-to-temporal-to-frontal connectivity; even during retention, bottom-up theta connectivity increased. In alpha band during retention, but not during encoding, the power in temporal-occipital regions increased, together with top-down frontal-to-occipital and temporal-to-occipital connectivity. From our results, we postulate a proactive cooperation between theta and alpha mechanisms: the first would mediate enhancement of target representation both during encoding and retention, and the second would mediate increased inhibition of sensory areas during retention only, to suppress the processing of imminent distractor without interfering with the processing of ongoing target stimulus during encoding.

Lateral prefrontal cortex controls interplay between working memory and actions

Humans must often keep multiple task goals in mind, at different levels of priority and immediacy, while also interacting with the environment. We might need to remember information for an upcoming task while engaged in more immediate actions. Consequently, actively maintained working memory (WM) content may bleed into ongoing but unrelated motor behavior. Here, we experimentally test the impact of WM maintenance on action execution, and we transcranially stimulate lateral prefrontal cortex (PFC) to parse its functional contributions to WM-motor interactions. We first created a task scenario wherein human participants (both sexes) executed cued hand movements during WM maintenance. We manipulated the compatibility between WM and movement goals at the trial level and the statistical likelihood that the two would be compatible at the block level. We found that remembering directional words (e.g., 'left', 'down') biased the trajectory and speed of hand movements that occurred during the WM delay, but the bias was dampened in blocks when WM content predictably conflicted with movement goals. Then we targeted left lateral PFC with two different transcranial magnetic stimulation (TMS) protocols before participants completed the task. We found that an intermittent theta-burst protocol, which is thought to be excitatory, dampened sensitivity to block-level control demands (i.e., proactive control), while a continuous theta-burst protocol, which is thought to be inhibitory, dampened adaptation to trial-by-trial conflict (i.e., reactive control). Therefore, lateral PFC is involved in controlling the interplay between WM content and manual action, but different PFC mechanisms may support different time-scales of adaptive control.

From long-term to short-term: Distinct neural networks underlying semantic knowledge and its recruitment in working memory

Although numerous studies suggest that working memory (WM) and semantic long-term knowledge interact, the nature and underlying neural mechanisms of this intervention remain poorly understood. Using functional magnetic resonance imaging (fMRI), this study investigated the extent to which neural markers of semantic knowledge in long-term memory (LTM) are activated during the WM maintenance stage in 32 young adults. First, the multivariate neural patterns associated with four semantic categories were determined via an implicit semantic activation task. Next, the participants maintained words - the names of the four semantic categories implicitly activated in the first task - in a verbal WM task. Multi-voxel pattern analyses showed reliable neural decoding of the four semantic categories in the implicit semantic activation and the verbal WM tasks. Critically, however, no between-task classification of semantic categories was observed. Searchlight analyses showed that for the WM task, semantic category information could be decoded in anterior temporal areas associated with abstract semantic category knowledge. In the implicit semantic activation task, semantic category information was decoded in superior temporal, occipital and frontal cortices associated with domain-specific semantic feature representations. These results indicate that item-level semantic activation during verbal WM involves shallow rather than deep semantic information.

Comparing Neural Correlates of Memory Encoding and Maintenance for Foveal and Peripheral Stimuli

Visual working memory is believed to rely on top-down attentional mechanisms that sustain active sensory representations in early visual cortex, a mechanism referred to as sensory recruitment. However, both bottom-up sensory input and top-down attentional modulations thereof appear to prioritize the fovea over the periphery, such that initially peripheral percepts may even be assimilated by foveal processes. This raises the question whether and how visual working memory differs for central and peripheral input. To address this, we conducted a delayed orientation recall task in which an orientation was presented either at the center of the screen or at 15° eccentricity to the left or right. Response accuracy, EEG activity, and gaze position were recorded from 30 participants. Accuracy was slightly but significantly higher for foveal versus peripheral memories. Decoding of EEG recordings revealed a clear dissociation between early sensory and later maintenance signals. Although sensory signals were clearly decodable for foveal stimuli, they were not for peripheral input. In contrast, maintenance signals were equally decodable for both foveal and peripheral memories, suggesting comparable top-down components regardless of eccentricity. Moreover, although memory representations were initially spatially specific and reflected in voltage fluctuations, later during the maintenance period, they generalized across locations, as emerged in alpha oscillations, thus revealing a dynamic transformation within memory from separate sensory traces to what we propose are common output-related codes. Furthermore, the combined absence of reliable decoding of sensory signals and robust presence of maintenance decoding indicates that storage activity patterns as measured by EEG reflect signals beyond primary visual cortex. We discuss the implications for the sensory recruitment hypothesis.

Inter-individual variability (but intra-individual stability) of overt versus covert rehearsal strategies in a digital Corsi task

The Corsi (block-tapping) paradigm is a classic and well-established visuospatial working memory task in humans involving internal computations (memorizing of item sequences, organizing and updating the memorandum, and recall processes), as well as both overt and covert shifts of attention to facilitate rehearsal, serving to maintain the Corsi sequences during the retention phase. Here, we introduce a novel digital version of a Corsi task in which i) the difficulty of the memorandum (using sequence lengths ranging from 3 to 8) was controlled, ii) the execution of overt and/or covert attention as well as the visuospatial working memory load during the retention phase was manipulated, and iii) shifts of attention were quantified in all experimental phases. With this, we present behavioral data that demonstrate, characterize, and classify the individual effects of overt and covert strategies used as a means of encoding and rehearsal. In a full within-subject design, we tested 28 participants who had to solve three different Corsi conditions. While in condition A neither of the two strategies were restricted, in condition B the overt and in condition C the overt as well as the covert strategies were suppressed. Analyzing Corsi span, (eye) exploration index, and pupil size (change), data clearly show a continuum between overt and covert strategies over all participants (indicating inter-individual variability). Further, all participants showed stable strategy choice (indicating intra-individual stability), meaning that the preferred strategy was maintained in all three conditions, phases, and sequence lengths of the experiment.

Towards optimized methodological parameters for maximizing the behavioral effects of transcranial direct current stimulation

Introduction

Transcranial direct current stimulation (tDCS) administers low-intensity direct current electrical stimulation to brain regions via electrodes arranged on the surface of the scalp. The core promise of tDCS is its ability to modulate brain activity and affect performance on diverse cognitive functions (affording causal inferences regarding regional brain activity and behavior), but the optimal methodological parameters for maximizing behavioral effects remain to be elucidated. Here we sought to examine the effects of 10 stimulation and experimental design factors across a series of five cognitive domains: motor performance, visual search, working memory, vigilance, and response inhibition. The objective was to identify a set of optimal parameter settings that consistently and reliably maximized the behavioral effects of tDCS within each cognitive domain.

Methods

We surveyed tDCS effects on these various cognitive functions in healthy young adults, ultimately resulting in 721 effects across 106 published reports. Hierarchical Bayesian meta-regression models were fit to characterize how (and to what extent) these design parameters differentially predict the likelihood of positive/negative behavioral outcomes.

Results

Consistent with many previous meta-analyses of tDCS effects, extensive variability was observed across tasks and measured outcomes. Consequently, most design parameters did not confer consistent advantages or disadvantages to behavioral effects-a domain-general model suggested an advantage to using within-subjects designs (versus between-subjects) and the tendency for cathodal stimulation (relative to anodal stimulation) to produce reduced behavioral effects, but these associations were scarcely-evident in domain-specific models.

Discussion

These findings highlight the urgent need for tDCS studies to more systematically probe the effects of these parameters on behavior to fulfill the promise of identifying causal links between brain function and cognition.

Neuronal representation of visual working memory content in the primate primary visual cortex

The human ability to perceive vivid memories as if they "float" before our eyes, even in the absence of actual visual stimuli, captivates the imagination. To determine the neural substrates underlying visual memories, we investigated the neuronal representation of working memory content in the primary visual cortex of monkeys. Our study revealed that neurons exhibit unique responses to different memory contents, using firing patterns distinct from those observed during the perception of external visual stimuli. Moreover, this neuronal representation evolves with alterations in the recalled content and extends beyond the retinotopic areas typically reserved for processing external visual input. These discoveries shed light on the visual encoding of memories and indicate avenues for understanding the remarkable power of the mind's eye.

Same, Same but Different? A Multi-Method Review of the Processes Underlying Executive Control

Attention, working memory, and executive control are commonly considered distinct cognitive functions with important reciprocal interactions. Yet, longstanding evidence from lesion studies has demonstrated both overlap and dissociation in their behavioural expression and anatomical underpinnings, suggesting that a lower dimensional framework could be employed to further identify processes supporting goal-directed behaviour. Here, we describe the anatomical and functional correspondence between attention, working memory, and executive control by providing an overview of cognitive models, as well as recent data from lesion studies, invasive and non-invasive multimodal neuroimaging and brain stimulation. We emphasize the benefits of considering converging evidence from multiple methodologies centred on the identification of brain mechanisms supporting goal-driven behaviour. We propose that expanding on this approach should enable the construction of a comprehensive anatomo-functional framework with testable new hypotheses, and aid clinical neuroscience to intervene on impairments of executive functions.

Visual working memories are abstractions of percepts

During perception, decoding the orientation of gratings depends on complex interactions between the orientation of the grating, aperture edges, and topographic structure of the visual map. Here, we aimed to test how aperture biases described during perception affect working memory (WM) decoding. For memoranda, we used gratings multiplied by radial and angular modulators to generate orthogonal aperture biases for identical orientations. Therefore, if WM representations are simply maintained sensory representations, they would have similar aperture biases. If they are abstractions of sensory features, they would be unbiased and the modulator would have no effect on orientation decoding. Neural patterns of delay period activity while maintaining the orientation of gratings with one modulator (e.g. radial) were interchangeable with patterns while maintaining gratings with the other modulator (e.g. angular) in visual and parietal cortex, suggesting that WM representations are insensitive to aperture biases during perception. Then, we visualized memory abstractions of stimuli using models of visual field map properties. Regardless of aperture biases, WM representations of both modulated gratings were recoded into a single oriented line. These results provide strong evidence that visual WM representations are abstractions of percepts, immune to perceptual aperture biases, and compel revisions of WM theory.

Neural Signatures of Competition between Voluntary and Involuntary Influences over the Focus of Attention in Visual Working Memory

Adaptive behavior relies on the selection and prioritization of relevant sensory inputs from the external environment as well as from among internal sensory representations held in working memory. Recent behavioral evidence suggests that the classic distinction between voluntary (goal-driven) and involuntary (stimulus-driven) influences over attentional allocation also applies to the selection of internal representations held in working memory. In the current EEG study, we set out to investigate the neural dynamics associated with the competition between voluntary and involuntary control over the focus of attention in visual working memory. We show that when voluntary and involuntary factors compete for the internal focus of attention, prioritization of the appropriate item is delayed-as reflected both in delayed gaze biases that track internal selection and in delayed neural beta (15-25 Hz) dynamics that track the planning for the upcoming memory-guided manual action. We further show how this competition is paralleled-possibly resolved-by an increase in frontal midline theta (4-8 Hz) activity that, moreover, predicts the speed of ensuing memory-guided behavior. Finally, because theta increased following retrocues that effectively reduced working-memory load, our data unveil how frontal theta activity during internal attentional focusing tracks demands on cognitive control over and above working-memory load. Together, these data yield new insight into the neural dynamics that govern the focus of attention in visual working memory, and disentangle the contributions of frontal midline theta activity to the processes of control versus retention in working memory.

Social prioritisation in scene viewing and the effects of a spatial memory load

When free-viewing scenes, participants tend to preferentially fixate social elements (e.g., people). In the present study, we tested whether this bias would be disrupted by increasing the demands of a secondary dual-task: holding a set of (one or six) spatial locations in memory, presented either simultaneously or sequentially. Following a retention interval, participants judged whether a test location was present in the to-be-remembered stimuli. During the retention interval participants free-viewed scenes containing a social element (a person) and a non-social element (an object) that served as regions of interest. In order to assess the impact of physical salience, the non-social element was presented in both an unaltered baseline version, and in a version where its salience was artificially increased. The results showed that the preference to look at social elements decreased when the demands of the spatial memory task were increased from one to six locations, regardless of presentation mode (simultaneous or sequential). The high-load condition also resulted in more central fixations and reduced exploration of the scene. The results indicate that the social prioritisation effect, and scene viewing more generally, can be affected by a concurrent memory load.

Divergent roles of early visual cortex and inferior frontal junction in visual working memory

BACKGROUND

Recent studies indicate that both prefrontal and visual regions play critical roles in visual working memory (VWM), with prefrontal regions mainly associated with executive functions, and visual cortices linked to representations of memory contents. VWM involves the selective filtering of irrelevant information, yet the specific contributions of the prefrontal regions and visual cortex in this process remain unclear.

OBJECTIVE

To understand the dynamic causal roles of prefrontal and visual regions in VWM.

METHODS

The differentiation of VWM components was achieved using a computational model that incorporated a swap rate for non-target stimuli. Single-pulse magnetic transcranial stimulation (spTMS) was delivered to the early visual cortex (EVC) and the inferior frontal junction (IFJ) across different phases of an orientation recall task that with or without distractors.

RESULTS

Our results indicate that spTMS over the EVC and IFJ influences VWM particularly when distractors are present. VWM precision can be impacted by spTMS applied to either region during the early retention, while spTMS effect is especially prominent when EVC is stimulated during the late retention phase and when directed at the ipsilateral EVC. Conversely, the probability of accurately recalling the target exhibited comparable patterns when spTMS was administered to either the EVC or IFJ.

CONCLUSIONS

We highlight the "sensory recruitment" of VWM characterized by critical involvement of EVC particularly in the information-filtering process within VWM. The maintenance of memory content representations necessitates ongoing communication between the EVC and IFJ throughout the entirety of the VWM process in a dynamic pattern.

Visual working memories are abstractions of percepts

Pioneering studies demonstrating that the contents of visual working memory (WM) can be decoded from the patterns of multivoxel activity in early visual cortex transformed not only how we study WM, but theories of how memories are stored. For instance, the ability to decode the orientation of memorized gratings is hypothesized to depend on the recruitment of the same neural encoding machinery used for perceiving orientations. However, decoding evidence cannot be used to test the so-called sensory recruitment hypothesis without understanding the underlying nature of what is being decoded. Although unknown during WM, during perception decoding the orientation of gratings does not simply depend on activities of orientation tuned neurons. Rather, it depends on complex interactions between the orientation of the grating, the aperture edges, and the topographic structure of the visual map. Here, our goals are to 1) test how these aperture biases described during perception may affect WM decoding, and 2) leverage carefully manipulated visual stimulus properties of gratings to test how sensory-like are WM codes. For memoranda, we used gratings multiplied by radial and angular modulators to generate orthogonal aperture biases despite having identical orientations. Therefore, if WM representations are simply maintained sensory representations, they would have similar aperture biases. If they are abstractions of sensory features, they would be unbiased and the modulator would have no effect on orientation decoding. Results indicated that fMRI patterns of delay period activity while maintaining the orientation of a grating with one modulator (eg, radial) were interchangeable with patterns while maintaining a grating with the other modulator (eg, angular). We found significant cross-classification in visual and parietal cortex, suggesting that WM representations are insensitive to aperture biases during perception. Then, we visualized memory abstractions of stimuli using a population receptive field model of the visual field maps. Regardless of aperture biases, WM representations of both modulated gratings were recoded into a single oriented line. These results provide strong evidence that visual WM representations are abstractions of percepts, immune to perceptual aperture biases, and compel revisions of WM theory.

Encoded and updated spatial working memories share a common representational format in alpha activity

Working memory (WM) flexibly updates information to adapt to the dynamic environment. Here, we used alpha-band activity in the EEG to reconstruct the content of dynamic WM updates and compared this representational format to static WM content. An inverted encoding model using alpha activity precisely tracked both the initially encoded position and the updated position following an auditory cue signaling mental updating. The timing of the update, as tracked in the EEG, correlated with reaction times and saccade latency. Finally, cross-training analyses revealed a robust generalization of alpha-band reconstruction of WM contents before and after updating. These findings demonstrate that alpha activity tracks the dynamic updates to spatial WM and that the format of this activity is preserved across the encoded and updated representations. Thus, our results highlight a new approach for measuring updates to WM and show common representational formats during dynamic mental updating and static storage.

The reactivation of task rules triggers the reactivation of task-relevant items

Working memory (WM) describes the temporary storage of task-relevant items and procedural rules to guide action. Despite its central importance for goal-directed behavior, the interplay between WM and long-term memory (LTM) remains poorly understood. Recent studies have shown that repeated use of the same task-relevant item in WM results in a hand-off of the storage of that item to LTM, and switching to a new item reactivates WM. To further elucidate the rules governing WM-LTM interactions, we here planned to probe whether a change in task rules, independent of a switch in task-relevant items, would also lead to WM reactivation of maintained items. To this end, we used scalp-recorded electroencephalogram (EEG) data, specifically the contralateral delay activity (CDA), to track WM item storage while manipulating repetitions and changes in task rules and task-relevant items across trials in a visual WM task. We tested two rival hypotheses: If changes in task rules result in a reactivation of the target item representation, then the CDA should increase when a task change is cued even when the same target has been repeated across trials. However, if the reactivation of a task-relevant item only depends on the mnemonic availability of the item itself instead of the task it is used for, then only the changes in task-relevant items should reactivate the representations. Accordingly, the CDA amplitude should decrease for repeated task-relevant items independently of a task change. We found a larger CDA on task-switch compared to task-repeat trials, suggesting that the reactivation of task rules triggers the reactivation of task-relevant items in WM. By demonstrating that WM reactivation of LTM is interdependent for task rules and task-relevant items, this study informs our understanding of visual WM and its interplay with LTM. PREREGISTERED STAGE 1 PROTOCOL: https://osf.io/zp9e8 (date of in-principle acceptance: 19/12/2021).

No obligatory trade-off between the use of space and time for working memory

Space and time can each act as scaffolds for the individuation and selection of visual objects in working memory. Here we ask whether there is a trade-off between the use of space and time for visual working memory: whether observers will rely less on space, when memoranda can additionally be individuated through time. We tracked the use of space through directional biases in microsaccades after attention was directed to memory contents that had been encoded simultaneously or sequentially to the left and right of fixation. We found that spatial gaze biases were preserved when participants could (Experiment 1) and even when they had to (Experiment 2) additionally rely on time for object individuation. Thus, space remains a profound organizing medium for working memory even when other organizing sources are available and utilized, with no evidence for an obligatory trade-off between the use of space and time.

Self-pacing ameliorates recall deficit when listening to vocoded discourse: a cochlear implant simulation

Introduction

In spite of its apparent ease, comprehension of spoken discourse represents a complex linguistic and cognitive operation. The difficulty of such an operation can increase when the speech is degraded, as is the case with cochlear implant users. However, the additional challenges imposed by degraded speech may be mitigated to some extent by the linguistic context and pace of presentation.

Methods

An experiment is reported in which young adults with age-normal hearing recalled discourse passages heard with clear speech or with noise-band vocoding used to simulate the sound of speech produced by a cochlear implant. Passages were varied in inter-word predictability and presented either without interruption or in a self-pacing format that allowed the listener to control the rate at which the information was delivered.

Results

Results showed that discourse heard with clear speech was better recalled than discourse heard with vocoded speech, discourse with a higher average inter-word predictability was better recalled than discourse with a lower average inter-word predictability, and self-paced passages were recalled better than those heard without interruption. Of special interest was the semantic hierarchy effect: the tendency for listeners to show better recall for main ideas than mid-level information or detail from a passage as an index of listeners' ability to understand the meaning of a passage. The data revealed a significant effect of inter-word predictability, in that passages with lower predictability had an attenuated semantic hierarchy effect relative to higher-predictability passages.

Discussion

Results are discussed in terms of broadening cochlear implant outcome measures beyond current clinical measures that focus on single-word and sentence repetition.

Interactions between functional networks in Parkinson's disease mild cognitive impairment

The study of mild cognitive impairment (MCI) is critical to understand the underlying processes of cognitive decline in Parkinson's disease (PD). Functional connectivity (FC) disruptions in PD-MCI patients have been observed in several networks. However, the functional and cognitive changes associated with the disruptions observed in these networks are still unclear. Using a data-driven methodology based on independent component analysis, we examined differences in FC RSNs among PD-MCI, PD cognitively normal patients (PD-CN) and healthy controls (HC) and studied their associations with cognitive and motor variables. A significant difference was found between PD-MCI vs PD-CN and HC in a FC-trait comprising sensorimotor (SMN), dorsal attention (DAN), ventral attention (VAN) and frontoparietal (FPN) networks. This FC-trait was associated with working memory, memory and the UPDRS motor scale. SMN involvement in verbal memory recall may be related with the FC-trait correlation with memory deficits. Meanwhile, working memory impairment may be reflected in the DAN, VAN and FPN interconnectivity disruptions with the SMN. Furthermore, interactions between the SMN and the DAN, VAN and FPN network reflect the intertwined decline of motor and cognitive abilities in PD-MCI. Our findings suggest that the memory impairments observed in PD-MCI are associated with reduced FC within the SMN and between SMN and attention networks.

Cognitive dysfunction in post-COVID-19 condition: Mechanisms, management, and rehabilitation

The long-term effects of COVID-19 on cognitive function have become an area of increasing concern. This paper provides an overview of characteristics, risk factors, possible mechanisms, and management strategies for cognitive dysfunction in post-COVID-19 condition (PCC). Prolonged cognitive dysfunction is one of the most common impairments in PCC, affecting between 17% and 28% of the individuals more than 12 weeks after the infection and persisting in some cases for several years. Cognitive dysfunctions can be manifested as a wide range of symptoms including memory impairment, attention deficit, executive dysfunction, and reduced processing speed. Risk factors for developing PCC, with or without cognitive impairments, include advanced age, preexisting medical conditions, and the severity of acute illness. The underlying mechanisms remain unclear, but proposed contributors include neuroinflammation, hypoxia, vascular damage, and latent virus reactivation not excluding the possibility of direct viral invasion of the central nervous system, illustrating complex viral pathology. As the individual variation of the cognitive impairments is large, a neuropsychological examination and a person-centered multidimensional approach are required. According to the World Health Organization, limited evidence on COVID-19-related cognitive impairments necessitates implementing rehabilitation interventions from established practices of similar conditions. Psychoeducation and compensatory skills training are recommended. Assistive products and environmental modifications adapted to individual needs might be helpful. In specific attention- and working memory dysfunctions, cognitive training-carefully monitored for intensity-might be effective for people who do not suffer from post-exertional malaise. Further research is crucial for evidence-based interventions specific to COVID-19-related cognitive impairments.

Learning efficient representations of environmental priors in working memory

Experience shapes our expectations and helps us learn the structure of the environment. Inference models render such learning as a gradual refinement of the observer's estimate of the environmental prior. For instance, when retaining an estimate of an object's features in working memory, learned priors may bias the estimate in the direction of common feature values. Humans display such biases when retaining color estimates on short time intervals. We propose that these systematic biases emerge from modulation of synaptic connectivity in a neural circuit based on the experienced stimulus history, shaping the persistent and collective neural activity that encodes the stimulus estimate. Resulting neural activity attractors are aligned to common stimulus values. Using recently published human response data from a delayed-estimation task in which stimuli (colors) were drawn from a heterogeneous distribution that did not necessarily correspond with reported population biases, we confirm that most subjects' response distributions are better described by experience-dependent learning models than by models with fixed biases. This work suggests systematic limitations in working memory reflect efficient representations of inferred environmental structure, providing new insights into how humans integrate environmental knowledge into their cognitive strategies.

A social-semantic working-memory account for two canonical language areas

Language and social cognition are traditionally studied as separate cognitive domains, yet accumulative studies reveal overlapping neural correlates at the left ventral temporoparietal junction (vTPJ) and the left lateral anterior temporal lobe (lATL), which have been attributed to sentence processing and social concept activation. We propose a common cognitive component underlying both effects: social-semantic working memory. We confirmed two key predictions of our hypothesis using functional MRI. First, the left vTPJ and lATL showed sensitivity to sentences only when the sentences conveyed social meaning; second, these regions showed persistent social-semantic-selective activity after the linguistic stimuli disappeared. We additionally found that both regions were sensitive to the socialness of non-linguistic stimuli and were more tightly connected with the social-semantic-processing areas than with the sentence-processing areas. The converging evidence indicates the social-semantic working-memory function of the left vTPJ and lATL and challenges the general-semantic and/or syntactic accounts for the neural activity of these regions.

Neuropsychological Assessment of the Relationship of Working Memory with K-BIT Matrices and Vocabulary in Normal Development and ADHD Children and Adolescents

BACKGROUND

The present report tries to understand the possible relationship between working memory (WM) and intelligence measurements, using the direct scores of the Working Memory Test Battery for Children (WMTBC) and Kaufman's Brief Intelligence Test (K-BIT), in normal development (ND) and diagnosed attention deficit hyperactivity disorder (ADHD) children and adolescents.

RESULTS

Partial correlations, discounting the effect of age, showed a significant correlation in ND subjects between the central executive (CE) component of WM and the WM visuospatial sketchpad (VSS) component and the WM phonological loop (PL); also, significant correlations were obtained for the WM VSS with the K-BIT Matrices scores, the WM PL with the K-BIT Vocabulary, and the K-BIT Matrices scores with the K-BIT Vocabulary. For ADHD subjects, there were significant correlations between WM VSS and WM CE, and WM VSS and K-BIT Matrices. We tested the robustness of these correlations by selecting a small number of subjects through permutations; a robust correlation between WM CE and WM PL in ND, and between WM VSS and WM CE and WM VSS and K-BIT Matrices scores was obtained. These results were also supported by mediation analysis.

CONCLUSIONS

There is a relationship during development between WM as measured with WMTBC and general intelligence as measured with K-BIT in ND and ADHD subjects. The dysexecutive character of ADHD has been shown, given that by controlling for intelligence, the differences in WM performance between ND and ADHD disappear, except for WM CE. The results suggest that in ADHD subjects, the WM VSS component presents a more pivotal role during cognitive processing compared to ND subjects.

Group analysis and classification of working memory task conditions using electroencephalogram cortical currents during an n-back task

Electroencephalographic studies of working memory have demonstrated cortical activity and oscillatory representations without clarifying how the stored information is retained in the brain. To address this gap, we measured scalp electroencephalography data, while participants performed a modified n-back working memory task. We calculated the current intensities from the estimated cortical currents by introducing a statistical map generated using Neurosynth as prior information. Group analysis of the cortical current level revealed that the current amplitudes and power spectra were significantly different between the modified n-back and delayed match-to-sample conditions. Additionally, we classified information on the working memory task conditions using the amplitudes and power spectra of the currents during the encoding and retention periods. Our results indicate that the representation of executive control over memory retention may be mediated through both persistent neural activity and oscillatory representations in the beta and gamma bands over multiple cortical regions that contribute to visual working memory functions.

Working memory and attention in choice

We study the role of attention and working memory in choices where options are presented sequentially rather than simultaneously. We build a model where a costly attention effort is chosen, which can vary over time. Evidence is accumulated proportionally to this effort and the utility of the reward. Crucially, the evidence accumulated decays over time. Optimal attention allocation maximizes expected utility from final choice; the optimal solution takes the decay into account, so attention is preferentially devoted to later times; but convexity of the flow attention cost prevents it from being concentrated near the end. We test this model with a choice experiment where participants observe sequentially two options. In our data the option presented first is, everything else being equal, significantly less likely to be chosen. This recency effect has a natural explanation with appropriate parameter values in our model of leaky evidence accumulation, where the decline is stronger for the option observed first. Analysis of choice, response time and brain imaging data provide support for the model. Working memory plays an essential role. The recency bias is stronger for participants with weaker performance in working memory tasks. Also activity in parietal areas, coding the stored value in working, declines over time as predicted.

Separate orexigenic hippocampal ensembles shape dietary choice by enhancing contextual memory and motivation

The hippocampus (HPC), traditionally known for its role in learning and memory, has emerged as a controller of food intake. While prior studies primarily associated the HPC with food intake inhibition, recent research suggests a critical role in appetitive processes. We hypothesized that orexigenic HPC neurons differentially respond to fats and/or sugars, potent natural reinforcers that contribute to obesity development. Results uncover previously-unrecognized, spatially-distinct neuronal ensembles within the dorsal HPC (dHPC) that are responsive to separate nutrient signals originating from the gut. Using activity-dependent genetic capture of nutrient-responsive HPC neurons, we demonstrate a causal role of both populations in promoting nutrient-specific preference through different mechanisms. Sugar-responsive neurons encode an appetitive spatial memory engram for meal location, whereas fat-responsive neurons selectively enhance the preference and motivation for fat intake. Collectively, these findings uncover a neural basis for the exquisite specificity in processing macronutrient signals from a meal that shape dietary choices.

Bend but don't break: Prioritization protects working memory from displacement but leaves it vulnerable to distortion from distraction

Perceptual distraction distorts visual working memory representations. Previous research has shown that memory responses are systematically biased towards passively viewed visual distractors that are similar to the memoranda. However, it remains unclear whether the prioritization of one working memory representation over another reduces the impact of perceptual distractors. We designed a study with five different types of visual distraction that varied in engagement and found evidence for both subtle distortions and catastrophic failures of memory. Importantly, prioritization protected working memories from catastrophic loss (fewer "swap errors") but rendered them more vulnerable to distortion (greater attractive "biases" towards the distractor). Our findings demonstrate that prioritization does not simply protect working memory from any and all interference, but rather it reduces the likelihood of catastrophic disruption from perceptual distraction at the cost of an increased likelihood of distortion.

Neural dynamics underlying successful auditory short-term memory performance

Listeners often operate in complex acoustic environments, consisting of many concurrent sounds. Accurately encoding and maintaining such auditory objects in short-term memory is crucial for communication and scene analysis. Yet, the neural underpinnings of successful auditory short-term memory (ASTM) performance are currently not well understood. To elucidate this issue, we presented a novel, challenging auditory delayed match-to-sample task while recording MEG. Human participants listened to 'scenes' comprising three concurrent tone pip streams. The task was to indicate, after a delay, whether a probe stream was present in the just-heard scene. We present three key findings: First, behavioural performance revealed faster responses in correct versus incorrect trials as well as in 'probe present' versus 'probe absent' trials, consistent with ASTM search. Second, successful compared with unsuccessful ASTM performance was associated with a significant enhancement of event-related fields and oscillatory activity in the theta, alpha and beta frequency ranges. This extends previous findings of an overall increase of persistent activity during short-term memory performance. Third, using distributed source modelling, we found these effects to be confined mostly to sensory areas during encoding, presumably related to ASTM contents per se. Parietal and frontal sources then became relevant during the maintenance stage, indicating that effective STM operation also relies on ongoing inhibitory processes suppressing task-irrelevant information. In summary, our results deliver a detailed account of the neural patterns that differentiate successful from unsuccessful ASTM performance in the context of a complex, multi-object auditory scene.

When the mind's eye prevails: The Internal Dominance over External Attention (IDEA) hypothesis

Throughout the 20th century, the psychological literature has considered attention as being primarily directed at the outside world. More recent theories conceive attention as also operating on internal information, and mounting evidence suggests a single, shared attentional focus between external and internal information. Such sharing implies a cognitive architecture where attention needs to be continuously shifted between prioritizing either external or internal information, but the fundamental principles underlying this attentional balancing act are currently unknown. Here, we propose and evaluate one such principle in the shape of the Internal Dominance over External Attention (IDEA) hypothesis: Contrary to the traditional view of attention as being primarily externally oriented, IDEA asserts that attention is inherently biased toward internal information. We provide a theoretical account for why such an internal attention bias may have evolved and examine findings from a wide range of literatures speaking to the balancing of external versus internal attention, including research on working memory, attention switching, visual search, mind wandering, sustained attention, and meditation. We argue that major findings in these disparate research lines can be coherently understood under IDEA. Finally, we consider tentative neurocognitive mechanisms contributing to IDEA and examine the practical implications of more deliberate control over this bias in the context of psychopathology. It is hoped that this novel hypothesis motivates cross-talk between the reviewed research lines and future empirical studies directly examining the mechanisms that steer attention either inward or outward on a moment-by-moment basis.

Artificial Neural Network Model with Astrocyte-Driven Short-Term Memory

In this study, we introduce an innovative hybrid artificial neural network model incorporating astrocyte-driven short-term memory. The model combines a convolutional neural network with dynamic models of short-term synaptic plasticity and astrocytic modulation of synaptic transmission. The model's performance was evaluated using simulated data from visual change detection experiments conducted on mice. Comparisons were made between the proposed model, a recurrent neural network simulating short-term memory based on sustained neural activity, and a feedforward neural network with short-term synaptic depression (STPNet) trained to achieve the same performance level as the mice. The results revealed that incorporating astrocytic modulation of synaptic transmission enhanced the model's performance.

A recruitment through coherence theory of working memory

The interactions between prefrontal cortex and other areas during working memory have been studied for decades. Here we outline a conceptual framework describing interactions between these areas during working memory, and review evidence for key elements of this model. We specifically suggest that a top-down signal sent from prefrontal to sensory areas drives oscillations in these areas. Spike timing within sensory areas becomes locked to these working-memory-driven oscillations, and the phase of spiking conveys information about the representation available within these areas. Downstream areas receiving these phase-locked spikes from sensory areas can recover this information via a combination of coherent oscillations and gating of input efficacy based on the phase of their local oscillations. Although the conceptual framework is based on prefrontal interactions with sensory areas during working memory, we also discuss the broader implications of this framework for flexible communication between brain areas in general.

Effect of stress on spatial working memory and EEG signal dynamics in the follicular and luteal phases of the menstrual cycle in young single girls

AIM

Women undergo behavioral changes during the menstrual cycle. This study aimed to investigate the effect of estradiol (Es) on stress and effect of stress on spatial working memory (WM) and also to investigate electroencephalogram (EEG) signal's dynamics in the early and late follicular (EF and LF) and luteal (LU) phases of unmarried girls' menstrual cycle.

METHODS

Stress was induced by presentation of a short (3 min) movie clip. Simultaneous with a memory test and stress induction, EEG, serum Es levels, and galvanic skin response (GSR) were assessed.

RESULTS

Serum Es concentrations were decreased in LF, LU, and EF phases. The mean GSR score decreased after stress induction in all three phases, but it increased in the LF and LU phases versus the EF phase. Spatial WM diminished after stress induction in all three phases, but it increased in the LF phase versus the two phases before and after stress induction. Average power spectrum density in all frequency bands increased after stress induction in the frontal and prefrontal channels in the spatial WM test.

CONCLUSION

The results showed that stress led to spatial WM dysfunction; however, Es improved spatial WM performance in the LF phase versus the other two phases.

Effects of cholinesterase inhibition on attention and working memory in Lewy body dementias

Cholinesterase inhibitors are frequently used to treat cognitive symptoms in Lewy body dementias (Parkinson's disease dementia and dementia with Lewy bodies). However, the selectivity of their effects remains unclear. In a novel rivastigmine withdrawal design, Parkinson's disease dementia and dementia with Lewy bodies patients were tested twice: once when taking rivastigmine as usual and once when they had missed one dose. In each session, they performed a suite of tasks (sustained attention, simple short-term recall, distractor resistance and manipulating the focus of attention) that allowed us to investigate the cognitive mechanisms through which rivastigmine affects attentional control. Consistent with previous literature, rivastigmine withdrawal significantly impaired attentional efficacy (quicker response latencies without a change in accuracy). However, it had no effects on cognitive control as assessed by the ability to withhold a response (inhibitory control). Worse short-term memory performance was also observed when patients were OFF rivastigmine, but these effects were delay and load independent, likely due to impaired visual attention. In contrast to previous studies that have examined the effects of dopamine withdrawal, cognitively complex tasks requiring control over the contents of working memory (ignoring, updating or shifting the focus of attention) were not significantly impaired by rivastigmine withdrawal. Cumulatively, these data support that the conclusion that cholinesterase inhibition has relatively specific and circumscribed-rather than global-effects on attention that may also affect performance on simple short-term memory tasks, but not when cognitive control over working memory is required. The results also indicate that the withdrawal of a single dose of rivastigmine is sufficient to reveal these impairments, demonstrating that cholinergic withdrawal can be an informative clinical as well as an investigative tool.

Cognitive neuroscience perspective on memory: overview and summary

This paper explores memory from a cognitive neuroscience perspective and examines associated neural mechanisms. It examines the different types of memory: working, declarative, and non-declarative, and the brain regions involved in each type. The paper highlights the role of different brain regions, such as the prefrontal cortex in working memory and the hippocampus in declarative memory. The paper also examines the mechanisms that underlie the formation and consolidation of memory, including the importance of sleep in the consolidation of memory and the role of the hippocampus in linking new memories to existing cognitive schemata. The paper highlights two types of memory consolidation processes: cellular consolidation and system consolidation. Cellular consolidation is the process of stabilizing information by strengthening synaptic connections. System consolidation models suggest that memories are initially stored in the hippocampus and are gradually consolidated into the neocortex over time. The consolidation process involves a hippocampal-neocortical binding process incorporating newly acquired information into existing cognitive schemata. The paper highlights the role of the medial temporal lobe and its involvement in autobiographical memory. Further, the paper discusses the relationship between episodic and semantic memory and the role of the hippocampus. Finally, the paper underscores the need for further research into the neurobiological mechanisms underlying non-declarative memory, particularly conditioning. Overall, the paper provides a comprehensive overview from a cognitive neuroscience perspective of the different processes involved in memory consolidation of different types of memory.

Hippocampal and Medial Prefrontal Cortex Fractal Spiking Patterns Encode Episodes and Rules

A central question in neuroscience is how the brain represents and processes information to guide behavior. The principles that organize brain computations are not fully known, and could include scale-free, or fractal patterns of neuronal activity. Scale-free brain activity may be a natural consequence of the relatively small subsets of neuronal populations that respond to task features, i.e., sparse coding. The size of the active subsets constrains the possible sequences of inter-spike intervals (ISI), and selecting from this limited set may produce firing patterns across wide-ranging timescales that form fractal spiking patterns. To investigate the extent to which fractal spiking patterns corresponded with task features, we analyzed ISIs in simultaneously recorded populations of CA1 and medial prefrontal cortical (mPFC) neurons in rats performing a spatial memory task that required both structures. CA1 and mPFC ISI sequences formed fractal patterns that predicted memory performance. CA1 pattern duration, but not length or content, varied with learning speed and memory performance whereas mPFC patterns did not. The most common CA1 and mPFC patterns corresponded with each region's cognitive function: CA1 patterns encoded behavioral episodes which linked the start, choice, and goal of paths through the maze whereas mPFC patterns encoded behavioral "rules" which guided goal selection. mPFC patterns predicted changing CA1 spike patterns only as animals learned new rules. Together, the results suggest that CA1 and mPFC population activity may predict choice outcomes by using fractal ISI patterns to compute task features.