An Analogue Front-End System with a Low-Power On-Chip Filter and ADC for Portable ECG Detection Devices

Medical diagnostic instruments can be made into portable devices for the purpose of home care, such as the diagnosis of heart disease. These assisting devices are not only used to monitor patients but are also beneficial as handy and convenient medical instruments. Hence, for reasons of both portability and durability, designers should reduce the power consumption of assistant devices as much as possible to extend their battery lifetime. However, achieving the low power requirement of the ECG sensing and the processing board for the ECG with commercial discrete components (A21-0003) is difficult because the low power consumer electronics for ECG acquisition systems are not yet available. With the help of the integrated circuit technology, the power-saving requirement of portable and durable equipment gives circuit designers the impetus to reduce the power consumption of analogue front-end circuits in ECG acquisition systems. In addition, the analogue front-end circuits, which are the interface between physical signals and the digital processor, must be operated at a low-supply voltage to be integrated into the low-voltage system-on-a-chip (SOC) system (Eshraghian, 2006). Therefore, the chapter will present two design examples of low-voltage (1 V) and low-power (<1 W) on-chip circuits including a low-pass filter (LPF) and an analogue-to-digital converter (ADC) to demonstrate the possibility of developing the low-voltage low-power ECG acquisition SO

Nanotools for Neuroscience and Brain Activity Mapping

Neuroscience is at a crossroads. Great effort is being invested into deciphering specific neural interactions and circuits. At the same time, there exist few general theories or principles that explain brain function. We attribute this disparity, in part, to limitations in current methodologies. Traditional neurophysiological approaches record the activities of one neuron or a few neurons at a time. Neurochemical approaches focus on single neurotransmitters. Yet, there is an increasing realization that neural circuits operate at emergent levels, where the interactions between hundreds or thousands of neurons, utilizing multiple chemical transmitters, generate functional states. Brains function at the nanoscale, so tools to study brains must ultimately operate at this scale, as well. Nanoscience and nanotechnology are poised to provide a rich toolkit of novel methods to explore brain function by enabling simultaneous measurement and manipulation of activity of thousands or even millions of neurons. We and others refer to this goal as the Brain Activity Mapping Project. In this Nano Focus, we discuss how recent developments in nanoscale analysis tools and in the design and synthesis of nanomaterials have generated optical, electrical, and chemical methods that can readily be adapted for use in neuroscience. These approaches represent exciting areas of technical development and research. Moreover, unique opportunities exist for nanoscientists, nanotechnologists, and other physical scientists and engineers to contribute to tackling the challenging problems involved in understanding the fundamentals of brain function

High-resolution three-dimensional extracellular recording of neuronal activity with microfabricated electrode arrays

Microelectrode array recordings of neuronal activity present significant opportunities for studying the brain with single-cell and spike-time precision. However, challenges in device manufacturing constrain dense multisite recordings to two spatial dimensions, whereas access to the three-dimensional (3D) structure of many brain regions appears to remain a challenge. To overcome this limitation, we present two novel recording modalities of silicon-based devices aimed at establishing 3D functionality. First, we fabricated a dual-side electrode array by patterning recording sites on both the front and back of an implantable microstructure. We found that the majority of single-unit spikes could not be simultaneously detected from both sides, suggesting that in addition to providing higher spatial resolution measurements than that of single-side devices, dual-side arrays also lead to increased recording yield. Second, we obtained recordings along three principal directions with a multilayer array and demonstrated 3D spike source localization within the enclosed measurement space. The large-scale integration of such dual-side and multilayer arrays is expected to provide massively parallel recording capabilities in the brain

Multiplexed, High Density Electrophysiology with Nanofabricated Neural Probes

Extracellular electrode arrays can reveal the neuronal network correlates of behavior with single-cell, single-spike, and sub-millisecond resolution. However, implantable electrodes are inherently invasive, and efforts to scale up the number and density of recording sites must compromise on device size in order to connect the electrodes. Here, we report on silicon-based neural probes employing nanofabricated, high-density electrical leads. Furthermore, we address the challenge of reading out multichannel data with an application-specific integrated circuit (ASIC) performing signal amplification, band-pass filtering, and multiplexing functions. We demonstrate high spatial resolution extracellular measurements with a fully integrated, low noise 64-channel system weighing just 330 mg. The on-chip multiplexers make possible recordings with substantially fewer external wires than the number of input channels. By combining nanofabricated probes with ASICs we have implemented a system for performing large-scale, high-density electrophysiology in small, freely behaving animals that is both minimally invasive and highly scalable

Transcranial Electric Stimulation Entrains Cortical Neuronal Populations in Rats

Low intensity electric fields have been suggested to affect the ongoing neuronal activity in vitro and in human studies. However, the physiological mechanism of how weak electrical fields affect and interact with intact brain activity is not well understood. We performed in vivo extracellular and intracellular recordings from the neocortex and hippocampus of anesthetized rats and extracellular recordings in behaving rats. Electric fields were generated by sinusoid patterns at slow frequency (0.8, 1.25 or 1.7 Hz) via electrodes placed on the surface of the skull or the dura. Transcranial electric stimulation (TES) reliably entrained neurons in widespread cortical areas, including the hippocampus. The percentage of TES phase-locked neurons increased with stimulus intensity and depended on the behavioral state of the animal. TES-induced voltage gradient, as low as 1 mV/mm at the recording sites, was sufficient to phase-bias neuronal spiking. Intracellular recordings showed that both spiking and subthreshold activity were under the combined influence of TES forced fields and network activity. We suggest that TES in chronic preparations may be used for experimental and therapeutic control of brain activity

Electrical modeling of the cell-electrode interface for recording neural activity from high-density microelectrode arrays

Accurate electrical models are needed to support the design of modern microelectrode arrays. The point-contact model is presented thoroughly, and an area-contact model is analytically derived in order to model the electrical characteristics of the cell-electrode interface at subcellular resolution. An optimum electrode diameter for recording the electrical activity of neurons is analytically determined at 8 um, with a cell diameter of 10 um and a typical load capacitance of 10 pF. Finally, three- dimensional tip electrodes are characterized using the area- contact model. An improvement of the electrical coupling up to 20 dB is observed for small electrodes, in simulation

Recent Advances in Neural Recording Microsystems

The accelerating pace of research in neuroscience has created a considerable demand for neural interfacing microsystems capable of monitoring the activity of large groups of neurons. These emerging tools have revealed a tremendous potential for the advancement of knowledge in brain research and for the development of useful clinical applications. They can extract the relevant control signals directly from the brain enabling individuals with severe disabilities to communicate their intentions to other devices, like computers or various prostheses. Such microsystems are self-contained devices composed of a neural probe attached with an integrated circuit for extracting neural signals from multiple channels, and transferring the data outside the body. The greatest challenge facing development of such emerging devices into viable clinical systems involves addressing their small form factor and low-power consumption constraints, while providing superior resolution. In this paper, we survey the recent progress in the design and the implementation of multi-channel neural recording Microsystems, with particular emphasis on the design of recording and telemetry electronics. An overview of the numerous neural signal modalities is given and the existing microsystem topologies are covered. We present energy-efficient sensory circuits to retrieve weak signals from neural probes and we compare them. We cover data management and smart power scheduling approaches, and we review advances in low-power telemetry. Finally, we conclude by summarizing the remaining challenges and by highlighting the emerging trends in the field