Cathodal Current Pulses Research Articles

Multielectrode spiral cuff for ordered and reversed activation of nerve fibres

In this paper we present the modelling, design, and experimental testing of a nerve cuff multielectrode system for selective activation of fibres in superficial peripheral nerve trunk regions which is capable of activating fibres in physiological order. The multielectrode system consists of 45 platinum electrodes embedded within a self-curling spiral silicone sheet organized in fifteen longitudinal groups consisting of three electrodes spaced equidistally around the circumference of the cuff. Electrodes in the centre band acted as stimulating cathodes while the two electrodes of the same group in the two outer bands were connected together and corresponded to the position of a particular cathode, serving as anodes to block the nascent action potentials by membrane hyperpolarization. The interpolar distance was 6 mm on both sides, resulting in a total cuff length of about 20 mm. The cuff was constructed with a diameter to fit the size of the dog sciatic nerve. Preliminary animal testing of the nerve cuff was performed on the sciatic nerve of a Bigley female dog. In the 45-electrode stimulation system, biphasic cathodic first pulses with quasitrapezoidal-shaped cathodic and square anodic parts were delivered through the particular group of tripolar electrodes to effect both selective stimulation of motor axons within the gastrocnemius muscle fascicle, and differential block by membrane hyperpolarization. The test was repeated using rectangular cathodic first biphasic current pulses delivered monopolarly on the central electrode of the same group while connected anodes were replaced by a common anode situated elsewhere in the surrounding tissue. In both experiments an isometric torque in the ankle joint elicited by the gastrocnemius muscle was measured and compared. It was shown that tripolar activation with quasitrapezoidal stimulation pulses elicited an isometric torque with a peak value of 0.83 Nm in 65 ms after onset of delivering stimulating pulses in comparison to the monopolar activation with rectangular biphasic pulses where the peak of the same value was observed in 45 ms after onset. Thus, the multipolar cuff stimulating monopolarly provided an effective means of activating motor axons selectively within the gastrocnemius muscle fascicle, while more physiological recruitment of the muscle fibres was evident when stimulating tripolarly.

Corrosion and protection of NdFeB type magnets

A general mechanism for the corrosion behaviour of NdFeB magnets is presented, related to the magnet heterogeneity with the presence of different phases. Cathodic control is outlined. An electrochemical method to assess the corrosion resistance of magnets, with and without coatings, is proposed; it is based on the study of the transient voltage at the magnet surface after a second cathodic current pulse in a suitable aggressive solution and its dependence on the amount of cathodic current circulating. Suitable pretreatments have been tried and interesting results obtained with passivation pretreatments, giving phosphorous Nd at grain boundaries. Coatings if sintered and plastic magnets have been tried using several methods. Good results are obtained with Zn-Co layers on sintered magnets and a sol-gel glass on powders for plastic magnets. Improved ACS (Autocatalytic Chemical Deposition) Ni=P coatings have been realized, with an alkaline brass flash plating to start ACD deposition.

Dissolution study of electrolytically deposited aluminium at a graphite electrode

The deposition and dissolution of aluminium in an acidic cryolite melt was studied using a graphite electrode. The techniques employed were cyclic voltammetry, current reversal chrono-potentiometry ( crc) with and without a varying delay time at zero current between the cathodic and anodic current pulses. The graphite electrode had to be preconditioned by immersion in the melt for 10–12 h so that the surface became saturated in sodium before Al deposition could be observed. Co-deposition of Na on the graphite surface could not be avoided. crc with delay was used to calculate the dissolution rate of aluminium in molten cryolite. The rate of aluminium dissolution was similar for both tungsten and graphite electrodes, showing little interaction between deposited aluminium and the substrate.

Mass transfer in pulse plating: an experimental study with rectangular cathodic current pulses

An experimental study has been made of mass transfer to a rotating disk electrode with a cathodic rectangular pulse current in 0.05 M CuSO 4 and 0.5 M H 2SO 4 at 23°C. The limiting pulse current densities were measured over a range of pulse periods of 0.001–0.1 s, duty cycles of 0.1–1.0, and electrode rotational speeds of 500–3000 rpm. The results agreed with Chin's mass transfer theory to within ±7.5% over a range of DT/gd 2 from 0.0017 to 10.

Pitting Corrosion of High Strength Alloy Stimulation Electrodes under Dynamic Conditions

Pitting corrosion is a major cause of in vivo failure of high strength alloy intramuscular (IM) stimulation electrodes. Avoidance of pitting corrosion can prolong the life expectancy of stimulation electrodes. Corrosion behavior of two candidate IM electrode materials, 316LVM and MP35N, was studied in a saline solution using fast sweep cyclic voltammetry with potential sweep rates ranging from 0.005 to 500 V/s. The potential at which pitting was observed to occur increased with increasing sweep rates, and was found to be related to sweep rate by the empirically fitted equations defines the maximum potential to which an electrode can be polarized under nonequilibrium conditions before pitting corrosion occurs. A state diagram analysis method was developed to predict operating limits for stimulation electrodes under pulsed conditions. These predictions were tested by carrying out 1h in vitro stimulation experiments with biphasic, rectangular, charge balanced, cathodic first current pulses for the two materials, and good agreement between experimental results and predictions was obtained. This study indicates that pitting corrosion processes are kinetically limited at the high rate of potential change encountered with electrodes used to excite neural tissue electrically. The results further suggest that an asymmetrical or charge imbalanced waveform may be the optimal choice to avoid pitting corrosion of stimulation electrodes.

Aluminium dissolution in NaF-AlF3-Al2O3 systems

The rate of dissolution of electrolytically deposited aluminium was determined by the method of current reversal chronopotentiometry at a tungsten electrode in NaF−AlF3−Al2O3 melts of varying NaF/AlF3 molar ratios or cryolite ratios (CR). The temperature was maintained at 1031±3°C and the alumina content at 4 wt%. More accurate data were obtained by introducing delay times of various lengths (at zero current) between the cathodic and anodic current pulses, compared to direct current reversal chronopotentiometry with varying forward (deposition) times. The rate of aluminium dissolution increased with increasing NaF/AlF3 molar ratio, the curve showing an inflexion in the vicinity of CR=3. This inflexion indicates two dissolution mechanisms, one being predominant depending on the CR. The main reaction in acidic melts (CR<3) may be represented by $$2Al(l) + AlF_6^{3 - } \rightleftarrows 3Al(I)F_x^{1 - x} + (6 - 3x)F^ - $$ while in basic melts (CR>3) $$Al(l) + 3Na^ + \rightleftarrows 3Na(soln) + Al(III)$$ is the likely dominant mechanism. For 0.8<CR<5.7 the rate of dissolution is of the order of 10−7 mol cm−2s−1.

Excitatory synaptic actions between pairs of neighboring pyramidal tract cells in the motor cortex.

1. By spike-triggered averaging, we documented recurrent individual excitatory postsynaptic potentials (EPSPs) produced in 33 pyramidal tract (PT) cells (target) by the activity of axon collaterals of neighboring single PT cells (reference) in the motor cortex of the cat. 2. The computer was triggered by the spontaneous activity of reference PT cells or by current pulses applied to reference PT cells through the extracellular recording electrode. 3. The threshold for direct activation of PT cells was less than 0.1 microA with an anodal current pulse and 0.2-0.3 microA with a cathodal current pulse. 4. Application of an anodal current pulse directly activated only a single reference PT cell, the surface membrane of which was presumably touched by and sucked with the extracellular recording electrode. 5. When a cathodal current pulse was used, simultaneous activation of neurons or axons other than the reference PT cell was checked by changing the stimulus parameters along the characteristic strength-duration curve for the reference PT cell and/or by comparing averaged EPSPs obtained by cathodal stimulation with those obtained from spontaneous spikes of the reference PT cell. 6. Recurrent individual EPSPs were produced in fast PT cells by activation of neighboring slow PT cells and also of neighboring fast PT cells. Some recurrent individual EPSPs were also observed in slow PT cells. 7. The mean latencies of recurrent individual EPSPs produced by the spontaneous activity of reference slow and fast PT cells were 1.61 (n = 12) and 1.12 ms (n = 8), respectively. Their amplitudes ranged between 30 and 390 microV (n = 33). The rise time observed in fast PT cells with activation of slow and fast PT cells ranged from 1.6 to 3.6 ms (n = 20) and from 0.8 to 1.9 ms (n = 10), respectively. 8. The average conduction velocity of axon collaterals of slow and fast PT cells was estimated to be as slow as that of unmyelinated fibers in the cat. 9. It is suggested that axon collaterals of slow PT cells synapse onto more distal dendrites of fast PT cells than axon collaterals of fast PT cells.

The Effect of Quaternary Ammonium Salts on Electro‐oxidation of Benzhydrol

A study was made of the effect of tetra‐alkylammonium salts on the anodic oxidation of benzhydrol using potential pulse and galvanostatic pulse techniques. The results of the studies were in agreement with the interpretation that, in addition to solubilization effects, the primary cause of the increased yields is the formation of a film on the surface, which excludes side reactions with water. Potential pulse studies were in agreement with the previous conclusion that this film undergoes reorganization at a potential around −0.6V vs. SCE. The galvanostatic pulse studies showed that it requires a cathodic current pulse to destroy this film in a short time.

Potassium translocation and spreading depression induced by electrical stimulation of the brain

Cathodal current pulses with durations from 20 ms to 80 s were applied to the surface of rat parietal neocortex, and the strength-duration properties of the threshold stimulus for initiation of spreading depression was determined. In one series, extradural stimulation was used. In a second series, a liquid electrode was used, the dura was opened, and K +-sensitive microelectrodes were used to determine the time course of extracellular K + concentration during and after each stimulus pulse. With the dura open, the strength-duration curve was of the form It 0.55 = constant. With extradural stimulation, the slope of the log-log plot relating current intensity to pulse duration changed gradually as the pulse duration increased, averaging 0.63. Theoretical analysis suggests that diffusion of K + away from a zone of current-induced accumulation can account for these slope data. Applicability of this mechanism of K + accumulation to observed changes in sensitivity of neurons to repeated stimulation at subcortical sites is considered.

Vestibular nerve and nuclei unit responses and eye movement responses to repetitive galvanic stimulation of the labyrinth in the rat.

Two-second cathodal current pulses were applied at one-minute intervals at a point external to the round window in the ear of each albino rat subject. Responses were recorded in the vestibular nerve ganglion, the vestibular nuclei (single units), or in the eye movements (search coil recording method) of anaesthetized, decerebrated, or alert rats. The unit responses to the galvanic stimuli were characterized and compared with responses to galvanic and rotational stimuli reported in the literature. The main focus of the study, however, was effects of stimulus repetition. In both the vestibular nerve and vestibular nuclei recordings, the responses of many units were substantially larger or smaller at the end of a 13-pulse stimulus train than at the beginning. In the vestibular nuclei, but not in the nerve, there was a slight bias towards a decrease in response magnitude, with 10/88 units showing decreases great enough to be considered as reflecting an habituation process. In contrast, the eye movement responses showed more consistent response decrements, especially in the alert condition, but also in the other conditions (none of the unit recordings were done in alert rats). It is concluded that some of the modifications underlying habituation of the vestibuloocular reflex probably occur in portions of the neuronal reflex pathways that are downstream from the vestibular nuclei.

Electrical and anatomic characteristics of cells of ferret paratracheal ganglion.

A preparation has been developed for study of the electrical properties of the neurons of the ferret paratracheal ganglia. Two cell types were identified. AH cells were characterized by the presence of a single action potential in response to cathodal current pulses, followed by a profound after hyperpolarization that lasted for several hundred milliseconds. Electrical stimulation of branches of the laryngeal nerves produced a fast excitatory postsynaptic potential (EPSP) that was often followed by an apparent inhibitory postsynaptic potential (IPSP). A similar response was seen with electrical stimulation of interganglionic nerve trunks. Hexamethonium reversibly inhibited fast EPSPs in these cells. Type B cells could not be excited by intracellular current injections. At least some of these cells appear to be neurons as electrical stimulation of nerve trunks resulted in a slow EPSP and, rarely, a fast IPSP. Ganglia have between 10 and 20 cell bodies, and their diameters are between 15 and 40 microns. Two types of nerve endings were seen: 1) those with mainly round agranular vesicles 50-60 nm in diameter, and 2) those with large dense-cored vesicles of approximately 100 nm with an electron-lucent halo around the core.

Electroluminescence Transients at ZnO‐Electrodes by Hole Injection during Persulfate Reduction

AbstractElectroluminescence transients at the ZnO‐electrolyte interface have been studied during pulsed reduction of persulfate. The spectral distribution of the emitted light centers around the band gap energy and indicates hole injection from the intermediately formed SO4‐ radicals and consecutive radiative recombination with electrons. The decay in the photon emission during a cathodic current pulse is attributed to the formation of recombination centers by hydrogen evolution and cathodic crystal decomposition. Such centers can be structural defects, Zn‐atoms on the ZnO surface or H‐atoms adsorbed on the surface and possibly also incorporated into the crystal lattice.

Long-term facilitation of excitatory synaptic transmission in single motor cortical neurones of the cat produced by repetitive pairing of synaptic potentials and action potentials following intracellular stimulation

The effects of postsynaptic firing activity on excitatory postsynaptic potentials (EPSPs) were studied in the motor cortex of anaesthetized cats. Postsynaptic firing was induced by 1–5 nA cathodal current pulses via the recording intracellular microelectrode, while EPSPs were elicited by thalamic, callosal, pyramidal tract and somatosensory stimuli. In 102 cells, EPSP-spike stimulus pairs were applied with 0.2–1/sec frequency and 10–100 msec interstimulus intervals. In 42 neurones, reversible facilitation of paired EPSPs appeared lasting from 4 to 47 min. The synaptic facilitation in most cases was accompanied by membrane depolarization and an increase in input resistance. The effectiveness of current induced action potentials upon test EPSPs provided evidence for the postsynaptic localization of plastic changes occurring in conditioning experiments.

Chronopotentiometry on a rotating disk electrode with periodic current inputs

Duhamel's theorem can be used to solve chronopotentiometric problems on a rotating disk electrode when the current input is an arbitrary function of time. Periodic state surface concentrations for a two-step pulsed current are calculated by this method. The two-step pulse incorporates single step and periodically reversed pulses as special cases. A comparison of the exact convective diffusion results with the predictions of the Nernst model, and Filinovskii's analytical approximation shows good agreement for the values of the instantaneous limiting current density. A kinetic model is developed for the extraction of kinetic parameters of a first-order irreversible reaction occurring on a rotating disk electrode perturbed by a two-step cathodic current pulse.

Chronopotentiometry on a rotating disk electrode with periodic current inputs

Duhamel's theorem can be used to solve chronopotentiometric problems on a rotating disk electrode when the current input is an arbitrary function of time. Periodic state surface concentrations for a two-step pulsed current are calculated by this method. The two-step pulse incorporates single step and periodically reversed pulses as special cases. A comparison of the exact convective diffusion results with the predictions of the Nernst model, and Filinovskii's analytical approximation shows good agreement for the values of the instantaneous limiting current density. A kinetic model is developed for the extraction of kinetic parameters of a first-order irreversible reaction occurring on a rotating disk electrode perturbed by a two-step cathodic current pulse.

Modulation of muscle force by recruitment during intramuscular stimulation.

The input?output relationships for modulation of force by recruitment during intramuscular electrical stimulation were examined for cat sleus muscles and human finger and thumb muscles. Recruitment was modulated by varying either the pulsewidth or amplitude of a monophasic, rectangular, cathodal current pulse train. Force was a nonlinear function of either pulsewidth or amplitude, and the shape of the nonlinearity was the same regardless of which parameter was modulated. The charge per stimulus pulse was lowest if pulsewidth was modulated with a fixed, high amplitude stimulus. The shape of the nonlinear relationship between pulsewidth and force (recruitment characteristic) depended on stimulus amplitude, electrode location in the muscle and muscle length. In most applications the amplitude and location would be fixed, so force would be a two-dimensional nonlinear function of pulsewidth and muscle length. The results are discussed with respect to possible mechanisns of recruitment during intramuscular stimulation, and the implications of the nonlinearities on the proportional control of orthoses employing electrically stimulated muscles.

Some prospective applications of silicon electrodeposition from molten fluorides to solar cell fabrication

Electrodeposition of both epitaxial and polycrystalline continuous films of dense, coherent, and well-adherent silicon coatings was achieved from molten fluorides. A dissolving Si anode and an operating temperature of about 750 C were utilized. Silicon electrocrystallization epitaxy (ECE) produced films with the (111) orientation on Si substrates of the same orientation. The unintentionally doped films were of p-type character with a resistivity in the range 0.05 - 0.10 Ω-cm. Polycrystalline Si films were similarly electroplated onto various polycrystalline metal substrates. Uniform coherent, and well-adherent coatings with grain diameters as large as 40 – 50 µm were obtained. The useful rate of electrodeposition of Si could be significantly increased by the application of an alternating square wave pulse (ASWP)2technique. Cathodic current pulses as high as 300 mA/cm2 (growth rate of about 5 µm/min) were demonstrated. The cathodic current efficiencies, for all modes of growth, were about 70 – 100%. The effects of the various operating parameters, and some prospective applications to the fabrication of solar cells, are discussed.

Prolonged action potential of glycerol-treated skeletal muscle fibres of frogs in Ca-free egta solution.

In glycerol-treated sartorius muscle fibres, membranes were depolarized to about-30 mV when muscle fibres were perfused with Ca-free solution containing 2 mM EGTA. Under such a condition, muscle fibres were able to produce not only an initial spike potential (initial SP) but also a following slow depolarizing response (slow DR) forming a plateau phase by cathodal current pulse when membrane was previously hyperpolarized up to -80 mV by extrinsic anodal currents. The membrane conductance during a generation of these responses increased. Both initial SP and slow DR were abolished reversibly by removing external sodium ions. Tetrodotoxin (TTX) blocked a generation of the initial SP but did not affect on the slow DR. On the other hand, D-600 did not affect on the initial SP but blocked a generation of the slow DR. It is concluded that these responses are generated in the surface membrane and that the initial SP is produced by a movement of sodium ions through the sodium channels and the slow DR is produced by a movement of sodium ions through the calcium channels.

Electrodissolution Kinetics of Iron in Chloride Solutions: Part I . Neutral Solutions

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Electrodissolution Kinetics of Iron in Chloride Solutions: Part I . Neutral Solutions

Anodic dissolution of iron in unbuffered neutral chloride solutions has been investigated by transient polarization techniques. A new method to correct for the ohmic potential drop has been proposed. It has been observed that the anodic Tafel slopes were 40 mV/decade for fast polarization and 80 mV/decade for slow or steady‐state polarization. Steady‐state anodic characteristics of iron have been studied by superimposing short cathodic potential and current pulses. At steady‐state anodic polarization a Tafel relation was obtained between the cathodic potential (φC) and the cathodic current (iC) with a Tafel slope of about 120 mV/decade for both potentiostatic and galvano‐static pulses. The difference in anodic Tafel slopes has been interpreted in terms of the formation of a hydroxochloro‐iron complex, . The cathodic pulse polarization results indicate that .