Activity Stabilization in a Population Model of Working Memory by Sinusoidal and Noisy Inputs
According to mechanistic theories of working memory (WM), information is retained as stimulus-dependent persistent spiking activity of cortical neural networks. Yet, how this activity is related to changes in the oscillatory profile observed during WM tasks remains a largely open issue. We explore joint effects of input gamma-band oscillations and noise on the dynamics of several firing rate models of WM. The considered models have a metastable active regime, i.e., they demonstrate long-lasting transient post-stimulus firing rate elevation. We start from a single excitatory-inhibitory circuit and demonstrate that either gamma-band or noise input could stabilize the active regime, thus supporting WM retention. We then consider a system of two circuits with excitatory intercoupling. We find that fast coupling allows for better stabilization by common noise compared to independent noise and stronger amplification of this effect by in-phase gamma inputs compared to anti-phase inputs. Finally, we consider a multi-circuit system comprised of two clusters, each containing a group of circuits receiving a common noise input and a group of circuits receiving independent noise. Each cluster is associated with its own local gamma generator, so all its circuits receive gamma-band input in the same phase. We find that gamma-band input differentially stabilizes the activity of the “common-noise” groups compared to the “independent-noise” groups. If the inter-cluster connections are fast, this effect is more pronounced when the gamma-band input is delivered to the clusters in the same phase rather than in the anti-phase. Assuming that the common noise comes from a large-scale distributed WM representation, our results demonstrate that local gamma oscillations can stabilize the activity of the corresponding parts of this representation, with stronger effect for fast long-range connections and synchronized gamma oscillations.
At the heart of the book all-round consideration of a problem EMC of vehicles lays. From system positions questions of a noise stability and noise emission are stated. The review of the basic test methods of motor transport is given. Parametres EMC an onboard electric equipment are resulted. Methods and means of multilevel maintenance EMC are in detail considered. The attention not only is paid to vehicles with hydrocarbonic engines, but also with alternative power units. In the book the big emphasis on problems of stability of an electric equipment to electromagnetic influences is placed. The material mentions questions EMC not only civil motor transport, but also a special purpose. Various variants of maintenance to parametres EMC of vehicles are resulted. The book will be useful to the technical experts, occupied in educational, research, industrial and other spheres of the automobile industry. It is possible to recommend the edition as the manual to bachelors, masters and post-graduate students of corresponding directions.
The degree of mental attention in childhood and adolescence determines in the future the effectiveness of working memory (ability to store and manipulate information). Attention has been previously found to be related to the prefrontal and parietal areas of the human cortex. But the relationship between attention and white matter properties are still largely unknown. The goal of this study was to identify the relationships between attention and fractional anisotropy (FA) of diffusion MRI in bilateral superior longitudinal fasciculus (in three subdivisions SLF 1- 3), arcuate fasciculus (AF), and corpus callosum (CC) in children and adolescents. Subjects: 14 children (9-11 years) and 13 teenagers (12-15 years). During the experiments participants had to establish a match between the colors on the screen and the colors on the previous slide. The task had six difficulty levels and both performance accuracy (m-score) and reaction time (RT) were measured. There was a positive correlation for m-score and a negative correlation for RT with FA in СС (levels 1-3) in the children's group (p<0.05). On the contrary, when FA increases in the right SLF 3 (level 6), there is a decrease in m-score, and when FA increases in the left SLF 3 and AF, there is an increase in RT at 2,3,4 and 6 levels. In contrast, a decrease in RT with an increase FA of bilateral SLF 3 (level 6) and left AF (level 4) was observed for adolescents, which reflects the redistribution of the roles between fiber tracts with age. FA values of the left (level 2) and right (level 1) SLF 2 negatively correlated with mscore (p <0.05) in the same group. For females (n=13) (regardless the age), there was only a negative correlation for m-score (2,3,5 levels) and the only positive correlation for RT (level 2) with FA of the right SLF 1, left and right SLF 2, in the left SLF 3 and СС (p<0.05). For males (n=13), on the contrary, there were positive correlations between m-score and FA of the СС (1,3,4 levels) and the left SLF 1 (5 level), and inverse correlations between RT and FA for the same fibers of the white matter (1 level) (p<0,05). Interestingly, an increase in FA with age was found in males in all the components of the white matter (p<0.01), except for the СС, and in females, on thecontrary – only in the СС. Further research is needed, taking into account gender, to fully understand the influence of white matter on the development of mental attention.
Working memory is involved in many cognitive processes, and it is essential in problem solving, manipulating temporary information and decision making. Critically little is known about the brain correlates of working memory capacity in children. In this study we examined brain correlates of working memory with functional neuroimaging in school-aged children.
Working memory (WM) is essential to auditory comprehension; thus, understanding of the nature of WM is vital to research and clinical practice to support people with aphasia. A key challenge in assessing WM in people with aphasia is related to the myriad deficits prevalent in aphasia, including deficits in attention, hearing, vision, speech, and motor control of the limbs. Eye-tracking methods augur well for developing alternative WM tasks and measures in that they enable researchers to address many of the potential confounds inherent in tasks traditionally used to study WM. Additionally, eye-tracking tasks allow investigation of trade-off patterns between storage and processing in complex span tasks, and provide on-line response measures. The goal of the study was to establish concurrent and discriminative validity of a novel eye movement WM task in individuals with and without aphasia. Additionally, we aimed to explore the relationship between WM and general language measures, and determine whether trade-off between storage and processing is captured via eye-tracking measures. Participants with (n=28) and without (n=32) aphasia completed a novel eye movement WM task. This task, incorporating natural response requirements, was designed to circumvent potential confounds due to concomitant speech, motor, and attention deficits. The task consisted of a verbal processing component intermixed with presentation of colors and symbols for later recall. Performance on this task was indexed solely via eye movements. Additionally, participants completed a modified listening span task that served to establish concurrent validity of the eye-tracking WM task. Performance measures of the novel eye movement WM task demonstrated concurrent validity with another established measure of WM capacity – the modified listening span task. Performance on the eye-tracking task discriminated effectively between participants with and without aphasia. No consistent relationship was observed between WM scores and Western Aphasia Battery aphasia quotient and subtest scores for people with aphasia. Additionally, eye tracking measures yielded no trade-off between processing and storage for either group of participants. Results support the feasibility and validity of employing a novel eye-tracking method to index WM capacity in participants with and without aphasia. Further research is required to determine the nature of the relationship between WM, as indexed through this method, and specific aspects of language impairments in aphasia.
A placebo effect occurs when the outcome of a participant's expectations change caused by either tablet intake or cognitive training. Placebo effects can cause improvement in cognitive test results including attention and working memory tests. Research shows that attention is used to maintain information in working memory. This study tested the hypothesis that placebo intake can affect attention span and cause temporary improvement of working memory as compared with a control group, if the participants in the experimental group are told they are taking a memory-improving pill. We analyzed how placebo affects working memory and attention and whether these effects are related. Trend level differences were found at the repeated performance of the Bourdon test: the experimental group had a tendency for improvement while the control group tended toward deterioration. No other significant differences were found, probably due to the small sample size.
The theory of constructive operators was used as a framework to design two versions of a paradigm (color matching task, CMT) in which items are parametrically ordered in difficulty, and differ only contextually. Items in CMT-Balloon are facilitating, whereas items in CMT-Clown contain misleading cues. Participants of ages 7–14 years and adults (N = 149) were studied. We found significant model-predicted graded differences in performance between the facilitating and misleading tasks, across and within age groups, expressing age versus items’ demand interactions. Younger children were differentially affected by contextual cues. Even though both task versions were highly correlated with a well-established developmental measure of attentional capacity, CMT-Clown, which contained misleading cues, was a better measure of working memory capacity. These results show a need to estimate degree of misleadingness whenever performance levels in working memory or mental attention tasks are compared and interpreted. Developmental profiles of both tasks are discussed in terms of contextual differences and neoPiagetian stages of development.
For the first time in the domestic technical literature questions of designing of system of power delivery network (PDN) of electronic modules of electronic equipment are considered. Noise in the power supply system of high-speed digital modules are one of the basic problems without which decision working capacity of modules cannot be guaranteed. These decisions should be based on deep physical understanding of the processes occurring in the power supply system of digital modules, the analysis of sources of noise and methods of their suppression, the account of features of traditional and new componental base and outcomes, and also specificity of topological designing of multilayered printed-circuit boards. In the book the listed questions are in details considered, the scientifically-proved recommendations on design of printing modules of digital equipment are given. The statement is accompanied by the big number of examples and numerical calculations. The stated material has a practical orientation and is focused, first of all, on developers and designers of electronic equipment. The book will be useful to the technical experts occupied in research, industrial and other spheres of creation of electronic means. It is possible to recommend the edition as the manual to bachelors, masters and post-graduate students of corresponding directions of preparation.
Let k be a field of characteristic zero, let G be a connected reductive algebraic group over k and let g be its Lie algebra. Let k(G), respectively, k(g), be the field of k- rational functions on G, respectively, g. The conjugation action of G on itself induces the adjoint action of G on g. We investigate the question whether or not the field extensions k(G)/k(G)^G and k(g)/k(g)^G are purely transcendental. We show that the answer is the same for k(G)/k(G)^G and k(g)/k(g)^G, and reduce the problem to the case where G is simple. For simple groups we show that the answer is positive if G is split of type A_n or C_n, and negative for groups of other types, except possibly G_2. A key ingredient in the proof of the negative result is a recent formula for the unramified Brauer group of a homogeneous space with connected stabilizers. As a byproduct of our investigation we give an affirmative answer to a question of Grothendieck about the existence of a rational section of the categorical quotient morphism for the conjugating action of G on itself.
Let G be a connected semisimple algebraic group over an algebraically closed field k. In 1965 Steinberg proved that if G is simply connected, then in G there exists a closed irreducible cross-section of the set of closures of regular conjugacy classes. We prove that in arbitrary G such a cross-section exists if and only if the universal covering isogeny Ĝ → G is bijective; this answers Grothendieck's question cited in the epigraph. In particular, for char k = 0, the converse to Steinberg's theorem holds. The existence of a cross-section in G implies, at least for char k = 0, that the algebra k[G]G of class functions on G is generated by rk G elements. We describe, for arbitrary G, a minimal generating set of k[G]G and that of the representation ring of G and answer two Grothendieck's questions on constructing generating sets of k[G]G. We prove the existence of a rational (i.e., local) section of the quotient morphism for arbitrary G and the existence of a rational cross-section in G (for char k = 0, this has been proved earlier); this answers the other question cited in the epigraph. We also prove that the existence of a rational section is equivalent to the existence of a rational W-equivariant map T- - - >G/T where T is a maximal torus of G and W the Weyl group.