Multi-electrode Devices Research Articles

Neurons on nanometric topographies: insights into neuronal behaviors in vitro.

Topography, the physical characteristics of an environment, is one of the most prominent stimuli neurons can encounter in the body. Many aspects of neurons and neuronal behavior are affected by the size, shape, and pattern of the physical features of the environment. A recent increase in the use of nanometric topographies, due to improved fabrication techniques, has resulted in new findings on neuronal behavior and development. Factors such as neuron adhesion, neurite alignment, and even the rate of neurite formation have all been highlighted through nanotopographies as complex phenomena that are driven by intricate intracellular mechanisms. Nanotopographies are suitable platforms, not only for fundamental studies on neuronal development, but also in practical applications, including multielectrode array devices and neuro-regenerative medicine. We reviewed recent publications that address the effects of nanotopography on neurons and categorized the observed behaviors as adherence, directional guidance, or accelerated outgrowth. We also discussed possible biological mechanisms of the molecular and cellular responses to topography, and suggested future perspectives for this field.

Editorial

Figure: From left, Blake Wilson, Ingeborg Hochmair, and Graeme Clark were presented with the 2013 Lasker~DeBakey Clinical Medical Research Award.We congratulate Graeme Clark, Ingeborg Hochmair, and Blake Wilson on receiving the 2013 Lasker~DeBakey Clinical Medical Research Award for their outstanding contributions to the development of the modern cochlear implant. While celebrating this long-deserved recognition, of which all in the hearing field should be proud, we take this opportunity to reflect on the achievement of the cochlear implant and its impact.Figure: Robert V. Shannon, PhDSince the U.S. Food and Drug Administration approved the first commercial device in 1984, more than 300,000 people have received the cochlear implant to restore partial hearing. Of these recipients, greater than half are children, with many able to develop nearly normal language skills and seamlessly merge into mainstream schools and professions. The cochlear implant has now been used to treat a range of disorders, from partial hearing loss and single-sided deafness to tinnitus, and has paved the way for research and development of other neural prostheses. By any measure, the cochlear implant has “conferred the greatest benefit to mankind” (Alfred Nobel's willhttp://www.nobelprize.org/alfred_nobel/will/will-full.html).Figure: Fan-Gang Zeng, PhDWe have been able to see further by standing on the shoulders of giants. William F. House was such a giant, who, despite his insistence on a single-electrode device and lack of commercial success, more than anybody deserves credit for making the cochlear implant a viable medical product and an acceptable medical practice. He was among the first to realize the need for a strong comprehensive team approach to fitting and rehabilitation. F. Blair Simmons and Robert L. White of Stanford University developed a multi-electrode device and evaluated its performance—how often do you see an article titled “Auditory Nerve: Electrical Stimulation in Man” these days ( Science 1965;148[3666]:104-106http://www.sciencemag.org/content/148/3666/104.long)? Robin P. Michelson and Michael M. Merzenich of the University of California, San Francisco, not only developed one of the first multichannel cochlear implants, but also organized the first international conference on cochlear implants, developed animal models, and established the first comprehensive evaluation standards. Donald K. Eddington of Utah and Claude-Henri Chouard of Paris developed multi-electrode devices that produced open-set speech recognition and were certainly precursors to the modern cochlear implants. Thanks to these pioneers, deafness is no longer a disability that separates people. They and many other engineers, researchers, and clinicians have greatly enriched and expanded the hearing health field. As we celebrate the great honor received by Drs. Clark, Hochmair, and Wilson, we cannot rest on our laurels. The contemporary cochlear implant has much room to improve. We also need to reduce the cost and increase access to the cochlear implant. The spotlight of the Lasker Award will help to raise public awareness. The future looks bright.

Measurement and modelling of anomalous polarity pulses in a multi-electrode diamond detector

In multi-electrode detectors, the motion of excess carriers generated by ionizing radiation induces charge pulses at the electrodes, whose intensities and polarities depend on the geometrical, electrostatic and carriers' transport properties of the device. The resulting charge-sharing effects may lead to bipolar currents, pulse height defects and anomalous polarity signals affecting the response of the device to ionizing radiation. This latter effect has recently attracted attention in commonly used detector materials, but different interpretations have been suggested, depending on the material, the geometry of the device and the nature of the ionizing radiation. In this letter, we report on the investigation in the formation of anomalous polarity pulses in a multi-electrode diamond detector with buried graphitic electrodes. In particular, we propose a purely electrostatic model based on the Shockley-Ramo-Gunn theory, providing a satisfactory description of anomalous pulses observed in charge collection efficiency maps measured by means of Ion Beam Induced Charge (IBIC) microscopy, and suitable for a general application in multi-electrode devices and detectors.

An unsupervised method for on-chip neural spike detection in multi-electrode recording systems.

Emerging multi-electrode-based brain-machine interfaces (BMIs) and large multi-electrode arrays used in in vitro experiments, enable recording of single neuron's activity on multiple electrodes and allow for an in-depth investigation of neural preparations, even at a sub-cellular level. However, the use of these devices entails stringent area and power consumption constraints for the signal-processing hardware units. In addition, the high autonomy of these units and an ability to automatically adapt to changes in the recorded neural preparations is required. Implementing spike detection in close proximity to recording electrodes offers the advantage of reducing the transmission data bandwidth. By eliminating the need of transmitting the full, redundant recordings of neural activity and by transmitting only the spike waveforms or spike times, significant power savings can be achieved in the majority of cases. Here, we present a low-complexity, unsupervised, adaptable, real-time spike-detection method targeting multi-electrode recording devices and compare this method to other spike-detection methods with regard to complexity and performance.

Charge sharing in multi-electrode devices for deterministic doping studied by IBIC

Following a single ion strike in a semiconductor device the induced charge distribution changes rapidly with time and space. This phenomenon has important applications to the sensing of ionizing radiation with applications as diverse as deterministic doping in semiconductor devices to radiation dosimetry. We have developed a new method for the investigation of this phenomenon by using a nuclear microprobe and the technique of Ion Beam Induced Charge (IBIC) applied to a specially configured sub-100μm scale silicon device fitted with two independent surface electrodes coupled to independent data acquisition systems. The separation between the electrodes is comparable to the range of the 2MeV He ions used in our experiments. This system allows us to integrate the total charge induced in the device by summing the signals from the independent electrodes and to measure the sharing of charge between the electrodes as a function of the ion strike location as a nuclear microprobe beam is scanned over the sensitive region of the device. It was found that for a given ion strike location the charge sharing between the electrodes allowed the beam-strike location to be determined to higher precision than the probe resolution. This result has potential application to the development of a deterministic doping technique where counted ion implantation is used to fabricate devices that exploit the quantum mechanical attributes of the implanted ions.

Chirp Reduction in Directly Modulated Multi-Electrode RSOA Devices in Passive Optical Networks

We demonstrate that the use of an optimized bi-electrode reflective semiconductor optical amplifier as remote modulator reduces the chirp. Our simulation shows that the chirp reduction is due to the carrier density profile in multi-electrode reflective semiconductor optical amplifiers. As a result of the chirp reduction, penalties for transmission are reduced from 6 to 4.5 dB on standard fiber at 2.5 Gb/s over 50 km. Using tri-electrode devices, a penalty of 3 dB is obtained for the same transmission conditions.

Dynamic Cell Fractionation and Transportation Using Moving Dielectrophoresis

This study presents a new cell manipulation method using a moving dielectrophoretic force to transport or fractionate cells along a microfluidic channel. The proposed moving dielectrophoresis (mDEP) is generated by sequentially energizing a single electrode or an array of electrodes to form an electric field that moves cells continuously along the microchannel. Cell fractionation is controlled by the applied electrical frequency, and cell transportation is controlled by the interelectrode activation time. The applicability of this method was demonstrated to simultaneously fractionate and transport Saccharomyces cerevisiae yeast cells, both viable and nonviable, by operating at conditions under which the cells were subjected to positive and negative dielectrophoresis, respectively. Compared to the conventional dielectrophoresis (cDEP and traveling wave dielectrophoresis (twDEP), moving dielectrophoresis allows cells to be separated on the basis of the real part of the Clausius-Mossotti factor, as in cDEP, but yet allows the direct transportation of separated cells without using fluid flow, as in twDEP. This dielectrophoresis technique provides a new way to manipulate cells and can be readily implemented on programmable multielectrode devices.

Image Processing Strategies Dedicated to Visual Cortical Stimulators: A Survey

Multi-electrode devices are constantly evolving toward a state where complexity and reliability are adequate for providing a breakthrough in visual cortical stimulation allowing the blind to recover partial vision. Yet few research teams have focused on the development of the front-end subsystem that transforms an input image from a camera into stimulation commands. This article collects state-of-the-art knowledge about the appearance and organization of phosphenes, and previous work in image processing dedicated to visual cortical stimulation. Observations and hypothesis about important issues are highlighted, and six image processing strategies that could be used in such a subsystem are presented, from the most optimistic that use brightness modulation to emulate grayscale to the most conservative that use only on/off phosphene evocation.

Factors limiting the performance of CdZnTe detectors

In the past few years, significant progress has been achieved in the development of room-temperature semiconductor detectors, particularly those based on CdZnTe (CZT) crystals. Several types of electron-transport-only detectors have been developed: pixel, coplanar-grid, cross-strip, drift-strip, orthogonal coplanar strip, and virtual Frisch grid, many of which are now commercially available. Despite all these varieties in the detector designs, they have many common features and problems. This review summarizes the common detector design constraints and related factors limiting performance of CZT detectors: bulk and surface leakage currents, surface effects, properties of Schottky contacts and surface interfacial layers, charge sharing and loss in multielectrode devices, charge transport nonuniformities, and fluctuations in the pulse height for long-drift-length devices. We also describe unique capabilities at Brookhaven National Laboratory, Upton, NY, for CZT device characterization and recent progress utilizing these tools.

Large area/volume CZT nuclear detectors

Cadmium zinc telluride (CZT) is one of the most promising materials for large-volume gamma-ray spectrometers and imaging arrays. However, because of deficiencies in the high quality material, high-resolution CZT spectrometers are still limited to relatively small dimensions (<2–3 cm3), which make them inefficient at detecting gamma rays. To extend the range of CZT detector applications, an increase in their efficiency is needed without sacrificing the ability to spectrally resolve gamma energies. Achieving this goal requires progress in the growth of large uniform single crystals, reductions in carrier trapping, increases in electrical resistivity, and improved device fabrication procedures. This paper summarizes the current developments in large area/volume CZT detectors and the common constraints on their designs: bulk and surface leakage currents, charge sharing and loss in multi-electrode devices, and charge transport non-uniformities. We also describe recent progress in characterization of CZT materials and devices using new capabilities at Brookhaven National Laboratory. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Noise selection in multielectrode devices by using a correlation spectrum analyzer

In this article, we present a technique to sort out in a multielectrode device a vanishing small noise component between two electrodes affected by a much larger overall noise. The technique is based on the use of a correlation spectrum analyzer and has proven to detect a current noise of interest as low as 1 fA/Hz in the presence of undesirable noise of 50 fA/Hz. The possibility offered by this technique is useful in a number of applications, ranging from gate current investigation in metal-oxide-semiconductor field effect transistors to the study of leakage currents in nanodevices.

Cochlear implantation in children with mondini deformity.

Objectives: This study reviews the results of cochlear implantation in 11 children between the ages of 2 to 18 years with Mondini deformity of the cochlea, who underwent surgery between 1988 and 2003. Of these, 7 children had a true Mondini with incomplete partition and 4 had a “cocks” common cavity. Methods: A Hortmann ball electrode device was used in 3 cases, a medel ball electrode device in 1 case, and a Medel compressed Combi40 in 1 case. Six cases received Clarion devices, 4 precurved enhanced bipolar, 1 HiFocus I, and 1 HiRes 90K. In all cases, there was complete insertion of electrodes and intraoperative sealing of the gusher. The precurved electrode was the safest and easiest to surgically introduce. Three cases with a common cavity developed a postoperative leak and had to have a lumboperitoneal shunt Results: The speech perception and speech production average scores attained were higher in patients with a true Mondini deformity and with multielectrode devices. The highest scores were attained with children using paired pulsatile stimuli strategies. On long-term follow-up, the 3 Hortmann single electrode devices failed between 3 and 4 years and the Medel single electrode device after 5 years, although functioning could not maintain sufficient hearing thresholds. Conclusions: From this study, we can conclude that children with true Mondini deformity (incomplete partition) and multielectrode devices, using a paired pulsatile strategy, although slower, perform as well as their matched counterparts with a normal cochlea.

Cochlear implants in China.

China has approximately 6 million totally deaf people according to an official survey conducted in 1990, although the actual number is probably higher. A primary cause of deafness is the use of ototoxic drugs. There does not appear to be any emergent deaf culture in China at present. As the only available medical device that can restore partial hearing to a totally deaf person, the cochlear implant has been in development in China since 1979. This paper provides an overview of cochlear implants in China and is based on a review of published materials, visits to research institutes and hospitals, and personal communication with Chinese colleagues. As of 1993, about 1,000 deaf people, including 50 children below age 12 years, have received four types of single-electrode cochlear implants that were developed and fabricated by institutions in China. These single-electrode devices have provided an aid to lip reading, but are no longer in use due to their inability to produce open-set speech recognition. Present implant research in China focuses on development of multi-electrode devices. Basic research in electrical stimulation is relatively lacking and standardized audiological evaluation for cochlear implant effectiveness needs to be developed. The present economic growth and legal system reform in China, combined with advances in implant technology, may make it possible to produce an affordable yet effective cochlear implant system. This paper discusses cochlear implants only in China, but the social and economic factors are similar in many developing countries in Asia, South America, Eastern Europe, and Africa, where a low-cost, high-performance cochlear implant system is also needed.

PPy thin layers grown onto copper salt replica for sensor array fabrication

Investigations on polypyrrole, a π-electron conjugated conducting polymer, aimed at the realization of amperometric biosensors are presented. The intent is to realize multi-electrode devices capable of transducing chemical changes into electrical signals. Thin patterned films of polypyrrole, which electrically interconnect Au microelectrodes, were grown from vapour phase by using a saline compound, CuCl 2+2H 2O, as oxidant. The salt has been obtained by a selective oxy-chloridization procedure of Cu thin layers on Au electrodized substrates. This technique has been used since it permits easier control, more than with electrochemical growth, of the polymer geometry which depends only on the salt geometry, hence on the Cu coating. Preliminary results obtained by means of cyclic voltammetry at a scan rate of 100 mV s −1, performed at different pHs (2, 7.8, 9, 12) on chemically grown PPy from CuCl 2+2H 2O salt, demonstrated that polymer conductivity increases in acid solution as the pH decreases.

Sensitivity and selectivity of intraneural stimulation using a silicon electrode array

Artificial electrical stimulation of peripheral nerves needs the development of multielectrode devices which stimulate individual fibers or small groups in a selective and sensitive way. To this end, a multielectrode array in silicon technology has been developed, as well as experimental paradigms and model calculations for sensitivity and selectivity measures. The array consists of twelve platinum electrode sites (10 x 50 microns at 50 microns interdistance) on a 45 microns thick tip-shaped silicon substrate and a Si3N4 insulating glass cover layer. The tip is inserted in the peroneal nerve of the rat during acute experiments to stimulate alpha motor fibers of the extensor digitorum longus muscle. Sensitivity calculations and experiments show a cubic dependence of the number of stimulated motor units on current amplitude of the stimulatory pulse (recruitment curves), starting at single motor level. Selectivity was tested by a method based on the refractory properties of neurons. At the lowest stimulus levels (for one motor unit) selectivity is maximal when two electrodes are separated by 200-250 microns, which was estimated also on theoretical grounds. The study provides clues for future designs of two- and three-dimensional devices.

Multielectrode intracochlear implants. Nerve survival and stimulation patterns.

A series of neurophysiological and anatomical experiments have been performed on cats implanted on a long-term basis with scala tympani electrodes. Auditory nerve survival was assessed for both neomycin sulfate-deafened and previously normal-hearing cats three weeks to 30 months after electrode implantation. Acute neurophysiological experiments were performed on nearly all of the cats and the spatial response to electrical stimulation was determined. The results of these experiments suggest that the auditory nerve can withstand surgical implantation and the long-term interface with scala tympani electrodes. In addition, restricted portions of the auditory nerve can be discretely excited with bipolar stimulation. Monopolar stimulation produced a very broad excitation pattern. These findings have important implications for the application of multielectrode prosthetic devices to the profoundly deaf.

Switching circuits using bi-directional non-linear impedances

In a brief general review of logic circuitry, a case is developed for a bi-directional, non-linear switching element. In order to compare circuits using such elements with those using standard semiconductor diodes, the main features of diode gates are considered in detail. Particular attention is paid to design of p-n-p transistor driver stages and their dependence on the logic sequence. Circuits using a bidirectional ?constant voltage? element are described, including a ?two-decision? AND gate. Possible types of constant voltage element are discussed and experimental results are given for multi-electrode silicon carbide devices. An interesting feature of the latter is the non-linear behaviour of capacitance. An attempt is made to compare gating circuits employing constant voltage, bi-directional elements with standard diode gates from a performance/cost point of view. A ?majority-logic? gate is made possible by a ?constant current,? bidirectional element. If one input is used as a control, this gate can become a many function gate, thus a 3-input gate can be controlled to act as a 3-AND, an OR, or a ?2 or more out of 3? logical unit without change of input or output connections. Some possible realisations of the constant current device are discusssed. A binary-octal decoder circuit and a simple binary full adder circuit are given as examples of the application of the non-linear elements and to illustrate their unusual features.