scholarly journals Neural Systems Under Change of Scale

2021 ◽  
Vol 15 ◽  
Author(s):  
Erik D. Fagerholm ◽  
W. M. C. Foulkes ◽  
Yasir Gallero-Salas ◽  
Fritjof Helmchen ◽  
Karl J. Friston ◽  
...  
Keyword(s):  
Calcium Imaging ◽  
Characteristic Length ◽  
Neural Systems ◽  
Renormalization Group Theory ◽  
Free System ◽  
Scale Free ◽  
Change Of Scale ◽  
Planetary Orbits ◽  
Task Irrelevant ◽  
Different Levels

We derive a theoretical construct that allows for the characterisation of both scalable and scale free systems within the dynamic causal modelling (DCM) framework. We define a dynamical system to be “scalable” if the same equation of motion continues to apply as the system changes in size. As an example of such a system, we simulate planetary orbits varying in size and show that our proposed methodology can be used to recover Kepler’s third law from the timeseries. In contrast, a “scale free” system is one in which there is no characteristic length scale, meaning that images of such a system are statistically unchanged at different levels of magnification. As an example of such a system, we use calcium imaging collected in murine cortex and show that the dynamical critical exponent, as defined in renormalization group theory, can be estimated in an empirical biological setting. We find that a task-relevant region of the cortex is associated with higher dynamical critical exponents in task vs. spontaneous states and vice versa for a task-irrelevant region.

scholarly journals Scarcity of scale-free topology is universal across biochemical networks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Harrison B. Smith ◽  
Hyunju Kim ◽  
Sara I. Walker
Keyword(s):  
Large Body ◽  
Biochemical Networks ◽  
Biological Organization ◽  
Scale Free ◽  
Levels Of Organization ◽  
Common Structure ◽  
Domains Of Life ◽  
Ecosystem Level ◽  
Different Levels ◽  
Organizing Principles

AbstractBiochemical reactions underlie the functioning of all life. Like many examples of biology or technology, the complex set of interactions among molecules within cells and ecosystems poses a challenge for quantification within simple mathematical objects. A large body of research has indicated many real-world biological and technological systems, including biochemistry, can be described by power-law relationships between the numbers of nodes and edges, often described as “scale-free”. Recently, new statistical analyses have revealed true scale-free networks are rare. We provide a first application of these methods to data sampled from across two distinct levels of biological organization: individuals and ecosystems. We analyze a large ensemble of biochemical networks including networks generated from data of 785 metagenomes and 1082 genomes (sampled from the three domains of life). The results confirm no more than a few biochemical networks are any more than super-weakly scale-free. Additionally, we test the distinguishability of individual and ecosystem-level biochemical networks and show there is no sharp transition in the structure of biochemical networks across these levels of organization moving from individuals to ecosystems. This result holds across different network projections. Our results indicate that while biochemical networks are not scale-free, they nonetheless exhibit common structure across different levels of organization, independent of the projection chosen, suggestive of shared organizing principles across all biochemical networks.

Impact of childhood maltreatment and resilience on behavioral and neural patterns of inhibitory control during emotional distraction

2021 ◽  
pp. 1-12
Author(s):  
Lauren A. Demers ◽  
Ruskin H. Hunt ◽  
Dante Cicchetti ◽  
Julia E. Cohen-Gilbert ◽  
Fred A. Rogosch ◽  
...  
Keyword(s):  
Inhibitory Control ◽  
Childhood Maltreatment ◽  
Adaptive Functioning ◽  
Comparison Group ◽  
Inferior Frontal Gyrus ◽  
Neural Systems ◽  
Behavioral Regulation ◽  
Frontal Pole ◽  
History Of ◽  
Task Irrelevant

Abstract Exposure to childhood maltreatment (CM) may disrupt typical development of neural systems underlying impulse control and emotion regulation. Yet resilient outcomes are observed in some individuals exposed to CM. Individual differences in adult functioning may result from variation in inhibitory control in the context of emotional distractions, underpinned by cognitive–affective brain circuits. Thirty-eight healthy adults with a history of substantiated CM and 34 nonmaltreated adults from the same longitudinal sample performed a Go/No-Go task in which task-relevant stimuli (letters) were presented at the center of task-irrelevant, negative, or neutral images, while undergoing functional magnetic resonance imaging. The comparison group, but not the maltreated group, made increased inhibitory control errors in the context of negative, but not neutral, distractor images. In addition, the comparison group had greater right inferior frontal gyrus and bilateral frontal pole activation during inhibitory control blocks with negative compared to neutral background images relative to the CM group. Across the full sample, greater adaptive functioning in everyday contexts was associated with superior inhibitory control and greater right frontal pole activation. Results suggest that resilience following early adversity is associated with enhanced attention and behavioral regulation in the context of task-irrelevant negative emotional stimuli in a laboratory setting.

Synapse Models for Neural Networks: From Ion Channel Kinetics to Multiplicative Coefficient wij

1995 ◽  
Vol 7 (4) ◽  
pp. 713-734 ◽  
Author(s):  
François Chapeau-Blondeau ◽  
Nicolas Chambet
Keyword(s):  
Neural Networks ◽  
Ion Channel ◽  
Neural Systems ◽  
Channel Kinetics ◽  
Modeling Process ◽  
Multiplicative Coefficient ◽  
Ion Channel Kinetics ◽  
Synaptic Coefficient ◽  
Synapse Model ◽  
Different Levels

This paper relates different levels at which the modeling of synaptic transmission can be grounded in neural networks: the level of ion channel kinetics, the level of synaptic conductance dynamics, and the level of a scalar synaptic coefficient. The important assumptions to reduce a synapse model from one level to the next are explicitly exhibited. This coherent progression provides control on what is discarded and what is retained in the modeling process, and is useful to appreciate the significance and limitations of the resulting neural networks. This methodic simplification terminates with a scalar synaptic efficacy as it is very often used in neural networks, but here its conditions of validity are explicitly displayed. This scalar synapse also comes with an expression that directly relates it to basic quantities of synaptic functioning, and it can be endowed with meaningful physical units and realistic numerical values. In addition, it is shown that the scalar synapse does not receive the same expression in neural networks operating with spikes or with firing rates. These coherent modeling elements can help to improve, adjust, and refine the investigation of neural systems and their remarkable collective properties for information processing.

scholarly journals Mechanisms of function of neural grafts in the adult mammalian brain

1987 ◽  
Vol 132 (1) ◽  
pp. 265-289
Author(s):  
S. B. Dunnett ◽  
A. Bjorklund
Keyword(s):  
Recovery Of Function ◽  
Model Systems ◽  
Neural Systems ◽  
Mammalian Brain ◽  
Neural Tissues ◽  
Graft Tissue ◽  
And Function ◽  
Different Levels ◽  
Adult Mammalian Brain ◽  
Host Brain

Evidence for the survival, growth and function of grafted neural tissues in the adult mammalian brain is reviewed. In addition to considering the viability of grafts in the different model systems that have been investigated, consideration is given to alternative mechanisms by which the grafts might exert a functional influence over the host brain and the host animal's behaviour: (a) acute influence over spontaneous recovery of function, (b) chronic but diffuse secretion of neurochemicals into the host neuropile, (c) tonic reinnervation of the host brain, (d) bridging grafts, and (e) reciprocal reinnervation and full incorporation of graft tissue into host circuitry. It is concluded that no one mechanism is primary, but that different levels of reorganization can take place in different graft paradigms and neural systems.

scholarly journals Testing the Efforts Model of Simultaneous Interpreting: An ERP Study

2017 ◽  
Author(s):  
Roman Koshkin ◽  
Yury Shtyrov ◽  
Alex Ossadtchi
Keyword(s):  
Working Memory ◽  
Neural Activity ◽  
Event Related Potential ◽  
Auditory Stimuli ◽  
Simultaneous Interpretation ◽  
Simultaneous Interpreting ◽  
Electrophysiological Evidence ◽  
Task Irrelevant ◽  
Different Levels

AbstractWe utilized the event-related potential (ERP) technique to study neural activity associated with different levels of working memory (WM) load during simultaneous interpretation (SI) in an ecologically valid setting. The amplitude of N1 and P1 components elicited by task-irrelevant tone probes was significantly modulated as a function of WM load but not the direction of interpretation. Furthermore, the latency of the N1 increased insignificantly with WM load. The P1 latency, however, mostly did not depend on either WM load or direction of interpretation. Larger negativity under lower WM loads suggests deeper processing of the auditory stimuli, providing tentative electrophysiological evidence in support of the Efforts Model of SI. Relationships between the direction of interpretation and median WM load are also discussed.

scholarly journals Evaluation on the analogy between the dynamic magnetosphere and a forced and/or self-organized critical system

2002 ◽  
Vol 9 (5/6) ◽  
pp. 399-407 ◽  
Author(s):  
A. T. Y. Lui
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Plasma Sheet ◽  
Critical State ◽  
Conclusive Evidence ◽  
Critical System ◽  
Scale Free ◽  
Self Organized ◽  
Dissipation Power ◽  
Different Levels

Abstract. The dissipation power and size of auroral blobs are investigated in detail to examine the possible analogy between the dynamic magnetosphere and a forced and/or self-organized critical system. The distributions of these auroral parameters are sorted in terms of different levels of activity, namely substorms, pseudo-breakups, and quiet conditions. A power law (scale-free) component is seen in all these distributions. In addition, a peak distribution is found for substorm intervals and a hump for pseudo-breakup intervals. The peak distribution is present prominently during magnetic storms, i.e. when the magnetosphere is strongly driven by the solar wind. It is interpreted that the scale-free component is associated with the activity of the diffuse aurora, corresponding to disturbances at all permissible scales within the plasma sheet. Ionospheric feedback appears to be essential for the presence of two components in the distribution for auroral dissipation power. These results are consistent with the concept that the magnetosphere is in a forced and/or self-organized critical state, although they do not constitute conclusive evidence for the analogy.

scholarly journals Fractal Modeling and Fractal Dimension Description of Urban Morphology

Entropy ◽  
2020 ◽  
Vol 22 (9) ◽  
pp. 961 ◽  
Author(s):  
Yanguang Chen
Keyword(s):  
Fractal Dimension ◽  
Urban Area ◽  
Fractal Geometry ◽  
Urban Form ◽  
Characteristic Length ◽  
Fractal Theory ◽  
Urban Morphology ◽  
Scaling Analysis ◽  
Mathematical Methods ◽  
Scale Free

The conventional mathematical methods are based on characteristic length, while urban form has no characteristic length in many aspects. Urban area is a scale-dependence measure, which indicates the scale-free distribution of urban patterns. Thus, the urban description based on characteristic lengths should be replaced by urban characterization based on scaling. Fractal geometry is one powerful tool for the scaling analysis of cities. Fractal parameters can be defined by entropy and correlation functions. However, the question of how to understand city fractals is still pending. By means of logic deduction and ideas from fractal theory, this paper is devoted to discussing fractals and fractal dimensions of urban landscape. The main points of this work are as follows. Firstly, urban form can be treated as pre-fractals rather than real fractals, and fractal properties of cities are only valid within certain scaling ranges. Secondly, the topological dimension of city fractals based on the urban area is 0; thus, the minimum fractal dimension value of fractal cities is equal to or greater than 0. Thirdly, the fractal dimension of urban form is used to substitute the urban area, and it is better to define city fractals in a two-dimensional embedding space; thus, the maximum fractal dimension value of urban form is 2. A conclusion can be reached that urban form can be explored as fractals within certain ranges of scales and fractal geometry can be applied to the spatial analysis of the scale-free aspects of urban morphology.

Hierarchies, similarity, and interactivity in object recognition: “Category-specific” neuropsychological deficits

2001 ◽  
Vol 24 (3) ◽  
pp. 453-476 ◽  
Author(s):  
Glyn W. Humphreys ◽  
Emer M. E. Forde
Keyword(s):  
Information Processing ◽  
Object Recognition ◽  
Semantic Knowledge ◽  
Visual Similarity ◽  
Neural Systems ◽  
Living Things ◽  
New Processing ◽  
Different Levels ◽  
Insight Into ◽  
Processing Framework

Category-specific impairments of object recognition and naming are among the most intriguing disorders in neuropsychology, affecting the retrieval of knowledge about either living or nonliving things. They can give us insight into the nature of our representations of objects: Have we evolved different neural systems for recognizing different categories of object? What kinds of knowledge are important for recognizing particular objects? How does visual similarity within a category influence object recognition and representation? What is the nature of our semantic knowledge about different objects? We review the evidence on category-specific impairments, arguing that deficits even for one class of object (e.g., living things) cannot be accounted for in terms of a single information processing disorder across all patients; problems arise at contrasting loci in different patients. The same apparent pattern of impairment can be produced by damage to different loci. According to a new processing framework for object recognition and naming, the hierarchical interactive theory (HIT), we have a hierarchy of highly interactive stored representations. HIT explains the variety of patients in terms of (1) lesions at different levels of processing and (2) different forms of stored knowledge used both for particular tasks and for particular categories of object.

scholarly journals Scarcity of scale-free topology is universal across biochemical networks

2020 ◽  
Author(s):  
Harrison B. Smith ◽  
Hyunju Kim ◽  
Sara I. Walker
Keyword(s):  
Biochemical Networks ◽  
Coarse Grained ◽  
Technological Systems ◽  
Sharp Transition ◽  
Scale Free ◽  
Levels Of Organization ◽  
Scale Free Networks ◽  
Ecosystem Level ◽  
Different Levels ◽  
Organizing Principles

AbstractBiochemical reactions underlie all living processes. Like many biological and technological systems, their complex web of interactions is difficult to fully capture and quantify with simple mathematical objects. Nonetheless, a huge volume of research has suggested many real-world biological and technological systems – including biochemical systems – can be described rather simply as ‘scale-free’ networks, characterized by a power-law degree distribution. More recently, rigorous statistical analyses across a variety of systems have upended this view, suggesting truly scale-free networks may be rare. We provide a first application of these newer methods across two distinct levels of biological organization: analyzing a large ensemble of biochemical networks generated from the reactions encoded in 785 ecosystem-level metagenomes and 1082 individual-level genomes (representing all three domains of life). Our results confirm only a few percent of individual and ecosystem-level biochemical networks meet the criteria necessary to be anything more than super-weakly scale-free. Leveraging the simultaneous analysis of the multiple coarse-grained projections of biochemistry, we perform distinguishability tests across properties of individual and ecosystem-level biochemical networks to determine whether or not they share common structure, indicative of common generative mechanisms across levels. Our results indicate there is no sharp transition in the organization of biochemistry across distinct levels of the biological hierarchy - a result that holds across different network projections. This suggests the existence of common organizing principles operating across different levels of organization in biochemical networks, independent of the project chosen.Author SummaryFully characterizing living systems requires rigorous analysis of the complex webs of interactions governing living processes. Here we apply statistical approaches to analyze a large data set of biochemical networks across two levels of organization: individuals and ecosystems. We find that independent of level of organization, the standard ‘scale-free’ model is not a good description of the data. Interestingly, there is no sharp transition in the shape of degree distributions for biochemical networks when comparing those of individuals to ecosystems. This suggests the existence of common organizing principles operating across different levels of biochemical organization that are revealed across different network projections.

scholarly journals Midfrontal theta and pupil dilation parametrically track subjective conflict (but also surprise) during intertemporal choice

2017 ◽  
Author(s):  
Hause Lin ◽  
Blair Saunders ◽  
Cendri Hutcherson ◽  
Michael Inzlicht
Keyword(s):  
Intertemporal Choice ◽  
Economic Modeling ◽  
Pupil Dilation ◽  
Self Control ◽  
Neural Systems ◽  
Costs And Benefits ◽  
Eeg Data ◽  
Adaptive Shifts ◽  
Neurophysiological Basis ◽  
Different Levels

Many everyday choices are based on personal, subjective preferences. When choosing between two options, we often feel conflicted, especially when trading off costs and benefits occurring at different times (e.g., saving for later versus spending now). Although previous work has investigated the neurophysiological basis of conflict during inhibitory control tasks, less is known about subjective conflict resulting from competing subjective preferences. In this pre-registered study, we investigated subjective conflict during intertemporal choice, whereby participants chose between smaller immediate versus larger delayed rewards (e.g., $15 today vs. $22 in 30 days). We used economic modeling to parametrically vary eleven different levels of conflict, and recorded EEG data and pupil dilation. Midfrontal theta power, derived from EEG, correlated with pupil responses, and our results suggest that these signals track different gradations of subjective conflict. Unexpectedly, both signals were also maximally enhanced when decisions were surprisingly easy. Therefore, these signals may track events requiring increased attention and adaptive shifts in behavioral responses, with subjective conflict being only one type of such event. Our results suggest that the neural systems underlying midfrontal theta and pupil responses interact when weighing costs and benefits during intertemporal choice. Thus, understanding these interactions might elucidate how individuals resolve self-control conflicts.

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