Showing papers on "Electrode array published in 2021"

Intraoperative Impedance-Based Estimation of Cochlear Implant Electrode Array Insertion Depth

Abstract: Objective: Cochlear implant impedances are influenced by the intracochlear position of the electrodes. Herein, we present an intuitive approach to calculate tissue resistances from transimpedance recordings, ultimately enabling to estimate the insertion depth of cochlear implant electrodes. Methods: Electrode positions were measured in computed-tomography images of 20 subjects implanted with the same lateral wall cochlear implant model. The tissue resistances were estimated from intraoperative telemetry data using bivariate spline extrapolation from the transimpedance recordings. Using a phenomenological model, the electrode insertion depths were estimated. Results: The proposed method enabled the linear insertion depth of all electrodes to be estimated with an average error of 0.76 $\pm$ 0.53 mm. Conclusion: Intraoperative telemetry recordings correlate with the linear and angular depth of electrode insertion, enabling estimations with an accuracy that can be useful for clinical applications. Significance: The proposed method can be used to objectively assess surgical outcomes during and after cochlear implantation based on non-invasive and readily available telemetry recordings.

Robot-assisted Cochlear Implant Electrode Array Insertion in Adults: A Comparative Study With Manual Insertion.

Abstract: OBJECTIVE To describe the first cochlear array insertions using a robot-assisted technique, with different types of straight or precurved electrode arrays, compared with arrays manually inserted into the cochlea. STUDY DESIGN Retrospective review. SETTING Tertiary otologic center. PATIENTS Twenty cochlear implantations in the robot-assisted group and 40 in the manually inserted group. INTERVENTIONS Cochlear implantations using a robot-assisted technique (RobOtol) with straight (eight Cochlear CI522/622, and eight Advanced Bionics Hifocus Slim J) or precurved (four Advanced Bionics Hifocus Mid-Scala) matched to manual cochlear implantations. Three-dimensional reconstruction images of the basilar membrane and the electrode array were obtained from pre- and postimplantation computed tomography. MAIN OUTCOME MEASURES Rate and localization of scalar translocations. RESULTS For straight electrode arrays, scalar translocations occurred in 19% (3/16) of the robot-assisted group and 31% (10/32) of the manually inserted group. Considering the number of translocated electrodes, this was lower in the robot-assisted group (7%) than in the manually inserted group (16%) (p < 0.0001, χ2 test). For precurved electrode arrays, scalar translocations occurred in 50% (2/4) of the robot-assisted group and 38% (3/8) of the manually inserted group. CONCLUSION This study showed a safe and reliable insertion of different electrode array types with a robot-assisted technique, with a less traumatic robotic insertion of straight electrode arrays when compared with manual insertion.

Electrode Materials for Chronic Electrical Microstimulation

Abstract: Electrical microstimulation has enabled partial restoration of vision, hearing, movement, somatosensation, as well as improving organ functions by electrically modulating neural activities. However, chronic microstimulation is faced with numerous challenges. The implantation of an electrode array into the neural tissue triggers an inflammatory response, which can be exacerbated by the delivery of electrical currents. Meanwhile, prolonged stimulation may lead to electrode material degradation., which can be accelerated by the hostile inflammatory environment. Both material degradation and adverse tissue reactions can compromise stimulation performance over time. For stable chronic electrical stimulation, an ideal microelectrode must present 1) high charge injection limit, to efficiently deliver charge without exceeding safety limits for both tissue and electrodes, 2) small size, to gain high spatial selectivity, 3) excellent biocompatibility that ensures tissue health immediately next to the device, and 4) stable in vivo electrochemical properties over the application period. In this review, the challenges in chronic microstimulation are described in detail. To aid material scientists interested in neural stimulation research, the in vitro and in vivo testing methods are introduced for assessing stimulation functionality and longevity and a detailed overview of recent advances in electrode material research and device fabrication for improving chronic microstimulation performance is provided.

In-Vitro Study of Speed and Alignment Angle in Cochlear Implant Electrode Array Insertions.

Abstract: Objective: The insertion of the electrode array is a critical step in cochlear implantation. Herein we comprehensively investigate the impact of the alignment angle and feed-forward speed on deep insertions in artificial scala tympani models with accurate macro-anatomy and controlled frictional properties. Methods: Motorized insertions (n=1033) were performed in six scala tympani models with varying speeds and alignment angles. We evaluated reaction forces and micrographs of the insertion process and developed a mathematical model to estimate the normal force distribution along the electrode arrays. Results: Insertions parallel to the cochlear base significantly reduce insertion energies and lead to smoother array movement. Non-constant insertion speeds allow to reduce insertion forces for a fixed total insertion time compared to a constant feed rate. Conclusion: In cochlear implantation, smoothness and peak forces can be reduced with alignment angles parallel to the scala tympani centerline and with non-constant feed-forward speed profiles. Significance: Our results may help to provide clinical guidelines and improve surgical tools for manual and automated cochlear implantation.

Transimpedance Matrix (TIM) Measurement for the Detection of Intraoperative Electrode Tip Foldover Using the Slim Modiolar Electrode: A Proof of Concept Study.

Abstract: Objectives The aim of this study is to report on our preliminary experience with Transimpedance Matrix (TIM)-measurement for the detection of cochlear implant electrode tip foldovers compared with intraoperative imaging in patients implanted with the slim modiolar electrode (SME). Study design Proof of concept study. Setting Tertiary university referral center. Patients Twenty five ears (in 22 patients) implanted consecutively with the SME. Intervention(s) Following cochlear implantation, intraoperative TIM-measurement and fluoroscopy were performed. One week postoperatively, the electrode position was evaluated using Computed Tomography (CT)-imaging. Main outcome measures Electrode array tip foldover. Results Electrode array tip foldover occurred in three of the 25 cochlear implantations performed (12%). In each case, the foldover was detected by both TIM and fluoroscopy, leading to reposition and correct intracochlear placement of the array. Conclusions TIM-measurement is a promising method for the intraoperative detection of an electrode array tip foldover. The TIM-tool with intuitive heatmap display is easy to use, fast, and readily available to clinics using TIM-software in the operating theatre.

Highly Stretchable Metal–Polymer Conductor Electrode Array for Electrophysiology

Abstract: Narrowing the mechanical mismatch between biological tissues (typically soft) and neural interfaces (hard) is essential for maintaining signal quality for the electrical recording of neural activity. However, only a few materials can satisfy all requirements for such electronics, which need to be both biocompatible and sufficiently soft. Here, a highly stretchable electrode array (SEA) is introduced, based on the liquid metal-polymer conductor (MPC), achieving high mechanical flexibility and good cytocompatability for neural interfaces. By utilizing the MPC, the SEA exhibits high stretchability (≈100%) and excellent cycling stability (>400 cycles). The cytocompatability of the SEA can allow for long-term culturing of primary neurons and enable signal recording of primary hippocampal neurons. In the future, the SEA could serve as a reliable and robust platform for diagnostics in neuronal tissues and greatly advance brain-machine interfaces.

Vertical Nanowire Electrode Array for Enhanced Neurogenesis of Human Neural Stem Cells via Intracellular Electrical Stimulation.

Abstract: Extracellular electrical stimulation (ES) can provide electrical potential from outside the cell membrane, but it is often ineffective due to interference from external factors such as culture medium resistance and membrane capacitance. To address this, we developed a vertical nanowire electrode array (VNEA) to directly provide intracellular electrical potential and current to cells through nanoelectrodes. Using this approach, the cell membrane resistivity and capacitance could be excluded, allowing effective ES. Human fetal neural stem cells (hfNSCs) were cultured on the VNEA for intracellular ES. Combining the structural properties of VNEA and VNEA-mediated ES, transient nanoscale perforation of the electrode was induced, promoting cell penetration and delivering current to the cell. Intracellular ES using VNEA improved the neuronal differentiation of hfNSCs more effectively than extracellular ES and facilitated electrophysiological functional maturation of hfNSCs because of the enhanced voltage-dependent ion-channel activity. The results demonstrate that VNEA with advanced nanoelectrodes serves as a highly effective culture and stimulation platform for stem-cell neurogenesis.

Microparticle transport along a planar electrode array using moving dielectrophoresis.

Abstract: We present a device that can achieve controlled transport of colloidal microparticles using an array of micro-electrodes. By exciting the micro-electrodes in regular sequence with an AC voltage, a time-varying moving dielectrophoretic force-field is created. This force propels colloidal microparticles along the electrode array. Using this method, we demonstrate bidirectional transport of polystyrene micro-spheres. Electromagnetic simulation of the device is performed, and the dielectrophoretic force profile around the electrode array is mapped. We develop a Brownian dynamics model of the trajectory of a particle under the influence of the time-varying force-field. Numerical and experimental results showing controlled particle transport are presented. The numerical model is found to be in good agreement with experimental data. The developed numerical framework can be useful in designing and modeling lab-on-a-chip devices that employ external non-contact forces for micro-/nanoparticle manipulation.

Patch-clamp and multi-electrode array electrophysiological analysis in acute mouse brain slices

Abstract: Summary Patch-clamp and multi-electrode array electrophysiology techniques are used to measure dynamic functional properties of neurons. Whole-cell and cell-attached patch-clamp recordings in brain slices can be performed in voltage-clamp and current-clamp configuration to reveal cell-type-specific synaptic and cellular parameters governing neurotransmission. Multi-electrode array electrophysiology can provide spike activity recordings from multiple neurons, enabling larger sample sizes, and long-term recordings. We provide our guide to preparing acute rodent brain slices with example experiments and analyses intended for novice and expert electrophysiologists. For complete details on the use and execution of this protocol, please refer to Manz et al. (2020b) .

Detection of Translocation of Cochlear Implant Electrode Arrays by Intracochlear Impedance Measurements.

Abstract: OBJECTIVES Misplacement of the electrode array is associated with impaired speech perception in patients with cochlear implants (CIs). Translocation of the electrode array is the most common misplacement. When a CI is translocated, it crosses the basilar membrane from the scala tympani into the scala vestibuli. The position of the implant can be determined on a postoperative CT scan. However, such a scan is not obtained routinely after CI insertion in many hospitals, due to radiation exposure and processing time. Previous studies have shown that impedance measures might provide information on the placement of the electrode arrays. The electrode impedance was measured by dividing the plateau voltage at the end of the first phase of the pulse by the injected current. The access resistance was calculated using the so-called access voltage at the first sampled time point after the start of the pulse divided by the injected current. In our study, we obtained the electrode impedance and the access resistance to detect electrode translocations using electrical field imaging. We have investigated how reliably these two measurements can detect electrode translocation, and which method performed best. DESIGN We calculated the electrode impedances and access resistances using electrical field imaging recordings from 100 HiFocus Mid-Scala CI (Advanced Bionics, Sylmar, CA) recipients. We estimated the normal values of these two measurements as the baselines of the implant placed in the cochlea without translocation. Next, we calculated the maximal electrode impedance deviation and the maximal access-resistance deviation from the respective baselines as predictors of translocation. We classified these two predictors as translocations or nontranslocations based on the bootstrap sampling method and receiver operating characteristics curves analysis. The accuracy could be calculated by comparing those predictive results to a gold standard, namely the clinical CT scans. To determine which measurement more accurately detected translocation, the difference between the accuracies of the two measurements was calculated. RESULTS Using the bootstrap sampling method and receiver operating characteristics-based optimized threshold criteria, the 95% confidence intervals of the accuracies of translocation detections ranged from 77.8% to 82.1% and from 89.5% to 91.2% for the electrode impedance and access resistance, respectively. The accuracies of the maximal access-resistance deviations were significantly larger than that of the maximal electrode impedance deviations. The location of the translocation as predicted by the access resistance was significantly correlated with the result derived from the CT scans. In contrast, no significant correlation was observed for the electrode impedance. CONCLUSIONS Both the electrode impedance and access resistance proved reliable metrics to detect translocations for HiFocus Mid-Scala electrode arrays. The access resistance had, however, significantly better accuracy and it also reliably detected the electrode-location of translocations. The electrode impedance did not correlate significantly with the location of translocation. Measuring the access resistance is, therefore, the recommended method to detect electrode-array translocations. These measures can provide prompt feedback for surgeons after insertion, improving their surgical skills, and ultimately reducing the number of translocations. In the future, such measurements may allow near-real-time monitoring of the electrode array during insertion, helping to avoid translocations.

Steering of target poles in an electrode array in a pulse generator system

Abstract: Techniques for steering of target poles formed by implantable electrodes in a stimulator device are disclosed. The steering technique modifies the relative amplitude of target poles once they are steered to an electrode array boundary. Once a target pole is steered to an electrode array boundary, further steering in the direction of that boundary results in a gradual decrease in the relative amplitude of that target pole. Eventually, continued steering in that direction will cause that target pole to disappear. Thus, in the case of a target tripole, continued steering will eventually cause the target tripole to be automatically converted into a target bipole. In another example of steering, target poles defined linearly in one direction can be split in an orthogonal direction to create a target pole configuration that is two-dimensional.

Flexible Tactile Sensor Based on Patterned Ag-Nanofiber Electrodes through Electrospinning.

Abstract: The growing demand for intelligent equipment has greatly inspired the development of flexible devices. Thus, disparate flexible multifunctional devices, including pressure sensitive flexible/stretchable displays, have drawn worldwide research attention. Electrodes maintaining conductivity and mechanical strength against deformations are indispensable components in all prospective applications. In this work, a flexible pressure mapping sensor array is developed based on patterned Ag-nanofibers (Ag-NFs) electrode through electrospinning and lithography. The metallic Ag layer is sputtered onto the electrospinning polyvinyl alcohol (PVA) NFs. A uniform and super conductive electrode layer with outstanding mechanical performance is thus formed after dissolving PVA. Followed by the traditional lithography method, a patterned electrode array (4 × 4 sensors) is obtained. Based on the newly developed triboelectric nanogenerator (TENG) technology, a flexible pressure-mapping sensor with excellent stability towards bending deformations is further demonstrated. Moreover, a letter "Z" is successfully visualized by this pressure sensor array, encouraging more human-machine interactive implementations, such as multi-functional tactile screens.

The Use of a Robot to Insert an Electrode Array of Cochlear Implants in the Cochlea: A Feasibility Study and Preliminary Results.

Abstract: Introduction Cochlear implants (CIs) are commonly used for the rehabilitation of profound bilateral hearing loss. However, patients with substantial residual acoustic hearing are potential CI candidates. Because of both improvements in technology and advancements in surgical techniques, it may be possible to preserve hearing to some extent. For more than a decade, it has been suggested that robots are used to perform middle ear surgery. We evaluated the use of the RobOtol® otologic robot specifically to insert CI electrodes into the inner ear. Methods CI surgery with the conventional approach was performed under general anesthesia. The MED-El Flex 24-electrode array was inserted using RobOtol®. Video recordings were used to calculate the speed of insertion. The positions of the electrodes were evaluated using a cone beam CT. All subjects underwent pure-tone audiometry tests before and after surgery, and the pure-tone average (PTA) was calculated from 250 to 4,000 Hz. Results The robot inserted implants in 5 patients, and complete insertion of the electrode array was achieved. The speed of insertion of the electrode array was 0.88 ± 0.12 mm/s. The mean loss of the PTA for 5 frequencies (250, 500, 1,000, 2,000, and 4,000 Hz) was 13.60 ± 7.70 dB. Only 1 patient showed a loss of the PTA by >20 dB. For these 5 patients, the cone beam CT findings showed that all the electrode arrays were in the tympanic ramp and had a grade of 0. The results were compared with those obtained from a cohort of 17 patients who underwent manual implantation of a MED-El Flex 24-electrode array. Conclusion To minimize disturbance to the cochlea while atraumatic electrode arrays are inserted, electrodes can be inserted at a constant, slow speed in the inner ear with the assistance of the RobOtol® robot in a normal clinical surgical setting.

Towards Improving the Quality of Electrophysiological Signal Recordings by Using Microneedle Electrode Arrays

Abstract: Objective: Electrophysiological signals are recorded generally by metal electrodes placed on body surface. For long term use, the signal quality may decay with the change of interface impedance between electrodes and skin due to the conductive hydrogel dehydration. Besides, electrodes may shift during body movements, which causes unstable signal recordings. Methods: To improve the quality of electrophysiological signal recordings on human body surface, a type of microneedle electrode array (MEA) with microneedles around 550 μm in length was fabricated with a magnetization-induce self-assembly method. Results: Compared with the commonly used dry electrode array, the MEA has lower and more stable interface impedance, especially when the electrode-skin interface is under unstable pressures. For electrophysiological signal recording, the MEA can acquire electromyography (EMG) with significantly lower noise energy, higher signal-to-noise ratio, and higher motion-classification accuracy based on the EMG pattern-recognition method. Additionally, high quality electrocardiography (ECG) can be recorded by using the MEA, where more accurate R-peaks are extracted in different scenarios. Besides, there was no report about any discomfort like bleeding or inflammation by all the subjects. Conclusion: This research proved that the microneedles on the MEA can penetrate through the corneum and reach the epidermis of the subjects, which could avoid the influence of corneum and fix the electrode on the body surface for high-quality signal recording especially during body movements. Furthermore, the microneedles would not touch the dermis, enabling a painless signal acquisition. Significance: This work is beneficial to the applications of wearable human-machine interface technology.

Atraumatic Insertion of a Cochlear Implant Pre-Curved Electrode Array by a Robot-Automated Alignment with the Coiling Direction of the Scala Tympani.

Abstract: Introduction Electrode array translocation is an unpredictable event with all types of arrays, even using a teleoperated robot in a clinical scenario. We aimed to compare the intracochlear trauma produced by the HiFocus™ Mid-Scala (MS) electrode array (Advanced Bionics, Valencia, CA, USA) using a teleoperated robot, with an automated robot connected to a navigation system to align the pre-curved tip of the electrode array with the coiling direction of the scala tympani (ST). Methods Fifteen freshly frozen temporal bones were implanted with the MS array using the RobOtol® (Collin, Bagneux, France). In the first group (n = 10), the robot was teleoperated to insert the electrode array into the basal turn of the ST under stereomicroscopic vision, and then the array was driven by a slow-speed hydraulic insertion technique with an estimated placement of the pre-curved electrode tip. In the second group (n = 5), 3 points were obtained from the preoperative cone-beam computed tomography: the 2 first defining the ST insertion axis of the basal turn and a third one at the center of the ST at 270°. They provided the information to the automated system (RobOtol® connected with a navigation system) to automatically align the electrode array with the ST insertion axis and to aim the pre-curved tip toward the subsequent coiling of the ST. After this, the electrode array was manually advanced. Finally, the cochleae were obtained and fixed in a crystal resin, and the position of each electrode was determined by a micro-grinding technique. Results In all cases, the electrode array was fully inserted into the cochlea and the depth of insertion was similar using both techniques. With the teleoperated robotic technique, translocations of the array were observed in 7/10 insertions (70%), but neither trauma nor array translocation occurred with automated robotic insertion. Conclusion We have successfully tested an automated insertion system (robot + navigation) that could accurately align a pre-curved electrode array to the axis of the basal turn of the ST and its subsequent coiling, which reduced intracochlear insertion trauma and translocation.

A 30-MHz, 3-D Imaging, Forward-Looking Miniature Endoscope Based on a 128-Element Relaxor Array

Abstract: This work describes the design, fabrication, and characterization of a 128-element crossed electrode array in a miniature endoscopic form factor for real-time 3-D imaging. Crossed electrode arrays address some of the key challenges surrounding probe fabrication for 3-D ultrasound imaging by reducing the number of elements required (2N compared with N2). However, there remain practical challenges in packaging a high-frequency crossed electrode array into an endoscopic form factor. A process has been developed that uses a thinly diced strip of flex circuit to bring the back-side connections to common bond surface, which allows the final size of the endoscope to measure only ${6}\,\,\text {mm} \times {5}$ mm. An electrostrictive ceramic composite design was developed for the crossed electrode array. A laser dicing system was used to cut the 1–3 composite as well as etch the array electrode pattern. A single quarter wavelength Parylene matching layer made was vacuum deposited to finish the array. The electrical impedance magnitude of array elements on resonance was measured to be $49~\Omega $ with a phase angle of −55.5°. The finished array elements produced pulses with −6-dB two-way bandwidth of 60% with a 34-MHz center frequency. The average measured electrical crosstalk on the nearest neighboring element and next to nearest neighboring element was −37 and −29 dB, respectively. One- and two-way pulse measurements were completed to confirm the pulse polarity and fast switching speed. Preliminary 3-D images were generated of a wire phantom using the previously described simultaneous azimuth and Fresnel elevation (SAFE) compounding imaging technique.

On the Intracochlear Location of Straight Electrode Arrays After Cochlear Implantation: How Lateral Are Lateral Wall Electrodes?

Abstract: Objective Cochlear implants are the gold standard for patients with severe sensorineural hearing loss. A focused electrical stimulation of individual spiral ganglion neurons has not been achieved yet because the scala tympani is a fluid-filled compartment and does not offer a matrix for neuritic outgrowth. Coating of the electrode contacts with swelling hydrogels could fill that gap between the electrode array and the medial wall of the cochlea. Therefore, the exact position of the electrode array within the scala tympani has to be known. Study design Retrospective analysis of patient data sets. Setting Tertiary referral center. A total of 95 patients with cochlear implants from one manufacturer were included in this study. The lateral wall, the modiolar wall, and the cochlear implant electrode were segmented using OsiriX MD. For repositioning and reconstructing the respective contours and measuring distances, files were analyzed in MATLAB. The distances from the edge of each electrode contact to the cochlear walls showed no significant differences. But between the different contacts within each patient, there were significant differences. Around 180 degree insertion, electrodes start to get in contact with the lateral wall. The tip of the electrode array was always facing toward the modiolar wall independent of the length of the electrode. We established a method to analyze the position of electrodes within the cochlea.

Hearing rehabilitation after subtotal cochleoectomy using a new, perimodiolar malleable cochlear implant electrode array: a preliminary report

Abstract: We here report about the first surgical experience and audiological outcome using a new, perimodiolar malleable cochlear implant electrode array for hearing rehabilitation after subtotal cochleoectomy for intralabyrinthine schwannoma (ILS). Based on a cochlear implant with MRI compatibility of the magnet in the receiver coil up to 3 T, a cochlear implant electrode array was developed that is malleable and can be placed perimodiolar after tumor removal from the cochlea via subtotal cochleoectomy. Malleability was reached by incorporating a nitinol wire into the silicone of the electrode array lateral to the electrode contacts. The custom-made device was implanted in four patients with intracochlear, intravestibulocochlear or transmodiolar schwannomas. Outcome was assessed by evaluating the feasibility of the surgical procedure and by measuring sound field thresholds and word recognition scores. After complete or partial tumor removal via subtotal cochleoectomy with or without labyrinthectomy, the new, perimodiolar malleable electrode array could successfully be implanted in all four patients. Six months after surgery, the averaged sound field thresholds to pulsed narrowband noise in the four patients were 36, 28, 41, and 35 dB HL, and the word recognitions scores for monosyllables at 65 dB SPL were 65, 80, 70, and 25% (one patient non-German speaking). The surgical evaluation demonstrated the feasibility of cochlear implantation with the new, perimodiolar malleable electrode array after subtotal cochleoectomy. The audiological results were comparable to those achieved with another commercially available type of perimodiolar electrode array from a different manufacturer applied in patients with ILS.

Graphene-electrode array for brain map remodeling of the cortical surface

Abstract: Cortical maps, which are indicative of cognitive status, are shaped by the organism’s experience. Previous mapping tools, such as penetrating electrodes and imaging techniques, are limited in their ability to be used to assess high-resolution brain maps largely owing to their invasiveness and poor spatiotemporal resolution, respectively. In this study, we developed a flexible graphene-based multichannel electrode array for electrocorticography (ECoG) recording, which enabled us to assess cortical maps in a time- and labor-efficient manner. The flexible electrode array, formed by chemical vapor deposition (CVD)-grown graphene, provided low impedance and electrical noise because a good interface between the graphene and brain tissue was created, which improved the detectability of neural signals. Furthermore, cortical map remodeling was induced upon electrical stimulation at the cortical surface through a subset of graphene spots. This result demonstrated the macroscale plasticity of cortical maps, suggesting perceptual enhancement via electrical rehabilitation at the cortical surface. The spatial organization of neural networks representing sensorimotor behavior and cognition has been mapped by flexible devices placed on the cortex, the outer layer of the brain. Sensory messages from each part of the body are processed in a specific area in the brain and maps of the cortex can help understand these areas. A person’s cortical map is shaped by their early development and experiences. Study of such maps can help identify and treat sensory disorders. Existing techniques for brain mapping require placement of penetrating electrodes which is time-consuming and risks brain damage. Minseok Lee from City University of Hong Kong and colleagues made arrays of electrodes using graphene membranes and constructed sensory maps of rats and mice by placing these arrays directly on the cortical surface. The timely and continuous measurement of cortical maps is required for studying the nature and plasticity of brain maps. In this work, we developed the multichannel graphene array that enables high-resolution brain mapping, facilitating rapid and repetitive assessments of brain maps. The advanced graphene array with intervening thru-hole enables large-scale mapping simultaneously in the surface and deep of cortical areas, also improving conformality for better detection of electrocorticography signals. In a subset of the graphene array, cortical surface stimulation can remodel cortical maps, therein enhancing cortical plasticity. This technology provides potential therapeutic applications for various brain disorders by correcting brain maps.

Characterizing the short-latency evoked response to intracortical microstimulation across a multi-electrode array

Abstract: Objective: Persons with tetraplegia can use brain-machine interfaces to make visually guided reaches with robotic arms. Without somatosensory feedback, these movements will likely be slow and imprecise, like those of persons who retain movement but have lost proprioception. Intracortical microstimulation (ICMS) has promise for providing artificial somatosensory feedback. If ICMS can mimic naturally occurring neural activity, afferent interfaces may be more informative and easier to learn than interfaces that evoke unnaturalistic activity. To develop such biomimetic stimulation patterns, it is important to characterize the responses of neurons to ICMS. Approach: Using a Utah multi-electrode array, we recorded activity evoked by single pulses, and short (~0.2 s) and long (~4 s) trains of ICMS at a wide range of amplitudes and frequencies. As the electrical artifact caused by ICMS typically prevents recording for many milliseconds, we deployed a custom rapid-recovery amplifier with nonlinear gain to limit signal saturation on the stimulated electrode. Across all electrodes after stimulation, we removed the remaining slow return to baseline with acausal high-pass filtering of time-reversed recordings. With these techniques, we could record ~0.7 ms after stimulation offset even on the stimulated electrode. Main results: We recorded likely transsynaptically-evoked activity as early as ~0.7 ms after single pulses of stimulation that was immediately followed by suppressed neural activity lasting 10-150 ms. Instead of this long-lasting inhibition, neurons increased their firing rates for ~100 ms after trains. During long trains, the evoked response on the stimulated electrode decayed rapidly while the response was maintained on non-stimulated channels. Significance: The detailed description of the spatial and temporal response to ICMS can be used to better interpret results from experiments that probe circuit connectivity or function of cortical areas. These results can also contribute to the design of stimulation patterns to improve afferent interfaces for artificial sensory feedback.

Crosstalk in Polymer Microelectrode Arrays.

Abstract: Thin-film polymer microelectrode arrays (MEAs) facilitate the high-resolution neural recording with its superior mechanical compliance. However, the densely packed electrodes and interconnects along with the ultra-thin polymeric encapsulation/substrate layers give rise to non-negligible crosstalk, which could result in severe interference in the neural signal recording. Due to the lack of standardized characterization or modeling of crosstalk in neural electrode arrays, to date, crosstalk in polymer MEAs remains poorly understood. In this work, the crosstalk between two adjacent polymer microelectrodes is measured experimentally and modeled using equivalent circuits. Importantly, this study demonstrated a two-well measuring platform and systematically characterized the crosstalk in polymer microelectrodes with true isolation of the victim channel and precise control of its grounding condition. A simple, unified equation from detailed circuit modeling was proposed to calculate the crosstalk in different environments. Finite element analysis (FEA) analysis was conducted further to explore the crosstalk in more aggressively scaled polymer electrode threads. In addition to standardizing neural electrode array crosstalk characterization, this study not only reveals the dependence of the crosstalk in polymer MEAs on a variety of key device parameters but also provides general guidelines for the design of thin polymer MEAs for high-quality neural signal recording.

Is the spread of excitation width correlated to the speech recognition in cochlear implant users

Abstract: To assess whether there is an interference of the spread of excitation (SOE) on speech recognition. Retrospective cross-sectional study, approved by the institution’s ethics committee (CAAE03409212.8.0000.0068). Adult patients with intraoperative neural response telemetry (NRT) performed on electrodes 6, 11 and 16 implanted with Cochlear Ltd (Sydney, Australia) devices were selected. Patients with partial array insertion, pre-lingual hearing loss, deafness etiology due to and CI experience less than 12 months were excluded. SOE was recorded at 10 current units above the NRT threshold (tNRT) and its width in millimeters was collected at point 0.75 of the function. Speech recognition test was 25-recorded monosyllables list, presented at 65 dBHL at 0° azimuth in a sound treated booth. The analysis was divided into groups by electrode array type, regarding the tNRT, SOE width, SOE’s peak amplitude and electrode peak. A 126 SOE measurements of the 3 tested electrodes were obtained from 43 patients. Patients with straight array had significantly wider SOE, greater peak amplitude at electrode 6 and higher tNRTs. In the perimodiolar array, there was a negative correlation between SOE and monosyllables recognition at electrodes 6 and 11, and in the combined average of the three electrodes, with a significant difference in electrode 11. Sixty-six percent of the SOE measurements had their peak shifted to adjacent electrodes. It was observed, in perimodiolar array, the greater the dispersion of electrical current, the worse the speech recognition, especially in the medial electrode.

A minimally invasive flexible electrode array for simultaneous recording of ECoG signals from multiple brain regions.

Abstract: The minimal invasiveness of electrocorticography (ECoG) enabled its widespread use in clinical areas as well as in neuroscience research. However, most existing ECoG arrays require that the entire surface area of the brain that is to be recorded be exposed through a large craniotomy. We propose a device that overcomes this limitation, i.e., a minimally invasive, polyimide-based flexible array of electrodes that can enable the recording of ECoG signals in multiple regions of the brain with minimal exposure of the surface of the brain. Magnetic force-assisted positioning of a flexible electrode array enables recording from distant brain regions with a small cranial window. Also, a biodegradable organic compound used for attaching a magnet on the electrodes allows simple retrieval of the magnet. We demonstrate with an in vivo chronic recording that an implanted ECoG electrode array can record ECoG signals from the visual cortex and the motor cortex during a rat's free behavior. Our results indicate that the proposed device induced minimal damage to the animal. We expect the proposed device to be utilized for experiments for large-scale brain circuit analyses as well as clinical applications for intra-operative monitoring of epileptic activity.

Design and 3D modeling investigation of a microfluidic electrode array for electrical impedance measurement of single yeast cells.

Abstract: High-resolution microscopic imaging may cause intensive image processing and potential impact of light irradiation on yeast replicative lifespan (RLS). Electrical impedance spectroscopy (EIS) could be alternatively used to perform high-throughput and label-free yeast RLS assays. Prior to fabricating EIS-integrated microfluidic devices for yeast RLS determination, systematic modeling and theoretical investigation are crucial for device design and optimization. Here, we report three-dimensional (3D) finite-element modeling and simulations of EIS measurement in a microfluidic single yeast in situ impedance array (SYIIA), which is designed by patterning an electrode matrix underneath a cell-trapping array. SYIIA was instantiated and modeled as a 5 × 5 sensing array comprising 25 units for cell immobilization, culturing, and time-lapse EIS recording. Simulations of yeast growing and budding in a sensing unit demonstrated that EIS signals enable the characterization of cell growth and daughter-cell dissections. In the 5 × 5 sensing array, simulation results indicated that when monitoring a target cell, daughter dissections in its surrounding traps may induce variations of the recorded EIS signals, which could cause mistakes in identifying target daughter-cell dissections. To eliminate the mis-identifications, electrode array pitch was optimized. Therefore, the results could conduct the design and optimization of microfluidic electrode-array-integrated devices for high-throughput and accurate yeast RLS assays.