Biphasic Constant Current Pulses Research Articles

Activation of the rat olfactory bulb by direct ventral stimulation after nerve transection.

The aim of this study was to demonstrate how direct electrical stimulation can activate the olfactory bulb after denervation of the olfactory nerve input. Sprague-Dawley rats (n = 5) were anesthetized and olfactory bulbs exposed. Olfactory nerves were transected by passing a Teflon blade between the cribriform plate and ventral surface of the bulb. A cochlear implant electrode array was used to stimulate 6 different positions along the ventral surface of the olfactory bulb. Biphasic constant-current pulses were used (50-1000 μA, 50-1000 μs) to stimulate the bulb, and a 16-electrode paddle array was used to record localized negative field potential responses at the dorsal surface of the bulb. Localized negative field potentials were reliably obtained using biphasic, 500-μA, 200-μs pulses. A shift in stimulating position by 1 mm resulted in a significant change in the dorsal field potential. Direct stimulation of the deafferented olfactory bulb was effective in generating localized field potential responses. These findings support the potential use of direct electrical stimulation for the treatment of anosmia.

Suprachoroidal electrical stimulation: effects of stimulus pulse parameters on visual cortical responses

Objective. Neural responses to biphasic constant current pulses depend on stimulus pulse parameters such as polarity, duration, amplitude and interphase gap. The objective of this study was to systematically evaluate and optimize stimulus pulse parameters for a suprachoroidal retinal prosthesis. Approach. Normally sighted cats were acutely implanted with platinum electrode arrays in the suprachoroidal space. Monopolar stimulation comprised of monophasic and biphasic constant current pulses with varying polarity, pulse duration and interphase gap. Multiunit responses to electrical stimulation were recorded in the visual cortex. Main results. Anodal stimulation elicited cortical responses with shorter latencies and required lower charge per phase than cathodal stimulation. Clinically relevant retinal stimulation required relatively larger charge per phase compared with other neural prostheses. Increasing the interphase gap of biphasic pulses reduced the threshold of activation; however, the benefits of using an interphase gap need to be considered in light of the pulse duration and polarity used and other stimulation constraints. Based on our results, anodal first biphasic pulses between 300–1200 µs are recommended for suprachoroidal retinal stimulation. Significance. These results provide insights into the efficacy of different pulse parameters for suprachoroidal retinal stimulation and have implications for the design of safe and clinically relevant stimulators for retinal prostheses.

Consonant testing of a tactile hearing aid based on amplitude‐ and time‐quantized speech

Speech was first prefiltered with a second‐order bandpass filter centered at 1.5 kHz. Speech was then amplitude quantized to two levels based on the zero crossings of the waveform. This signal was then time quantized such that it could only change states in association with a clock signal. The intelligibility of the processed speech remains high for clock frequencies above 10 kHz (which was the quantizing rate used for this study). The discrete digital frequencies in the resulting waveform were easily detected with a digital logic circuit. These were then displayed onto the skin of the abdomen with a linear array of concentric ring electrodes. Thirty‐one electrodes (representing frequencies between 151 and 2500 Hz) were used for the array. Biphasic constant current pulses were used as the stimuli. Five normal hearing college age students served as the subjects. Discrimination of consonant pairs was used to test the ability of the tactile aid to transmit speech information to the subjects. The following ranges of accuracy (corrected for guessing) were observed: stops and constituents, 18% to 87%; voiced and unvoiced consonants, 3% to 27%; consonants with different places of articulation, 27% to 90%; nasal, glides, and semivowels, 17% to 49%.

Psychophysical studies relevant to the design of a digital electrotactile speech processor.

Psychophysical tests were carried out to investigate the perception of electrocutaneous stimuli delivered to the digital nerve bundles. The tests provided data for defining the operating range of a tactile aid for patients with profound-to-total hearing loss, as well as the individual differences between subjects and the information that could be transmitted. Monopolar biphasic constant current pulses with variable pulse widths were used. Threshold pulse widths varied widely between subjects and between fingers for the same subject. Thresholds were reasonably stable, but maximum comfortable levels increased with time. Perceived intensity was weakly dependent on pulse rate. Absolute identification of stimuli differing in pulse width gave information transmissions from 1.3-2.1 bits, limited by the dynamic ranges of the stimuli (3-17 dB). Stimuli from electrodes placed on either side of each finger were identified easily by all subjects. Absolute identification of stimuli differing in pulse rate gave information transmissions from 0.5-2.0 bits. Difference limens for pulse rate varied between subjects and were generally poor above 100 pps. On the basis of the results, an electrotactile speech processor is proposed, which codes the speech amplitude as pulse width, the fundamental frequency as pulse rate, and the second formant frequency as electrode position. Variable performances on tasks relying on amplitude and fundamental frequency cues are expected to arise from the intersubject differences in dynamic range and pulse rate discrimination. The psychophysical results for electrotactile stimulation are compared with previously published results for electroauditory stimulation with a multiple-channel cochlear implant.

An automatic, optically isolated, biphasic constant current stimulator adapter for artefact suppression

A stimulator adapter is described that automatically generates true biphasic constant current pulses from the single pulse output of a standard stimulator. Variations in the width or amplitude of the driving pulse are automatically duplicated in the biphasic pulses generated, permitting great ease of control of stimulating parameters. The device is simple, small in size and has a low current drain, permitting battery operation.

Improvements on a radio-controlled stimulator system for primate studies

A commercially available model airplane radio control transmitter-receiver system has been modified for nonhuman primate telestimulation studies. The circuit design has since been improved to decrease the size and weight and increase the performance of this system. The stimulator provides symmetrical, biphasic constant current pulses to electrodes implanted in the monkey brain.