Philip R. Troyk

A Power and Data Link for a Wireless-Implanted Neural Recording System

A wireless cortical neural recording system with a miniature-implanted package is needed in a variety of neuroscience and biomedical applications. Toward that end, we have developed a transcutaneous two-way communication and power system for wireless neural recording. Wireless powering and forward data transmission (into the body) at 1.25 Mbps is achieved using a frequency-shift keying modulated class E converter. The reverse telemetry (out of the body) carrier frequency is generated using an integer-N phase-locked loop, providing the necessary wideband data link to support simultaneous reverse telemetry from multiple implanted devices on separate channels. Each channel is designed to support reverse telemetry with a data rate in excess of 3 Mbps, which is sufficient for our goal of streaming 16 channels of raw neural data. We plan to incorporate this implantable power and telemetry system in a 1-cm diameter single-site cortical neural recording implant.

Intracortical Visual Prosthesis Research - Approach and Progress

Following the early work of Brindley in the late 1960s, the NIH began intramural and extramural funding for stimulation of the primary visual cortex using fine-wire electrodes that are inserted into area V1 for the purpose of restoring vision in individuals with blindness. More recently researchers with experience in this project became part of our multi-institutional team with the intention to identify and close technological gaps so that the intracortical approach might be tested in humans on a chronic basis. Our team has formulated an approach for testing a prototype system in a human volunteer. Here, we describe our progress and expectations

In vitro and in vivo charge capacity of AIROF microelectrodes.

Activated Iridium Oxide Film (AIROF) microelectrodes are thought to be well-suited for neural stimulation of the cortex because they can sustain high charge capacity (about ten times higher than Pt microelectrodes) when characterized in phosphate-buffered saline (PBS) or other high ionic strength electrolytes. However, it is known that their capacity diminishes after they are implanted in vivo. It has been suggested that tissue encapsulation is an underlying cause. In this paper, we report electrochemical measurements of AIROF microelectrodes that were performed acutely in the brain of the zebra finch. The experiment showed that the interstitial fluid environment in the birds brain did not maintain the high charge delivery capacity of the AIROF microelectrodes. A simple compensation for access resistance may create hazards to sustained electrode integrity

Inductive link design for miniature implants

Advances in microfabrication have allowed the integration of large numbers of electrodes onto one platform. The small size and high channel density of these microelectrode arrays which promise improved performance of a neural prosthesis also complicate the design of an inductive link to achieve efficient powering and communication with the implant. Stimulating or recording with many channels requires high data rate transmission. At the same time, power must be transmitted to the implanted device without exceeding power dissipation limits within the body. Using conventional design techniques, achieving all of these competing requirements simultaneously can require many time consuming iterations. It is proposed that a transcutaneous power and data link can be optimized to meet system level design parameters (power dissipation, data rate, secondary voltage, etc.) by having an analytic understanding of the interacting link level design parameters (receiver radius, carrier frequency, number of turns, implant location, etc.). We demonstrated this technique with the design of a transcutaneous power and data link for an intracortical visual prosthesis.

Active Floating Micro Electrode Arrays (AFMA)

Neuroscientists have widely used metal microelectrodes inserted into the cortex to record neural signals from, and provide electrical stimulation to, neural tissue for many years. Recently, the demand for implanting electrode arrays within the cortex, for both stimulation and recording, has rapidly increased. We are developing Active-floating-micro-electrode-arrays (AFMA) that are intended for use as a multielectrode cortical interface while minimizing the number of wires leading from the array to extra-dural circuitry or connectors. When combined with a wireless module, these new microelectrode arrays should allow for simulation and recording within free-roaming animals. This paper mainly discusses the design, fabrication, and packing of the first generation AFMA. Our long-term vision is a wireless-transmission electrode system, for stimulation and recording in free-roaming animals, which uses a family of modular active implantable electrode arrays

A 96-channel neural stimulation system for driving AIROF microelectrodes

We present the design and testing of a 96-channel stimulation system to drive activated iridium oxide (AIROF) microelectrodes within safe charge-injection limits. Our system improves upon the traditional capacitively coupled, symmetric charge-balanced biphasic stimulation waveform so as to maximize charge-injection capacity without endangering the microelectrodes. It can deliver computer-controlled cathodic current pulse for to up to 96 AIROF microelectrodes and positively bias them during the inter-pulse interval. The stimulation system is comprised of (1) 12 custom-designed PCB boards each hosting an 8-channel ASIC chip, (2) a motherboard to communicate between these 12 boards and the PC, (3) the PC interface equipped with a DIO card and the corresponding software. We plan to use this system in animal experiments for intracortical neural stimulation of implanted electrodes within our visual prosthesis project.

Power and data for a wireless implanted neural recording system

This paper reports a two-way communication and inductive power link for a neural recording system. For this system a telemetry circuit was designed which utilizes an Integer-N PLL to support multiple outward data channels. The PLL design consumes less than 1.3mW below 100MHz, uses self-biasing techniques for supply rejection, has dimensions of 350um × 680um, and generates frequencies with a phase noise of -83dBc/Hz @100kHz offset, as measured at 80MHz. A wireless demonstration of the implanted circuitry is presented. Wireless powering is achieved with the help of a Class E Converter and demodulation of ASK data sent from the implant at 10Mbps is achieved with a simple asynchronous receiver.

Estimating Phosphene Maps for Psychophysical Experiments used in Testing a Cortical Visual Prosthesis Device

Visual prosthesis devices are being developed to restore vision for those with blindness. Researchers working in the field of visual prosthesis are taking different approaches to develop a practical device. Some are targeting the retina for stimulation, whereas at least one group is targeting the optical nerve, and our laboratory is developing a system for the visual cortex. To estimate the kind of response they might expect from a typical user, researchers are conducting psychophysical experiments on normally-sighted persons. The device being developed in our laboratory is a first generation visual prosthesis system, designed to test the limits of artificial visual pattern recognition. Targeting the visual cortex area with our first generation device has limitations including limitations in lateral cortical surface area for electrode implantation, surgical difficulties and the lack of understanding as to how to use an artificial interface for communication with the visual cortex. Here, we discuss the uncertainties related to visotopic mapping of the lateral surface of the occipital lobe in humans.

Some Solutions to Technical Hurdles for Developing a Practical Intracortical Visual Prosthesis Device

The goal of cortical neuroprosthesis researchers of last four decades is to develop a practical intracortical visual prosthesis device. Although the concept of such a system seems straightforward, details of its configuration remain undefined. Knowledge of how the human visual system will respond to artificially-induced visually-based input is sparse. Combined with technological limitations, these have hindered the progress in developing a practical intracortical visual prosthesis device. The long-term objective of this research is to develop a continuously wearable intracortical visual prosthesis device. Earlier studies have used relatively small numbers of cortical electrodes, and these have been insufficient to generate an integrated visual perception. Surgical difficulties also complicate problem. A prototype visual prosthesis system needs to be adaptable to varying stimulation, image processing, and user interface needs. It also has the obvious requirement portability, implying extremely low power consumption and low weight so that the system can be used outside the confinement of a lab. We feel that available technology has sufficiently advanced to develop a first-generation intracortical visual prosthesis device. In this paper we propose some solutions to the challenges for developing this visual prosthesis device using existing technologies

A proposed intracortical visual prosthesis image processing system

It has been a goal of neuroprosthesis researchers to develop a system, which could provide artificial vision to a large population of individuals with blindness. It has been demonstrated by earlier researches that stimulating the visual cortex area electrically can evoke spatial visual percepts, i.e. phosphenes. The goal of visual cortex prosthesis is to stimulate the visual cortex area and generate a visual perception in real time to restore vision. Even though the normal working of the visual system is not been completely understood, the existing knowledge has inspired research groups to develop strategies to develop visual cortex prosthesis which can help blind patients in their daily activities. A major limitation in this work is the development of an image processing system for converting an electronic image, as captured by a camera, into a real-time data stream for stimulation of the implanted electrodes. This paper proposes a system, which will capture the image using a camera and use a dedicated hardware real time image processor to deliver electrical pulses to intracortical electrodes. This system has to be flexible enough to adapt to individual patients and to various strategies of image reconstruction. Here we consider a preliminary architecture for this system