http://download.neurosky.com/docs/papers/bcq/Klimesch_1999_EEG_alpha_and_theta_oscillations_reflect_cognitive_and_memory_performance.pdf

EEG alpha and theta oscillations reflect cognitive and memory performance: a review and analysis

Neuronal activity in the brain gives rise to transmembrane currents that can be measured in the extracellular medium. Although the major contributor of the extracellular signal is the synaptic transmembrane current, other sources — including Na+ and Ca2+ spikes, ionic fluxes through voltage- and ligand-gated channels, and intrinsic membrane oscillations — can substantially shape the extracellular field. High-density recordings of field activity in animals and subdural grid recordings in humans, combined with recently developed data processing tools and computational modelling, can provide insight into the cooperative behaviour of neurons, their average synaptic input and their spiking output, and can increase our understanding of how these processes contribute to the extracellular signal.

/pdf/the-origin-of-extracellular-fields-and-currents-eeg-ecog-lfp-2e79zygxj0.pdf

The origin of extracellular fields and currents — EEG, ECoG, LFP and spikes

Interneurons of the hippocampus

The mammalian visual system is endowed with a nearly infinite capacity for the recognition of patterns and objects. To have acquired this capability the visual system must have solved what is a fundamentally combinatorial prob­ lem. Any given image consists of a collection of features, consisting of local contrast borders of luminance and wavelength, distributed across the visual field. For one to detect and recognize an object within a scene, the features comprising the object must be identified and segregated from those comprising other objects. This problem is inherently difficult to solve because of the combinatorial nature of visual images. To appreciate this point, consider a simple local feature such as a small vertically oriented line segment placed within a fixed location of the visual field. When combined with other line segments, this feature can form a nearly infinite number of geometrical objects. Any one of these objects may coexist with an equally large number of other

Visual feature integration and the temporal correlation hypothesis

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Pyramidal cells in the CA1 hippocampal region displayed transient network oscillations (200 hertz) during behavioral immobility, consummatory behaviors, and slow-wave sleep. Simultaneous, multisite recordings revealed temporal and spatial coherence of neuronal activity during population oscillations. Participating pyramidal cells discharged at a rate lower than the frequency of the population oscillation, and their action potentials were phase locked to the negative phase of the simultaneously recorded oscillatory field potentials. In contrast, interneurons discharged at population frequency during the field oscillations. Thus, synchronous output of cooperating CA1 pyramidal cells may serve to induce synaptic enhancement in target structures of the hippocampus.

https://science.sciencemag.org/content/sci/256/5059/1025.full.pdf

High-frequency network oscillation in the hippocampus.

This paper describes the development of a high-density electronic interface to the central nervous system. Silicon micromachined electrode arrays now permit the long-term monitoring of neural activity in vivo as well as the insertion of electronic signals into neural networks at the cellular level. Efforts to understand and engineer the biology of the implant/tissue interface are also underway. These electrode arrays are facilitating significant advances in our understanding of the nervous system, and merged with on-chip circuitry, signal processing, microfluidics, and wireless interfaces, they are forming the basis for a family of neural prostheses for the possible treatment of disorders such as blindness, deafness, paralysis, severe epilepsy, and Parkinson's disease.

/pdf/wireless-implantable-microsystems-high-density-electronic-2s60s28lz9.pdf

Wireless implantable microsystems: high-density electronic interfaces to the nervous system

The interface between micromachined neural microelectrodes and neural tissue plays an important role in chronic in vivo recording Electrochemical polymerization was used to optimize the surface of the metal electrode sites Electrically conductive polymers (polypyrrole) combined with biomolecules having cell adhesion functionality were deposited with great precision onto microelectrode sites of neural probes The biomolecules used were a silk-like polymer having fibronectin fragments (SLPF) and nonapeptide CDPGYIGSR The existence of protein polymers and peptides in the coatings was confirmed by reflective microfocusing Fourier transform infrared spectroscopy (FTIR) The morphology of the coating was rough and fuzzy, providing a high density of bioactive sites for interaction with neural cells This high interfacial area also helped to lower the impedance of the electrode site and, consequently, to improve the signal transport Impedance spectroscopy showed a lowered magnitude and phase of impedance around the biologically relevant frequency of 1 kHz Cyclic voltammetry demonstrated the intrinsic redox reaction of the doped polypyrrole and the increased charge capacity of the coated electrodes Rat glial cells and human neuroblastoma cells were seeded and cultured on neural probes with coated and uncoated electrodes Glial cells appeared to attach better to polypyrrole/SLPF-coated electrodes than to uncoated gold electrodes Neuroblastoma cells grew preferentially on and around the polypyrrole/CDPGYIGSR-coated electrode sites while the polypyrrole/CH(3)COO(-)-coated sites on the same probe did not show a preferential attraction to the cells These results indicate that we can adjust the chemical composition, morphology, electronic transport, and bioactivity of polymer coatings on electrode surfaces on a multichannel micromachined neural probe by controlling electrochemical deposition conditions

/pdf/surface-modification-of-neural-recording-electrodes-with-1zmu4cs88e.pdf

Surface modification of neural recording electrodes with conducting polymer/biomolecule blends

An important aspect of the development of cortical prostheses is the enhancement of suitable implantable microelectrode arrays for chronic neural recording. The objective of this study was to investigate the recording performance of silicon-substrate micromachined probes in terms of reliability and signal quality. These probes were found to consistently and reliably provide high-quality spike recordings over extended periods of time lasting up to 127 days. In a consecutive series of ten rodents involving 14 implanted probes, 13/14 (93%) of the devices remained functional throughout the assessment period. More than 90% of the probe sites consistently recorded spike activity with signal-to-noise ratios sufficient for amplitudes and waveform-based discrimination. Histological analysis of the tissue surrounding the probes generally indicated the development of a stable interface sufficient for sustained electrical contact. The results of this study demonstrate that these planar silicon probes are suitable for long-term recording in the cerebral cortex and provide an effective platform technology foundation for microscale intracortical neural interfaces for use in humans.

Chronic neural recording using silicon-substrate microelectrode arrays implanted in cerebral cortex

This study investigated the use of planar, silicon-substrate microelectrodes for chronic unit recording in the cerebral cortex. The 16-channel microelectrodes consisted of four penetrating shanks with four recording sites on each shank. The chronic electrode assembly included an integrated silicon ribbon cable and percutaneous connector. In a consecutive series of six rats, 5/6 (83%) of the implanted microelectrodes recorded neuronal spike activity for more than six weeks, with four of the implants (66%) remaining functional for more than 28 weeks. In each animal, more than 80% of the electrode sites recorded spike activity over sequential recording sessions during the postoperative time period. These results provide a performance baseline to support further electrode system development for intracortical neural implant systems for medical applications.

/pdf/silicon-substrate-intracortical-microelectrode-arrays-for-1bhey3eheh.pdf

Jamille Farraye Hetke

Papers

High-frequency network oscillation in the hippocampus.

Wireless implantable microsystems: high-density electronic interfaces to the nervous system

Surface modification of neural recording electrodes with conducting polymer/biomolecule blends

Chronic neural recording using silicon-substrate microelectrode arrays implanted in cerebral cortex

Silicon-substrate intracortical microelectrode arrays for long-term recording of neuronal spike activity in cerebral cortex