Electrical stimulation through extracellular electrodes is an important method of neuroscience research. By injecting controlled amounts of charge into neural tissue, the membrane potential of nearby nerve cells can be raised sufficiently to elicit action potentials or spikes. If the resulting neural activity is then observed, scientists can us the complementary tools of stimulation and recording to study the structure and function of neural networks in the brain. In the past two decades, advances in microfabrication have led to the development of multisite extracellular electrodes that can contact more than 100 sites in a local region of a brain. Several companies have commercialized various types of miniature multisite electrodes, and these are now in widespread use in the neuroscience research community. However, the size and expense of traditional rack-mounted instruments required to interface with a large number of electrode sites presents a significant bottleneck in the adoption of multi-channel neural stimulation and recording. Stimulator units currently cost more than $1,000 per channel. Neural signal amplifier units are similarly expensive, and it can be difficult to coordinate stimulation and recording between these two separate units so that the electrical transients produced by stimulation pulses do not saturate the amplifiers and produce long blind spots in the neural recordings. In the past three years, Intan Technologies has developed and commercialized a series of microchips that integrates all functions of neural signal acquisition - low-noise amplification, programmable band-pass filtering, analog-to-digital conversion, and electrode impedance measurement - onto a single silicon chip that can process signals from up to 64 extracellular electrodes at the cost of less than $10 per channel. These chips are currently used in more than 30 countries worldwide, and have been adopted by many third-party instrumentation companies. However, these chips are not capable of delivering stimulation pulses, and they are not directly compatible with traditional stimulator units. Intan Technologies proposes to integrate all the sensitive electronics needed for both stimulation and recording onto a small, inexpensive silicon microchip (StimAmpChip) that will replace traditional rack-mounted stimulators and amplifiers. The use of advanced microelectronics will reduce bulky and expensive stimulation and amplifier systems down to the size of a postage stamp. By integrating stimulators and amplifiers on the same chip, their actions may be precisely coordinated to minimize amplifier saturation after stimulation pulses and allow neural activity immediately following stimulation to be observed. A combined stimulation/recording chip could be mounted in close proximity to a multisite electrode, reducing noise pickup, size, and weight. The StimAmpChip will have the capability to deliver charge-balanced current pulses of programmable amplitude and duration, and will have sufficient sensitivity to monitor extracellular voltages in the microvolt range.
The proposed program seeks to develop a microchip to reduce the size and cost of electrically stimulating neural tissue and monitoring the resulting activity. Integrating both stimulator and amplifier electronics onto a single silicon chip will facilitate the development of large-scale neural interfaces for scientific and medical research.
