sEEG Electrodes Research Articles

Subject-Agnostic Transformer-Based Neural Speech Decoding from Surface and Depth Electrode Signals.

This study investigates speech decoding from neural signals captured by intracranial electrodes. Most prior works can only work with electrodes on a 2D grid (i.e., Electrocorticographic or ECoG array) and data from a single patient. We aim to design a deep-learning model architecture that can accommodate both surface (ECoG) and depth (stereotactic EEG or sEEG) electrodes. The architecture should allow training on data from multiple participants with large variability in electrode placements and the trained model should perform well on participants unseen during training. We propose a novel transformer-based model architecture named SwinTW that can work with arbitrarily positioned electrodes by leveraging their 3D locations on the cortex rather than their positions on a 2D grid. We train subject-specific models using data from a single participant and multi-patient models exploiting data from multiple participants. The subject-specific models using only low-density 8×8 ECoG data achieved high decoding Pearson Correlation Coefficient with ground truth spectrogram (PCC=0.817), over N=43 participants, outperforming our prior convolutional ResNet model and the 3D Swin transformer model. Incorporating additional strip, depth, and grid electrodes available in each participant (N=39) led to further improvement (PCC=0.838). For participants with only sEEG electrodes (N=9), subject-specific models still enjoy comparable performance with an average PCC=0.798. The multi-subject models achieved high performance on unseen participants, with an average PCC=0.765 in leave-one-out cross-validation. The proposed SwinTW decoder enables future speech neuropros-theses to utilize any electrode placement that is clinically optimal or feasible for a particular participant, including using only depth electrodes, which are more routinely implanted in chronic neurosurgical procedures. Importantly, the generalizability of the multi-patient models suggests that such a model can be applied to new patients that do not have paired acoustic and neural data, providing an advance in neuroprostheses for people with speech disability, where acoustic-neural training data is not feasible.

Analysis of DNA from brain tissue on stereo-EEG electrodes reveals mosaic epilepsy-related variants.

Somatic mosaic variants contribute to focal epilepsy, but genetic analysis has been limited to patients with drug-resistant epilepsy (DRE) who undergo surgical resection, as the variants are mainly brain-limited. Stereoelectroencephalography (sEEG) has become part of the evaluation for many patients with focal DRE, and sEEG electrodes provide a potential source of small amounts of brain-derived DNA. We aimed to identify, validate, and assess the distribution of potentially clinically relevant mosaic variants in DNA extracted from trace brain tissue on individual sEEG electrodes. We enrolled a prospective cohort of eleven pediatric patients with DRE who had sEEG electrodes implanted for invasive monitoring, one of whom was previously reported. We extracted unamplified DNA from the trace brain tissue on each sEEG electrode and also performed whole-genome amplification for each sample. We extracted DNA from resected brain tissue and blood/saliva samples where available. We performed deep panel and exome sequencing on a subset of samples from each case and analysis for potentially clinically relevant candidate germline and mosaic variants. We validated candidate mosaic variants using amplicon sequencing and assessed the variant allele fraction (VAF) in amplified and unamplified electrode-derived DNA and across electrodes. We extracted DNA from >150 individual electrodes from 11 individuals and obtained higher concentrations of whole-genome amplified vs unamplified DNA. Immunohistochemistry confirmed the presence of neurons in the brain tissue on electrodes. Deep sequencing and analysis demonstrated similar depth of coverage between amplified and unamplified samples but significantly more called mosaic variants in amplified samples. In addition to the mosaic PIK3CA variant detected in a previously reported case from our group, we identified and validated four potentially clinically relevant mosaic variants in electrode-derived DNA in three patients who underwent laser ablation and did not have resected brain tissue samples available. The variants were detected in both amplified and unamplified electrode-derived DNA, with higher VAFs observed in DNA from electrodes in closest proximity to the electrical seizure focus in some cases. This study demonstrates that mosaic variants can be identified and validated from DNA extracted from trace brain tissue on individual sEEG electrodes in patients with drug-resistant focal epilepsy and in both amplified and unamplified electrode-derived DNA samples. Our findings support a relationship between the extent of regional genetic abnormality and electrophysiology, and suggest that with further optimization, this minimally invasive diagnostic approach holds promise for advancing precision medicine for patients with DRE as part of the surgical evaluation.

Using magnetic resonance-guided laser interstitial thermal therapy corpus callosotomy to lateralize a seizure focus for staged surgical approach

New onset refractory status epilepticus (NORSE) is an etiologically heterogeneous condition that is associated with high morbidity and mortality. NORSE is often refractory to medical management prompting a workup for epilepsy surgery. Because NORSE remains etiologically elusive in most cases, surgical evaluations are challenging, especially when the epileptogenic zone (EZ) is not easy to lateralize as can be seen in frontal lobe seizures. Lateralizing a frontal lobe EZ may be challenging due to bilateral synchrony from commissural connections through the corpus callosum and low spatiotemporal resolution of the scalp electroencephalography (EEG). We report a pediatric patient with NORSE presenting with focal impaired awareness seizures clustering into super refractory status epilepticus (SRSE). She required surgical intervention for the treatment of her seizures after failing therapeutic doses of antiseizure medications, anesthetic drips, immunomodulation with methylprednisolone, intravenous immunoglobulin and anakinra, and the ketogenic diet. Despite her semiology being focal, the seizures were not well lateralized on scalp EEG and during phase 2 stereo-EEG (sEEG). Anterior magnetic resonance-guided laser interstitial thermal therapy corpus callosotomy (MRgLITT CC) was performed in a multistage surgical approach to successfully lateralize the EZ with a left-lateralized ictal pattern seen after reimplantation of sEEG electrodes. Our case suggests that minimally invasive MRgLITT CC can be successfully used to lateralize an EZ in frontal lobe epilepsy and that epilepsy surgery should be considered in patients with NORSE with SRSE. We also demonstrate that laser interstitial thermal therapy (LITT), while not always resulting in seizure freedom, can sufficiently disrupt a network to abort status epilepticus and lead to seizure improvements.

Seizure freedom without seizure medication following stereoelectroencephalography implantation: a case report of drug-resistant post-traumatic epilepsy.

Achieving seizure freedom following failure of several antiseizure medications (ASMs) is rare, with the likelihood of achieving further control decreasing with each successive ASM trial. When cases of drug-resistant epilepsy arise, a diagnostic procedure known as stereoelectroencephalography (sEEG) can be used to identify epileptogenic zones (EZ) within the brain. After localization of these zones, they can be targeted for future surgical intervention. Here, we describe a case of complete seizure freedom off medication after sEEG without resection or other therapeutic intervention. In 2017, a 36-year-old right-handed male presented with drug-resistant epilepsy stemming from prior traumatic brain injury. Due to ongoing seizures, in 2020 a robotic-assisted sEEG electrode placement procedure was employed to localize the seizure onset zone. During sEEG monitoring, a single event was captured where the patient had dysarthric speech, left arm dystonic flexion, and difficulty responding to questioning. Notably, this event had no sEEG correlate, suggesting seizure occurrence in a region not monitored by implanted electrodes, which prompted the placement of scalp electrodes following this event. However, no further clinical events consistent with seizure were provoked through the remainder of recording. Following the 13-day admission, the patient chose to self-discontinue all seizure medications and has remained seizure free as of October 2023, more than 3.5 years later. While sEEG is considered a relatively safe procedure for seizure localization in drug resistant epilepsy, the possibility of microlesions created by sEEG depth electrodes remains largely unexplored. Further evaluation should be performed into potential tissue injury produced by depth electrode insertion.

1139 Retrospective Review of Stereotactic Electroencephalogram Recordings in Temporal Lobectomy Patients Demonstrates the Predictive Value of Interictal Cross-frequency Correlations

INTRODUCTION: Positive correlations between low and high frequency spectra in invasive electroencephalogram (EEG) have been implicated in pathological brain activity interictally and have been used for ictal detection in both focal and network models. METHODS: We retrospectively analyzed interictal signals from 22 patients who underwent SEEG at our institution between 12/2/14 to 12/8/20. We then analyzed significant HG/Beta cross-frequency correlations using similar processing to our previous publication. These signals were then separated based on temporal and extra-temporal locations. We further evaluated any statistical differences between the seizure free (SF) and non-seizure free (NSF) groups, and mesial (M) versus mesial temporal-plus (M+) onset location. RESULTS: 1) Clinical recordings from SEEG electrodes can detect cross-frequency correlations between HG/Beta using our previous methodology. 2) Positive correlations are significantly increased in temporal versus other sampled areas. 3) Positive correlations are more predictive of seizure onset during asleep recordings. 4) NSF patients show a significantly higher proportion of positive electrodes in the resected temporal lobe than SF patients. 5) SF patients have a greater proportion of significant contacts in the mesial versus the lateral temporal lobe than NSF patients. 6) Significant HG/Beta correlations in the mesial versus lateral temporal lobe predict seizure freedom better than ictal SEEG localization of seizure onset to M or M+ locations. CONCLUSIONS: We present preliminary data that local HG/Beta correlations may be predictive for epilepsy focus and surgical outcome and may have utility as adjunct methods to conventional SEEG analysis. Further studies are needed to determine strategies for prospective studies and clinical use.

Implantation accuracy of novel polyimide stereotactic electroencephalographic depth electrodes-a human cadaveric study.

Stereoelectroencephalography (sEEG) is a minimally invasive procedure that uses depth electrodes stereotactically implanted into brain structures to map the origin and propagation of seizures in epileptic patients. Implantation accuracy of sEEG electrodes plays a critical role in the safety and efficacy of the procedure. This study used human cadaver heads, simulating clinical practice, to evaluate (1) neurosurgeon's ability to implant a new thin-film polyimide sEEG electrode according to the instructions for use (IFU), and (2) implantation accuracy. Four neurosurgeons (users) implanted 24 sEEG electrodes into two cadaver heads with the aid of the ROSA robotic system. Usability was evaluated using a questionnaire that assessed completion of all procedure steps per IFU and user errors. For implantation accuracy evaluation, planned electrode trajectories were compared with post-implantation trajectories after fusion of pre- and postoperative computer tomography (CT) images. Implantation accuracy was quantified using the Euclidean distance for entry point error (EPE) and target point error (TPE). All sEEG electrodes were successfully placed following the IFU without user errors, and post-implant survey of users showed favorable handling characteristics. The EPE was 1.28 ± 0.86 mm and TPE was 1.61 ± 0.89 mm. Long trajectories (>50 mm) had significantly larger EPEs and TPEs than short trajectories (<50 mm), and no differences were found between orthogonal and oblique trajectories. Accuracies were similar or superior to those reported in the literature when using similar experimental conditions, and in the same range as those reported in patients. The results demonstrate that newly developed polyimide sEEG electrodes can be implanted as accurately as similar devices in the marker without user errors when following the IFU in a simulated clinical environment. The human cadaver ex-vivo test system provided a realistic test system, owing to the size, anatomy and similarity of tissue composition to that of the live human brain.

Somatic Mosaicism in PIK3CA Variant Correlates With Stereoelectroencephalography-Derived Electrophysiology.

Brain-limited pathogenic somatic variants are associated with focal pediatric epilepsy, but reliance on resected brain tissue samples has limited our ability to correlate epileptiform activity with abnormal molecular pathology. We aimed to identify the pathogenic variant and map variant allele fractions (VAFs) across an abnormal region of epileptogenic brain in a patient who underwent stereoelectroencephalography (sEEG) and subsequent motor-sparing left frontal disconnection. We extracted genomic DNA from peripheral blood, brain tissue resected from peri-sEEG electrode regions, and microbulk brain tissue adherent to sEEG electrodes. Samples were mapped based on an anatomic relationship with the presumed seizure onset zone (SOZ). We performed deep panel sequencing of amplified and unamplified DNA to identify pathogenic variants with subsequent orthogonal validation. We detect a pathogenic somatic PIK3CA variant, c.1624G>A (p.E542K), in the brain tissue samples, with VAF inversely correlated with distance from the SOZ. In addition, we identify this variant in amplified electrode-derived samples, albeit with lower VAFs. We demonstrate regional mosaicism across epileptogenic tissue, suggesting a correlation between variant burden and SOZ. We also validate a pathogenic variant from individual amplified sEEG electrode-derived brain specimens, although further optimization of techniques is required.

Triggered Seizures for Ictal SPECT Imaging: A Case Series and Feasibility Study.

Ictal SPECT is an informative seizure imaging technique to tailor epilepsy surgery. However, capturing the onset of unpredictable seizures is a medical and logistic challenge. Here, we sought to image planned seizures triggered by direct stimulation of epileptic networks via stereotactic electroencephalography (sEEG) electrodes. Methods: In this case series of 3 adult participants with left temporal epilepsy, we identified and stimulated sEEG contacts able to trigger patient-typical seizures. We administered 99mTc-HMPAO within 12 s of ictal onset and acquired SPECT images within 40 min without any adverse events. Results: Ictal hyperperfusion maps partially overlapped concomitant sEEG seizure activity. In both participants known for periictal aphasia, SPECT imaging revealed hyperperfusion in the speech cortex lacking sEEG coverage. Conclusion: Triggering of seizures for ictal SPECT complements discrete sEEG sampling with spatially complete images of early seizure propagation. This readily implementable method revives interest in seizure imaging to guide resective epilepsy surgery.

Network coupling and surgical treatment response in temporal lobe epilepsy: A proof-of-concept study

ObjectiveThis proof-of-concept study aimed to examine the overlap between structural and functional activity (coupling) related to surgical response. MethodsWe studied intracranial rest and ictal stereoelectroencephalography (sEEG) recordings from 77 seizures in thirteen participants with temporal lobe epilepsy (TLE) who subsequently underwent resective/laser ablation surgery. We used the stereotactic coordinates of electrodes to construct functional (sEEG electrodes) and structural connectomes (diffusion tensor imaging). A Jaccard index was used to assess the similarity (coupling) between structural and functional connectivity at rest and at various intraictal timepoints. ResultsWe observed that patients who did not become seizure free after surgery had higher connectome coupling recruitment than responders at rest and during early and mid seizure (and visa versa). SignificanceStructural networks provide a backbone for functional activity in TLE. The association between lack of seizure control after surgery and the strength of synchrony between these networks suggests that surgical intervention aimed to disrupt these networks may be ineffective in those that display strong synchrony. Our results, combined with findings of other groups, suggest a potential mechanism that explains why certain patients benefit from epilepsy surgery and why others do not. This insight has the potential to guide surgical planning (e.g., removal of high coupling nodes) following future research.

Stereo-EEG-guided network modulation for psychiatric disorders: Surgical considerations

BackgroundDeep brain stimulation (DBS) and other neuromodulatory techniques are being increasingly utilized to treat refractory neurologic and psychiatric disorders. Objective/Hypothesis: To better understand the circuit-level pathophysiology of treatment-resistant depression (TRD) and treat the network-level dysfunction inherent to this challenging disorder, we adopted an approach of inpatient intracranial monitoring borrowed from the epilepsy surgery field. MethodsWe implanted 3 patients with 4 DBS leads (bilateral pair in both the ventral capsule/ventral striatum and subcallosal cingulate) and 10 stereo-electroencephalography (sEEG) electrodes targeting depression-relevant network regions. For surgical planning, we used an interactive, holographic visualization platform to appreciate the 3D anatomy and connectivity. In the initial surgery, we placed the DBS leads and sEEG electrodes using robotic stereotaxy. Subjects were then admitted to an inpatient monitoring unit for depression-specific neurophysiological assessments. Following these investigations, subjects returned to the OR to remove the sEEG electrodes and internalize the DBS leads to implanted pulse generators. ResultsIntraoperative testing revealed positive valence responses in all 3 subjects that helped verify targeting. Given the importance of the network-based hypotheses we were testing, we required accurate adherence to the surgical plan (to engage DBS and sEEG targets) and stability of DBS lead rotational position (to ensure that stimulation field estimates of the directional leads used during inpatient monitoring were relevant chronically), both of which we confirmed (mean radial error 1.2±0.9 mm; mean rotation 3.6±2.6°). ConclusionThis novel hybrid sEEG-DBS approach allows detailed study of the neurophysiological substrates of complex neuropsychiatric disorders.

Characterization of spatiotemporal dynamics of binary and graded tonic pain in humans using intracranial recordings.

Pain is a complex experience involving sensory, emotional, and cognitive aspects, and multiple networks manage its processing in the brain. Examining how pain transforms into a behavioral response can shed light on the networks' relationships and facilitate interventions to treat chronic pain. However, studies using high spatial and temporal resolution methods to investigate the neural encoding of pain and its psychophysical correlates have been limited. We recorded from intracranial stereo-EEG (sEEG) electrodes implanted in sixteen different brain regions of twenty patients who underwent psychophysical pain testing consisting of a tonic thermal stimulus to the hand. Broadband high-frequency local field potential amplitude (HFA; 70-150 Hz) was isolated to investigate the relationship between the ongoing neural activity and the resulting psychophysical pain evaluations. Two different generalized linear mixed-effects models (GLME) were employed to assess the neural representations underlying binary and graded pain psychophysics. The first model examined the relationship between HFA and whether the patient responded "yes" or "no" to whether the trial was painful. The second model investigated the relationship between HFA and how painful the stimulus was rated on a visual analog scale. GLMEs revealed that HFA in the inferior temporal gyrus (ITG), superior frontal gyrus (SFG), and superior temporal gyrus (STG) predicted painful responses at stimulus onset. An increase in HFA in the orbitofrontal cortex (OFC), SFG, and striatum predicted pain responses at stimulus offset. Numerous regions, including the anterior cingulate cortex, hippocampus, IFG, MTG, OFC, and striatum, predicted the pain rating at stimulus onset. However, only the amygdala and fusiform gyrus predicted increased pain ratings at stimulus offset. We characterized the spatiotemporal representations of binary and graded painful responses during tonic pain stimuli. Our study provides evidence from intracranial recordings that the neural encoding of psychophysical pain changes over time during a tonic thermal stimulus, with different brain regions being predictive of pain at the beginning and end of the stimulus.

YAEL: Your Advanced Electrode Localizer.

Intracranial electroencephalography (iEEG) provides a unique opportunity to record and stimulate neuronal populations in the human brain. A key step in neuroscience inference from iEEG is localizing the electrodes relative to individual subject anatomy and identified regions in brain atlases. We describe a new software tool, Your Advanced Electrode Localizer (YAEL), that provides an integrated solution for every step of the electrode localization process. YAEL is compatible with all common data formats to provide an easy-to-use, drop-in replacement for problematic existing workflows that require users to grapple with multiple programs and interfaces. YAEL's automatic extrapolation and interpolation functions speed localization, especially important in patients with many implanted stereotactic (sEEG) electrode shafts. The graphical user interface is presented in a web browser for broad compatibility and includes an interactive 3D viewer for easier localization of nearby sEEG contacts. After localization is complete, users may enter or import data into YAEL's 3D viewer to create publication-ready visualizations of electrodes and brain anatomy, including identified brain areas from atlases; the response to experimental tasks measured with iEEG; and clinical measures such as epileptiform activity or the results of electrical stimulation mapping. YAEL is free and open source and does not depend on any commercial software. Installation instructions for Mac, Windows, and Linux are available at https://yael.wiki.

Radiofrequency ablation during stereoelectroencephalography: from diagnostic tool to therapeutic intervention. Illustrative case.

Radiofrequency thermocoagulation (RFTC) during intracranial stereoelectroencephalography (sEEG) was first described as a safe technique for creating lesions of epileptic foci in 2004. Since that time, the method has been applied as a diagnostic and/or palliative intervention. Although widely practiced in European epilepsy surgical programs, the technique has not been popularized in the United States given the lack of Food and Drug Administration (FDA)-approved technologies permitting safe usage of in situ sEEG electrodes for this purpose. The authors present a case report of a young female patient with refractory left neocortical temporal lobe epilepsy undergoing sEEG electrode implantation, who underwent sEEG-guided RFTC via a stereotactic temperature-sensing pallidotomy probe. Although used as a diagnostic step in her workup, the patient has remained seizure-free for nearly 18 months. The use of in situ sEEG electrodes for RFTC remains limited in the United States. In this context, this case highlights a safe alternative and temporizing approach to performing diagnostic sEEG-guided RFTC, using a temperature-sensing pallidotomy probe to create small, precise stereotactic lesions. The authors caution careful consideration of this technique as a temporary work-around solution while also highlighting the rising need for new FDA-approved technologies for safe RFTC through in situ temperature-sensing sEEG electrodes.

What is the effect of benzodiazepines on deep brain activity? A study in pediatric patients with dystonia.

Benzodiazepines (BDZs) are commonly used to treat the symptoms of movement disorders; however, deep brain stimulation (DBS) has become a popular treatment for these disorders. Previous studies have investigated the effects of BDZ on cortical activity, no data are currently available on their effects on deep brain regions, nor on these regions' responses to DBS. How the BDZ affects the thalamus and basal ganglia in dystonia patients remains unknown. DBS recordings were performed in ventral oralis anterior/posterior (VoaVop), ventral intermediate (VIM) and ventral anterior (VA) thalamic subnuclei, as well as globus pallidus interna (GPi) and subthalamic nucleus (STN). Evoked potentials (EP) and frequency domain analysis were performed to determine the BDZ effect on neural activities compared to the control condition (off-BDZ). Three male pediatric patients with dystonia treated with BDZ and undergoing depth electrode evaluation for clinical targeting were recruited for the study. Stimulation was administered at 25 and 55 Hz frequencies and recordings were simultaneously gathered through pairs of externalized stereoelectroencephalography (sEEG) electrodes. EP amplitude and the effect of stimulation on the frequency spectrum of activity were compared at baseline and following clinical administration of BDZ. Frequency analysis showed consistent reductions in activity during BDZ treatment in all studied brain regions for all patients. Evoked potential (EP) analysis showed increased subthalamic nucleus (STN) EP amplitude and decreased ventral intermediate (VIM) and STN EP amplitude during BDZ treatment. BDZs reduce thalamic and basal ganglia activity in multiple regions and alter the efficacy of transmission between these regions. While the mechanism is unknown our results confirm the known widespread effects of this class of medications and identify specific areas within the motor system that are directly affected.

Utility of hybrid PET/MRI in stereoelectroencephalography guided radiofrequency thermocoagulation in MRI negative epilepsy patients.

Hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) is a novel advanced non-invasive presurgical examination tool for patients with drug-resistant epilepsy (DRE). This study aims to evaluate the utility of PET/MRI in patients with DRE who undergo stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-guided RFTC). This retrospective study included 27 patients with DRE who underwent hybrid PET/MRI and SEEG-guided RFTC. Surgery outcome was assessed using a modified Engel classification, 2 years after RFTC. Potential areas of the seizure onset zone (SOZ) were identified on PET/MRI and confirmed by SEEG. Fifteen patients (55%) became seizure-free after SEEG-guided RFTC. Engel class II, III, and IV were achieved in six, two, and four patients, respectively at the 2 years follow-up. MRI was negative in 23 patients and structural abnormalities were found in four patients. Hybrid PET/MRI contributed to the identification of new structural or metabolic lesions in 22 patients. Concordant results between PET/MRI and SEEG were found in 19 patients in the identification of SOZ. Among the patients with multifocal onset, seizure-free status was achieved in 50% (6/12). SEEG-guided RFTC is an effective and safe treatment for drug-resistant epilepsy. Hybrid PET/MRI serves as a useful tool for detecting the potential SOZs in MRI-negative patients and guide the implantation of SEEG electrodes. Patients with multifocal epilepsy may also benefit from this palliative treatment.

Operative Technique and Nuances for the Stereoelectroencephalographic (SEEG) Methodology Utilizing a Robotic Stereotactic Guidance System.

The SEEG methodology has gained favor in North America over the last decade as a means of localizing the epileptogenic zone (EZ) prior to epilepsy surgery. Recently, the application of a robotic stereotactic guidance system for implantation of SEEG electrodes has become more popular in many epilepsy centers. The technique for the use of the robot requires extreme precision in the pre-surgical planning phase and then the technique is streamlined during the operative portion of the methodology, as the robot and surgeon work in concert to implant the electrodes. Herein is detailed precise operative methodology of using the robot to guide implantation of SEEG electrodes. A major limitation of the procedure, namely its heavy reliance on the ability to register the patient to a preoperative volumetric magnetic resonance image (MRI), is also discussed. Overall, this procedure has been shown to have a low morbidity rate and an extremely low mortality rate. The use of a robotic stereotactic guidance system for the implantation of SEEG electrodes is an efficient, fast, safe, and accurate alternative to conventional manual implantation strategies.

ID: 203253 Electrochemical Characterization of the First FDA-Cleared Thin-Film Electrodes for Recording and Stimulation of Brain Activity

Introduction: Subdural strip and grid (SDE) and stereoelectroencephalography (sEEG) electrodes are essential tools for pre-surgical evaluation of patients suffering from drug resistant epilepsy (DRE). Both device types are used to precisely localize the origin and spread of seizures and the relationship with eloquent cortex. The electrodes must accurately and reliably record brain activity over a wide frequency band needed for seizure event detection and deliver electrical stimulation within safety limits for brain mapping. The ability of the devices to meet these performance criteria is tested using electrochemical evaluation, which is a critical step in the path to commercialization of implantable medical devices. Driven by a constant need to develop new technologies or improve upon existing ones with potential to enhance the tissue/electrode interaction, here we present a thorough electrochemical characterization of two implantable thin-film SDG and sEEG arrays.??

Resting-State fMRI Can Detect Alterations in Seizure Onset and Spread Regions in Patients with Non-Lesional Epilepsy: A Pilot Study.

Epilepsy is defined as non-lesional (NLE) when a lesion cannot be localized via standard neuroimaging. NLE is known to have a poor response to surgery. Stereotactic electroencephalography (sEEG) can detect functional connectivity (FC) between zones of seizure onset (OZ) and early (ESZ) and late (LSZ) spread. We examined whether resting-state fMRI (rsfMRI) can detect FC alterations in NLE to see whether noninvasive imaging techniques can localize areas of seizure propagation to potentially target for intervention. This is a retrospective study of 8 patients with refractory NLE who underwent sEEG electrode implantation and 10 controls. The OZ, ESZ, and LSZ were identified by generating regions around sEEG contacts that recorded seizure activity. Amplitude synchronization analysis was used to detect the correlation of the OZ to the ESZ. This was also done using the OZ and ESZ of each NLE patient for each control. Patients with NLE were compared to controls individually using Wilcoxon tests and as a group using Mann-Whitney tests. Amplitude of low-frequency fluctuations (ALFF), fractional ALFF (fALFF), regional homogeneity (ReHo), degree of centrality (DoC), and voxel-mirrored homotopic connectivity (VMHC) were calculated as the difference between NLE and controls and compared between the OZ and ESZ and to zero. A general linear model was used with age as a covariate with Bonferroni correction for multiple comparisons. Five out of 8 patients with NLE showed decreased correlations from the OZ to the ESZ. Group analysis showed patients with NLE had lower connectivity with the ESZ. Patients with NLE showed higher fALFF and ReHo in the OZ but not the ESZ, and higher DoC in the OZ and ESZ. Our results indicate that patients with NLE show high levels of activity but dysfunctional connections in seizure-related areas. rsfMRI analysis showed decreased connectivity directly between seizure-related areas, while FC metric analysis revealed increases in local and global connectivity in seizure-related areas. FC analysis of rsfMRI can detect functional disruption that may expose the pathophysiology underlying NLE.

0610 The effects of wakefulness promoting agents on neuronal activity in nucleus accumbens

Abstract Introduction Both modafinil and methylphenidate are frequently utilized for maintenance of wakefulness in narcolepsy and other sleep disorders. Both have been demonstrated to affect dopamine transporter, leading to an increase extracellular dopamine. Subsequent functional connectivity changes between nucleus accumbens and pallidum are noted. Animal studies demonstrate changes in neuronal activity with methylphenidate in nucleus accumbens. To our knowledge there has been no direct examination of human neural activity in nucleus accumbens after administration of modafinil or methylphenidate, compared to baseline. Methods Two subjects with placement of stereotactic electroencephalographic (sEEG) electrodes to identify optimal location for permanent deep brain stimulation electrodes in nucleus accumbens were given wakefulness promoting agents to optimize testing of stimulation sites during inpatient hospitalization. Assessment occurred at least 48 hours following surgical electrode insertion under inhaled general anesthesia. Retrospective analysis was performed on neural activity in nucleus accumbens during rest on and off medication. Frequency content was calculated in the following bands: delta (1-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz), gamma (30-50 Hz), and high gamma (70-100 Hz). Power in each band is reported as the percentage contribution of each band to summed power across all bands. Results Total power was noted to be lower with both modafinil and methylphenidate. With modafinil, the beta band ratio was decreased (22.3% vs. 30.5%), the gamma band ratio was increased (24% vs. 22.4%), and the high gamma band was increased (39.5% vs. 32.9%). With methylphenidate, only the high gamma band was increased (40.3% vs. 22.9%). Conclusion Both methylphenidate and modafinil increase high gamma band neural activity in nucleus accumbens, while modafinil has additional effects on beta and gamma bands. Further assessment of modafinil and methylphenidate’s effects on neural activity are indicated to help better understand their mechanism of action and appropriate use as wakefulness promoting agents. Support (if any)

Yield of Stereotactic Electroencephalography for evaluation of Drug Resistant Focal Epilepsy: Single-Center Experience. (P2-1.009)

<h3>Objective:</h3> This study aims to report our initial experience with the effectiveness, safety, and outcomes following the adoption of stereotactic electroencephalography (sEEG) technique for surgical evaluation of patients with drug-resistant focal epilepsy. <h3>Background:</h3> A growing number of North American epilepsy centers are looking to offer intracranial evaluation for epilepsy surgery. This invasive procedure can result in symptomatic and asymptomatic hemorrhage, neurologic deficits, electrode malfunction, and failure to complete investigation. <h3>Design/Methods:</h3> This was a retrospective, single-center, observational study which reviewed every patient undergoing Phase II monitoring at our center from 2019 to 2022. At our center, 21 patients underwent sEEG monitoring, and 225 sEEG electrodes were implanted. Variables collected included demographic data, Phase I data, type of coverage (unilateral vs. bilateral), length of in-hospital stay, rate of complications, and seizure-free outcome using the ENGEL surgical outcome scale. <h3>Results:</h3> Among the 21 patients who were implanted, 7 (33.3%) were completely asymptomatic following the procedure. The most common complication was a headache in 9 patients (42.8%), followed by asymptomatic hemorrhage in 3 patients (14.2%). Only one patient (4.76%) experienced symptomatic hemorrhage but required no surgical intervention. Other less common complications included vasogenic edema at the surgical site, perceived cognitive slowing, visual hallucinations, and dislodged electrodes requiring revision. One patient had a complete resolution of seizures following sEEG implantation. The average duration of hospitalization was eight days, with a trend towards more extended hospitalization in patients experiencing procedural complications. SEEG method confirmed the epileptogenic zone in 15 patients (68%). Of these, 11 patients (50%) underwent surgical resection or ablation, and four (18%) received neuromodulation. 72% (n=8/11) achieved seizure freedom (i.e., ENGEL-I outcome). <h3>Conclusions:</h3> New surgical epilepsy centers can safely adopt sEEG while anticipating a relatively low rate of debilitating complications from the procedure. The rate of complications documented in our cohort is comparable to other established surgical epilepsy programs. <b>Disclosure:</b> Dr. Luan has nothing to disclose. Dr. Singh has nothing to disclose.