The long-term objective of this study is to develop neural prostheses for people with spinal cord injuries who are unable to voluntarily control their bladder. This feasibility study was performed in 22 adult cats. We implanted an array of microelectrodes into locations in the sacral spinal cord that are involved in the control of micturition reflexes.
View Article and Find Full Text PDFConf Proc IEEE Eng Med Biol Soc
September 2007
Use of anodic bias improves the charge-injection limits of activated iridium oxide (AIROF) microelectrodes. Asymmetric waveforms, in which the charge balancing anodic phase is delivered at a lower current density and longer pulse width, has been found to allow for higher values of anodic bias voltages, thus maximizing the AIROF charge-injection capacity. Limiting the voltage excursion of the AIROF below the value at which electrolysis of water occurs is essential to maintaining the long-term viability of implanted electrodes.
View Article and Find Full Text PDFIEEE Trans Neural Syst Rehabil Eng
March 2006
In order to use recorded neural activities from the brain as control signals for neuroprosthesis devices, it is important to maintain a stable interface between chronically implanted microelectrodes and neural tissue. Our previous paper introduced a method to quantify the stability of the recording microelectrodes. In this paper, the method is refined 1) by incorporating stereotypical behavioral patterns into the spike sorting program and 2) by using a classifier based on Bayes theorem for assigning the recorded action potentials to the underlying neural generators.
View Article and Find Full Text PDFIEEE Trans Neural Syst Rehabil Eng
June 2004
Our objective is to develop neural prostheses based on an array of microelectrodes implanted into the sacral spinal cord, that will allow persons with spinal cord injuries to regain control of their bladder and bowels. For our chronic cat model, we have developed two microelectrode arrays, one type containing nine discrete activated iridium microelectrodes and the second utilizing silicon substrate probes with multiple electrode sites on each probe. Both types can elicit an increase in the pressure within the urinary bladder of more than 40-mm Hg and/or relaxation of the urethral sphincter.
View Article and Find Full Text PDFThis study was conducted to examine the excitability changes induced in cerebral cortical neurons during prolonged microstimulation with a spatially dense microelectrodes array. The arrays of 16 iridium microelectrodes were implanted chronically into the postcruciate gyrus of cats. Neuronal responses characteristic of single pyramidal tract axons (ULRs) were recorded in the medullary pyramid.
View Article and Find Full Text PDFThis study was conducted to help to establish the feasibility of a multi-channel auditory prosthesis based on microstimulation within the human ventral cochlear nucleus, and to define the range of stimulus parameters that can be used safely with such a device. We chronically implanted activated iridium microelectrodes into the feline ventral cochlear nucleus and, beginning 80-250 days after implantation, they were pulsed for 7 h/day, on up to 21 successive days. The stimulus was charge-balanced pulses whose amplitude was modulated by a simulated human voice.
View Article and Find Full Text PDFIEEE Trans Rehabil Eng
September 1999
The stability of the interface between neural tissue and chronically implanted microelectrodes is very important for obtaining reliable control signals for neuroprosthetic devices. Stability is also crucial for chronic microstimulation of the cerebral cortex. However, changes of the electrode-tissue interface can be caused by a variety of mechanisms.
View Article and Find Full Text PDFWe describe the evolution of axonal injury following the induction of neural damage by electrical stimulation. The sciatic nerves of cats were stimulated continuously for 8 h with charge-balanced waveforms at high intensities, 50 Hz and 2100-4500 microA, using circumneural helical electrodes. Computer-assisted morphometric and ultrastructural studies indicate that many of the damaged fibers had not regenerated by 125 days after stimulation.
View Article and Find Full Text PDFLocalized, long-lasting stimulation-induced depression of neuronal excitability (SIDNE) is a consequence of prolonged, high-frequency microstimulation in the central nervous system (CNS). It represents a persisting refractory state in the neurons and axons near the stimulating microelectrode, that occurs in the absence of histologically detectable tissue injury. It does not involve a change in synaptic efficacy and, in this respect, it differs from the more familiar phenomenon of long-term depression (LTD).
View Article and Find Full Text PDFWe describe a computer-assisted morphometric procedure for quantifying acute axonal injury induced in peripheral nerves by prolonged electrical stimulation. The procedure is a two-phase process, with the image analysis implemented via a commercial image analysis program, followed by an automated editing of the morphometric parameters of each object identified by the image analysis software. Both phases are implemented on IBM-compatible personal computers.
View Article and Find Full Text PDFJ Neuropathol Exp Neurol
September 1996
Active microelectrodes were implanted for a period of 2 weeks to 3 months into the sacral spinal cord of 10 male cats in order to test the feasibility and the safety of discrete stimulation of the parasympathetic preganglionic nucleus for future clinical applications of microelectrode technology in micturition control. An array of four 50 microns-diameter iridium microelectrodes was inserted beneath the dura in each cat. At weekly intervals, bladder pressure was measured as hydrostatic pressure on an intraluminal catheter.
View Article and Find Full Text PDFThe relation is investigated between stimulus frequency, stimulus pulse amplitude and the neural damage induced by continuous stimulation of the cat's sciatic nerve. The chronically implanted electrodes were pulsed continuously and the effects of the electrical stimulation were quantified as the amount of early axonal degeneration (EAD) present in the nerves seven days after the continuous stimulation. The primary effect of stimulating at 100 Hz rather than 50 Hz was to cause an increase in the slope of the plot of the amount of EAD versus stimulus amplitude, but the threshold stimulus for the induction of EAD also was slightly lower.
View Article and Find Full Text PDFWe investigated the effects of continuous microstimulation in the cats' posteroventral cochlear nucleus, using chronically implanted activated iridium microelectrodes. We examined 51 electrode sites (39 pulsed sites, and 12 unpulsed sites). Seven hours of continuous stimulation at 500 Hz often produced tissue injury near the tips of the pulsed microelectrodes.
View Article and Find Full Text PDFNeuroscience
January 1993
The ability of MK-801, a non-competitive N-methyl-D-aspartate receptor antagonist, to protect neurons in the cerebral cortex from injury induced by prolonged electrical stimulation was assessed in cats. Platinum disc electrodes 8.0 mm in diameter and with a surface area of 0.
View Article and Find Full Text PDFThe effects of several hours of continuous electrical stimulation in the cats' cochlear nucleus with chronically implanted activated iridium microelectrodes was investigated from the changes in the evoked response near the inferior colliculus and also by histologic evaluation of the stimulated tissue. The stimulating microelectrodes had geometric surface areas of 75-500 microns2. They were pulsed continuously for 4 h, at a pulse repetition rate of 200 Hz, using charge-balanced pulse pairs.
View Article and Find Full Text PDFMed Biol Eng Comput
January 1992
The propensity for two types of charge-balanced stimulus waveforms to induce injury during eight hours of continuous electrical stimulation of the cat sciatic nerve was investigated. One waveform was a biphasic, controlled-current pulse pair, each phase 50 microseconds in duration, with no delay between the phases ('short pulse', selected to excite primarily large axons), whereas in the second type each phase was 100 microseconds in duration, with a 400 microsecond delay between the phases (selected to excite axons of a broader spectrum of diameters). The sciatic nerve was examined for early axonal degeneration (EAD) seven days after the session of continuous stimulation.
View Article and Find Full Text PDFIEEE Trans Biomed Eng
October 1990
The possibility of neural injury during prolonged electrical stimulation of the brain imposes some constraints on the use of this technique for therapeutic and experimental applications. Stimulating electrodes of various sizes were used to investigate the interactions of two stimulus parameters, charge density and charge per phase, in determining the threshold of neural injury induced by electrical stimulation. Platinum electrodes ranging in size from 0.
View Article and Find Full Text PDFThe studies were performed to elucidate the mechanism underlying the neural damage which may occur during prolonged electrical stimulation of either brain tissue or peripheral nerve. The partial pressure of oxygen (pO2) was measured in the sciatic nerve and the cerebral cortex of adult cats before and during direct, local electrical stimulation of these neural tissues, using stimulus parameters capable of inducing neural injury. pO2 was monitored by the polarographic method, employing a platinum microelectrode inserted into the tissue adjacent to or beneath the stimulating electrode.
View Article and Find Full Text PDFThis study is one of a series addressing the mechanisms involved in the production of neural damage caused by continuous, prolonged electrical stimulation of peripheral nerve. It has been previously shown that sustained, high frequency electrical stimulation of the cat's peroneal nerve may cause irreversible neural damage in the form of axonal degeneration of the large myelinated fibres. In this study we demonstrate that blocking the action potentials on most of the nerve fibres with local anaesthetics (10% procaine or 2% lidocaine) almost completely prevents the axonal degeneration.
View Article and Find Full Text PDFHelical electrodes were implanted around the left and right common peroneal nerves of cats. Three weeks after implantation one nerve was stimulated for 4-16 hours using charge-balanced, biphasic, constant current pulses. Compound action potentials (CAP) evoked by the stimulus were recorded from over the cauda equina before, during and after the stimulation.
View Article and Find Full Text PDFArrays of platinum (faradaic) and anodized, sintered tantalum pentoxide (capacitor) electrodes were implanted bilaterally in the subdural space of the parietal cortex of the cat. Two weeks after implantation both types of electrodes were pulsed for seven hours with identical waveforms consisting of controlled-current, charge-balanced, symmetric, anodic-first pulse pairs, 400 microseconds/phase and a charge density of 80-100 microC/cm2 (microcoulombs per square cm) at 50 pps (pulses per second). One group of animals was sacrificed immediately following stimulation and a second smaller group one week after stimulation.
View Article and Find Full Text PDFBiomaterials
March 1987
A histologic study was made of the response of the leptomeninges and underlying cerebral cortex of the cat to subdural implantation of 3 insulating materials (HR605-P, Parylene-C and PI-2555) and a polymeric electrode component (MMA/MAPTAC) for periods of 8 and 16 wk. The tissue reactions were compared with those elicited by the arrays of Dacron mesh matrices, pure platinum controls and by positive controls (Ag-AgCl) known to cause reactions in the brain. Sites beneath the Dacron mesh matrix, pure platinum control implants and beneath all insulating materials implanted for 8 and 16 wk appeared indistinguishable, exhibiting little tissue reaction.
View Article and Find Full Text PDFChronic stimulating microelectrodes fabricated from platinum-30% iridium (Pt-30%Ir) or activated iridium were implanted in assemblies of three in the left sensorimotor cortex of the cat and pulsed continuously at currents of 10 to 320 microA (100 to 3200 microC/cm2 X ph, 2 to 64 nC/ph) for periods of 24 h or for 23 h/day for 7 days. The microelectrodes had beveled tips with uninsulated geometric surface areas of 20 X 10(-6) cm2. Neuronal activity evoked by the focal stimulation was monitored by recording compound action potentials from the ipsilateral pyramidal tract.
View Article and Find Full Text PDFThe averaged evoked compound action potentials (AECAPs) were recorded from the ipsilateral pyramidal tract of awake, unrestrained cats before, during, and after continuous electrical stimulation of the cerebral cortex via chronically implanted activated iridium or platinum-30% iridium (Pt30%Ir) microelectrodes. After stimulating 24 h at 20 pulses per second (pps), using charge-balanced, 200-microseconds pulse pairs of 40 to 80 microA (400 to 800 microC/cm2, 8 to 16 nC/phase (ph), 2 to 4 A/cm2), there was a transient elevation of the threshold of the early (direct) and of the alte (transynaptic) components of the AECAP. After cessation of continuous stimulation at 80 microA, the threshold of the early component of the AECAP remained elevated for as long as 24 h and the late component as long as 4 days, indicating significant but reversible depression of the electrical excitability of cortical neurons close to the microelectrodes.
View Article and Find Full Text PDFHistological evaluations of dog sacral nerves were carried out after stimulation for electromicturition with three types of circumneural electrodes. The use of two types of cuff arrays was associated with a marked buildup of connective tissue around the nerve and filling the lumen of the array. Nerves within the first type of cuff array (having diameters approximately that of the nerve they surrounded) were often extruded from the lumen of the cuff.
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