An implanted system for multi-site nerve cuff-based ENG recording using velocity selectivity

Abstract

This paper describes the design of an implantable system for velocity-selective electroneurogram (ENG) recording. The system, which relies on the availability of multielectrode nerve cuffs (MECs) consists of two CMOS ASICs. One ASIC called the electrode unit (EU) is a mixed analogue/digital signal acquisition system which is mounted directly on an MEC in order to optimize the interface between the two. It is linked to the other ASIC by means of a 5-core cable through which it receives power and commands in addition to transmitting data. The second ASIC, called the monitoring unit (MU) manages the interface between the EUs (each MU can control up to three EUs) and an RF transcutaneous link to the external signal processor. The ASICs are fabricated in 0.8 lm CMOS technology. The EUs measure 3 mm 9 4 mm each and consume 105 mW (35 mW each), while the MU measures 1.5 mm 9 2 mm and consumes 4 mW. The power consumption on the communication channels (including cable losses) between the MU and EUs is 129 mW. A digital communication strategy between the two parts of the implanted system and the external controller is described.

Fibre-selective discrimination of physiological ENG using velocity selective recording: Report on pilot rat experiments

“…While it is possible to calculate CV using only a single pair of electrodes (a dipole) it has been shown that the velocity selectivity of a system can be increased by using multiple electrodes [2]. The use of velocity selective recording (VSR) enables discrimination of action potentials based both on direction of propagation (afferent or efferent) and CV, without the need to submit the nerve to invasive and potentially damaging procedures [3], [4]. This method provides a viable interface for neural recording systems that have potential use in a range of prosthetic devices.…”

Improved Signal Processing Methods for Velocity Selective Neural Recording Using Multi-Electrode Cuffs

“…To these signals controlled amounts of uncorrelated additive white Gaussian noise were added [3]. Blocks 2 and 3 are the two principal sections of a neural recording system intended for ultimate implantation as a pair of remotely powered modules connected together using a multicore implantable cable [7]. Block 2 is referred to as the electrode unit and is intended to be mounted on the MEC for optimum performance.…”

“…It consists of a set of speciallydesigned low noise differential amplifiers (nominal gain 10,000) whose 10 bipolar (or single differential) outputs are digitized (10 bits resolution) and multiplexed into one channel for transmission along the implantable cable [6]. In a distributed sensor architecture, several electrode units are placed at different sites in the peripheral nervous system and connected by implanted cables to a single monitoring unit [7]. The monitoring unit is a demultiplexer (DEMUX) and digital signal processing system that interfaces with an RF telemetry system (not described in this paper).…”

“…Although a single monitoring unit can process the data from and control and power several electrode units [7], in the experiments described in this paper only one of each type of unit is used as shown in Fig 1. In addition, the electrode unit employed is a complete prototype custom integrated circuit whereas the monitoring unit is realised in FPGA. Although for ultimate implantation the monitoring unit will be a second integrated circuit, the comparison of different VSR signal processing strategies that lies at the heart of this investigation requires easy flexibility of design suggesting the use of FPGA.…”

“…Tripolar recording from peripheral nerves cannot generally extract much of the information in the neural traffic, so we and others have been investigating velocity selective recording (VSR) since it allows the possibility of increasing the information obtainable from peripheral nerves (electroneurogram-ENG) by carrying out a spectral analysis in the velocity domain [1]- [7]. The resulting spectrum shows not only the direction of action potential (AP) propagation (afferent or efferent) but also provides a measure of the differential levels of excitation of the fibre populations in the nerve.…”