Multiplexed Surface Electrode Arrays Based on Metal Oxide Thin-Film Electronics for High-Resolution Cortical Mapping

Electrode grids are used in neuroscience research and clinical practice to record electrical activity from the surface of the brain. However, existing passive electrocorticography (ECoG) technologies are unable to offer both high spatial resolution and wide cortical coverage, while ensuring a compact acquisition system. The electrode count and density are restricted by the fact that each electrode must be individually wired. This work presents an active micro-electrocorticography (µECoG) implant that tackles this limitation by incorporating metal oxide thin-film transistors (TFTs) into a flexible electrode array, allowing to address multiple electrodes through a single shared readout line. By combining the array with an incremental-ΔΣ readout integrated circuit (ROIC), the system is capable of recording from up to 256 electrodes virtually simultaneously, thanks to the implemented 16:1 time-division multiplexing scheme, offering lower noise levels than existing active µECoG arrays. In vivo validation is demonstrated acutely in mice by recording spontaneous activity and somatosensory evoked potentials over a cortical surface of ≈8×8 mm2 . The proposed neural interface overcomes the wiring bottleneck limiting ECoG arrays, holding promise as a powerful tool for improved mapping of the cerebral cortex and as an enabling technology for future brain-machine interfaces.

Comparison of Speech Recognition and Hearing Preservation Outcomes Between the Mid-Scala and Lateral Wall Electrode Arrays

OBJECTIVE

To assess speech recognition and hearing preservation (HP) outcomes with the Advanced Bionics Mid-Scala and SlimJ electrodes.

STUDY DESIGN

Retrospective cohort.

SETTING

Tertiary referral center.

PATIENTS

A total of 237 adult patients implanted between 2013 and 2020 (Mid-Scala, n = 136; SlimJ, n = 101).

MAIN OUTCOME MEASURES

Consonant-nucleus-consonant (CNC) and AzBio (Arizona Biomedical) scores at 6 and 12 months; postoperative HP, defined as low-frequency pure-tone average ≤ 80 dB HL; scalar position.

RESULTS

Mean CNC scores did not significantly differ between Mid-Scala and SlimJ recipients at 6 (45.8% versus 46.0%, p = 0.962) and 12 (51.9% versus 48.8%, p = 0.363) months. Similarly, mean AzBio in quiet scores were equivalent for both groups at 6 (55.1% versus 59.2%, p = 0.334) and 12 (60.6% versus 62.3%, p = 0.684) months. HP rates were significantly higher with the SlimJ (48.4%) than the Mid-Scala (30.8%; p = 0.033). Scalar translocations were 34.8 and 16.1% for the Mid-Scala and SlimJ groups, respectively ( p = 0.019). Ears with postoperative HP had significantly fewer scalar translocations (16.7% versus 37.2%, p = 0.048), and postoperative HP was associated with higher AzBio in noise scores at the most recent follow-up interval (38.7% versus 25.1%, p = 0.042). CNC, AzBio in quiet and noise, low-frequency pure-tone average shifts, and PTA at 6 and 12 months were not significantly different between patients with scala tympani insertions of the SlimJ versus the Mid-Scala ( p > 0.05).

CONCLUSIONS

Compared with the Mid-Scala, the lateral wall electrode has superior HP rates and fewer scalar translocations, whereas speech recognition scores are equivalent between both electrode arrays. These findings can help providers with electrode selection and patient counseling.

Monitoring Gut Epithelium Serotonin and Melatonin Overflow Provides Spatial Mapping of Inflammation

Electrochemical arrays were used to measure the overflow of serotonin (5-HT) and melatonin (MEL) from the entire colon of healthy mice and mice with chemical-induced inflammatory bowel disease (IBD), to understand the interplay between inflammation and colonic function. We show that 5-HT overflow is increased, whilst MEL levels are reduced, in inflamed tissues. The levels of MEL are increased at the interface between healthy and inflamed regions within the colon and may limit the spread of inflammation. Understanding the interplay between inflammation and mucosal epithelial signalling can provide key insight into colonic function and aid the development of effective therapeutic strategies to treat gastrointestinal diseases.

Technical Note: Evaluation of methods for reducing edge current density under electrode arrays for tumor treating fields therapy

BACKGROUND

Tumor treating fields therapy is increasingly utilized clinically because of its demonstrated efficacy in cancer treatment. However, the risk of skin burns must still be reduced to improve patient safety and post-treatment quality of life.

PURPOSE

The purpose of this study was to evaluate methods of constructing electrode arrays that reduce current density exceeding threshold values, which can cause skin burns during tumor treating fields therapy.

METHODS

Electrode and body models were generated using COMSOL software. The body model had the dielectric properties of the scalp. The average current density beneath the central region of the electrode was maintained at ∼31 mA/cm² RMS. The deviations in current density at the edges of the electrode were reduced by three methods: adjustment of the ceramic thickness ratio of the center to the edge from 1/5 to 4/5, adjustment of the radius of the metal plate from 5.0 to 8.0 mm, and insertion of an insulator of width 0.5 to 2 mm at the edge.

RESULTS

When using a single circular electrode, adjustment of the ceramic thickness ratio, adjustment of the metal plate radius and insertion of an insulator near the edge reduced the deviations of current density by 14.6%, 67.7% and 75.3%, respectively. Similarly, when using circular electrode arrays, inserting an insulator at the edge of each electrode reduced the deviations of current density significantly, from 8.62 mA/cm² to 2.40 mA/cm² .

CONCLUSIONS

Insertion of an insulator at the edge of each electrode was found to be the most effective method of attaining uniform current density distribution beneath the electrode, thereby lowering the risk of adverse effects of tumor treating fields therapy. This article is protected by copyright. All rights reserved.

Interfacing Neurons with Nanostructured Electrodes Modulates Synaptic Circuit Features

Understanding neural physiopathology requires advances in nanotechnology-based interfaces, engineered to monitor the functional state of mammalian nervous cells. Such interfaces typically contain nanometer-size features for stimulation and recording as in cell-non-invasive extracellular microelectrode arrays. In such devices, it turns crucial to understand specific interactions of neural cells with physicochemical features of electrodes, which could be designed to optimize performance. Herein, versatile flexible nanostructured electrodes covered by arrays of metallic nanowires are fabricated and used to investigate the role of chemical composition and nanotopography on rat brain cells in vitro. By using Au and Ni as exemplary materials, nanostructure and chemical composition are demonstrated to play major roles in the interaction of neural cells with electrodes. Nanostructured devices are interfaced to rat embryonic cortical cells and postnatal hippocampal neurons forming synaptic circuits. It is shown that Au-based electrodes behave similarly to controls. Contrarily, Ni-based nanostructured electrodes increase cell survival, boost neuronal differentiation, and reduce glial cells with respect to flat counterparts. Nonetheless, Au-based electrodes perform superiorly compared to Ni-based ones. Under electrical stimulation, Au-based nanostructured substrates evoke intracellular calcium dynamics compatible with neural networks activation. These studies highlight the opportunity for these electrodes to excite a silent neural network by direct neuronal membranes depolarization.

Laser-Cut Polymer Tape Templates for Scalable Filtration Fabrication of User-Designed and Carbon-Nanomaterial-Based Electrochemical Sensors

We report here a simple filtration method for the scalable fabrication of user-designed and carbon-nanomaterial-based electrode arrays using laser-cut poly(vinyl chloride) (PVC) tape templates. This method can produce electrode arrays with high uniformity and low resistance from the dilute dispersions of single-walled carbon nanotubes (SWNTs) and graphene nanoplatelets (GNPs). For these two carbon arrays, the SWNT array is demonstrated to possess several interesting properties, e.g., good mechanical properties, excellent flexibility, and favorable electrochemical behavior. Moreover, its porous structure enables the construction of a paperlike solid-state electrochemical sensor using Nafion electrolytes, which is suitable for the on-site monitoring of trace phenol pollutants in electrolyte-free water. Besides, an electrochemically addressable 36-zone sensor was constructed by this method. With the aid of an inexpensive 3D printer, the addressable sensor can achieve the semiautomatic and high-throughput evaluation of antioxidant capacity on a series of vegetables and fruits using a single-channel electrochemical analyzer.

Neuronal Correlations in MT and MST Impair Population Decoding of Opposite Directions of Random Dot Motion

The study of neuronal responses to random-dot motion patterns has provided some of the most valuable insights into how the activity of neurons is related to perception. In the opposite directions of motion paradigm, the motion signal strength is decreased by manipulating the coherence of random dot patterns to examine how well the activity of single neurons represents the direction of motion. To extend this paradigm to populations of neurons, studies have used modelling based on data from pairs of neurons, but several important questions require further investigation with larger neuronal datasets. We recorded neuronal populations in the middle temporal (MT) and medial superior temporal (MST) areas of anaesthetized marmosets with electrode arrays, while varying the coherence of random dot patterns in two opposite directions of motion (left and right). Using the spike rates of simultaneously recorded neurons, we decoded the direction of motion at each level of coherence with linear classifiers. We found that the presence of correlations had a detrimental effect to decoding performance, but that learning the correlation structure produced better decoding performance compared to decoders that ignored the correlation structure. We also found that reducing motion coherence increased neuronal correlations, but decoders did not need to be optimized for each coherence level. Finally, we showed that decoder weights depend of left-right selectivity at 100% coherence, rather than the preferred direction. These results have implications for understanding how the information encoded by populations of neurons is affected by correlations in spiking activity.

A Ferroelectric Ceramic/Polymer Composite-Based Capacitive Electrode Array for In Vivo Recordings

A new implantable capacitive electrode array for electrocorticography signal recording is developed with ferroelectric ceramic/polymer composite. This ultrathin and electrically safe capacitive electrode array is capable of attaching to the biological tissue conformably. The barium titanate/polyimide (BaTiO₃ /PI) nanocomposite with high dielectric constant is successfully synthesized and employed as the ultrathin dielectric layer of the capacitive BaTiO₃ /PI electrode array. The performance of the capacitive BaTiO₃ /PI electrode array is evaluated by electrical characterization and 3D finite-element modeling. In vivo, neural experiments on the visual cortex of rats show the reliability of the capacitive BaTiO₃ /PI electrode array. This work shows the potentials of capacitive BaTiO₃ /PI electrode array in the field of brain/computer interfaces.

A New Semi-Automatic Approach to Find Suitable Virtual Electrodes in Arrays Using an Interpolation Strategy

Functional Electrical Stimulation via electrode arrays enables the user to form virtual electrodes (VEs) of dynamic shape, size, and position. We developed a feedback-control-assisted manual search strategy which allows the therapist to conveniently and continuously modify VEs to find a good stimulation area. This works for applications in which the desired movement consists of at least two degrees of freedom. The virtual electrode can be moved to arbitrary locations within the array, and each involved element is stimulated with an individual intensity. Meanwhile, the applied global stimulation intensity is controlled automatically to meet a predefined angle for one degree of freedom. This enables the therapist to concentrate on the remaining degree(s) of freedom while changing the VE position. This feedback-control-assisted approach aims to integrate the user’s opinion and the patient’s sensation. Therefore, our method bridges the gap between manual search and fully automatic identification procedures for array electrodes. Measurements in four healthy volunteers were performed to demonstrate the usefulness of our concept, using a 24-element array to generate wrist and hand extension.

Vertical Nanowire Electrode Arrays as Novel Electrochemical Label-Free Immunosensors

A new method for the fabrication of a label-free electrochemical immunosensor based on vertical nanowires (VNWs) is proposed. The VNWs are functionalized to detect antibodies against a major astrocytic structural protein component, glial fibrillary acidic protein (GFAP). It is revealed that the interaction of GFAP-antibody with functionalized VNWs leads to a clear change in device conductance and the corresponding capacitance.

MANTA--an open-source, high density electrophysiology recording suite for MATLAB

The distributed nature of nervous systems makes it necessary to record from a large number of sites in order to decipher the neural code, whether single cell, local field potential (LFP), micro-electrocorticograms (μECoG), electroencephalographic (EEG), magnetoencephalographic (MEG) or in vitro micro-electrode array (MEA) data are considered. High channel-count recordings also optimize the yield of a preparation and the efficiency of time invested by the researcher. Currently, data acquisition (DAQ) systems with high channel counts (>100) can be purchased from a limited number of companies at considerable prices. These systems are typically closed-source and thus prohibit custom extensions or improvements by end users. We have developed MANTA, an open-source MATLAB-based DAQ system, as an alternative to existing options. MANTA combines high channel counts (up to 1440 channels/PC), usage of analog or digital headstages, low per channel cost (<$90/channel), feature-rich display and filtering, a user-friendly interface, and a modular design permitting easy addition of new features. MANTA is licensed under the GPL and free of charge. The system has been tested by daily use in multiple setups for >1 year, recording reliably from 128 channels. It offers a growing list of features, including integrated spike sorting, PSTH and CSD display and fully customizable electrode array geometry (including 3D arrays), some of which are not available in commercial systems. MANTA runs on a typical PC and communicates via TCP/IP and can thus be easily integrated with existing stimulus generation/control systems in a lab at a fraction of the cost of commercial systems. With modern neuroscience developing rapidly, MANTA provides a flexible platform that can be rapidly adapted to the needs of new analyses and questions. Being open-source, the development of MANTA can outpace commercial solutions in functionality, while maintaining a low price-point.

A Novel Method of Fabricating Convoluted Shaped Electrode Arrays for Neural and Retinal Prostheses

A novel fabrication technique has been developed for creating high density (6.25 electrodes/mm(2)), out of plane, high aspect ratio silicon-based convoluted microelectrode arrays for neural and retinal prostheses. The convoluted shape of the surface defined by the tips of the electrodes could compliment the curved surfaces of peripheral nerves and the cortex, and in the case of retina, its spherical geometry. The geometry of these electrode arrays has the potential to facilitate implantation in the nerve fascicles and to physically stabilize it against displacement after insertion. This report presents a unique combination of variable depth dicing and wet isotropic etching for the fabrication of a variety of convoluted neural array geometries. Also, a method of deinsulating the electrode tips using photoresist as a mask and the limitations of this technique on uniformity are discussed.