Neural Activity in Quarks Language: Lattice Field Theory for a Network of Real Neurons.

Brain-computer interfaces have seen extraordinary surges in developments in recent years, and a significant discrepancy now exists between the abundance of available data and the limited headway made in achieving a unified theoretical framework. This discrepancy becomes particularly pronounced when examining the collective neural activity at the micro and meso scale, where a coherent formalization that adequately describes neural interactions is still lacking. Here, we introduce a mathematical framework to analyze systems of natural neurons and interpret the related empirical observations in terms of lattice field theory, an established paradigm from theoretical particle physics and statistical mechanics. Our methods are tailored to interpret data from chronic neural interfaces, especially spike rasters from measurements of single neuron activity, and generalize the maximum entropy model for neural networks so that the time evolution of the system is also taken into account. This is obtained by bridging particle physics and neuroscience, paving the way for particle physics-inspired models of the neocortex.

Large-deviation theory of increasing returns.

An influential theory of increasing returns was proposed by the economist W. B. Arthur in the 1980s to explain the lock-in phenomenon between two competing commercial products. In the most simplified situation there are two competing products that gain customers according to a majority mechanism: each new customer arrives and asks which product they bought to a certain odd number of previous customers, and then buys the most shared product within this sample. It is known that one of these two companies becomes a monopoly almost surely in the limit of infinite customers. Here we consider a generalization [Dosi, Ermoliev, and Kaniovsky, J. Math. Econom. 23, 1 (1994)10.1016/0304-4068(94)90032-9] in which the new customer follows the indication of the sample with some probability, and buys the other product otherwise. Other than economy, this model can be reduced to the urn of Hill, Lane, and Sudderth, and it includes several models of physical interest as special cases, such as the Elephant Random Walk, Friedman's urn, and other generalized urn models. We provide a large-deviation analysis of this model at the sample-path level, and we provide a formula that allows us to find the most likely trajectories followed by the market share variable. Interestingly, in the parameter range where the lock-in phase is expected, we observe a whole region of convergence where the entropy cost is sublinear. We also find a nonlinear differential equation for the cumulant-generating function of the market share variable, which can be studied with a suitable perturbation theory.

Energy of the interacting self-avoiding walk at the θ point.

We perform a numerical study of a new microcanonical polymer model on a three-dimensional cubic lattice, consisting of ideal chains whose range and number of nearest-neighbor contacts are fixed to given values. Our simulations suggest an interesting exact relation concerning the internal energy per monomer of the interacting self-avoiding walk at the θ point.

Pyruvate cellular uptake and enzymatic conversion probed by dissolution DNP-NMR: the impact of overexpressed membrane transporters.

Pyruvate membrane crossing and its lactate dehydrogenase-mediated conversion to lactate in cells featuring different levels of expression of membrane monocarboxylate transporters (MCT4) were probed by dissolution dynamic nuclear polarization-enhanced NMR. Hyperpolarized 13 C-1-labeled pyruvate was transferred to suspensions of rodent tumor cell carcinoma, cell line 39. The pyruvate-to-lactate conversion rate monitored by dissolution dynamic nuclear polarization-NMR in carcinoma cells featuring native MCT4 expression level was lower than the rate observed for cells in which the human MCT4 gene was overexpressed. The enzymatic activity of lactate dehydrogenase was also assessed in buffer solutions, following the real-time pyruvate-to-lactate conversion speeds at different enzyme concentrations. Copyright © 2016 John Wiley & Sons, Ltd.

Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR.

The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of metabolic transformations. Hyperpolarization via dissolution DNP circumvents part of the sensitivity issues thanks to the large out-of-equilibrium nuclear magnetization stemming from the electron-to-nucleus spin polarization transfer. The high NMR signal obtained can be used to monitor chemical reactions in real time. The downside of hyperpolarized NMR resides in the limited time window available for signal acquisition, which is usually on the order of the nuclear spin longitudinal relaxation time constant, T1, or, in favorable cases, on the order of the relaxation time constant associated with the singlet-state of coupled nuclei, TLLS. Cellular uptake of endogenous molecules and metabolic rates can provide essential information on tumor development and drug response. Numerous previous hyperpolarized NMR studies have demonstrated the relevancy of pyruvate as a metabolic substrate for monitoring enzymatic activity in vivo. This work provides a detailed description of the experimental setup and methods required for the study of enzymatic reactions, in particular the pyruvate-to-lactate conversion rate in presence of lactate dehydrogenase (LDH), by hyperpolarized NMR.

Hyperpolarized (6)Li as a probe for hemoglobin oxygenation level.

Hyperpolarization by dissolution dynamic nuclear polarization (DNP) is a versatile technique to dramatically enhance the nuclear magnetic resonance (NMR) signal intensity of insensitive long-T1 nuclear spins such as (6)Li. The (6)Li longitudinal relaxation of lithium ions in aqueous solutions strongly depends on the concentration of paramagnetic species, even if they are present in minute amounts. We herein demonstrate that blood oxygenation can be readily detected by taking advantage of the (6)Li signal enhancement provided by dissolution DNP, together with the more than 10% decrease in (6)Li longitudinal relaxation as a consequence of the presence of paramagnetic deoxyhemoglobin.

Over 35% liquid-state 13C polarization obtained via dissolution dynamic nuclear polarization at 7 T and 1 K using ubiquitous nitroxyl radicals.

The most versatile method to increase liquid-state (13)C NMR sensitivity is dissolution dynamic nuclear polarization. The use of trityl radicals is usually required to obtain very large (13)C polarization via this technique. We herein demonstrate that up to 35% liquid-state (13)C polarization can be obtained in about 1.5 h using ubiquitous nitroxyl radicals in (13)C-labeled sodium salts by partially deuterating the solvents and using a polarizer operating at 1 K and 7 T.