Expanding the possibilities of two-dimensional multielectrode systems, with consideration to earlier geoelectric arrays

Recent two-dimensional multielectrode measurements are restricted to only a few geoelectric arrays. Realizing that specific features of nearly 90 other arrays are totally ignored, all original intentions as published about the development of new geoelectric arrays were reviewed. Apart from arrays, either already applied in two-dimensional geoelectric arrays or impossible to be applied in such systems, 61 forgotten once-developed arrays were found. These provide altogether 102 various solutions, which would be able to increase the efficiency of two-dimensional multielectrode measurements in some respect. 46 array solutions are able to enhance the depth of investigation; 9/11 array solutions give better vertical/horizontal resolution; 17 array solutions provide better planview images; 8 array solutions are worth applying in areas with limited access; 11 array solutions may reduce the effect of near-surface inhomogeneities. By reviving these forgotten arrays, it will be possible to develop versatile multielectrode systems, which are more adaptive to the diverse field needs

Neuroelectronic interfacing with cultured multielectrode arrays toward a cultured probe

Efficient and selective electrical stimulation and recording of neural activity in peripheral, spinal, or central pathways requires multielectrode arrays at micrometer scale. ¿Cultured probe¿ devices are being developed, i.e., cell-cultured planar multielectrode arrays (MEAs). They may enhance efficiency and selectivity because neural cells have been grown over and around each electrode site as electrode-specific local networks. If, after implantation, collateral sprouts branch from a motor fiber (ventral horn area) and if they can be guided and contacted to each ¿host¿ network, a very selective and efficient interface will result. Four basic aspects of the design and development of a cultured probe, coated with rat cortical or dorsal root ganglion neurons, are described. First, the importance of optimization of the cell-electrode contact is presented. It turns out that impedance spectroscopy, and detailed modeling of the electrode-cell interface, is a very helpful technique, which shows whether a cell is covering an electrode and how strong the sealing is. Second, the dielectrophoretic trapping method directs cells efficiently to desired spots on the substrate, and cells remain viable after the treatment. The number of cells trapped is dependent on the electric field parameters and the occurrence of a secondary force, a fluid flow (as a result of field-induced heating). It was found that the viability of trapped cortical cells was not influenced by the electric field. Third, cells must adhere to the surface of the substrate and form networks, which are locally confined, to one electrode site. For that, chemical modification of the substrate and electrode areas with various coatings, such as polyethyleneimine (PEI) and fluorocarbon monolayers promotes or inhibits adhesion of cells. Finally, it is shown how PEI patterning, by a stamping technique, successfully guides outgrowth of collaterals from a neonatal rat lumbar spinal cord explant, after six days in cultur

Effect of Positional Inaccuracies on Multielectrode Results

We have started to investigate the consequences of various noises o the interpreted results for various multielectrode arrays. We expect, it will be possible to find out, what kinds of noise have the most effect on the resulting data. Such an investigation may lead to a better elimination of potential errors due to noises. In the first step (presented in this paper) we studied the appearance of false anomalies due to positioning errors of the electrodes. In realistic field conditions, in spite of the greatest possible care, the electrode positions contain some inaccuracy: either in case of dense undergrowth, or varied topography, or very rocky field. In all these cases, it is not possible to put the electrodes in their theoretical position. As a consequence, the position data will contain some error. The extent of such inaccuracies was exactly determined by using a laser distance meter. Then, we computed their effect on the resulting apparent- and inverted resistivity data. We carried out such a study for Wenner, Wenner-beta, pole-dipole and pole-pole arrays. In the light of our conclusions, the usual assumption about random noise seems to be an oversimplification

Large-scale multielectrode recording and stimulation of neural activity

Large circuits of neurons are employed by the brain to encode and process information. How this encoding and processing is carried out is one of the central questions in neuroscience. Since individual neurons communicate with each other through electrical signals (action potentials), the recording of neural activity with arrays of extracellular electrodes is uniquely suited for the investigation of this question. Such recordings provide the combination of the best spatial (individual neurons) and temporal (individual action-potentials) resolutions compared to other large-scale imaging methods. Electrical stimulation of neural activity in turn has two very important applications: it enhances our understanding of neural circuits by allowing active interactions with them, and it is a basis for a large variety of neural prosthetic devices. Until recently, the state-of-the-art in neural activity recording systems consisted of several dozen electrodes with inter-electrode spacing ranging from tens to hundreds of microns. Using silicon microstrip detector expertise acquired in the field of high-energy physics, we created a unique neural activity readout and stimulation framework that consists of high-density electrode arrays, multi-channel custom-designed integrated circuits, a data acquisition system, and data-processing software. Using this framework we developed a number of neural readout and stimulation systems: (1) a 512-electrode system for recording the simultaneous activity of as many as hundreds of neurons, (2) a 61-electrode system for electrical stimulation and readout of neural activity in retinas and brain-tissue slices, and (3) a system with telemetry capabilities for recording neural activity in the intact brain of awake, naturally behaving animals. We will report on these systems, their various applications to the field of neurobiology, and novel scientific results obtained with some of them. We will also outline future directions

Classification of Surface Geoelectric Arrays

We have found in the geophysical literature more than ninety different surface geoelectric arrays, fulfilling an updated definition (specifying the current feeding, the potential difference measurement and the geometry of the electrodes). Several composite configurations, with widely varying geometry, have also been collected. We have presented the geoelectric arrays in a systematic way and with a unified notation. The classification is based on three divalent parameters: “superposition” of measurements, “focusing” of currents and “colinearity” of the array, creating 8 groups of geoelectric arrays. For the simplest group (the group of nonfocused, nonsuperposed, colinear arrays) we cover all theoretically possible arrays. For the other groups – due to the infinite variety – we collected only the already existing arrays, but it is easy to create further example arrays. The proposed classification may facilitate a systematic comparison of properties of different arrays and inspire testing new arrays, to find optimal configurations for actual field problems. Finally, the classification certainly helps to avoid rediscovering already published arrays

Effect of positional inaccuracies on multielectrode results

This paper investigates the effect of electrode positioning errors on the inverted pseudosection. Instead of random spacing errors (as usually assumed in geoelectrics) we exactly measured this effect among field conditions. In the field, in spite of the greatest possible care, the electrode positions contain some inaccuracy: either in case of dense undergrowth, or varied topography, or very rocky field. In all these cases, it is not possible to put the electrodes in their theoretical position. As a consequence, the position data will contain some error. The inaccuracies were exactly determined by using a laser distance meter. The geometrical data from real field conditions and by using Wenner-α, Wenner-β, pole-dipole and pole-pole arrays were then considered over homogeneous half space. As we have found, the positioning errors can be regarded as insignificant, even in case of relatively uncomfortable field conditions. However, in case of very rocky surface the distortions are more significant, but it is still possible to make some corrections: either by neglecting a few electrode positions with the greatest positioning error, or to minimize the inline errors, even on the price that offline deviations are high

In vivo measurements with robust silicon-based multielectrode arrays with extreme shaft lengths

In this paper, manufacturing and in vivo testing of extreme-long Si-based neural microelectrode arrays are presented. Probes with different shaft lengths (15–70 mm) are formed by deep reactive ion etching and have been equipped with platinum electrodes of various configurations. In vivo measurements on rats indicate good mechanical stability, robust implantation, and targeting capability. High-quality signals have been recorded from different locations of the cerebrum of the rodents. The accompanied tissue damage is characterized by histology

Direct evidence for local oscillatory current sources and intracortical phase gradients in turtle visual cortex

Visual stimuli induce oscillations in the membrane potential of neurons in cortices of several species. In turtle, these oscillations take the form of linear and circular traveling waves. Such waves may be a consequence of a pacemaker that emits periodic pulses of excitation that propagate across a network of excitable neuro-nal tissue or may result from continuous and possibly reconfigu-rable phase shifts along a network with multiple weakly coupled neuronal oscillators. As a means to resolve the origin of wave propagation in turtle visual cortex, we performed simultaneous measurements of the local field potential at a series of depths throughout this cortex. Measurements along a single radial pen-etration revealed the presence of broadband current sources, with a center frequency near 20 Hz ( g band), that were activated by visual stimulation. The spectral coherence between sources at two well-separated loci along a rostral– caudal axis revealed the pres-ence of systematic timing differences between localized cortical oscillators. These multiple oscillating current sources and their timing differences in a tangential plane are interpreted as the neuronal activity that underlies the wave motion revealed in previous imaging studies. The present data provide direct evidence for the inference from imaging of bidirectional wave motion that the stimulus-induced electrical waves in turtle visual cortex corre-spond to phase shifts in a network of coupled neuronal oscillators

Adhesion and growth of electrically-active cortical neurons on polyethyleimine patterns microprinted on PEO-PPO-PEO triblockcopolymer-coated hydrophobic surfaces

This paper describes the adhesion and growth of dissociated cortical neurons on chemically patterned surfaces over a time period of 30 days. The presence of neurons was demonstrated by measurement of spontaneous bioelectrical activity on a micropatterned multielectrode array. Chemical patterns were prepared with a combination of neurophobic layers of polyethylenoxide-polypropylenoxide-polyethylenoxide (PEO-PPO-PEO) triblockcopolymers adsorbed onto hydrophobic surfaces and neurophilic microprinted tracks of polyethylenimine (PEI). Results showed that commercially available PEO-PPO-PEO triblockcopolymers F108 and F127 (Synperonics, ICI) significantly reduced the adhesion of neuronal tissue when adsorbed on hydrophobic Polyimide (PI) and Fluorocarbon (FC) surfaces over a time period of eight days. In general, both F108- and F127-coated PI displayed equal or better neurophobic background properties after 30 days. Viability of neuronal tissue after 30 days on PEI microprinted F108- and F127-coated PI was comparable with relatively high viability factors between 0.9 and 1 (scale from 0 to 1). Summarizing, the strategy to combine the neurophobic adsorbed triblock-copolymers F108 and F127 onto hydrophobic surfaces with neurophilic microprinted PEI resulted in relatively long-term neuronal pattern preservation with high numbers of viable neurons present after 30 days