Abstract
Neuromodulation technologies are progressing from pacemaking and sensory operations to full closed-loop control. In particular, optogenetics-the genetic modification of light sensitivity into neural tissue allows for simultaneous optical stimulation and electronic recording. This paper presents a neural interface application-specified integrated circuit (ASIC) for intelligent optoelectronic probes. The architecture is designed to enable simultaneous optical neural stimulation and electronic recording. It provides four low noise (2.08 μV) recording channels optimized for recording local field potentials (LFPs) (0.1-300Hz bandwidth, 5mV range, sampled 10-bit@4kHz), which are more stable for chronic applications. For stimulation, it provides six independently addressable optical driver circuits, which can provide both intensity (8-bit resolution across a 1.1mA range) and pulse-width modulation for high-radiance light emitting diodes (LEDs). The system includes a fully digital interface using a serial peripheral interface (SPI) protocol to allow for use with embedded controllers. The SPI interface is embedded within a finite state machine (FSM), which implements a command interpreter that can send out LFP data whilst receiving instructions to control LED emission. The circuit has been implemented in a commercially available 0.35 μm CMOS technology occupying a 1.95mm 1.10mm footprint for mounting onto the head of a silicon probe. Measured results are given for a variety of bench-top, in vitro and in vivo experiments, quantifying system performance and also demonstrating concurrent recording and stimulation within relevant experimental models.
Highlights
N EUROPROSTHETIC technologies have been steadily improving over the decades
In the 1990’s deep brain stimulus (DBS) technologies became available with implantable control systems which provided therapeutic modulation [1]
This paper describes a neural interface application-specified integrated circuit (ASIC) that records field potentials from electrode sites on the sides of a silicon probe, and facilitates optogenetic stimulation through driving μLEDs with a precise pulse output
Summary
N EUROPROSTHETIC technologies have been steadily improving over the decades. In the 1990’s deep brain stimulus (DBS) technologies became available with implantable control systems which provided therapeutic modulation [1]. A key advance in this drive towards closed loop systems has been optogenetics – the genetic modification of light sensitivity into nervous tissue. This can be achieved by genetically expressing Channelrhodopsin-2 photosensitive ion-channels [7] (or variants thereof) onto the membranes of neurons. There is a strong stimulus artefact in electronic systems This can be important for real-time closed loop requirements such as for epilepsy. The second is that through genetic manipulation, it is possible to target specific cells in specific neural sub-circuits [8] It allows for simultaneous optical stimulation and electrical recording.
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