A Low-Noise Low-Power 0.001Hz-1kHz Neural Recording System-on-Chip With Sample-Level Duty-Cycling.

Advances in brain-machine interfaces and wearable biomedical sensors for healthcare and human-computer interactions call for precision electrophysiology to resolve a variety of biopotential signals across the body that cover a wide range of frequencies, from the mHz-range electrogastrogram (EGG) to the kHz-range electroneurogram (ENG). Existing integrated wearable solutions for minimally invasive biopotential recordings are limited in detection range and accuracy due to trade-offs in bandwidth, noise, input impedance, and power consumption. This article presents a 16-channel wide-band ultra-low-noise neural recording system-on-chip (SoC) fabricated in 65nm CMOS for chronic use in mobile healthcare settings that spans a bandwidth of 0.001 Hz to 1 kHz through a featured sample-level duty-cycling (SLDC) mode. Each recording channel is implemented by a delta-sigma analog-to-digital converter (ADC) achieving 1.0 µ V rms input-referred noise over 1Hz-1kHz bandwidth with a Noise Efficiency Factor (NEF) of 2.93 in continuous operation mode. In SLDC mode, the power supply is duty-cycled while maintaining consistently low input-referred noise levels at ultra-low frequencies (1.1 µV rms over 0.001Hz-1Hz) and 435 M Ω input impedance. The functionalities of the proposed SoC are validated with two human electrophysiology applications: recording low-amplitude electroencephalogram (EEG) through electrodes fixated on the forehead to monitor brain waves, and ultra-slow-wave electrogastrogram (EGG) through electrodes fixated on the abdomen to monitor digestion.

An Open Expandable Data Protocol for Multipolar Stimulation in Cochlear Implants.

Cochlear implants (CI) have restored hearing to many deaf patients. It is the most successful neuroprosthetic in the field. However, in past decades technical improvements have plateaued and the market has solidified among 3 manufacturers. Proprietary software, and know-how are some of the barriers to innovation and disruption in CIs. In this paper we propose an open data communication protocol for cochlear implants that supports multipolar stimulation, accommodates an expandable number of channels, and minimizes the transmission of redundant information. We also present a method for implementing multipolar stimulation in single supply stimulators with a bridge-type switch matrix through pulse-polarity modulation. This combines the advantages of lower voltage (lower power) operation with more targeted stimulation.Clinical Relevance- In addition to enabling the development of new tools for research and clinical deployment, the presented data communication protocol will promote clinical research in more advanced auditory coding strategies.

A 3 mm × 3 mm Fully Integrated Wireless Power Receiver and Neural Interface System-on-Chip.

A miniaturized, fully integrated wireless power receiver system-on-chip with embedded 16-channel electrode array and data transceiver for electrocortical neural recording and stimulation is presented. An H-tree power and signal distribution network throughout the SoC maintains high quality factor up to 11 in the on-chip receiver coil at 144 MHz resonant frequency while rejecting RF interference in sensitive neural interface circuits owing to its perpendicular and equidistant geometry. A multi-mode buck-boost resonant regulating rectifier (B 2R 3) offers greater than 11-dB input dynamic range in RF reception and less than 1 mV overshoot in transient load regulation. At 10 mm link distance, the 9 mm 2 neural interface SoC fabricated in a 180 nm silicon-on-insulator (SOI) process attains an overall wireless power transmission system efficiency (WSE) of 3.4% in driving a 160  µW load yielding a WSE figure-of-merit of 131, while maintaining signal integrity in analog recording and wireless data transmission that comprise the on-chip load.

Integrated In-Ear Device for Auditory Health Assessment.

Clinical assessment of the human auditory system is an integral part of evaluating the health of a patient's cognitive processes. Conventional tests performed by audiologists include the Auditory Steady State Response (ASSR) and the Auditory Brainstem Response (ABR), both of which present an audio stimulus to the patient in order to elicit a change in brain state measurable by electroencephalography (EEG) techniques. Spatial monitoring of the electrophysiological activity in the auditory cortex, temporal cortex, and brain stem during auditory stimulus evaluation can be used to pinpoint to location of auditory dysfunction along the auditory pathway. However, given the obtrusive nature of conventional auditory evaluation techniques and the lack of information about sound transduction and cochlear dynamics usually irrecoverable by EEG, a better approach is needed to improve its clinical utility. Here, we present an in-ear device for auditory health assessment that integrates a sound engine for stimulation and high-density dry-electrode EEG for real-time simultaneous recording of brain activity. This system provides ease-of-use and patient comfort. We also investigate the auditory transfer function of the hearing system as an intricate convolution of the tympanic membrane, middle ear bones, and the cochlear subsystems.

In Vivo Photovoltaic Performance of a Silicon Nanowire Photodiode-Based Retinal Prosthesis.

Purpose: For more than 20 years, there has been an international, multidisciplinary effort to develop retinal prostheses to restore functional vision to patients blinded by retinal degeneration. We developed a novel subretinal prosthesis with 1512 optically addressed silicon nanowire photodiodes, which transduce incident light into an electrical stimulation of the remaining retinal circuitry. This study was conducted to evaluate the efficacy of optically driving the subretinal prosthesis to produce visual cortex activation via electrical stimulation of the retina. Methods: We measured electrically evoked potential responses (EEPs) in rabbit visual cortex in response to illumination of the subretinal nanowire prosthesis with pulsed 852-nm infrared (IR) light. We compared the EEP responses to visually evoked potential responses (VEPs) to pulsed 532-nm visible light (positive control) and pulsed 852-nm IR light (negative control). Results: Activating the devices with IR light produced EEP responses with a significantly higher trough-to-peak amplitude (54.17 ± 33.4 µV) than IR light alone (24.07 ± 22.1 µV) or background cortical activity (23.22 ± 17.2 µV). EEP latencies were significantly faster than focal VEP latencies. Focal VEPs produced significantly higher amplitudes (94.88 ± 43.3 µV) than EEPs. We also demonstrated how an electrode placed on the cornea can be used as a noninvasive method to monitor the function of the implant. Conclusions: These results show that subretinal electrical stimulation with nanowire electrodes can elicit EEPs in the visual cortex, providing evidence for the viability of a subretinal nanowire prosthetic approach for vision restoration.

Assimilation of Biophysical Neuronal Dynamics in Neuromorphic VLSI.

Representing the biophysics of neuronal dynamics and behavior offers a principled analysis-by-synthesis approach toward understanding mechanisms of nervous system functions. We report on a set of procedures assimilating and emulating neurobiological data on a neuromorphic very large scale integrated (VLSI) circuit. The analog VLSI chip, NeuroDyn, features 384 digitally programmable parameters specifying for 4 generalized Hodgkin-Huxley neurons coupled through 12 conductance-based chemical synapses. The parameters also describe reversal potentials, maximal conductances, and spline regressed kinetic functions for ion channel gating variables. In one set of experiments, we assimilated membrane potential recorded from one of the neurons on the chip to the model structure upon which NeuroDyn was designed using the known current input sequence. We arrived at the programmed parameters except for model errors due to analog imperfections in the chip fabrication. In a related set of experiments, we replicated songbird individual neuron dynamics on NeuroDyn by estimating and configuring parameters extracted using data assimilation from intracellular neural recordings. Faithful emulation of detailed biophysical neural dynamics will enable the use of NeuroDyn as a tool to probe electrical and molecular properties of functional neural circuits. Neuroscience applications include studying the relationship between molecular properties of neurons and the emergence of different spike patterns or different brain behaviors. Clinical applications include studying and predicting effects of neuromodulators or neurodegenerative diseases on ion channel kinetics.

Towards high-resolution retinal prostheses with direct optical addressing and inductive telemetry.

OBJECTIVE: Despite considerable advances in retinal prostheses over the last two decades, the resolution of restored vision has remained severely limited, well below the 20/200 acuity threshold of blindness. Towards drastic improvements in spatial resolution, we present a scalable architecture for retinal prostheses in which each stimulation electrode is directly activated by incident light and powered by a common voltage pulse transferred over a single wireless inductive link. APPROACH: The hybrid optical addressability and electronic powering scheme provides separate spatial and temporal control over stimulation, and further provides optoelectronic gain for substantially lower light intensity thresholds than other optically addressed retinal prostheses using passive microphotodiode arrays. The architecture permits the use of high-density electrode arrays with ultra-high photosensitive silicon nanowires, obviating the need for excessive wiring and high-throughput data telemetry. Instead, the single inductive link drives the entire array of electrodes through two wires and provides external control over waveform parameters for common voltage stimulation. MAIN RESULTS: A complete system comprising inductive telemetry link, stimulation pulse demodulator, charge-balancing series capacitor, and nanowire-based electrode device is integrated and validated ex vivo on rat retina tissue. SIGNIFICANCE: Measurements demonstrate control over retinal neural activity both by light and electrical bias, validating the feasibility of the proposed architecture and its system components as an important first step towards a high-resolution optically addressed retinal prosthesis.

Integrated circuits and electrode interfaces for noninvasive physiological monitoring.

This paper presents an overview of the fundamentals and state of the-art in noninvasive physiological monitoring instrumentation with a focus on electrode and optrode interfaces to the body, and micropower-integrated circuit design for unobtrusive wearable applications. Since the electrode/optrode-body interface is a performance limiting factor in noninvasive monitoring systems, practical interface configurations are offered for biopotential acquisition, electrode-tissue impedance measurement, and optical biosignal sensing. A systematic approach to instrumentation amplifier (IA) design using CMOS transistors operating in weak inversion is shown to offer high energy and noise efficiency. Practical methodologies to obviate 1/f noise, counteract electrode offset drift, improve common-mode rejection ratio, and obtain subhertz high-pass cutoff are illustrated with a survey of the state-of-the-art IAs. Furthermore, fundamental principles and state-of-the-art technologies for electrode-tissue impedance measurement, photoplethysmography, functional near-infrared spectroscopy, and signal coding and quantization are reviewed, with additional guidelines for overall power management including wireless transmission. Examples are presented of practical dry-contact and noncontact cardiac, respiratory, muscle and brain monitoring systems, and their clinical applications.

Visual evoked potential characterization of rabbit animal model for retinal prosthesis research.

Visual evoked potentials (VEP) are used to confirm the function of prosthetic devices designed to stimulate retinas with damaged photoreceptors in vivo. In this work, we focus on methods and experimental consideration for recording visual evoked potential in rabbit models and assesses the use for retinal prosthesis research. We compare both invasive and noninvasive methods for recording VEPs, the response of the rabbit retina to various light wavelengths and intensities, focal vs. full field stimulation, and the effect of light bleaching on the retinal response.

The role of proprioceptive feedback in Parkinsonian resting tremor.

In this paper we use a closed-loop force feedback system to investigate the effect of altering proprioceptive feedback on EEG and resting tremor in Parkinson's Disease. A velocity dependent counterforce simulating viscous friction was provided by haptic robots with simultaneous recording of kinematics, EMG and EEG while a patient was on and off dopaminergic medication' We were able to reduce the amplitude of the tremor. We also showed that force feedback shifts the center of EEG-EMG coherence posteriorly toward the somatosensory regions, which may have ramifications for noninvasive therapies.