neuroBi: A Highly Configurable Neurostimulator for a Retinal Prosthesis and Other Applications

Kyle D Slater, Nicholas C Sinclair, Timothy S Nelson, Peter J Blamey, Hugh J McDermott, Bionic Vision Australia Consortium, Kyle D Slater, Nicholas C Sinclair, Timothy S Nelson, Peter J Blamey, Hugh J McDermott, Bionic Vision Australia Consortium

Abstract

To evaluate the efficacy of a suprachoroidal retinal prosthesis, a highly configurable external neurostimulator is required. In order to meet functional and safety specifications, it was necessary to develop a custom device. A system is presented which can deliver charge-balanced, constant-current biphasic pulses, with widely adjustable parameters, to arbitrary configurations of output electrodes. This system is shown to be effective in eliciting visual percepts in a patient with approximately 20 years of light perception vision only due to retinitis pigmentosa, using an electrode array implanted in the suprachoroidal space of the eye. The flexibility of the system also makes it suitable for use in a number of other emerging clinical neurostimulation applications, including epileptic seizure suppression and closed-loop deep brain stimulation. Clinical trial registration number NCT01603576 (www.clinicaltrials.gov).

Keywords: Neurostimulator; bionic eye; cortical stimulation; deep brain stimulation; electrical stimulation; neural prosthesis; suprachoroidal; visual prosthesis.

Figures

FIGURE 1.
FIGURE 1.
Prototype suprachoroidal retinal prosthesis with percutaneous connector. (a) An electrode array (top left) designed to be implanted in the suprachoroidal space of the eye is connected to a percutaneous connector (bottom right) via a leadwire. Photo provided by D A X Nayagam. (b) The percutaneous connector is implanted behind the ear and provides an external electrical connection to the implanted electrodes. (c) A schematic illustration of the electrode layout of the array (not to scale). Twenty stimulating electrodes ( and diameter) are arranged in a hexagonal grid, which is surrounded by thirteen interconnected diameter electrodes that form a guard-ring return. The array also includes two large return electrodes (2mm diameter). An additional return electrode (not shown) is implanted subcutaneously close to the percutaneous connector.
FIGURE 2.
FIGURE 2.
Charge-balanced, constant-current biphasic stimulus pulse parameters.
FIGURE 3.
FIGURE 3.
Block diagram illustrating the major functional components of neuroBi and its place within a typical patient-testing setup.
FIGURE 4.
FIGURE 4.
Current source used to generate stimulus pulses, consisting of a linearized BJT and an Improved Wilson current mirror with additional current scaling.
FIGURE 5.
FIGURE 5.
Stimulus delivery process. Electrode configurations and pulse parameters are first loaded into neuroBi. Stimuli comprising different electrode configurations and pulse parameters can then be delivered, either one at a time or in a sequence.
FIGURE 6.
FIGURE 6.
Stimulation waveform recorded across a 10k test load using a Fluke 190-204 Scopemeter (Fluke Corporation, USA). The measured pulse parameters correspond with the defined settings of phase width, interphase gap, 1.5ms stimulation period and 1mA current amplitude.
FIGURE 7.
FIGURE 7.
(a) Measured output impedance as a function of output current. (b) Measured compliance voltage as a function of output current using a 3ms phase width (worst case) with nominal settings of 10, 20, 30, and 40V. Voltage compliance is reduced for long phase widths and large currents due to charging of the output coupling capacitors.
FIGURE 8.
FIGURE 8.
Example current and voltage waveforms used to measure electrode impedance. (a) Current waveform measured by stimulating a test load and dividing the recorded voltage samples by the known resistance. (b) Voltage waveform recorded from an implanted electrode using a common-ground return. Both waveforms were recorded using the neuroBi waveform capture circuit and are the average of 50 pulses. Filled circles = averaged samples, open circle (marked by arrow) = voltage data point used to calculate impedance. Samples were not recorded during the interphase gap.
FIGURE 9.
FIGURE 9.
Photo of neuroBi (top right), electrode enable switch box (bottom) and ‘stop’ button (top left).

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Source: PubMed

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