Selection History Modulates Working Memory Capacity

The nature of parietal contributions to working memory (WM) remain poorly understood but of considerable interest. We previously reported that posterior parietal damage selectively impaired WM probed by recognition (Berryhill and Olson, 2008a). Recent studies provided support using a neuromodulatory technique, transcranial direct current stimulation (tDCS) applied to the right parietal cortex (P4). These studies confirmed parietal involvement in WM because parietal tDCS altered WM performance: anodal current tDCS improved performance in a change detection task, and cathodal current tDCS impaired performance on a sequential presentation task. Here, we tested whether these complementary results were due to different degrees of parietal involvement as a function of WM task demands, WM task difficulty, and/or participants’ WM capacity. In Experiment 1, we applied cathodal and anodal tDCS to the right parietal cortex and tested participants on both previously used WM tasks. We observed an interaction between tDCS (anodal, cathodal), WM task difficulty, and participants’ WM capacity. When the WM task was difficult, parietal stimulation (anodal or cathodal) improved WM performance selectively in participants with high WM capacity. In the low WM capacity group, parietal stimulation (anodal or cathodal) impaired WM performance. These nearly equal and opposite effects were only observed when the WM task was challenging, as in the change detection task. Experiment 2 probed the interplay of WM task difficulty and WM capacity in a parametric manner by varying set size in the WM change detection task. Here, the effect of parietal stimulation (anodal or cathodal) on the high WM capacity group followed a linear function as WM task difficulty increased with set size. The low WM capacity participants were largely unaffected by tDCS. These findings provide evidence that parietal involvement in WM performance depends on both WM capacity and WM task demands. We discuss these findings in terms of alternative WM strategies employed by low and high WM capacity individuals. We speculate that low WM capacity individuals do not recruit the posterior parietal lobe for WM tasks as efficiently as high WM capacity individuals. Consequently, tDCS provides greater benefit to individuals with high WM capacity.

Inhibitory control is a key executive function and has been studied extensively using the stop signal task. By applying a simple race model that posits an independent race between a GO process responsible for initiation of responses and a STOP process responsible for inhibition of responses, one can estimate how long it takes an individual to inhibit an ongoing response, the stop signal reaction time. Here, we examined how stop signal reaction time can be affected by working memory. Participants engaged in a dual task; they completed a stop signal task under low and high working memory load conditions. Working memory capacity was also measured. We found that the STOP process was lengthened in the high, compared to the low, working memory load condition, as evidenced by differences in stop signal reaction time. The GO process was unaffected and working memory capacity could not account for differences across the load conditions. These results indicate that inhibitory control can be influenced by placing demands on working memory.

EDITORIAL article Front. Psychol., 20 March 2014Sec. Cognition Volume 5 - 2014 | https://doi.org/10.3389/fpsyg.2014.00248

The study of working memory capacity is of outmost importance in cognitive psychology as working memory is at the basis of general cognitive function. Although the working memory capacity limit has been thoroughly studied, its origin still remains a matter of strong debate. Only recently has the role of visual saliency in modulating working memory storage capacity been assessed experimentally and proved to provide valuable insights into working memory function. In the computational arena, attractor networks have successfully accounted for psychophysical and neurophysiological data in numerous working memory tasks given their ability to produce a sustained elevated firing rate during a delay period. Here we investigate the mechanisms underlying working memory capacity by means of a biophysically-realistic attractor network with spiking neurons while accounting for two recent experimental observations: 1) the presence of a visually salient item reduces the number of items that can be held in working memory, and 2) visually salient items are commonly kept in memory at the cost of not keeping as many non-salient items.Our model suggests that working memory capacity is determined by two fundamental processes: encoding of visual items into working memory and maintenance of the encoded items upon their removal from the visual display. While maintenance critically depends on the constraints that lateral inhibition imposes to the mnemonic activity, encoding is limited by the ability of the stimulated neural assemblies to reach a sufficiently high level of excitation, a process governed by the dynamics of competition and cooperation among neuronal pools. Encoding is therefore contingent upon the visual working memory task and has led us to introduce the concept of effective working memory capacity (eWMC) in contrast to the maximal upper capacity limit only reached under ideal conditions.

Neural correlates of working memory training: Evidence for plasticity in older adults

Sex differences in verbal working memory performance emerge at very high loads of common neuroimaging tasks

Rodent aging research often utilizes spatial mazes, such as the water radial-arm-maze (WRAM), to evaluate cognition. The WRAM can simultaneously measure spatial working and reference memory, wherein these two memory types are often represented as orthogonal. There is evidence, however, that these two memory forms yield interference at a high working memory load. The current study systematically evaluated whether the presence of a reference memory component impacts handling of an increasing working memory load. Young and aged female rats were tested to assess whether aging impacts this relationship. Cholinergic projections from the basal forebrain to the hippocampus and cortex can affect cognitive outcomes, and are negatively impacted by aging. To evaluate whether age-related changes in working and reference memory profiles are associated with cholinergic functioning, we assessed choline acetyltransferase activity in these behaviorally-tested rats. Results showed that young rats outperformed aged rats on a task testing solely working memory. The addition of a reference memory component deteriorated the ability to handle an increasing working memory load, such that young rats performed similar to their aged counterparts. Aged rats also had challenges when reference memory was present, but in a different context. Specifically, aged rats had difficulty remembering which reference memory arms they had entered within a session, compared to young rats. Further, aged rats that excelled in reference memory also excelled in working memory when working memory demand was high, a relationship not seen in young rats. Relationships between cholinergic activity and maze performance differed by age in direction and brain region, reflecting the complex role that the cholinergic system plays in memory and attentional processes across the female lifespan. Overall, the addition of a reference memory requirement detrimentally impacted the ability to handle working memory information across young and aged timepoints, especially when the working memory challenge was high; these age-related deficits manifested differently with the addition of a reference memory component. This interplay between working and reference memory provides insight into the multiple domains necessary to solve complex cognitive tasks, potentially improving the understanding of complexities of age- and disease- related memory failures and optimizing their respective treatments.

Objectives: The purpose of the study was to identify the impact of age-related working memory capacity and cognitive load to word recognition using an eye tracker.Methods: A total of 48 participants (24 young, 24 elderly adults) who were divided according to working memory capacity (high, low) participated in the study. This study consisted of a digit load and word recognition task.Results: First, the elderly group had lower accuracy and slower response times than the young group. There was a significant difference between working memory capacity and cognitive load in response time. In the group with low working memory capacity, the response time increased under lower cognitive load, which was different from the group with a high working memory capacity. Next, the elderly group had a lower proportion of fixation than the young group by time interval. In addition, there was a significant interaction between group and cognitive load by time interval. In particular, the proportion of fixation decreased over time under a high cognitive load while the proportion of fixation increased under a low cognitive load in the elders, because the inhibition and switching abilities were weakened which made the elders unable to process information efficiently.Conclusion: The study results showed significant effects between working memory capacity and cognitive load in response time and proportion of fixation. This implies that complex factors influence language processing, which makes measuring accuracy insufficient. Thus, this research confirms the correlation among aging, working memory, and cognitive load through both online and offline measurement.

Working memory (WM) is limited in its temporal length and capacity. Classic conceptions of WM capacity assume the system possesses a finite number of slots, but recent evidence suggests WM may be a continuous resource. Resource models typically assume there is no hard upper bound on the number of items that can be stored, but WM fidelity decreases with the number of items. We analyze a neural field model of multi-item WM that associates each item with the location of a bump in a finite spatial domain, considering items that span a one-dimensional continuous feature space. Our analysis relates the neural architecture of the network to accumulated errors and capacity limitations arising during the delay period of a multi-item WM task. Networks with stronger synapses support wider bumps that interact more, whereas networks with weaker synapses support narrower bumps that are more susceptible to noise perturbations. There is an optimal synaptic strength that both limits bump interaction events and the effects of noise perturbations. This optimum shifts to weaker synapses as the number of items stored in the network is increased. Our model not only provides a circuit-based explanation for WM capacity, but also speaks to how capacity relates to the arrangement of stored items in a feature space.

Author(s): Bolden, Khalima Alicia | Advisor(s): Brown, Gregory G | Abstract: The neural substrate of interactions of working memory (WM) with socio-emotional processing is poorly understood in schizophrenia. This study builds on published papers using a delayed match to sample design to study the interaction of WM load with type of distracter (socially relevant faces vs. socially irrelevant geometric designs [FvG]) presented briefly during the WM maintenance period. Based on previously published findings, we hypothesize: (1) The FvG difference in brain activity in the dorsolateral prefrontal cortex (DLPFC) in the task maintenance period will be largest at the highest WM load. (2) Among schizophrenia/ schizoaffective patients and healthy controls the magnitude of the face vs. geometric design (FvG) contrast in brain activity in the amygdala during the task maintenance period will follow a quadratic pattern across WM load when averaged over face type. (3) Among schizophrenia patients, the magnitude of the FvG contrast in brain activity in the amygdala and DLPFC at the greatest WM load will be correlated with negative symptoms. Individuals between the ages of 18-55 diagnosed with schizophrenia/schizoaffective disorder (N = 12) and non-psychiatric controls (N = 20) matched with the patients on age, gender, paternal education and paternal socioeconomic status underwent structural and functional magnetic resonance imaging (fMRI). To assess the effect of implicit socioemotional modulation on brain activity during WM, the effect of facial distraction on brain activation was assessed for WM of pseudowords at three syllable loads (1, 2, and 3) across several face valence types and contrasted with the effect of a geometric distracter. Results: Although patients performed significantly above chance, they were less accurate than controls with no difference in response latency. When the FvG contrast was tested for response latency, we observed a significant quadratic effect of WM load in healthy controls (F[1,19] = 6.108, p = .023, η2 = .24) but a linear effect among patients (F[1,10] = 4.012, p = .073, η2 = .29). Similar patterns were found for response accuracy but were not statistically significant. With regard to neural activity, we found a significant bilateral linear trend of percent signal change on WM load for the FvG contrast in the DLPFC (F[1,19] = 5.818, p = .026, MSE = .077, η2 = .23). among controls, with brain activation to faces greater than activation to designs only at the highest WM load. In the amygdala we observed a significant bilateral quadratic effect of percent signal change on WM load for the FvG contrast in the control group (F[1,19] = 10.423, p = .004, MSE = .121, η2 = .35). We observed a significant difference in neural activation patterns in patients compared to controls in the DLPFC and the amygdala. Specifically, in patients, we observed a quadratic instead of a linear trend in the DLPFC but only in the right hemisphere (hemisphere x quadratic: F[1,11] = 9.362, p = .011, η2 = .40). In the amygdala, the patients displayed a quadratic trend also only in the right hemisphere, (hemisphere x quadratic: F[1,11] = 10.442 p = .008, η2 = .49). In neither controls nor patients did individual differences in the quadratic effect of brain activity in the amygdala correlate with the quadratic effect in response time or accuracy. Although the correlation between the magnitude of the quadratic trend in the right amygdala at the highest WM load with general psychopathology was moderately large in patients, neither this effect nor any other brain activation effects were significantly correlated with psychopathology. Confirming hypothesis one, controls showed the largest difference in brain activity of the FvG contrast in the DLPFC during the maintenance period at the highest WM load. However, in patients we saw significantly decreased percent signal change in DLPFC at the highest WM load on the FvG contrast in the maintenance period. For hypothesis two we observed a quadratic pattern of WM load on the FvG contrast in the maintenance period for both controls and patients, although this effect was only present in the right hemisphere of patients. Furthermore, contrary to hypothesis 3 we did not observe significant correlations between symptom severity and the magnitude of the FvG contrast in brain activity in the amygdala and DLPFC at the greatest WM load. These results suggest a separate process of social-discrimination is taking place in controls. However, this process appears to be impaired in individuals with schizophrenia. This disruption may be due to poor integration of different brain areas and interhemispheric communication.

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Working memory (WM) temporarily holds and processes information, with its precision decreasing as load increases. Although retro-cues enhance WM precision by focusing attention on relevant items, neural mechanisms driving this effect across varying loads remain unclear. We recorded electroencephalography (EEG) signals during two experiments where participants performed a retrospective-cue WM task under low and high loads. We found that retro-cues significantly enhanced recall precision and sped response times, with larger precision benefits under high load. Alpha (8-12 Hz) activity showed load-dependent attentional modulation during retention, including later delayed desynchronization (ERD) and prolonged lateralization modulation index (MI) under higher load. Under high load, the retro-cues caused slower theta frequency, suggesting phase coding mechanisms in WM. Inverted encoding model (IEM) results revealed more precise mnemonic representation under low load, supporting less noise and more refined encoding. These findings highlight WM adaptive nature, flexibly adjusting to changing cognitive demands through dynamic attentional control.

The effects of working memory (WM) capacity on mathematical ability are well known. This relationship is seen mainly for the capacity of visuospatial WM, while the capacity of the phonological loop of WM, which is associated with processing sound and speech information, has been suggested to have a minor effect on mathematical ability in adults. Nonetheless, involvement of the language neural networks in mathematical thought remains controversial. We have studied the effects of the capacity of the phonological loop of WM on the rate and correctness of solution of mathematical and verbal tasks in young, healthy, right-handed volunteers who either had higher education or were students at institutions teaching mathematics and humanities. Subjects in the mathematics group (N = 10) solved all tasks with measures of solution correctness (CA) and response time (RT) which were significantly better than values for subjects of the humanities group (N = 10). The capacity of the phonological loop of WM showed no difference between the two groups but had different effects on CA and RT values for tasks in mathematicians and humanities specialists. Spearman correlation analysis for each group separately showed that the capacity of WM had positive effects on CA for all mathematical tasks only in the mathematicians group, where it had no effect on RT, while the reverse tendency was seen in the humanities group. The capacity of WM in the mathematicians group correlated inversely with RT for logical tasks on arithmetic sequences. Our results provide indirect evidence that WM in the verbal domain can influence mathematical ability, especially when tasks require the involvement of logical thought.

of Employees with ADHD, 6 • Research Findings, 8 Working memory has been a highly important theoretical construct in cognitive psychology and has been defined as “a brain system that provides temporary storage and manipulation of the information necessary for... complex cognitive tasks” (Baddeley, 1992, p. 556). Recently, much interest has been created by claims that cognitive training can enhance working memory capacity (e.g., Diamond & Lee, 2011; Klingberg, 2010). On this basis, it has been suggested that working memory training programs can ameliorate a range of different learning disorders, such as ADHD, reading and language disorders, and mathematics disorder. It has also been claimed that working memory training can enhance cognitive abilities and scholastic attainment in typically developing children and adults. Theoretically, a range of different models has been suggested to explain the nature of the relationship between working memory and cognitive functioning (see Case, 1985). A model that has been highly cited in the literature on working memory training is based on the view that working memory capacity puts constraints on executive attentional capacity in general (Engle, 2002). In this sense, working memory capacity is seen as isomorphic with executive attention. Therefore, researchers have suggested that such constraints on working memory capacity will have important repercussions for cognitive development (see Case, 1985). Thus, an impairment in working memory has been put forward as a possible explanation for such learning disorders as reading disorders (Swanson, 2006), mathematics disorders (Passolunghi, 2006), autism spectrum disorder (Kenworthy, Yerys, Anthony, & Wallace, 2008), and specific language impairment (Archibald & Gathercole, 2006). For ADHD, numerous of studies have demonstrated that children with this disorder typically have poor performance on working memory tests compared with children without such problems, and impaired working memory has often been considered a core feature of ADHD (see Barkley, 2005; Martinussen et al., 2005). A dominant account in the field of ADHD has been that working memory problems not only lead to problems related to attention and keeping stimuli in mind but also in guiding goal-directed behavior, effective self-regulation, and

Working memory (WM) is vulnerable to age-related decline, particularly under high loads. Visual alpha oscillations contribute to WM performance in younger adults, and although alpha decreases in power and frequency with age, it is unclear if alpha activity supports WM in older adults. We recorded electroencephalography (EEG) while 24 younger (aged 18-35years) and 30 older (aged 50-86) adults performed a modified Sternberg task with varying load conditions. Older adults demonstrated slower reaction times at all loads, but there were no significant age differences in WM capacity. Regardless of age, alpha power decreased and alpha frequency increased with load during encoding, and the magnitude of alpha suppression during retention was larger at higher loads. While alpha power during retention was lower than fixation in older, but not younger adults, the relative change from fixation was not significantly different between age groups. Individual differences in alpha power did not predict performance for either age groups or at any WM loads. We demonstrate that alpha power and frequency are modulated in a similar task- and load-dependent manner during WM in both older and younger adults when WM performance is comparable across age groups. IMPACT STATEMENT: Aging is associated with a marked decrease in the power and frequency of alpha oscillations. Here, we demonstrate that when verbal working memory performance is matched across age groups, alpha power and frequency are modulated in a similar task- and load-dependent manner in both young and older adults.