Cerebellar Nuclear Neurons Use Time and Rate Coding to Transmit Purkinje Neuron Pauses

Copyright: © 2015 Sudhakar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedNeurons of the cerebellar nuclei convey the final output of the cerebellum to their targets in various parts of the brain. Within the cerebellum their direct upstream connections originate from inhibitory Purkinje neurons. Purkinje neurons have a complex firing pattern of regular spikes interrupted by intermittent pauses of variable length. How can the cerebellar nucleus process this complex input pattern? In this modeling study, we investigate different forms of Purkinje neuron simple spike pause synchrony and its influence on candidate coding strategies in the cerebellar nuclei. That is, we investigate how different alignments of synchronous pauses in synthetic Purkinje neuron spike trains affect either time-locking or rate-changes in the downstream nuclei. We find that Purkinje neuron synchrony is mainly represented by changes in the firing rate of cerebellar nuclei neurons. Pause beginning synchronization produced a unique effect on nuclei neuron firing, while the effect of pause ending and pause overlapping synchronization could not be distinguished from each other. Pause beginning synchronization produced better time-locking of nuclear neurons for short length pauses. We also characterize the effect of pause length and spike jitter on the nuclear neuron firing. Additionally, we find that the rate of rebound responses in nuclear neurons after a synchronous pause is controlled by the firing rate of Purkinje neurons preceding it.Peer reviewedFinal Published versio

An electromagnetic theory of turbulence driven poloidal rotation

International audienceAn electromagnetic theory of turbulence driven poloidal rotation is developed with particular emphasis on understanding poloidal rotation in finite-β plasmas. A relation linking the flux of polarization charge to the divergence of the total turbulent stress is derived for electromagnetic gyrokinetic modes. This relation is subsequently utilized to derive a constraint on the net electromagnetic turbulent stress exerted on the poloidal flow. Various limiting cases of this constraint are considered, where it is found that electromagnetic contributions to the turbulent stress may either enhance or reduce the net turbulent stress depending upon the branch of turbulence excited

Toroidal Rotation Driven by the Polarization Drift

International audienceStarting from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers a novel mechanism by which microturbulence may drive intrinsic rotation. This mechanism, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. The derivation and physical discussion of this mechanism will be pursued throughout this Letter

Poloidal rotation and its relation to the potential vorticity flux

International audienceA kinetic generalization of a Taylor identity appropriate to a strongly magnetized plasma is derived. This relation provides an explicit link between the radial mixing of a fourdimensional (4D) gyrocenter fluid and the poloidal Reynolds stress. This kinetic analog of a Taylor identity is subsequently utilized to link the turbulent transport of poloidal momentum to the mixing of potential vorticity. A quasilinear calculation of the flux of potential vorticity is carried out, yielding diffusive, turbulent equipartition, and thermoelectric convective components. Self-consistency is enforced via the quasineutrality relation, revealing that for the case of a stationary small amplitude wave population, deviations from neoclassical predictions of poloidal rotation can be closely linked to the growth/damping profiles of the underlying drift wave microturbulence

The heat engine analogy in understanding of toroidal rotation: thermodynamics of L-H spin-up

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A novel mechanism for exciting intrinsic toroidal rotation

International audienceBeginning from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers two physically distinct mechanisms by which microturbulence may drive intrinsic rotation. The first mechanism, which emanates from E×B convection of parallel momentum, has already been analyzed [ O. D. Gurcan et al., Phys. Plasmas 14, 042306 (2007) ; R. R. Dominguez and G. M. Staebler, Phys. Fluids B 5, 3876 (1993) ] and was shown to follow from radial electric field shear induced symmetry breaking of the spectrally averaged parallel wave number. Thus, this mechanism is most likely active in regions with steep pressure gradients or strong poloidal flow shear. The second mechanism uncovered, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. This novel means of driving intrinsic rotation, while nominally higher order in an expansion of the mode frequency divided by the ion cyclotron frequency, does not depend on radial electric field shear. Thus, while the magnitude of the former mechanism is strongly reduced in regions of weak radial electric field shear, this mechanism remains unabated and is thus likely relevant in complementary regimes

A simple model of intrinsic rotation in high confinement regime tokamak plasmas

International audienceA simple unified model of intrinsic rotation and momentum transport in high confinement regime (H-mode) tokamak plasmas is presented. Motivated by the common dynamics of the onset of intrinsic rotation and the L-H transition, this simple model combines E×B shear-driven residual stress in the pedestal with a turbulent equipartition pinch to yield rotation profiles. The residual stress is the primary mechanism for buildup of intrinsic rotation in the H-mode pedestal, while the pinch drives on-axis peaking of rotation profiles. Analytical estimates for pedestal flow velocities are given in terms of the pedestal width, the pedestal height, and various model parameters. The predicted scaling of the toroidal flow speed with pedestal width is found to be consistent with the International Tokamak Physics Activity database global scaling of the flow speed on-axis with the total plasma stored energy

A simple model for turbulent driven poloidal rotation in the vicinity of a transport barrier

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Exploring the use of structure and polymer incorporation to tune silver ion release and antibacterial activity of silver coordination polymers

The use of silver as an antibacterial agent has seen renewed interest as a result of its ability to combat a broad range of bacterial species, including those resistant to multiple classes of antibiotics. Silver coordination polymers (CPs) provide the opportunity to control the release of silver ions, thus avoiding unwanted side effects and toxicity; however, the parameters that tune release remain poorly understood. Here, four silver CPs, namely [Ag₂(Me₄bpz)] as both four‐ and eightfold interpenetrated forms, and [Ag(dpzm)(ClO₄)] in its open 3D and close‐packed 2D forms, were used to probe the role of structure in the release of silver ions. Release was measured by inductively‐coupled plasma mass spectrometry (ICP‐MS) and shown to be more marked for the charged networks, [Ag(dpzm)(ClO₄)] (complete dissolution). Incorporation of the silver CPs into inert polymer matrices, polyethylene and polycaprolactone, to provide surface coatings was also investigated, and shown to significantly retard silver ion release. The antibacterial activities of all materials as their polymer composites were analysed by disk diffusion and bacterial growth assays. All CPs showed antibacterial activity, with the Gram‐positive Staphylococcus aureus exhibiting greater sensitivity to silver than the Gram‐negative Escherichia coli. Metal–ligand bond strength and anion availability were found to influence silver release into aqueous solution but this did not always correlate with the in vitro antibacterial activity.Rosemary J. Young, Stephanie L. Begg, Campbell J. Coghlan, Christopher A. McDevitt and Christopher J. Sumb

Residual parallel Reynolds stress due to turbulence intensity gradient in tokamak plasmas

International audienceA novel mechanism for driving residual stress in tokamak plasmas based on k∥ symmetry breaking by the turbulence intensity gradient is proposed. The physics of this mechanism is explained and its connection to the wave kinetic equation and the wave-momentum flux is described. Applications to the H-mode pedestal in particular to internal transport barriers, are discussed. Also, the effect of heat transport on the momentum flux is discussed