ECoG Electrodes Research Articles

Flexible, high-density, laminated ECoG electrode array for high spatiotemporal resolution foci diagnostic localization of refractory epilepsy

Flexible, high-density, laminated ECoG electrode array for high spatiotemporal resolution foci diagnostic localization of refractory epilepsy

Using fMRI to localize target regions for implanted brain-computer interfaces in locked-in syndrome

ObjectiveElectrocorticography (ECoG)-based brain-computer interface (BCI) systems have the potential to improve quality of life of people with locked-in syndrome (LIS) by restoring their ability to communicate independently. Before implantation of such a system, it is important to localize ECoG electrode target regions. Here, we assessed the predictive value of functional magnetic resonance imaging (fMRI) for the localization of suitable target regions on the sensorimotor cortex for ECoG-based BCI in people with locked-in syndrome. MethodsThree people with locked-in syndrome were implanted with a chronic, fully implantable ECoG-BCI system. We compared pre-surgical fMRI activity with post-implantation ECoG activity from areas known to be active and inactive during attempted hand movement (sensorimotor hand region and dorsolateral prefrontal cortex, respectively). ResultsResults showed a spatial match between fMRI activity and changes in ECoG low and high frequency band power (10 – 30 and 65 – 95 Hz, respectively) during attempted movement. Also, we found that fMRI can be used to select a sub-set of electrodes that show strong task-related signal changes that are therefore likely to generate adequate BCI control. ConclusionsOur findings indicate that fMRI is a useful non-invasive tool for the pre-surgical workup of BCI implant candidates. SignificanceIf these results are confirmed in more BCI studies, fMRI might be used for more efficient surgical BCI procedures with focused cortical coverage and lower participant burden.

Restoring vision in blind patients: From optogenetic to sonogenetic therapies

AbstractVisual restoration is certainly the greatest challenge for brain‐machine interfaces with the high pixel number and high refreshing rate. In the recent year, we brought retinal prostheses and optogenetic therapy up to successful clinical trials. Optogenetics relies on the expression of a microbial opsin in residual neurons by gene therapy. These strategies can provide some vision in blind patients with diseases of photoreceptors such as retinal dystrophies or age‐related macular degeneration. They can reintroduce some information in at the retinal level by activating residual neurons after the loss of photoreceptors. For patients with optic nerve atrophy as in glaucoma and diabetic retinopathy, visual restoration requires the direct activation of the visual cortex. However, cortical prostheses have shown efficacy for limited periods of time and limited pixel numbers.In the present project, we are investigating a novel approach to restore vision at the cortical level with sonogenetic therapy. This approach relies on expressing an ultrasound‐sensitive ionic channel in cortical neurons to imprint images at this level by ultrasound stimulations.The Mscl ionic channel fused to the tdTomato reporter gene was expressed in the visual cortex of rats following a cortical AAV injection. The channel expression was indicated by the red fluorescence of tdTomato. Recording with penetrating electrodes indicated responses to cortical ultrasound stimulation with a high temporal resolution but a shorter latency than natural visual responses. In the absence of AAV injection, the visual cortex was not responsive to ultrasounds. Moving the ultrasound stimulator moved the activated area as indicated by Ecog electrode array recording. Finally, mice having learned to associate a flash of light to a water delivery responded similarly to an ultrasound cortical stimulation if the MscL protein was expressed in their cortex.These results indicate that the MscL channel induces an ultrasound sensitivity of cortical neurons generating a cortical activations with a spatiotemporal resolution suitable for vision restoration and perceived as phosphenes. Further studies will have to demonstrate true vision of forms by this sonogenetic approach prior to a clinical translation.

An Immersive Virtual Reality Platform Integrating Human ECOG & sEEG: Implementation & Noise Analysis.

Virtual reality (VR) offers a robust platform for human behavioral neuroscience, granting unprecedented experimental control over every aspect of an immersive and interactive visual environment. VR experiments have already integrated non-invasive neural recording modalities such as EEG and functional MRI to explore the neural correlates of human behavior and cognition. Integration with implanted electrodes would enable significant increase in spatial and temporal resolution of recorded neural signals and the option of direct brain stimulation for neurofeedback. In this paper, we discuss the first such implementation of a VR platform with implanted electrocorticography (ECoG) and stereo-electroencephalography ( sEEG) electrodes in human, in-patient subjects. Noise analyses were performed to evaluate the effect of the VR headset on neural data collected in two VR-naive subjects, one child and one adult, including both ECOG and sEEG electrodes. Results demonstrate an increase in line noise power (57-63Hz) while wearing the VR headset that is mitigated effectively by common average referencing (CAR), and no significant change in the noise floor bandpower (125-240Hz). To our knowledge, this study represents first demonstrations of VR immersion during invasive neural recording with in-patient human subjects. Clinical Relevance- Immersive virtual reality tasks were well-tolerated and the quality of clinical neural signals preserved during VR immersion with two in-patient invasive neural recording subjects.

A soft and stretchable bilayer electrode array with independent functional layers for the next generation of brain machine interfaces

Objective. Brain-Machine Interfaces (BMIs) hold great promises for advancing neuroprosthetics, robotics, and for providing treatment options for severe neurological diseases. The objective of this work is the development and in vivo evaluation of electrodes for BMIs that meet the needs to record brain activity at sub-millimeter resolution over a large area of the cortex while being soft and electromechanically robust (i.e. stretchable). Approach. Current electrodes require a trade-off between high spatiotemporal resolution and cortical coverage area. To address the needs for simultaneous high resolution and large cortical coverage, the prototype electrode array developed in this study employs a novel bilayer routing of soft and stretchable lead wires from the recording sites on the surface of the brain (electrocorticography, ECoG) to the data acquisition system. Main results. To validate the recording characteristics, the array was implanted in healthy felines for up to 5 months. Neural signals recorded from both layers of the device showed elevated mid-frequency structures typical of local field potential (LFP) signals that were stable in amplitude over implant duration, and also exhibited consistent frequency-dependent modulation after anesthesia induction by Telazol. Significance. The successful development of a soft and stretchable large-area, high resolution micro ECoG electrode array (lahrμECoG) is an important step to meet the neurotechnological needs of advanced BMI applications.

Кросскорреляционный и когерентный анализ электрокортикограмм крыс, перенесших черепно-мозговую травму

Traumatic brain injury (TBI) is a leading cause of disability and mortality among young population both in Russian Federation and abroad. The development of adequate and reproducible models of TBI in laboratory animals as well as precise methods for assessment of neurological disorders degree will optimize investigation of new effective neuroprotective drugs. Aim of the study: to perform the comparative crosscorrelation and coherent analysis of ECOG signal in non-injured rats and rats with TBI rats. The open penetrating brain injury was modeled following the craniotomy over the motor cortex of the left hemisphere by controlled cortical impact injury method (CCI). The recording nichrome ECoG electrodes were implanted bilaterally in the primary and secondary motor cortex areas and also in the area of primary somatosensory cortex (over the hippocampus). ECoG recordings were performed on the 3rd and 7th day after the operation in condition of the home cage at resting state. Crosscorrelation analysis comprised the calculation of crosscorrelation coefficient, mean frequency and maximum span of crosscorrelation function (CCF). Also the calculated mean coherence power of delta-, tetha-, alpha- and beta-rhythms. Unilateral traumatic damage of motor cortex and near situated brain areas lead to disturbances of inter- and intrahemispheric connections, these changes are recorded not only in the damaged area, but also in the remote areas of the cortex on the 3rd and 7th day after the injury.

Direct Electrical Stimulation in Electrocorticographic Brain-Computer Interfaces: Enabling Technologies for Input to Cortex.

Electrocorticographic brain computer interfaces (ECoG-BCIs) offer tremendous opportunities for restoring function in individuals suffering from neurological damage and for advancing basic neuroscience knowledge. ECoG electrodes are already commonly used clinically for monitoring epilepsy and have greater spatial specificity in recording neuronal activity than techniques such as electroencephalography (EEG). Much work to date in the field has focused on using ECoG signals recorded from cortex as control outputs for driving end effectors. An equally important but less explored application of an ECoG-BCI is directing input into cortex using ECoG electrodes for direct electrical stimulation (DES). Combining DES with ECoG recording enables a truly bidirectional BCI, where information is both read from and written to the brain. We discuss the advantages and opportunities, as well as the barriers and challenges presented by using DES in an ECoG-BCI. In this article, we review ECoG electrodes, the physics and physiology of DES, and the use of electrical stimulation of the brain for the clinical treatment of disorders such as epilepsy and Parkinson’s disease. We briefly discuss some of the translational, regulatory, financial, and ethical concerns regarding ECoG-BCIs. Next, we describe the use of ECoG-based DES for providing sensory feedback and for probing and modifying cortical connectivity. We explore future directions, which may draw on invasive animal studies with penetrating and surface electrodes as well as non-invasive stimulation methods such as transcranial magnetic stimulation (TMS). We conclude by describing enabling technologies, such as smaller ECoG electrodes for more precise targeting of cortical areas, signal processing strategies for simultaneous stimulation and recording, and computational modeling and algorithms for tailoring stimulation to each individual brain.

Arbitrary-Waveform Electro-Optical Intracranial Neurostimulator With Load-Adaptive High-Voltage Compliance

A hybrid 16-channel current-mode and the 8-channel optical implantable neurostimulating system is presented. The system generates arbitrary-waveform charge-balanced current-mode electrical pulses with an amplitude ranging from 50 [Formula: see text] to 10 mA. An impedance monitoring feedback loop is employed to automatically adjust the supply voltage, yielding a load-optimized power dissipation. The 8-channel optical stimulator drives an array of LEDs, each with a maximum of 25 mA current amplitude, and reuses the arbitrary-waveform generation function of the electrical stimulator. The LEDs are assembled within a custom-made 4×4 ECoG grid electrode array, enabling precise optical stimulation of neurons with a 300 [Formula: see text] pitch between the LEDs and simultaneous monitoring of the neural response by the ECoG electrode, at different distances of the stimulation site. The hybrid stimulation system is implemented on a mini-PCB, and receives power and stimulation commands inductively through a second board and a coil stacked on top of it. The entire system is sized at 3×2 . 5×1 cm3 and weighs 7 grams. The system efficacy for electrical and optical stimulation is validated in-vivo using separate chronic and acute experiments.

Simultaneous Recordings of Cortical Local Field Potentials and Electrocorticograms in Response to Nociceptive Laser Stimuli from Freely Moving Rats.

Electrocortical responses, elicited by laser heat pulses that selectively activate nociceptive free nerve endings, are widely used in many animal and human studies to investigate the cortical processing of nociceptive information. These laser-evoked brain potentials (LEPs) consist of several transient responses that are time-locked to the onset of laser stimuli. However, the functional properties of the LEP responses are still largely unknown, due to the lack of a sampling technique that can simultaneously record neural activities at the surface of the cortex (i.e., electrocorticogram [ECoG] and scalp electroencephalogram [scalp EEG]) and inside the brain (i.e., local field potential [LFP]). To address this issue, we present here an animal protocol using freely moving rats. This protocol is composed of three main procedures: (1) animal preparation and surgical procedures, (2) a simultaneous recording of ECoG and LFP in response to nociceptive laser stimuli, and (3) data analysis and feature extraction. Specifically, with the help of a 3D-printed protective shell, both ECoG and LFP electrodes implanted on the rat's skull were securely held together. During data collection, laser pulses were delivered on the rat's forepaws through gaps in the bottom of the chamber when the animal was in spontaneous stillness. Ongoing white noise was played to avoid the activation of the auditory system by the laser-generated ultrasounds. As a consequence, only nociceptive responses were selectively recorded. Using the standard analytical procedures (e.g., band-pass filtering, epoch extraction, and baseline correction) to extract stimulus-related brain responses, we obtained results showing that LEPs with a high signal-to-noise ratio were simultaneously recorded from ECoG and LFP electrodes. This methodology makes the simultaneous recording of ECoG and LFP activities possible, which provides a bridge of electrocortical signals at the mesoscopic and macroscopic levels, thereby facilitating the investigation of nociceptive information processing in the brain.

S129. An open source platform for concurrent EEG/ECoG comparisons

Concurrent EEG/ECoG recordings are crucial in providing a gold standard to develop EEG models, especially using primate models. These could be crucial for selecting methods for determining valid brain connectivity measures. Two essential points are to eliminate the unavoidable artifacts that contaminate such types of recordings as well as to provide sufficiently detailed biophysical models, such as lead fields, for both EEG and ECoG data that take into consideration intracranial electrode materials. We present a Matlab open source platform for EEG/ECoG comparisons, based upon the Multidimensional Recording in Nagasaka et al. (2011) data set shared at http://neurotycho.org. EEG/ECoG registration, artifact rejection, and preprocessing routines are illustrated with data obtained from awake and anesthetized monkeys. This platform has already been used to produce the results described in Papadopuoulus et al. (2014) and Todaro et al. (2017). The platform uses BrainSuite2 for T1 MRI pre-processing (intensity bias correction and segmentation). The white/gray matter interface surface was chosen as the source space model for both EEG/ECoG. The specific head compartments considered were (1) brain (enclosed by the pial surface), (2) brain plus surrounding cerebrospinal fluid, (3) skull and (4) skin. Final manually correction was carried out by an expert. Our volume conduction model comprises compartments (2), (3) and (4). Lead Field Calculation: Tetrahedral meshes were created from the surfaces of the head model using Tetgen 2.0. Both EEG and ECoG lead fields were calculated by NeuroFEM using Finite Element Method from SimBio. Care was taken to model the plastic strips supporting ECoG electrodes. Model-Based Artifact Removal: The raw EEG data suffered from mainly 2 types of artifacts: Low frequency drifting, and Sparse spikes. We introduce the Transient Artifact Reduction Algorithm. We formulate the artifact removal process as minimizing the residual, and penalizing sparsity of both the trend and spikes. More details can be found in Selesnick et al. (2014). Time Frequency Analysis: Spectrogram (squared magnitude of the Short-Time Fourier Transform (STFT)) is useful in analyzing neurological signals, but with drawback of leakage effect. To overcome this, we use the multi-tapper method and the implementation from Chronux (Bokil et al., 2006) and we also calculate the cross-spectrum. Spectrogram: EEG and ECoG show slower oscillation in anesthesia state than the awake state (<5 Hz), but ECoG can detect obvious beta rhythm (13–30 Hz) in the awake state while EEG cannot; Cross-Spectrum: Averagely(0.3–45 Hz), EEG is stronger in the frontal area while ECoG is stronger in the occipital and temporal areas in both awake and anesthesia states. The proposed open source platform and allows co-registration, artifact removal and biophysical modeling of use in both sensor and source level analyses. We believe that this platform will be helpful for EEG/ECoG multimodal comparisons and integration.

ALICE: A tool for automatic localization of intra-cranial electrodes for clinical and high-density grids

BackgroundElectrocorticographic (ECoG) measurements require the accurate localization of implanted electrodes with respect to the subject’s neuroanatomy. Electrode localization is particularly relevant to associate structure with function. Several procedures have attempted to solve this problem, namely by co-registering a post-operative computed tomography (CT) scan, with a pre-operative magnetic resonance imaging (MRI) anatomy scan. However, this type of procedure requires a manual and time-consuming detection and transcription of the electrode coordinates from the CT volume scan and restricts the extraction of smaller high-resolution ECoG grid electrodes due to the downsampling of the CT. New methodALICE automatically detects electrodes on the post-operative high-resolution CT scan, visualizes them in a combined 2D and 3D volume space using AFNI and SUMA software and then projects the electrodes on the individual’s cortical surface rendering. The pipeline integrates the multiple-step method into a user-friendly GUI in Matlab®, thus providing an easy, automated and standard tool for ECoG electrode localization. ResultsALICE was validated in 13 subjects implanted with clinical ECoG grids by comparing the calculated electrode center-of-mass coordinates with those computed using a commonly used method. Comparison with existing methodsA novel aspect of ALICE is the combined 2D-3D visualization of the electrodes on the CT scan and the option to also detect high-density ECoG grids. Feasibility was shown in 5 subjects and validated for 2 subjects. ConclusionsThe ALICE pipeline provides a fast and accurate detection, discrimination and localization of ECoG electrodes spaced down to 4 mm apart.

Connectivity maps based analysis of EEG for the advanced diagnosis of schizophrenia attributes.

This article presents a novel connectivity analysis method that is suitable for multi-node networks such as EEG, MEG or EcOG electrode recordings. Its diagnostic power and ability to interpret brain states in schizophrenia is demonstrated on a set of 50 subjects that constituted of 25 healthy and 25 diagnosed with schizophrenia and treated with medication. The method can also be used for the automatic detection of schizophrenia; it exhibits higher sensitivity than state-of-the-art methods with no false positives. The detection is based on an analysis from a minute long pattern-recognition computer task. Moreover, this connectivity analysis leads naturally to an optimal choice of electrodes and hence to highly statistically significant results that are based on data from only 3–5 electrodes. The method is general and can be used for the diagnosis of other psychiatric conditions, provided an appropriate computer task is devised.

Mechanisms underlying different onset patterns of focal seizures.

Focal seizures are episodes of pathological brain activity that appear to arise from a localised area of the brain. The onset patterns of focal seizure activity have been studied intensively, and they have largely been distinguished into two types—low amplitude fast oscillations (LAF), or high amplitude spikes (HAS). Here we explore whether these two patterns arise from fundamentally different mechanisms. Here, we use a previously established computational model of neocortical tissue, and validate it as an adequate model using clinical recordings of focal seizures. We then reproduce the two onset patterns in their most defining properties and investigate the possible mechanisms underlying the different focal seizure onset patterns in the model. We show that the two patterns are associated with different mechanisms at the spatial scale of a single ECoG electrode. The LAF onset is initiated by independent patches of localised activity, which slowly invade the surrounding tissue and coalesce over time. In contrast, the HAS onset is a global, systemic transition to a coexisting seizure state triggered by a local event. We find that such a global transition is enabled by an increase in the excitability of the “healthy” surrounding tissue, which by itself does not generate seizures, but can support seizure activity when incited. In our simulations, the difference in surrounding tissue excitability also offers a simple explanation of the clinically reported difference in surgical outcomes. Finally, we demonstrate in the model how changes in tissue excitability could be elucidated, in principle, using active stimulation. Taken together, our modelling results suggest that the excitability of the tissue surrounding the seizure core may play a determining role in the seizure onset pattern, as well as in the surgical outcome.

Registering imaged ECoG electrodes to human cortex: A geometry-based technique

BackgroundThe accurate localization of implanted ECoG electrodes over the brain is of critical importance to invasive diagnostic work-up for the surgical treatment of intractable epileptic seizures. The implantation of subdural electrodes is an invasive procedure which typically introduces non-uniform deformations of a subject’s brain, increasing the difficulty of determining the precise location of the electrodes vis-à-vis cortex. Formalization of this problem is used to define a novel solution for the optimal localization of subdural electrodes. New methodWe demonstrate that nonlinear transformation is required to accurately register the implanted electrodes to the non-deformed pre-surgical cortical surface, and that this problem is accommodated by utilizing known features of electrode geometry. Techniques to register chronically implanted subdural electrodes to the undistorted brain image are described and evaluated using simulated and clinical data. ResultsPrincipal Axis, our novel analysis method that estimates an electrode’s orientation by the moment of inertia of the solid electrode volume, proved to be the most reliable measure in both the simulated and clinical datasets. Comparison with existing methodsThis method of electrode translation along its principal axis is an improvement over other techniques, such as the limited view provided by intraoperative photography, and the image degradation inherent in post-operative MRI. ConclusionsThis technique compensates for alterations due to post-operative brain edema, and translates subdural electrodes to their original location on pre-operative MRI 3D models. This is helpful in the correct localization of seizure foci and functional mapping of epilepsy patients.

Mechanisms underlying different onset patterns of focal seizures

Event Abstract Back to Event Mechanisms underlying different onset patterns of focal seizures Yujiang Wang1* 1 Newcastle University, School of Computing Science, United Kingdom Focal seizures typically begin with an electrographic onset pattern that is highly stereotyped in individual patients. Qualitative classifications of these onset patterns describe two frequently occurring waveforms – low amplitude fast oscillations (LAF), or high amplitude spikes (HAS). Interestingly, only the former of the patterns is associated with a good surgical outcome. Given the importance of this clinical distinction, we therefore explored whether these two patterns arise from fundamentally different spatio-temporal dynamics. We used a previously established computational model of neocortical tissue, and validated it as an adequate model using clinical recordings of focal seizures. Using this model we then investigated the possible mechanisms underlying the different focal seizure onset patterns. We show that the two patterns are associated with different mechanisms at the spatial scale of a single ECoG electrode. The LAF onset is initiated by independent patches of localised activity, which slowly invade the surrounding tissue and coalesce over time (see Fig. 1A). In contrast, the HAS onset is a global, systemic transition to a coexisting seizure state triggered by a local event (see Fig. 1B). We find that such a global transition is enabled by an increase in excitability of the surrounding tissue, essentially creating a seizure supporting surrounding. In our simulations, the difference in surrounding tissue excitability also offers a simple explanation of the clinically observed difference in surgical outcomes. Finally, we demonstrate how changes in tissue excitability could be elucidated in principle using active stimulation. We conclude that the excitability of the tissue surrounding the seizure core plays a determining role in the seizure onset pattern, as well as in the surgical outcome. Figure 1 Keywords: Epilepsy, neural mass model, Seizures, Seizure onset pattern, cortical excitability Conference: Neuroinformatics 2016, Reading, United Kingdom, 3 Sep - 4 Sep, 2016. Presentation Type: Investigator presentations Topic: Brain disorders Citation: Wang Y (2016). Mechanisms underlying different onset patterns of focal seizures. Front. Neuroinform. Conference Abstract: Neuroinformatics 2016. doi: 10.3389/conf.fninf.2016.20.00016 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 26 Apr 2016; Published Online: 18 Jul 2016. * Correspondence: Dr. Yujiang Wang, Newcastle University, School of Computing Science, Newcastle upon Tyne, NE1 7RU, United Kingdom, Yujiang.Wang@newcastle.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Yujiang Wang Google Yujiang Wang Google Scholar Yujiang Wang PubMed Yujiang Wang Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Development of a bending test procedure for the characterization of flexible ECoG electrode arrays

Abstract An automatized mechanical test has been developed to characterize flexible ECoG and grid electrode arrays under cyclic bending load. Electrodes with different test structures were designed and the bending cycle dependant failure rate was found to follow a Weibull distribution. A corresponding failure mode analysis revealed a characteristic lifetime of more than 25000 bending cycles for some designs. However, design parameters as e.g. a smaller track width reduced this lifetime by a factor of two. In comparison to a similar BMI grid electrode array which was implanted for several months in an animal, failure patterns were comparable to those simulated with the bending test.

Modulation of intracranial field potential responses in the human large-scale attention network during a spatial attention task

Spatial attention is mediated through a large-scale network that includes occipital, temporal, parietal and frontal cortical regions. While the network architecture has been well characterized using neuroimaging methods, less is known about the temporal dynamics in local regions and across the network. Here, we explored the modulatory effects of spatial attention throughout this cortical network by analyzing intracranial field potentials recorded from 538 ECoG electrodes implanted in 6 epilepsy patients. We examined the effects of attention using a variant of the Eriksen flanker task, where subjects were cued by an exogenous stimulus to the spatial location of an upcoming target stimulus which, after a variable delay period, was presented embedded in a circular array of shapes. Subjects had to differentiate between barrel or bowtie target stimuli flanked either by congruent or incongruent shapes. Using our probabilistic atlas of the human visual system, we localized the recorded ECoG signals to topographically organized brain areas and linked them to functional brain imaging data from normal subjects. We found spatially constrained visual response fields in 175 electrodes, as indicated by differential cue-related activity, obtained from both induced broadband power and evoked potentials. We examined response modulation from those electrodes during the delay period of the task when subjects either attended to or away from the response field. Further, we related these results to changes in the BOLD signal measured in normal subjects performing the same task. We found that covert spatial attention affected evoked event-related potentials and induced low frequency (4-20Hz) and broadband high gamma (50-200Hz) power differentially along the dorsal pathway through nodes of the fronto-parietal attention network, from V1 through intraparietal sulcus areas IPS0-IPS5 and the frontal eye fields. Meeting abstract presented at VSS 2015

Comparison of subdural and subgaleal recordings of cortical high-gamma activity in humans

ObjectiveThe purpose of this study is to determine the relationship between cortical electrophysiological (CE) signals recorded from the surface of the brain (subdural electrocorticography, or ECoG) and signals recorded extracranially from the subgaleal (SG) space. MethodsWe simultaneously recorded several hours of continuous ECoG and SG signals from 3 human pediatric subjects, and compared power spectra of signals between a differential SG montage and several differential ECoG montages to determine the nature of the transfer function between them. ResultsWe demonstrate the presence of CE signals in the SG montage in the high-gamma range (HG, 70–110Hz), and the transfer function between 70 and 110Hz is best characterized as a linear function of frequency. We also test an alternative transfer function, i.e. a single pole filter, to test the hypothesis of frequency dependent attenuation in that range, but find this model to be inferior to the linear model. ConclusionsOur findings indicate that SG electrodes are capable of recording HG signals without frequency distortion compared with ECoG electrodes. SignificanceHG signals could be recorded minimally invasively from outside the skull, which could be important for clinical care or brain–computer interface applications.

A multi-channel, flex-rigid ECoG microelectrode array for visual cortical interfacing.

High-density electrocortical (ECoG) microelectrode arrays are promising signal-acquisition platforms for brain-computer interfaces envisioned, e.g., as high-performance communication solutions for paralyzed persons. We propose a multi-channel microelectrode array capable of recording ECoG field potentials with high spatial resolution. The proposed array is of a 150 mm2 total recording area; it has 124 circular electrodes (100, 300 and 500 μm in diameter) situated on the edges of concentric hexagons (min. 0.8 mm interdistance) and a skull-facing reference electrode (2.5 mm2 surface area). The array is processed as a free-standing device to enable monolithic integration of a rigid interposer, designed for soldering of fine-pitch SMD-connectors on a minimal assembly area. Electrochemical characterization revealed distinct impedance spectral bands for the 100, 300 and 500 μm-type electrodes, and for the array's own reference. Epidural recordings from the primary visual cortex (V1) of an awake Rhesus macaque showed natural electrophysiological signals and clear responses to standard visual stimulation. The ECoG electrodes of larger surface area recorded signals with greater spectral power in the gamma band, while the skull-facing reference electrode provided higher average gamma power spectral density (γPSD) than the common average referencing technique.

Fast presurgical functional mapping using task-related intracranial high gamma activity

Electrocorticography (ECoG) is a powerful tool for presurgical functional mapping. Power increase in the high gamma band has been observed from ECoG electrodes on the surface of the sensory motor cortex during the execution of body movements. In this study the authors aim to validate the clinical usage of high gamma activity in presurgical mapping by comparing ECoG mapping with traditional direct electrical cortical stimulation (ECS) and functional MRI (fMRI) mapping. Seventeen patients with epilepsy participated in an ECoG motor mapping experiment. The patients executed a 5-minute hand/tongue movement task while the ECoG signal was recorded. All 17 patients also underwent extraoperative ECS mapping to localize the motor cortex. Eight patients also participated in a presurgical fMRI study. The high gamma activity on ECoG was modeled using the general linear model (GLM), and the regions showing significant gamma power increase during the task condition compared with the rest condition were localized. The maps derived from GLM-based ECoG mapping, ECS, and fMRI were then compared. High gamma activity in the motor cortex can be reliably modulated by motor tasks. Localization of the motor regions achieved with GLM-based ECoG mapping was consistent with the localization determined by ECS. The maps also appeared to be highly localized compared with the fMRI activations. Using the ECS findings as the reference, GLM-based ECoG mapping showed a significantly higher sensitivity than fMRI (66.7% for ECoG, 52.6% for fMRI, p<0.05), while the specificity was high for both techniques (>97%). If the current-spreading effect in ECS is accounted for, ECoG mapping may produce maps almost identical to those produced by ECS mapping (100% sensitivity and 99.5% specificity). General linear model-based ECoG mapping showed a superior performance compared to traditional ECS and fMRI mapping in terms of efficiency and accuracy. Using this method, motor functions can be reliably mapped in less than 5 minutes.