A fully implantable rodent neural stimulator

Abstract

The ability to electrically stimulate neural and other excitable tissues in behaving experimental animals is invaluable for both the development of neural prostheses and basic neurological research. We developed a fully implantable neural stimulator that is able to deliver two channels of intra-cochlear electrical stimulation in the rat. It is powered via a novel omni-directional inductive link and includes an on-board microcontroller with integrated radio link, programmable current sources and switching circuitry to generate charge-balanced biphasic stimulation. We tested the implant in vivo and were able to elicit both neural and behavioural responses. The implants continued to function for up to five months in vivo. While targeted to cochlear stimulation, with appropriate electrode arrays the stimulator is well suited to stimulating other neurons within the peripheral or central nervous systems. Moreover, it includes significant on-board data acquisition and processing capabilities, which could potentially make it a useful platform for telemetry applications, where there is a need to chronically monitor physiological variables in unrestrained animals.

Figure 1

(A) Block diagram of implant system, consisting of implanted stimulator, wireless power delivery and controller. (B) Photo of implant, prior to attachment of polyester mesh. (C) Photo of stimulation enclosure, without controller.

Figure 2

Example of AM stimulus output (600pps, f_m=60Hz, depth=100%, 100μs pulse width, 10μs inter-phase gap, 1kΩ load, 600μA peak current). (A) Detail of a single pulse (B) A 20ms segment of the AM pulse train. The current spikes at the pulse onsets are over-emphasized by the oscilloscope sampling, and are minimal when driving a reactive biological load.

Figure 3

Overview of implanted components, showing intracochlear electrode array, fixation at the skull (using polyester mesh), leadwire, and stimulator.

Figure 4

Comparison of EABRs produced by a fully implanted stimulator (left) versus a laboratory based stimulator (right), using a bipolar stimulus with 25μs pulse width, and 10μs inter-phase gap, averaged over 100 pulses delivered at 30pps. The first 1ms of the response was blanked to remove any stimulus artifact.