Non-equilibrium landscape and flux reveal the stability-flexibility-energy tradeoff in working memory

A balance has to be struck between supporting distractor-resistant representations in working memory and allowing those representations to be updated. Catecholamine, particularly dopamine, transmission has been proposed to modulate the balance between the stability and flexibility of working memory representations. However, it is unclear whether drugs that increase catecholamine transmission, such as methylphenidate, optimize this balance in a task-dependent manner or bias the system toward stability at the expense of flexibility (or vice versa). Here we demonstrate, using pharmacological fMRI, that methylphenidate improves the ability to resist distraction (cognitive stability) but impairs the ability to flexibly update items currently held in working memory (cognitive flexibility). These behavioral effects were accompanied by task-general effects in the striatum and opposite and task-specific effects on neural signal in the pFC. This suggests that methylphenidate exerts its cognitive enhancing and impairing effects through acting on the pFC, an effect likely associated with methylphenidate's action on the striatum. These findings highlight that methylphenidate acts as a double-edged sword, improving one cognitive function at the expense of another, while also elucidating the neurocognitive mechanisms underlying these paradoxical effects.

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Spike-Driven Synaptic Dynamics Generating Working Memory States

Neural Computation ◽

10.1162/089976603321192086 ◽

2003 ◽

Vol 15 (3) ◽

pp. 565-596 ◽

Cited By ~ 48

Author(s):

Daniel J. Amit ◽

Gianluigi Mongillo

Keyword(s):

Working Memory ◽

Spike Timing ◽

Spiking Neurons ◽

Large Network ◽

Synaptic Structure ◽

Hebbian Plasticity ◽

Timing Effects ◽

Synaptic Dynamics ◽

The Stability ◽

External Stimuli

The collective behavior of a network, modeling a cortical module of spiking neurons connected by plastic synapses is studied. A detailed spike-driven synaptic dynamics is simulated in a large network of spiking neurons, implementing the full double dynamics of neurons and synapses. The repeated presentation of a set of external stimuli is shown to structure the network to the point of sustaining working memory (selective delay activity). When the synaptic dynamics is analyzed as a function of pre- and postsynaptic spike rates in functionally defined populations, it reveals a novel variation of the Hebbian plasticity paradigm: in any functional set of synapses between pairs of neurons (e.g., stimulated—stimulated, stimulated—delay, stimulated—spontaneous), there is a finite probability of potentiation as well as of depression. This leads to a saturation of potentiation or depression at the level of the ratio of the two probabilities. When one of the two probabilities is very high relative to the other, the familiar Hebbian mechanism is recovered. But where correlated working memory is formed, it prevents overlearning. Constraints relevant to the stability of the acquired synaptic structure and the regimes of global activity allowing for structuring are expressed in terms of the parameters describing the single-synapse dynamics. The synaptic dynamics is discussed in the light of experiments observing precise spike timing effects and related issues of biological plausibility.

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Non-Equilibrium Generation of Catalytic Supramolecular Polymers of Pre-RNA Nucleobases

10.26434/chemrxiv.13558055 ◽

2021 ◽

Author(s):

Syed Pavel Afrose ◽

Chiranjit Mahato ◽

Pooja Sharma ◽

Lisa Roy ◽

Dibyendu Das

Keyword(s):

Information Storage ◽

Supramolecular Polymers ◽

Polymer Backbone ◽

Available Energy ◽

Reversible Covalent ◽

The Stability ◽

Equilibrium Polymers ◽

Emergence Of Life ◽

Hydrolysis Of ◽

Non Equilibrium

<p>Bioenergetics played critical roles for the chemical emergence of life where available energy resources drove the generation of primitive polymers and fueled early metabolism. Further, apart from information storage, the catalytic roles of primitive nucleic acid fragments have also been argued to be important for biopolymer evolution. Herein, we have demonstrated the non-equilibrium generation of catalytic supramolecular polymers of a possible proto-RNA building block (melamine) driven by a thermodynamically activated ester of low molecular weight. We utilized reversible covalent linkage to install a catalytic imidazole moiety in the polymer backbone. This resulted in energy dissipation via hydrolysis of the substrate predominantly from the assembled state and subsequent disassembly, thus installing kinetic asymmetry in the energy consumption cycle. Non-catalytic analogues led to kinetically stable polymers while inactivated substrates were unable to drive the polymerization. The non-equilibrium polymers of the pre-RNA bases were capable to spatiotemporally bind to a model cofactor. Notably, presence of an exogenous aromatic base augmented the stability of the polymers, reminiscent to what the molecular midwives did during early evolution. </p>

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Impact of Thermal Non-equilibrium on the Stability of Natural Convection in an Oldroyd-B Fluid-Saturated Vertical Porous Layer with Internal Heat Sources

Transport in Porous Media ◽

10.1007/s11242-020-01431-y ◽

2020 ◽

Vol 133 (3) ◽

pp. 437-458

Author(s):

B. M. Shankar ◽

I. S. Shivakumara ◽

S. B. Naveen

Keyword(s):

Natural Convection ◽

Porous Layer ◽

Internal Heat ◽

Heat Sources ◽

Internal Heat Sources ◽

The Stability ◽

Non Equilibrium

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Material’s Chemical Reaction Progression Variables Fluctuating and Detailed Equilibrium Principle

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.424-425.861 ◽

2012 ◽

Vol 424-425 ◽

pp. 861-864

Author(s):

Qing Hua Zou

Keyword(s):

Chemical Reaction ◽

Equilibrium Equation ◽

Internal Variable ◽

Local System ◽

Mean Square ◽

Mean Square Deviation ◽

Variable Chemical ◽

The Mean ◽

The Stability ◽

Non Equilibrium

The paper derived and gave the mean square deviation formula relating to the internal variable (chemical reaction progression variable) fluctuating of the linear non–equilibrium local system, and also rendered the condition of the stability. Furthermore, It discussed the related relations among the corresponding mean square deviation, the detailed equilibrium equation, the relax time and other thermal mechanics variables

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On the Evidence of Thermodynamic Self-Organization during Fatigue: A Review

Entropy ◽

10.3390/e22030372 ◽

2020 ◽

Vol 22 (3) ◽

pp. 372

Author(s):

Mehdi Naderi

Keyword(s):

Single Crystals ◽

Excess Entropy ◽

Dissipative Structures ◽

Self Organization ◽

Persistent Slip Bands ◽

Equilibrium Process ◽

Far From Equilibrium ◽

The Stability ◽

New Generation ◽

Non Equilibrium

In this review paper, the evidence and application of thermodynamic self-organization are reviewed for metals typically with single crystals subjected to cyclic loading. The theory of self-organization in thermodynamic processes far from equilibrium is a cutting-edge theme for the development of a new generation of materials. It could be interpreted as the formation of globally coherent patterns, configurations and orderliness through local interactivities by “cascade evolution of dissipative structures”. Non-equilibrium thermodynamics, entropy, and dissipative structures connected to self-organization phenomenon (patterning, orderliness) are briefly discussed. Some example evidences are reviewed in detail to show how thermodynamics self-organization can emerge from a non-equilibrium process; fatigue. Evidences including dislocation density evolution, stored energy, temperature, and acoustic signals can be considered as the signature of self-organization. Most of the attention is given to relate an analogy between persistent slip bands (PSBs) and self-organization in metals with single crystals. Some aspects of the stability of dislocations during fatigue of single crystals are discussed using the formulation of excess entropy generation.

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Silicon Compounds in the Jupiter Atmosphere

Zeitschrift für Naturforschung A ◽

10.1515/zna-1979-1224 ◽

1979 ◽

Vol 34 (12) ◽

pp. 1541-1543

Author(s):

Glenn Howland ◽

Paul Harteck ◽

Robert R. Reeves

Keyword(s):

Model Atmosphere ◽

Silicon Compounds ◽

Cosmic Abundance ◽

Equilibrium Profile ◽

Nonequilibrium Conditions ◽

Equilibrium Transition ◽

The Stability ◽

The Universe ◽

Calculated Equilibrium ◽

Non Equilibrium

Abstract Due to the relatively large cosmic abundance of Si and the stability of colored silicon compounds easily formed under various nonequilibrium conditions, it is concluded here that silicon should be strongly considered as a potential major component in the observed colored material in the Jupiter atmosphere. Silicon is one of the most abundant elements in the universe (after H, He, 0, N, and C) and in the same order of abundance as Mg and Fe. In the high temperature and pressure regions of Jupiter most of the Si should be present as SiH4. At higher altitudes, corresponding to a total pressure of less than 1000 bar and a temperature below 1200 K, SiC>2 and other compounds of silicon should dominate. These equilibria and the chemistry depend strongly upon the H9O concentration, which is assumed to be in the order of 10~ 3 . A calculated equilibrium profile had been proposed for a model atmosphere [1] and our own estimates confirm the main features within reasonable limits. Recent photographs taken of Jupiter emphasize the fact that the atmosphere of the planet is not in equilibrium. Atmospheric turbulence is observed corresponding to movement in the colored areas including the well-known great red spot. Assuming, therefore, that non-equilibrium processes may occur on Jupiter, the nature of such processes may be sought in the laboratory. The non-equilibrium transition of SiH4 to Si(>2 can be observed in various ways. We have found that many of these lead to intermediates that are relatively stable and yield strong colorations very similar in appearance to those observed on Jupiter. The purpose of this paper is to emphasize the possibility of the silicon compounds contributing

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