The basic mechanism for the electrical stimulation of the nervous system (original) (raw)

Analysis of the electrical excitation of CNS neurons

IEEE Transactions on Biomedical Engineering, 1998

The artificial excitation process of neurons of the central nervous system depends on the applied extracellular field, on the geometry of the neuron and on the electrical properties of the neural subunits. Results of computer simulations are based on a compartment model of the neuron and its equivalent electrical network. Furthermore, a theory is presented which generalizes the activating function concept known from peripheral nerve stimulation. The theory predicts the influence of electrical and geometrical parameters on the excitation threshold. Generally, the myelinated axon is the part of a neuron which is most excitable to a given applied field. An example demonstrates that for a target neuron the quotient (anodic threshold current)/(cathodic threshold current) essentially depends on the position and orientation of the neuron relative to the electrode.

Analysis of Models for External Stimulation of Axons

IEEE Transactions on Biomedical Engineering, 2000

Extracellular electrodes produce electrical fields at the outside of nerve fibers. Discretization of the axon's length coordinate allows simulation of the excitation by a system of differential equations in time, and difference equations in space. For myelinated fibers this segmentation is naturally given by the nodes of Ranvier, whereas unmyelinated axons can be segmented arbitrarily. In both cases the equations are similar and can be treated in parallel. The activity of the axon depends on the second space derivative of the extracellular medium. The activating function is discussed for monopolar electrodes but the principle can be extended to arbitrary configurations of electrodes.

Direct and indirect activation of nerve cells by electrical pulses applied extracellularly

The Journal of physiology, 1976

1. The mode of activation of nerve cells by extracellular stimuli was investigated while recording from a selected cell with one electrode, and applying current pulses around this cell with another electrode. The analysis was done on motoneurones and on spinal border cells from lower lumbar segments in the cat. 2. Directly evoked action potentials were defined by their appearance in an all-or-none fashion with stable latencies of less than 0-5 ms. The lowest thresholds for their generation were 0-15-0-20 muA in the spinal border cells and 0-35-0-40 muA in the motoneurones. In the main series on motoneurones a correlation has been established between different positions of the extracellular stimulating electrode in relation to the cells and the thresholds for the direct excitation of these cells. The position of the electrode were defined on the basis of an analysis of the IS and SD components of the action potentials recorded extracellularly around the cell when evoked by current pu...

A Novel Electrode Array for Diameter-Dependent Control of Axonal Excitability: A Simulation Study

IEEE Transactions on Biomedical Engineering, 2004

Electrical extracellular stimulation of peripheral nerve activates the large-diameter motor fibers before the small ones, a recruitment order opposite the physiological recruitment of myelinated motor fibers during voluntary muscle contraction. Current methods to solve this problem require a long-duration stimulus pulse which could lead to electrode corrosion and nerve damage. The hypothesis that the excitability of specific diameter fibers can be suppressed by reshaping the profile of extracellular potential along the axon using multiple electrodes is tested using computer simulations in two different volume conductors. Simulations in a homogenous medium with a nine-contact electrode array show that the current excitation threshold (th) of large diameter axons (13-17 m) (0.6-3.0 mA) is higher than that of small-diameter axons (2-7 m) (0.4-0.7 mA) with 200-m axon-electrode distance and 10-s stimulus pulse. The electrode array is also tested in a three-dimensional finite-element model of the sacral root model of dog (ventral root of S3). A single cathode activates large-diameter axons before activating small axons. However, a nine-electrode array activates 50% of small axons while recruiting only 10% of large ones and activates 90% of small axons while recruiting only 50% of large ones. The simulations suggest that the near-physiological recruitment order can be achieved with an electrode array. The diameter selectivity of the electrode array can be controlled by the electrode separation and the method is independent of pulse width. Index Terms-Neural prostheses, recruitment order, selective neural stimulation. I. INTRODUCTION T HE goal of functional electrical stimulation (FES) research is to develop systems capable of restoring function in patients with neurological deficits by stimulating nerve and muscles. Several types of electrodes have been developed for this purpose, e.g., intramuscular [1], epimysial [2], intraneural [3], and epineural electrodes [4]. Each has its own advantages and disadvantages depending on the specific application. The ideal neural stimulation should have the following features: 1) axon-diameter selectivity; 2) spatial selectivity; 3) minimal charge injection; and 4) biocompatibility. Conventional neural stimulation methods activate larger motor units before smaller ones [5], a recruitment order opposite the Manuscript

New Currents in Electrical Stimulation of Excitable Tissues 1

Annual review of biomedical engineering, 2000

▪ Abstract Electric fields can stimulate excitable tissue by a number of mechanisms. A uniform long, straight peripheral axon is activated by the gradient of the electric field that is oriented parallel to the fiber axis. Cortical neurons in the brain are excited when the electric field, which is applied along the axon-dendrite axis, reaches a particular threshold value. Cardiac tissue is thought to be depolarized in a uniform electric field by the curved trajectories of its fiber tracts. The bidomain model provides a coherent conceptual ...

Neuronal Excitability st223(13)021.pdf

In experimental studies, the electrical stimulation (ES) has been applied to induce neuronal activity or to disrupt pathological patterns. Nevertheless, the underlying mechanisms of these activity pattern transitions are not clear. To study these phenomena, we simulated a model of the hippocampal region CA1. The computational simulations using different amplitude levels and duration of ES revealed three states of neuronal excitability: burst-firing mode, depolarization block and spreading depression wave. We used the bifurcation theory to analyse the interference of ES in the cellular excitability and the neuronal dynamics. Understanding this process would help to improve the ES techniques to control some neurological disorders. a

Neuronal Excitability Level Transition Induced by Electrical Stimulation.pdf

Effects of high-rate electrical stimulation upon firing in modelled and real neurons

Medical & Biological Engineering & Computing, 2002

Many medical devices use high-rate, low-amplitude currents to affect neural function. This study examined the effect of stimulation rate upon action potential threshold and sustained firing rate for two model neurons, the rabbit myelinated fibre and the unmyelinated leech touch sensory cell These model neurons were constructed with the NEURON simulator from electrophysiological data. Alternating-phase current pulses (0-1250Hz), of fixed phase duration (O.2 ms), were used to stimulate the neurons, and propagation success or failure was measured. One effect of the high pulse rates was to cause a net depolarisation, and this was verified by the relief of action potential conduction block by 500Hz extracellular stimulation in leech neurons. The models also predicted that the neurons would maintain maximum sustained firing at a number of different stimulation rates. For example, at twice threshold, the myelinated model followed the stimulus up to 500 Hz stimulation, half the stimulus rate up to 850 Hz stimulation, and it did not fire at 1250Hz stimulation. By contrast, the unmyelinated neuron model had a lower maximum firing rate of 190Hz, and this rate was obtained at a number of stimulation rates, up to 1250 Hz. The myelinated model also predicted sustained firing with 1240Hz stimulation at threshold current, but no firing when the current level was doubled. Most of these effects are explained by the interaction of stimulus pulses with the cell's refractory period.

Neuronal excitability level transition induced by electrical stimulation

The European Physical Journal Special Topics, 2014

In experimental studies, electrical stimulation (ES) has been applied to induce neuronal activity or to disrupt pathological patterns. Nevertheless, the underlying mechanisms of these activity pattern transitions are not clear. To study these phenomena, we simulated a model of the hippocampal region CA1. The computational simulations using different amplitude levels and duration of ES revealed three states of neuronal excitability: burst-firing mode, depolarization block and spreading depression wave. We used the bifurcation theory to analyse the interference of ES in the cellular excitability and the neuronal dynamics. Understanding this process would help to improve the ES techniques to control some neurological disorders.

The influence of stimulus type on the magnetic excitation of nerve structures

Electroencephalography and clinical neurophysiology, 1990

The voltage measured was that induced in a measuring coil from 3 different commercially available magnetic stimulators. The strongest stimulus was from the Cadwell, followed by Novametrix and then Digitimer. The Digitimer and Novametrix produced a monophasic pulse, whilst the Cadwell stimulator produced a polyphasic pulse, all measured by an induction coil. This is thought to be the reason why reversed coil polarity does not influence the position of peripheral nerve excitation with a Cadwell stimulator; this is, however, the case with the two other magnetic stimulators. Nevertheless, electrical stimulation was found to be the most useful method for exciting peripheral nerves. The lack of influence of Cadwell coil polarity on the excitation of spinal roots and motor cortex is also thought to be due to the bipolar stimulus effect mentioned above. The stimuli induced by Digitimer and Novametrix are monophasic, exciting one hemisphere first, depending on the direction of the current im...

The basic mechanism for the electrical stimulation of the nervous system (original) (raw)

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