NRV: An open framework for in silico evaluation of peripheral nerve electrical stimulation strategies.

Electrical stimulation of peripheral nerves has been used in various pathological contexts for rehabilitation purposes or to alleviate the symptoms of neuropathologies, thus improving the overall quality of life of patients. However, the development of novel therapeutic strategies is still a challenging issue requiring extensive in vivo experimental campaigns and technical development. To facilitate the design of new stimulation strategies, we provide a fully open source and self-contained software framework for the in silico evaluation of peripheral nerve electrical stimulation. Our modeling approach, developed in the popular and well-established Python language, uses an object-oriented paradigm to map the physiological and electrical context. The framework is designed to facilitate multi-scale analysis, from single fiber stimulation to whole multifascicular nerves. It also allows the simulation of complex strategies such as multiple electrode combinations and waveforms ranging from conventional biphasic pulses to more complex modulated kHz stimuli. In addition, we provide automated support for stimulation strategy optimization and handle the computational backend transparently to the user. Our framework has been extensively tested and validated with several existing results in the literature.

BIMMS: A versatile and portable system for biological tissue and electrode-tissue interface electrical characterization.

The presented design is a low-cost, compact, and open-source USB-controlled platform for biological tissue and electrode-tissue interface electrical measurements, capable of potentiostatic and galvanostatic electrical impedance spectroscopy up to 10 MHz and cyclic voltammetry with voltage compliance of +-8 V and up to 2.4 mA while ensuring tissue-safety conditions. The data acquisition and generation are based on an Analog Discovery 2 platform (Digilent, USA). We provide accuracy analysis and comparisons with a commercially available calibrated impedance analyzer. Impedance measurements are demonstrated on implanted electrodes for neural stimulation and on an isolated ex-vivo calf brain as an example use case of the presented design.

In vivo validation of a new portable stimulator for chronic deep brain stimulation in freely moving rats.

BACKGROUND: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is considered as a gold standard therapy for the alleviation of motor symptoms in Parkinson's disease (PD). This success paved the way to its application for other neurological and psychiatric disorders. In this context, we aimed to develop a rodent-specific stimulator with characteristics similar to those used in patients. NEW METHOD: We designed a stimulator that can be connected to an electrode container with options for bilateral or unilateral stimulation selection and offers a wide range of frequencies, pulse widths and intensities, constant current, biphasic current-control and charge balancing. Dedicated software was developed to program these parameters and the device was tested on a bilateral 6-hydroxydopamine (6-OHDA) rat model of PD. RESULTS: The equipment was well tolerated by the animals with a good general welfare. STN stimulation (130 Hz frequency, 0.06 ms pulse width, 150 µA average intensity) improved the motor deficits induced by 6-OHDA as it significantly increased the number of movements compared to the values obtained in the same animals without STN stimulation. Furthermore, it restored motor coordination by significantly increasing the time spent on the rotarod bar. CONCLUSION: We successfully developed and validated a new portable and programmable stimulator for freely moving rats that delivers a large range of stimulation parameters using bilateral biphasic current-control and charge balancing to maximize tissue safety. This device can be used to test deep brain stimulation in different animal models of human brain diseases.

Unidirectional ephaptic stimulation between two myelinated axons.

Providing realistic sensory feedback for prosthetic devices strongly relies on an accurate modelling of machine-nerve interfaces. Models of these interfaces in the peripheral nervous system usually neglect the effects that ephaptic coupling can have on the selectivity of stimulating electrodes. In this contribution, we study the ephaptic stimulation between myelinated axons and show its relation with the separation between fibers and the conductivity of the medium that surrounds them.

An IC-based controllable stimulator for respiratory muscle stimulation investigations.

Functional Electrical Stimulation can be used to restore motor functions loss consecutive to spinal cord injury, such as respiratory deficiency due to paralysis of ventilatory muscles. This paper presents a fully configurable IC-centered stimulator designed to investigate muscle stimulation paradigms. It provides 8 current stimulation channels with high-voltage compliance and real-time operation capabilities, to enable a wide range of FES applications. The stimulator can be used in a standalone mode, or within a closed-loop setup. Primary in vivo results show successful drive of respiratory muscles stimulation using a computer-based dedicated controller.

An Embedded Deep Brain Stimulator for Biphasic Chronic Experiments in Freely Moving Rodents.

This paper describes a Deep Brain Stimulation device, portable, for chronic experiments on rodents in the context of Parkinson's disease. Our goal is to equip the animal with a device that mimics the human therapeutic conditions. It implies to respect a set of properties such as bilateral current-mode and charge-balanced stimulation, as well as programmability, low power consumption and re-usability to finally reach a suitable weight for long-term experiments. After the analysis of the solutions found in the literature, the full design of the device is explained. First, the stimulation front-end circuit driven by a processor unit, then the choice of supply sources which is a critical point for the weight and life-time of our system. Our low cost system has been realized using commercial discrete components and the overall power consumption was minimized. We achieved 6 days of maximal current stimulation with the chosen battery for a weight of 13.8 g . Finally, the device was carried out in vivo on rats during a 3 weeks experiment as the used implantation technique allows battery changing. This experiment also permits to emphasize the mechanical aspects including the packaging and electrodes holding.

A figure of merit for neural electrical stimulation circuits.

Electrical stimulators are widely used in neuro-prostheses. Many different implementations exist. However, no quantitative ranking criterion is available to allow meaningful comparison of the various stimulation circuits and systems to aid the designer. This paper presents a novel Figure of Merit (FOM) dedicated to stimulation circuits and systems. The proposed optimization performance metric takes into account tissue safety conditions and energy efficiency which can be evaluated by measurement. The FOM is used to rank several stimulator circuits and systems.