A CMOS Neural Interface for a Multichannel Vestibular Prosthesis

Abstract

We present a high-voltage CMOS neural-interface chip for a multichannel vestibular prosthesis (MVP) that measures head motion and modulates vestibular nerve activity to restore vision- and posture-stabilizing reflexes. This application specific integrated circuit neural interface (ASIC-NI) chip was designed to work with a commercially available microcontroller, which controls the ASIC-NI via a fast parallel interface to deliver biphasic stimulation pulses with 9-bit programmable current amplitude via 16 stimulation channels. The chip was fabricated in the ONSemi C5 0.5 micron, high-voltage CMOS process and can accommodate compliance voltages up to 12 V, stimulating vestibular nerve branches using biphasic current pulses up to 1.45 ± 0.06 mA with durations as short as 10 µs/phase. The ASIC-NI includes a dedicated digital-to-analog converter for each channel, enabling it to perform complex multipolar stimulation. The ASIC-NI replaces discrete components that cover nearly half of the 2nd generation MVP (MVP2) printed circuit board, reducing the MVP system size by 48% and power consumption by 17%. Physiological tests of the ASIC-based MVP system (MVP2A) in a rhesus monkey produced reflexive eye movement responses to prosthetic stimulation similar to those observed when using the MVP2. Sinusoidal modulation of stimulus pulse rate from 68–130 pulses per second at frequencies from 0.1 to 5 Hz elicited appropriately-directed slow phase eye velocities ranging in amplitude from 1.9–16.7°/s for the MVP2 and 2.0–14.2°/s for the MVP2A. The eye velocities evoked by MVP2 and MVP2A showed no significant difference (t-test, p = 0.034), suggesting that the MVP2A achieves performance at least as good as the larger MVP2.

A CMOS Current Steering Neurostimulation Array With Integrated DAC Calibration and Charge Balancing

“…This work, as well as that of [10] and [18] demonstrate multipolar stimulation, but rely on inter-channel matching for the accuracy of such patterned stimulation, whereas here, a calibration method ensures such accuracy. Any neurostimulator system with multiple of independent current sources can be used as a current-steering stimulator.…”

“…DAC topologies used for neurostimulators include current steering DACs, implemented with binary [18] or unary [10] weighted current source arrays, and R-2R ladders [12]. An advantage of current steering DACs is that only the current sources needed for stimulation are switched on, whereas in a splitter the entire current is consumed regardless of the selected code.…”

“…This has been leveraged in many neuroprosthetic applications such as cochlear implants, vestibular prostheses, visual prostheses, spinal stimulators, deep-brain stimulators, and peripheral nerve prosthetics [6], [7]. Due to its widespread use, VLSI neurostimulator systems should be designed to accurately stimulate in modes other than the standard monopolar and bipolar [8]–[10]. …”

A Low-Power ASIC Signal Processor for a Vestibular Prosthesis

“…While it is challenging to compare the host of approaches to realizing a VP, it is useful to examine the contributions of each. For example, when compared with systems using off-the-shelf components and processors [4, 6, 36], the signal processor ASIC has the advantage of energy-efficiency and small footprint without compromising the functionality. Our design advances the other custom design reported in [5, 37, 38] through a coordinate system transformation, which could potentially improve stimulation efficacy [13].…”

Severe streptomycin ototoxicity in the mouse utricle leads to a flat epithelium but the peripheral neural degeneration is delayed

“…A vestibular prosthesis is under development to treat patients with severe vestibular dysfunction (Hageman et al, 2016; Merfeld et al, 2007; Phillips et al, 2015; Wall et al, 2002). Similar to the cochlear implant, surviving primary ganglion neurons are the targets of stimulation by the proposed vestibular prosthesis.…”