Shapes of direct cortical responses vs. short-range axono-cortical evoked potentials: The effects of direct electrical stimulation applied to the human brain.

Objective: Direct cortical responses (DCR) and axono-cortical evoked potentials (ACEP) are generated by electrically stimulating the cortex either directly or indirectly through white matter pathways, potentially leading to different electrogenic processes. For ACEP, the slow conduction velocity of axons (median ≈ 4 m.s) is anticipated to induce a delay.

New insights into muscle activity associated with phantom hand movements in transhumeral amputees.

Introduction: Muscle activity patterns in the residual arm are systematically present during phantom hand movements (PHM) in transhumeral amputees. However, their characteristics have not been directly investigated yet, leaving their neurophysiological origin poorly understood. This study pioneers a neurophysiological perspective in examining PHM-related muscle activity patterns by characterizing and comparing them with those in the arm, forearm, and hand muscles of control participants executing intact hand movements (IHM) of similar types.

How far does electrical stimulation activate white matter tracts? A computational modeling study.

Objective: The aim of this study was to model how the different parameters of electrical stimulation (intensity, pulse shape, probe geometry) influence the extent of white matter activation.

Methods: The electrical potentials generated by the stimulating electrodes were determined by solving Laplace equation. The temporal evolution of membrane potentials at each nodes of Ranvier of an axon was then computed by solving the coupled system of differential equations describing membrane dynamics and cable propagation.

Short-range axono-cortical evoked-potentials in brain tumor surgery: Waveform characteristics as markers of direct connectivity.

Objective: Intraoperative measurement of axono-cortical evoked potentials (ACEP) has emerged as a promising tool for studying neural connectivity. However, it is often difficult to determine if the activity recorded by cortical grids is generated by stimulated tracts or by spurious phenomena. This study aimed to identify criteria that would indicate a direct neurophysiological connection between a recording contact and a stimulated pathway.

Quantitative assessment of near-infrared spectroscopy time course under hypercapnia using an a priori model-based fitting.

Background: Partial arterial pressure of carbon dioxide (CO) modulates cerebral blood flow through a vasoreactivity mechanism. Near infrared spectroscopy (NIRS) can be used to record these changes in cerebral hemodynamics. However, no laterality comparison of the NIRS signal has been performed despite being a prerequisite for the use of such a method in a vasoreactivity monitoring context.

Relevance of selective neural stimulation with a multicontact cuff electrode using multicriteria analysis.

Neural multicontact cuff electrodes have the potential to activate selectively different groups of muscles and offer more possibilities of electrical configurations compared to whole ring cuffs. Several previous studies explored multicontact electrodes with a limited set of configurations which were sorted using a selectivity index only. The objective of the present study is to classify a larger number of configurations, i.

Comparison of the efficiency of chopped and non-rectangular electrical stimulus waveforms in activating small vagus nerve fibers.

Background: In the context of morbid obesity, vagus nerve stimulation could be used to control gastric function targeting the small afferent B-fibers and C-fibers. Compared to large A-fibers, activation thresholds of these small efferent fibers are 10 to 100 times greater, inducing technical constraints and possible nerve damages. Although rectangular waveform is commonly used in nerve stimulation, recent modeling and experimental studies suggest that non-rectangular waveforms could reduced the charge injected by the stimulator.

Investigation of the efficiency of the shape of chopped pulses using earthworm model.

In neural electrical stimulation, limiting the charge delivered during a stimulus pulse is essential to avoid nerve tissue damage and to save power. Previous experimental and modeling studies indicated that waveforms such as non-rectangular continuous pulses or rectangular chopped pulse were able to improve stimulation efficiency. The goal of this study is to evaluate if non-rectangular chopped pulses such as quarter sine and ramp are more charge efficient than rectangular chopped pulse.

Model based optimal multipolar stimulation without a priori knowledge of nerve structure: application to vagus nerve stimulation.

Objective: Multipolar cuff electrode can selectively stimulate areas of peripheral nerves and therefore enable to control independent functions. However, the branching and fascicularization are known for a limited set of nerves and the specific organization remains subject-dependent. This paper presents general modeling and optimization methods in the context of multipolar stimulation using a cuff electrode without a priori knowledge of the nerve structure.

Numerical simulation of multipolar configuration and prepulse technique to obtain spatially reverse recruitment order.

In the context of functional electrical stimulation of peripheral nerves, the control of a specific motor or sensory functions may need selective stimulation to target the desired effect without others. In implanted stimulation, spatial selectivity is obtained using multipolar CUFF electrodes with specific spread of the current over each contact. Furthermore, electrical stimulation recruits large fibers before small ones, whereas the targeted function could be elicited by a specific fiber type i.

A measure of cortico-cortical potentials evoked by 10 Hz direct electrical stimulation of the brain and by means of a differential recording mode of electrocorticographic signals.

Direct electrical stimulation (DES) at 60 Hz is used to perform real-time functional mapping of the brain during wide-awake neurosurgery. The electrophysiological effects of DES are largely unknown, locally and at a more remote distance. Here, by lowering the DES frequency to 10 Hz and by using a differential recording mode of electro-corticographic (ECoG) signals to improve the focality, we were able to record cortico-cortical evoked potentials easily with standard current amplitude of stimulation (2 mA).

Fast Simulation and Optimization Tool to Explore Selective Neural Stimulation.

In functional electrical stimulation, selective stimulation of axons is desirable to activate a specific target, in particular muscular function. This implies to simulate a fascicule without activating neighboring ones i.e.

Exploring Selective Neural Electrical Stimulation for Upper Limb Function Restoration.

This article introduces a new approach of selective neural electrical stimulation of the upper limb nerves. Median and radial nerves of individuals with tetraplegia are stimulated via a multipolar cuff electrode to elicit movements of wrist and hand in acute conditions during a surgical intervention. Various configurations corresponding to various combinations of a 12-poles cuff electrode contacts are tested.

Vagus nerve stimulation: state of the art of stimulation and recording strategies to address autonomic function neuromodulation.

Objective: Neural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.

A phantom axon setup for validating models of action potential recordings.

Electrode designs and strategies for electroneurogram recordings are often tested first by computer simulations and then by animal models, but they are rarely implanted for long-term evaluation in humans. The models show that the amplitude of the potential at the surface of an axon is higher in front of the nodes of Ranvier than at the internodes; however, this has not been investigated through in vivo measurements. An original experimental method is presented to emulate a single fiber action potential in an infinite conductive volume, allowing the potential of an axon to be recorded at both the nodes of Ranvier and the internodes, for a wide range of electrode-to-fiber radial distances.

The difference between electrical microstimulation and direct electrical stimulation - towards new opportunities for innovative functional brain mapping?

Both electrical microstimulation (EMS) and direct electrical stimulation (DES) of the brain are used to perform functional brain mapping. EMS is applied to animal fundamental neuroscience experiments, whereas DES is performed in the operating theatre on neurosurgery patients. The objective of the present review was to shed new light on electrical stimulation techniques in brain mapping by comparing EMS and DES.

Sensitivity of a frequency-selective electrode based on spatial spectral properties of the extracellular AP of myelinated nerve fibers.

In the context of functional electrical stimulation, neural recording is one of the main issues. For instance, the control of the limbs in people with motor deficiencies needs information about the muscle lengths and speeds that can be extracted from electroneurograms (ENG) carried on afferent peripheral nerves. The aim of this study is to propose an non-invasive and spatial-selective electrode (because specific informations are carried into different fascicles).

Fascicle-selective multi-contact cuff electrode.

Neural recording is one of the main issues to be addressed in order to allow closed-loop functional electrical stimulation systems. Because each fascicle in nerves carry specific information, new sensors providing high spatial selectivity are required for chronic implantable devices. This work aims at evaluating the feasibility of a new device using a highly spatial-selective multi-contact cuff electrode.

New electrode layout for internal selectivity of nerves.

A nerve is an enclosed, cable-like bundle of peripheral axons. Each axon or set of axons carries neural afferent or efferent information. Many applications need to detect or record these specific nervous data inside the nerve but it is a big challenge.