Working Memory Consolidation Research Articles

Acute transient cognitive dysfunction and acute brain injury induced by systemic inflammation occur by dissociable IL-1-dependent mechanisms

Systemic inflammation can impair cognition with relevance to dementia, delirium and post-operative cognitive dysfunction. Episodes of delirium also contribute to rates of long-term cognitive decline, implying that these acute events induce injury. Whether systemic inflammation-induced acute dysfunction and acute brain injury occur by overlapping or discrete mechanisms remains unexplored. Here we show that systemic inflammation, induced by bacterial LPS, produces both working-memory deficits and acute brain injury in the degenerating brain and that these occur by dissociable IL-1-dependent processes. In normal C57BL/6 mice, LPS (100 µg/kg) did not affect working memory but impaired long-term memory consolidation. However prior hippocampal synaptic loss left mice selectively vulnerable to LPS-induced working memory deficits. Systemically administered IL-1 receptor antagonist (IL-1RA) was protective against, and systemic IL-1β replicated, these working memory deficits. Dexamethasone abolished systemic cytokine synthesis and was protective against working memory deficits, without blocking brain IL-1β synthesis. Direct application of IL-1β to ex vivo hippocampal slices induced non-synaptic depolarisation and irreversible loss of membrane potential in CA1 neurons from diseased animals and systemic LPS increased apoptosis in the degenerating brain, in an IL-1RI-dependent fashion. The data suggest that LPS induces working memory dysfunction via circulating IL-1β but direct hippocampal action of IL-1β causes neuronal dysfunction and may drive neuronal death. The data suggest that acute systemic inflammation produces both reversible cognitive deficits, resembling delirium, and acute brain injury contributing to long-term cognitive impairment but that these events are mechanistically dissociable. These data have significant implications for management of cognitive dysfunction during acute illness.

Working memory consolidation: insights from studies on attention and working memory.

Working memory, the system that maintains a limited set of representations for immediate use in cognition, is a central part of human cognition. Three processes have recently been proposed to govern information storage in working memory: consolidation, refreshing, and removal. Here, we discuss in detail the theoretical construct of working memory consolidation, a process critical to the creation of a stable working memory representation. We present a brief overview of the research that indicated the need for a construct such as working memory consolidation and the subsequent research that has helped to define the parameters of the construct. We then move on to explicitly state the points of agreement as to what processes are involved in working memory consolidation.

The relationship between masking and short-term consolidation during recall from visual working memory.

The presentation of a similar but irrelevant stimulus immediately following presentation of a memory item is called masking. Masking is known to reduce performance on working memory tests. This is the type of memory used to hold information in mind for brief periods of time for use in ongoing cognition. Two approaches to understanding masking effects have been proposed in different literatures. Working memory researchers often assume that the reduction in working memory performance after masking is because masking interferes with a transient sensory representation that is needed to complete consolidation into a working memory state. Researchers focused on the attentional blink, a finding that attention cannot be directed to new stimuli during working memory consolidation, have an alternative theory. Attentional blink researchers assume that masking slows the short-term consolidation process, thereby extending the length of the attentional blink. In two experiments, we contrast these two approaches to explaining masking effects and investigate the validity of both hypotheses. Some aspects of both approaches are validated, but neither theoretical perspective alone sufficiently explains the entire pattern of results.

The nature of short-term consolidation in visual working memory.

Short-term consolidation is the process by which stable working memory representations are created. This process is fundamental to cognition yet poorly understood. The present work examines short-term consolidation using a Bayesian hierarchical model of visual working memory recall to determine the underlying processes at work. Our results show that consolidation functions largely through changing the proportion of memory items successfully maintained until test. Although there was some evidence that consolidation affects representational precision, this change was modest and could not account for the bulk of the consolidation effect on memory performance. The time course of the consolidation function and selective influence of consolidation on specific serial positions strongly indicates that short-term consolidation induces an attentional blink. The blink leads to deficits in memory for the immediately following item when time pressure is introduced. Temporal distinctiveness accounts of the consolidation process are tested and ruled out. (PsycINFO Database Record

Retro-Active Emotion: Do Negative Emotional Stimuli Disrupt Consolidation in Working Memory?

While many studies have shown that a task-irrelevant emotionally arousing stimulus can interfere with the processing of a shortly following target, it remains unclear whether an emotional stimulus can also retro-actively interrupt the ongoing processing of an earlier target. In two experiments, we examined whether the presentation of a negative emotionally arousing picture can disrupt working memory consolidation of a preceding visual target. In both experiments, the effects of negative emotional pictures were compared with the effects of neutral pictures. In Experiment 1, the pictures were entirely task-irrelevant whereas in Experiment 2 the pictures were associated with a 2-alternative forced choice task that required participants to respond to the color of a frame surrounding the pictures. The results showed that the appearance of the pictures did not interfere with target consolidation when the pictures were task-irrelevant, whereas such interference was observed when the pictures were associated with a 2-AFC task. Most importantly, however, the results showed no effects of whether the picture had neutral or emotional content. Implications for further research are discussed.

Effects of spatial distance on visual working memory consolidation

Effects of spatial distance on visual working memory consolidation

Interference control theory: A new perspective on dual-task interference in memorizing and responding to visual targets

In a recent study, Nieuwenstein and Wyble (2014) showed that the consolidation of a masked visual target can be disrupted for up to one second by a trailing 2-alternative forced choice task. Aside from demonstrating that working memory consolidation involves a time-consuming process that continues after a mask, the results of Nieuwenstein and Wyble are remarkable in demonstrating retroactive interference (RI) with little to no proactive interference (RI) – the opposite of what is typically found in studies on the attentional blink and psychological refractory period effect. Here, we show that the reversal from PI to RI depends on the probability of T2 presence (p[T2]), such that a high p(T2) results in strong PI with little RI whereas a low p(T2) results in strong RI with little PI. To explain these findings, we propose that the degree of PI and RI reflects the workings of an attentional control mechanism that aims to protect T1 consolidation against interference, and that is applied in accordance with the risk of such interference. In this view, a high p(T2) entails a high risk of interference with T1 processing, and this results in the protection of T1 at the expense of a postponement of T2 processing. Converely, a low p(T2) means that the risk of interference is low and this entails that T1 is left vulnerable, while T2 can be processed unabated. Consistent with this account, we show that if the risk of interference with T1 processing is increased by embedding the targets in an RSVP stream of distractors, we find strong PI with little RI even when p(T2) is low. Aside from offering a new perspective on dual-task interference, this work makes clear that attentional control plays a central role in phenomena observed in studies using RSVP.

On the interplay between working memory consolidation and attentional selection in controlling conscious access: parallel processing at a cost--a comment on 'The interplay of attention and consciousness in visual search, attentional blink and working memory consolidation'.

Theories of human cognition generally agree in assuming the existence of a fundamental limit in information processing, but these theories are challenged by findings that appear to circumvent these limitations. We argue that theories are needed that offer a principled account of why the limitations

Stimulating occipital cortex enhances visual working memory consolidation

Visual working memory (WM) enables us to store and manipulate visual information for a short duration. Traditionally, prefrontal and parietal regions have been associated with visual WM processing; however recent fMRI studies have shown that visual WM information can be decoded from the visual cortex as well. In this study, we used transcranial direct current stimulation (tDCS) to investigate the role of the visual cortex in retaining visual WM information. All subjects participated in two sessions of sham and active tDCS followed by a standard visual WM task. Two conditions were tested: in short encoding trials, the memory array (6 colored circles) was presented for 200ms whereas in long encoding trials it was presented for 500ms. We hypothesized that if stimulation over visual cortex modulates WM retention, then performance should be enhanced in both encoding conditions. However, if stimulation over visual cortex modulates mainly WM consolidation, then performance should improve only in the short encoding condition. The results supported the latter possibility as stimulation improved performance in the short encoding condition but not in the long encoding condition. Consequently, the robust advantage of the long encoding condition over the short encoding condition after sham stimulation was eliminated after active stimulation. These results suggest that the visual cortex is significant for WM consolidation, while it plays a smaller part in holding visual WM representations.

Effect of Cognitive Aging on Working Memory Consolidation

This study was conducted to investigate the hypothesis that the decline in memory consolidation in aging may be determined by the reduction of inhibitory control processes. To this end an Attentional Blink (AB) paradigm was employed. AB effect was more pronounced and lengthened for older adults (60–85 years) than young (18–22 years) and middle aged (45–55 years) groups, which could be due to interference at the perceptual stage itself. The onset of the first target involuntarily captures attentional resources, impairing subsequent target identification due to decrease in inhibitory control. Experiment 2 was conducted manipulating perceptual load in working memory to study interference as a function of load. The effect of load was more pronounced for older and middle-aged adults. The decline in memory consolidation in this group may be due to difficulties in early stages of perceptual processing, inhibitory control and unsuccessful suppression of irrelevant stimuli. These effects were also observed among middle-aged individuals.

Disruption reduces accuracy and P3b amplitudes in the attentional blink

In everyday life, distracting stimuli often interfere with daily tasks, and disrupt successful task performance. The attentional blink paradigm (a deficit in reporting the second target (T2) in a rapid stream of visual stimuli) allows for an investigation of disruption by rapidly appearing stimuli. Specifically, the magnitude of the attentional blink deficit can be manipulated by positioning relevant stimuli at strategic locations within the visual stream. The current study therefore designed and tested a disruption paradigm that aimed to reduce T2 accuracy using a disruptor stimulus. Electroencephalography was used to reveal the neural correlates of the effect. To that end, targets were defined by task-set colours. The item immediately preceding T2 appeared in a task-set colour (disrupted trials) or a different colour (non-disrupted trials). The results revealed that T2 accuracy was reduced on disrupted trials, and disruption appeared to be worse when T2 appeared inside the attentional blink window. The behavioural data were paralleled by the neural results. On trials where T2 appeared within the AB window and was correctly reported, T2-P3b amplitude (a neural correlate of working memory consolidation) was significantly depressed on disrupted trials compared with non-disrupted trials. Single trial plots of P3b amplitude confirmed a weaker neural trace for T2 on disrupted trials. These data indicate that the magnitude and neural signature of the attentional blink deficit is malleable, and can be influenced by non-target, task-relevant stimuli.

Beyond a mask and against the bottleneck: Retroactive dual-task interference during working memory consolidation of a masked visual target.

While studies on visual memory commonly assume that the consolidation of a visual stimulus into working memory is interrupted by a trailing mask, studies on dual-task interference suggest that the consolidation of a stimulus can continue for several hundred milliseconds after a mask. As a result, estimates of the time course of working memory consolidation differ more than an order of magnitude. Here, we contrasted these opposing views by examining if and for how long the processing of a masked display of visual stimuli can be disturbed by a trailing 2-alternative forced choice task (2-AFC; a color discrimination task or a visual or auditory parity judgment task). The results showed that the presence of the 2-AFC task produced a pronounced retroactive interference effect that dissipated across stimulus onset asynchronies of 250-1,000 ms, indicating that the processing elicited by the 2-AFC task interfered with the gradual consolidation of the earlier shown stimuli. Furthermore, this interference effect occurred regardless of whether the to-be-remembered stimuli comprised a string of letters or an unfamiliar complex visual shape, and it occurred regardless of whether these stimuli were masked. Conversely, the interference effect was reduced when the memory load for the 1st task was reduced, or when the 2nd task was a color detection task that did not require decision making. Taken together, these findings show that the formation of a durable and consciously accessible working memory trace for a briefly shown visual stimulus can be disturbed by a trailing 2-AFC task for up to several hundred milliseconds after the stimulus has been masked. By implication, the current findings challenge the common view that working memory consolidation involves an immutable central processing bottleneck, and they also make clear that consolidation does not stop when a stimulus is masked.

The interplay of attention and consciousness in visual search, attentional blink and working memory consolidation

Despite the acknowledged relationship between consciousness and attention, theories of the two have mostly been developed separately. Moreover, these theories have independently attempted to explain phenomena in which both are likely to interact, such as the attentional blink (AB) and working memory (WM) consolidation. Here, we make an effort to bridge the gap between, on the one hand, a theory of consciousness based on the notion of global workspace (GW) and, on the other, a synthesis of theories of visual attention. We offer a theory of attention and consciousness (TAC) that provides a unified neurocognitive account of several phenomena associated with visual search, AB and WM consolidation. TAC assumes multiple processing stages between early visual representation and conscious access, and extends the dynamics of the global neuronal workspace model to a visual attentional workspace (VAW). The VAW is controlled by executive routers, higher-order representations of executive operations in the GW, without the need for explicit saliency or priority maps. TAC leads to newly proposed mechanisms for illusory conjunctions, AB, inattentional blindness and WM capacity, and suggests neural correlates of phenomenal consciousness. Finally, the theory reconciles the all-or-none and graded perspectives on conscious representation.

Differences between presentation methods in working memory procedures: A matter of working memory consolidation.

Understanding forgetting from working memory, the memory used in ongoing cognitive processing, is critical to understanding human cognition. In the past decade, a number of conflicting findings have been reported regarding the role of time in forgetting from working memory. This has led to a debate concerning whether longer retention intervals necessarily result in more forgetting. An obstacle to directly comparing conflicting reports is a divergence in methodology across studies. Studies that find no forgetting as a function of retention-interval duration tend to use sequential presentation of memory items, while studies that find forgetting as a function of retention-interval duration tend to use simultaneous presentation of memory items. Here, we manipulate the duration of retention and the presentation method of memory items, presenting items either sequentially or simultaneously. We find that these differing presentation methods can lead to different rates of forgetting because they tend to differ in the time available for consolidation into working memory. The experiments detailed here show that equating the time available for working memory consolidation equates the rates of forgetting across presentation methods. We discuss the meaning of this finding in the interpretation of previous forgetting studies and in the construction of working memory models.

Improving Reading Strategy for Comprehension: ?Does Recall Compete with Working Memory Manipulation??

We investigated whether reading comprehension could be improved by strategic updating of working memory during reading, by providing upper elementary students with working memory consolidation training. We report data from ten fifth-grade students, half of which underwent strategic reading comprehension intervention. Response time data indicated that training in consolidating verbal information increased automaticity of recall. However, this improvement negatively correlated with post-training performance on Backward Digit Span, indicating possible tradeoffs between resource allocation toward the component of executive function moderating maintenance/recall, or toward the component moderating manipulation of working memory content

Understanding the Properties of Visual Working Memory Consolidation and Comparison Processes Examined by Simultaneous- and Backward-Masking Manipulation

Understanding the Properties of Visual Working Memory Consolidation and Comparison Processes Examined by Simultaneous- and Backward-Masking Manipulation

Working memory consolidation does not necessarily delay response selection: Disentangling the costs of task initiation and execution

Working memory consolidation does not necessarily delay response selection: Disentangling the costs of task initiation and execution

Mask similarity impacts short-term consolidation in visual working memory

Short-term consolidation is the process by which perceptual representations are stabilized into visual working memory (VWM) representations to prevent interference from subsequent visual input. The present article reports how short-term consolidation is affected by the similarity of the subsequent visual items (i.e., visual masks) by using a color change detection task. In the task, masks were either similar or dissimilar to the memory stimuli and were displayed at varying intervals following the memory array. The similar masks were made up of the same colored squares as the to-be-remembered stimuli, whereas the dissimilar masks were black-and-white grids. The results showed more interference from similar than from dissimilar masks: Similar masks required more time to consolidate and elicited lower overall performance than did dissimilar masks. These results suggest that a simple overwriting process cannot fully account for the impact of mask type on short-term consolidation performance and that other cognitive mechanisms are involved (e.g., controlled attention).

Loss of Dickkopf-1 Restores Neurogenesis in Old Age and Counteracts Cognitive Decline

Memory impairment has been associated with age-related decline in adult hippocampal neurogenesis. Although Notch, bone morphogenetic protein, and Wnt signaling pathways are known to regulate multiple aspects of adult neural stem cell function, the molecular basis of declining neurogenesis in the aging hippocampus remains unknown. Here, we show that expression of the Wnt antagonist Dickkopf-1 (Dkk1) increases with age and that its loss enhances neurogenesis in the hippocampus. Neural progenitors with inducible loss of Dkk1 increase their Wnt activity, which leads to enhanced self-renewal and increased generation of immature neurons. This Wnt-expanded progeny subsequently matures into glutamatergic granule neurons with increased dendritic complexity. As a result, mice deficient in Dkk1 exhibit enhanced spatial working memory and memory consolidation and also show improvements in affective behavior. Taken together, our findings show that upregulating Wnt signaling by reducingDkk1 expression can counteract age-related decrease in neurogenesis and its associated cognitive decline.

Consolidation of statistical information of multiple objects in working memory

The present study investigated working memory consolidation in focused and distributed attention tasks by examining the time course of the consolidation process (Experiment 1) and its dependence on capacity-limited central resources (Experiment 2) in both tasks. In a match-to-sample design using masks at various intervals to vary consolidation rates, the participants performed either an identification task (focused attention) or a mean estimation task (distributed attention) with (Experiment 1) or without (Experiment 2) prior knowledge of what task they were to perform. We found that consolidation in the distributed attention task was more efficient and was about twice as fast as in the focused attention task. In addition, both tasks suffered interference when they had to be performed together, indicating that both types of attention rely on a common set of control processes. These findings can be attributed to differences in the resolution of object representations and in the scope of attention associated with focused and distributed attention.