Stimulation Circuit Research Articles

A multichannel neural signal detecting module: Its design and test in animal experiments

Abstract A four-channel neural signal detecting module with an implantable 12-contact cuff electrode was designed for real-time neural signal recording on peripheral and central nerves. The mathematic coupling model between nerve and electronic system was analyzed. Electrode connection configurations were considered. The detecting circuit included an input coupling network, a pre-amplifier, and some filtering and notching stages. Shield guarding and the right-leg-driven circuit were developed for further climination of common mode interference. By electrode switches, the module could cooperate with a nerve functional electrical stimulation circuit, building a neural channel bridge-connection system. It was tested by recording experiments on rat's sciatic and spine nerves. The signals is spontaneous and evoked conditions have been captured successfully. In addition, an implantable neural signal detecting CMOS IC has been introduced. *Supported by National Natural Science Foundation of China (Grant Nos. 698...

Stimulating and Sensing Network Inside the Human Body

The Alfred Mann Foundation is developing a network of up to 850 injectable devices that have stimulating, sensing and communication capabilities. Each of the devices is coordinated via radio signals a hundred times a second by an external small module. All the devices are powered by lithium-ion rechargeable batteries. The stimulating, sensing, and communication circuits are designed to be highly power efficient to maximize battery life. The stimulator can be programmed to deliver pulses in the range: 5 µA to 20 mA, 7 µs to 2000 µs, and frequencies up to 4000 Hz. Bursting, ramping, and other stimulation features are included. The voltage sensor covers the range 10 µV to 1.0 V with bandpass filtering and data analysis. The implant also contains sensors for pressure, temperature, DC magnetic field, and distances between implants.

Evaluation of Platinum-Black Stimulus Electrode Array for Electrical Stimulation of Retinal Cells in Retinal Prosthesis System

A retinal prosthesis system with a three-dimensionally (3D) stacked LSI chip has been proposed. We fabricated a new implantable stimulus electrode array deposited with Platinum-black (Pt-b) on a polyimide-based flexible printed circuit (FPC) for the electrical stimulation of the retinal cells. Impedance measurement of the Pt-b electrode–electrolyte interface in a saline solution was performed and the Pt-b electrode realized a very low impedance. The power consumption at the electrode array when retinal cells were stimulated by a stimulus current was evaluated. The power consumption of the Pt-b stimulus electrode array was 91% lower than that of a previously fabricated Al stimulus electrode array due to a convexo-concave surface. In the cytotoxicity test (CT), we confirmed that Pt implantation induced no cellular degeneration of the rat retina. In the animal experiments, electrically evoked potential (EEP) was successfully recorded using Japanese white rabbits. These results indicate that electrical stimulation using the Pt-b stimulus electrode array can restore visual sensation.

Nanopowder molding method for creating implantable high-aspect-ratio electrodes on thin flexible substrates

Metal nanoparticles and a nanopowder molding process were used to fabricate 2D and 3D patternable structures having a height-to-width ratio of up to 10:1. By means of this process, an entire neural stimulation circuit, including stimulating electrode, connection trace, and contact pad, can be fused into one continuous, integrated structure where different sections can have different heights, widths, and shapes. The technique is suitable for mass production, and the fabricated electrode is robust and very flexible. More importantly for biomedical applications, the entire fabricated structure can be packed at room temperature onto a biocompatible flexible substrate, such as polydimethylsiloxane, parylene, and polyimide as well as other temperature-sensitive or vacuum-sensitive materials. The electrodes and wires have about the same electrical resistivities as bulk materials and desirable electrochemical properties, including low impedance.

Band-Tunable and Multiplexed Integrated Circuits for Simultaneous Recording and Stimulation With Microelectrode Arrays

Two thin-film microelectrode arrays with integrated circuitry have been developed for extracellular neural recording in behaving animals. An eight-site probe for simultaneous neural recording and stimulation has been designed that includes on-chip amplifiers that can be individually bypassed, allowing direct access to the iridium sites for electrical stimulation. The on-probe amplifiers have a gain of 38.9 dB, an upper-cutoff frequency of 9.9 kHz, and an input-referred noise of 9.2 microV rms integrated from 100 Hz to 10 kHz. The low-frequency cutoff of the amplifier is tunable to allow the recording of field potentials and minimize stimulus artifact. The amplifier consumes 68 microW from +/- 1.5 V supplies and occupies 0.177 mm2 in 3 microm features. In vivo recordings have shown that the preamplifiers can record single-unit activity 1 ms after the onset of stimulation on sites as close as 20 microm to the stimulating electrode. A second neural recording array has been developed which multiplexes 32 neural signals onto four output data leads. Providing gain on this array eliminates the need for bulky headmounted circuitry and reduces motion artifacts. The time-division multiplexing circuitry has crosstalk between consecutive channels of less than 6% at a sample rate of 20 kHz per channel. Amplified, time-division-multiplexed multichannel neural recording allows the large-scale recording of neuronal activity in freely behaving small animals with minimum number of interconnect leads.

Anode-break excitation during end-diastolic stimulation is explained by half-cell double layer discharge.

The phenomenon of anodal-break excitation during end-diastolic stimulation of the heart was discovered many years ago by B. Hoffman. Yet, the existence and mechanistic explanation of this effect remain controversial. We sought to confirm its existence and to determine a possible role of half-cell potential. We used isolated Langendorff-perfused rabbit hearts (n = 6) which were stained with di-4-ANEPPS and perfused with 15-mM butanedione monoxime (BDM). Transmembrane potentials were optically recorded at the left ventricular epicardium with a high spatial and temporal resolution (200 microm/343 micros) near the tip of a 120-microm platinum-iridium Teflon-coated unipolar pacing electrode to detect virtual electrode polarization and to reconstruct an activation pattern. Hearts were paced at a cycle length of 300 ms by anodal square pulses with an amplitude of 0.1-10 mA and a duration of 5-60 ms. Data revealed that the anodal-break excitation does exists and is accompanied by an overshoot in the recordings of the pacing current. Addition of a diode in the stimulation circuit eliminated both the overshoot and the break excitation. The findings suggest that a half-cell surface potential at the pacing electrode metal-saline interface may influence the pacing currents during unipolar anodal cardiac stimulation providing "break"-like activation. We also confirmed that the threshold of "break"-like excitation is lower than make-excitation. We suggest that further exploration of this effect is needed in order to design improved multiphasic pacing waveforms.

Correction to "How electrode size affects the electrical potential distribution in cardiac tissue"

[3] R. Butikofer and P. Lawrence, “Electrocutaneous nerve stimulation—II:Stimuluswaveformselection,” IEEETrans.Biomed.Eng.,vol.BME-26,Feb. 1979.[4] A. Peper and C. Grimbergen, “EEG measurement during electrical stim-ulation,” IEEE Trans. Biomed. Eng., vol. BME-30, Apr. 1983.[5] C. Poletto and C. Van Doren, “A high voltage, constant current stimu-lator for electrocutaneous stimulation through small electrodes,” IEEETrans. Biomed. Eng., vol. 46, Aug. 1999.[6] E. Hochmair, “An implantable current source for electrical nerve stim-ulation,” IEEE Trans. Biomed. Eng., vol. BME-27, May 1980.[7] K. Kaczmarek, K. Kramer, J. Webster, and R. Radwin, “A 16-channel8-parameter waveform electrotactile stimulation system,” IEEE Trans.Biomed. Eng., vol. 38, Oct. 1991.[8] G. Gudnason, E. Bruun, and M. Haugland, “An implantable mixedanalog/digital neural stimulator circuit,” in Proc. ISCAS, FL, 1999, pp.V.375–V.378.[9] L. Rosenthal, “Inductively tuned astable multivibrator,” IEEE Trans.Circuits Syst, vol. CAS-27, pp. 963–964, Oct. 1980.[10] K. Harada and G. Zhao, “Controlled power interface between solar cellsand AC source,” IEEE Trans. Power Electronics, vol. 8, pp. 654–662,Oct. 1993.

Chronaxie calculated from current–duration and voltage–duration data

To determine the rheobase and the chronaxie of excitable cells from strength–duration curves both constant-current pulses and constant-voltage pulses are applied. Since the complex impedance of the electrode-tissue interface varies with both the pulsewidth and the stimulation voltage, chronaxie values estimated from voltage–duration measurements will differ from the proper values as determined from current–duration measurements. To allow a comparison of chronaxie values obtained by the two stimulation methods, voltage–duration curves were measured in human subjects with a deep brain stimulation electrode implanted, while the current and the load impedance of the stimulation circuit were determined in vitro as a function of both stimulation voltage and pulsewidth. Chronaxie values calculated from voltage–duration data were shown to be 30–40% below those estimated from current–duration data. It was also shown that in the normal range of stimulation amplitudes (up to 7 V) the load impedance increases almost linearly with the pulsewidth. This result led us to present a simple method to convert voltage–duration data into current–duration data, thereby reducing the error in the calculated chronaxie values to ≈6%. For this purpose voltage–duration data have to be measured for pulses up to 10–20 times the expected chronaxie.

Magnetic stimulation coil and circuit design.

A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation [1]. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

Isolated constant-current stimulation circuits for neuroscience applications

A group of mains-powered circuits is described for constant-current stimulation of neuronal tissue. The circuits are linear in form and can be used for sine wave, ramp, or pulse stimulation. Both quasi-isolated and fully-isolated circuits are described.

A circuit for safe diagnostic electrical stimulation of the human brain.

An electronic circuit for controlled electrical stimulation of the human brain has been designed to optimize safety in charge transfer from electrodes to brain and to eliminate the likelihood of unwanted currents from the neurostimulator resulting from component failure. The circuit schematics feature the following designs: (1) a highly accurate and versatile rate generator 0.5 p.p.s. to 99 in increments of 0.5 p.p.s., (2) symmetrically-biphasic lead and lag pulses of 100 musec duration, (3) photo-isolated driver amplifiers with accurate waveform, reproduction, (4) true biphasic passive-current regulators driven by an isolated battery supply voltage for switch-selectable currents of 0.25 to 5 ma or variable current regulation, (5) accurate current and voltage waveform monitors that isolate the stimulating electrodes from the monitors, and (6) capacity-coupled outputs to guarantee no net D.C. component at the end of each biphasic pulse. Relay-switching circuits are also shown that allow sequential stimulation and recording from one or several electrodes. This neurostimulator has been in use for over two years without evidence of electrolytic damage at identifiable electrode tips. The utility of simultaneous stimulation of several different electrodes at safe charge levels is described.

A simple IC pulse-pair stimulator

The present paper describes a simple and relatively inexpensive brain stimulator circuit for generating trains of conditioning (C) and test (T) pulse pairs for refractory period and excitability cycle analyses. G and T outputs are constant-current monophasic cathodal pulses of adjustable frequency, duration, amplitude, and delay. C and T pulses can be controlled manually or through logic programming and can be fed out the same or separate channels. The stimulator can be operated on either ac or dc supplies and, when battery operated, features a high degree of stimulus isolation.

A digitally controlled stimulator for neurophysiological applications.

A stimulator circuit is presented which is capable of generating pulse train waveforms suitable for neurophysiological experiments are available, as well as special test conditions such as dishabituation. Digital and linear integrated circuits are used to provide precise control over the stimulus parameters.

The contact method: A simple technique for electrical self-stimulation without external leads

Electrical currents to reward areas of the brain were administered without the use of external leads by utilizing a method conceptually similar to that of the electronic drinkometer. A wire brush connected to the intracranial electrode protudes above the rat's head. By lifting its head the rat can make contact between the brush and a stimulation plate mounted horizontally overhead. The stimulation circuit is completed through the contact of the rat's feet with a grounded metal floor. Current thresholds and stimulation rates obtained by this method were identical to those obtained by the conventional method of stimulation.

Facilitation and Inhibition in Centrally Induced Switch-off Behavior in Cats

This chapter is concerned with a learned response in which the cat pushes a plate to terminate the stimulation applied. The chapter presents an experimental box designed for escape learning has been used throughout the present studies. This box has two small windows in a wall. In front of one window is a plate, pushing of which breaks the stimulation circuit. The animal placed in the box can be trained to push the plate to turn off the stimulation delivered to that animal. This type of response is designated as the switch-off behavior (SOB) in the present experiment. The term “hypothalamic SOB” can be applied to the SOB induced by hypothalamic stimulation. Hess demonstrated in cats that flight reactions develop during hypothalamic stimulation. This result suggests that the SOB may occur when a flight response is produced by hypothalamic stimulation. The animal with a hypothalamic electrode that could give rise to a flight response was placed in the experimental box, and the hypothalamus was stimulated monopolarly. The response was considered to be positive if an animal maintained a highly stable value of the response time during several hundred trials.

New principle of electric stimulation: ambipolar stimulation by alternating current, purely sinusoidal, of middle-frequency

Impulses of amplitude-modulated middle-frequency current (20 000 c.p.s.) stimulate nerve simultaneously at both poles. No polarity effect is observed, because no rectification occurs in the stimulation circuit if pure sine-wave middle-frequency current is employed. This principle is demonstrated by using bipolar longitudinal stimulation that, above threshold, elicits action currents, with latency difference corresponding to the distance between the stimulating electrodes. With supramaximum strength, maximum action currents are obtained at either pole, as is the case with ordinary cathodal stimuli of supramaximum strength applied to one pole or the other. Middle-frequency stimulation, therefore, has to be regarded asambipolar, i.e. does not depend on polarity. With second harmonic distortion, however, rectification occurs in the stimulation circuit and contamination by direct-current component ensues. Middle-frequency stimulation can be applied across nerve, since the excitatory effect does not apparently depend on longitudinal current flow. This method allows the action current to be recorded at the site of stimulation with minimum stimulus artefact.

A circuit to synchronise time marker, time base and stimulator

A circuit is described which permits synchronisation between a time marker and the time base and stimulator circuits. A frequency dividing circuit is also described which triggers the time base just before the stimulator is triggered.

Excitability of Muscle to Direct and Indirect Stimulation During Prolonged Direct Stimulation.

Although electrical stimulation is used widely in diagnosis and in physical therapy and is the only practical procedure to test muscle function in animals, the effects of prolonged direct stimulation have not been studied extensively.Alternating 60-cycle current was used in 3 independent but in phase circuits for stimulation through 3 pairs of electrodes, the first pair being inserted into the knee and tendon of the gastrocnemius muscle in situ of anesthetized rats (nembutal) and cats (dial), (D1 electrodes); the second pair (D2) inserted into the muscle itself at its upper and lower ends; the third pair (I) being employed for stimulation of the peripheral end of the cut sciatic nerve. The strength of the stimulus was adjusted with a rheostat and measured by a volt meter; in addition, the resistance in the muscle was measured by means of an oscilloscope in a shunt parallel to the muscle. Stimulation was continued either with D1 or with D2 until the muscle length reached the pre-stimulus resting value. Dur...