Setting reference level in the human safety guidelines via nerve activation intercomparison at IF

International guidelines/standards have been published for human protection from electromagnetic field exposure. The research in the intermediate frequencies (IF: 300 Hz-10 MHz) is scattered unlike for other frequencies, and thus the limit prescribed in the guidelines/standards are different by a factor of 10. The IEEE International Committee on Electromagnetic Safety has published a research agenda for exploring the electrostimulation thresholds. However, the consistency of the excitation models for specific target tissue needs to be revised. For this purpose, we present the first intercomparison study using multiphysics modelling to investigate stimulation thresholds during transcranial magnetic stimulation (TMS). To define the stimulation threshold, a noninvasive technique for brain stimulation has been used. In this study, by incorporating individual neurons into electromagnetic computation in realistic head models, stimulation thresholds can be determined. The study case of one subject showed that the allowable external magnetic field strength in the current guidelines/standard is conservative

Dependence of excitability indices on membrane channel dynamics, myelin impedance, electrode location and stimulus waveforms in myelinated and unmyelinated fibre models

Neuronal excitability is determined in a complex way by several interacting factors, such as membrane dynamics, fibre geometry, electrode configuration, myelin impedance, neuronal terminations This study aims to increase understanding in excitability, by investigating the impact of these factors on different models of myelinated and unmyelinated fibres (five well-known membrane models are combined with three electrostimulation models, that take into account the spatial structure of the neuron). Several excitability indices (rheobase, polarity ratio, bi/monophasic ratio, time constants) are calculated during extensive parameter sweeps, allowing us to obtain novel findings on how these factors interact, e.g. how the dependency of excitability indices on the fibre diameter and myelin impedance is influenced by the electrode location and membrane dynamics. It was found that excitability is profoundly impacted by the used membrane model and the location of the neuronal terminations. The approximation of infinite myelin impedance was investigated by two implementations of the spatially extended non-linear node model. The impact of this approximation on the time constant of strength-duration plots is significant, most importantly in the Frankenhaeuser-Huxley membrane model for large electrode-neuron separations. Finally, a multi-compartmental model for C-fibres is used to determine the impact of the absence of internodes on excitability

SECONIC : towards multi-compartmental models for ultrasonic brain stimulation by intramembrane cavitation

Objective. To design a computationally efficient model for ultrasonic neuromodulation (UNMOD) of morphologically realistic multi-compartmental neurons based on intramembrane cavitation.Approach. A Spatially Extended Neuronal Intramembrane Cavitation model that accurately predicts observed fast Charge Oscillations (SECONIC) is designed. A regular spiking cortical Hodgkin-Huxley type nanoscale neuron model of the bilayer sonophore and surrounding proteins is used. The accuracy and computational efficiency of SECONIC is compared with the Neuronal Intramembrane Cavitation Excitation (NICE) and multiScale Optimized model of Neuronal Intramembrane Cavitation (SONIC).Main results. Membrane charge redistribution between different compartments should be taken into account via fourier series analysis in an accurate multi-compartmental UNMOD-model. Approximating charge and voltage traces with the harmonic term and first two overtones results in reasonable goodness-of-fit, except for high ultrasonic pressure (adjusted R-squared >= 0.61). Taking into account the first eight overtones results in a very good fourier series fit (adjusted R-squared >= 0.96) up to 600 kPa. Next, the dependency of effective voltage and rate parameters on charge oscillations is investigated. The two-tone SECONIC-model is one to two orders of magnitude faster than the NICE-model and demonstrates accurate results for ultrasonic pressure up to 100 kPa.Significance. Up to now, the underlying mechanism of UNMOD is not well understood. Here, the extension of the bilayer sonophore model to spatially extended neurons via the design of a multi-compartmental UNMOD-model, will result in more detailed predictions that can be used to validate or falsify this tentative mechanism. Furthermore, a multi-compartmental model for UNMOD is required for neural engineering studies that couple finite difference time domain simulations with neuronal models. Here, we propose the SECONIC-model, extending the SONIC-model by taking into account charge redistribution between compartments

Optimisation de la phytoextraction : caractérisation et sélection de bactéries PGPB associées à une plante hyperaccumulatrice de Zn et Cd : Arabidopsis halleri

National audiencePhytotechnologies are microbial-assisted techniques that use living plants for the treatment of contaminated sites. Among these, phytoextraction based on hyperaccumulator plants such as Arabidopsis halleri, may be an option to remove trace elements in soil. One method to optimize Arabidopsis halleri phytoextraction is the inoculation of plant roots by plant growth promoting bacteria (PGPB). In this study, we proposed a protocol for sampling bacteria in three different soil fractions neared root system of Arabidopsis halleri: global, rhizospheric and rhizoplan. The cultivable bacteria were isolated for a Zn and Cd contaminated industrial soil (Auby, France) and were isolated and characterized for their PGPB traits : 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophores and Indol-Acetic-Acid (IAA) productions). Bacteria answering positively to the three PGPB tests have been preferentially selected to be inoculated to Arabidopsis halleri root system. Bacteria effects on plant biomass and/or accumulating yield will be presented.Les phytotechnologies consistent en l'utilisation de plantes qui, par leur association avec la microflore du sol, ont la capacité de dépolluer les sites contaminés (eau, sol, sédiments). Parmi ces technologies, la phytoextraction, basée sur l'utilisation de plantes hyperaccumulatrices telle qu'Arabidopsis halleri, semble être une option pour décontaminer les sols pollués en éléments traces métalliques. Une des voies d'amélioration de la phytoextraction d'A. halleri serait l'inoculation du système racinaire de la plante par des bactéries capables de stimuler la croissance végétale (PGPB pour Plant Growth Promoting Bacteria). Dans cette étude, nous proposons un protocole d'échantillonnage des différentes fractions de sol autour de la racine : sols global, rhizosphérique et rhizoplan. Les bactéries cultivables, collectées sur un sol industriel contaminé en Zn et Cd (Auby, France), ont été isolées et analysées pour leurs caractéristiques PGPB : activité 1-aminocyclopropane-1-carboxylate (ACC) désaminase, productions de sidérophores et d'acide indole acétique (IAA). Les bactéries qui présentent trois caractères PGPB ont été préférentiellement sélectionnées pour être inoculées au niveau du système racinaire d'Arabidopsis halleri. Les effets de ces bactéries sur les paramètres de croissance de la plante et sa biomasse ou sur le rendement d'accumulation des éléments traces métalliques seront présentés

Comparison between direct electrical and optogenetic subthalamic nucleus stimulation

Subthalamic nucleus deep brain stimulation is a treatment for Parkinson’s disease. In this study, a computational model of a plateau-potential generating subthalamic nucleus neuron (Otsuka-model) and a four-state ChR2(H134R) model (Williams-model) are combined, in order to compare electrical and optogenetic neuromodulation capabilities. The impact of the stimulation modality (optogenetic or electric) on firing rates, strength-duration curves and action potential shape is investigated. First, in contrast to electrical stimulation, mean instantaneous firing rates saturate for optical stimulation at intensities higher than 0.1 W/cm2. Second, rheobase and chronaxie are 175% and 9.6% larger in optogenetic stimulation compared to electrical stimulation, respectively. Third, action potential shape is not significantly impacted by the neurostimulation modality

Phytoextraction process optimization : characterization of the soil bacteria flora associated to the hyperaccumulator Arabidopsis halleri

International audiencePhytotechnologies are microbial-assisted techniques that use living plants for the treatment of contaminated sites. Among these, phytoextraction based on hyperaccumulator plants such as Arabidopsis halleri, may be an option to remove trace elements in soil. One method to optimize Arabidopsis halleri's phytoextraction is the inoculation of plant roots by plant growth promoting bacteria (PGPB). In this study, we analyzed the total bacterial diversity in a Zn and Cd contaminated industrial soil (Auby, France) with restriction fragment length polymorphism (RFLP). Preliminary results showed a large bacterial diversity in Auby's soil. Cultivable bacteria were isolated and characterized for their PGPB traits (ACC deaminase activity, siderophores and Indol-Acetic-Acid (IAA) productions). Bacteria that will answer positively to the three PGPB tests will be preferentially selected, and inoculated to Arabidopsis halleri roots. Bacteria effects on plant biomass and/or accumulating yield will be presented

Investigation of the stimulation capabilities of a high-resolution neurorecording probe for the application of closed-loop deep brain stimulation

Deep brain stimulation is an established surgical treatment for several neurological and movement disorders, such as Parkinson's disease, in which electrostimulation is applied to targeted deep nuclei in the basal ganglia through implanted electrode leads. Recent technological improvements in the field have focused on the theoretical advantage of current steering and adaptive (closed-loop) deep brain stimulation. Current steering between several active electrodes would allow for improved accuracy when targeting the desired brain structures. This has the additional benefit of avoiding undesired stimulation of neural tracts that are related to side effects, e.g., internal capsule fibres of passage in subthalamic nucleus deep brain stimulation. Closed-loop deep brain stimulation is based on the premise of continuous recording of a proxy for pathological neural activity (such as beta-band power of measured local field potentials in patients with Parkinson's disease) and accordingly adapting the used stimulus parameters. In this study, we investigate the suitability of an existing highresolution neurorecording probe for high-precision neurostimulation. If a subset of the probe's recording electrodes can be used for stimulation, then the probe would be a suitable candidate for closed-loop deep brain stimulation. A finiteelement model is used to calculate the electric potential, induced by current injection through the high-resolution probe, for different sets of active electrodes. Volumes of activated tissue are calculated and a comparison is made between the highresolution probe and a conventional stimulation lead. We investigate the capability of the probe to shift the volume of activated tissue by steering currents to different sets of active electrodes. Finally, safety limits for the injected current are used to determine the size of the volume in which neurons can be activated with the relatively small electrodes patches on the highresolution probe