Electrocorticography Monitoring Research Articles

Customized Flexible Osteoid Electrode for Traumatic Brain Injury Induced Posttraumatic Epilepsy Monitoring

AbstractTraumatic brain injury (TBI)‐induced post‐traumatic epilepsy (PTE) is a serious brain disease that causes the loss of motor functions, cognitive impairments, and even death. Real‐time and long‐term electrophysiological signal monitoring has significant implication for the treatment of patient with TBI. Brain–computer interfaces (BCIs) utilizing flexible electrodes enable accurate epilepsy identification by electrocorticography (ECoG) signal monitoring. In this study, a customized flexible osteoid electrode is developed, which contributes to demands and personal differentiation among patients with TBI. The end product of osteoid electrode after full osseointegration will be a stable and firmly integrated structure within the bone tissue, providing a secure platform for continuous electrophysiological signal monitoring. The flexibility and conductivity of the osteoid electrode enables high‐quality and long‐term epilepsy monitoring. Biocompatibility of the osteoid electrode is also demonstrated by in vitro cell experiments. Simultaneously, the porous osteoid electrode also exhibits osseointegration ability based on potential long‐term ECoG signal monitoring, which suggests its potential for the comprehensive treatment of TBI patients. This work not only introduces a potential therapeutic scaffold for TBI‐related diseases, but also provides promising techniques for clinical ECoG monitoring in patients with TBI.

Automatic Epilepsy Detection using Machine Learning

Epilepsy is a brain disorder which causes seizures. Nerve cell activity of brain is disturbed which repeated seizures and disrupts the normal life of human. The nerve cells are connected with each other in complex way to communicate with each other. Epilepsy is neurological disorder where these nerve cells function in different way. This can be evaluated with help of Electroencephalogram (EEG) and Electrocorticography (ECoG) monitoring. Electroencephalogram help to check the signals of brain through images. These when monitored through machine learning system can help to evaluate whether the person has epilepsy disorder. The high-volume data is used to classify the disorder with machine learning classifier and statistical features The system is implemented with convolutional neural network for high dataset of image of signals of Electroencephalogram to classify the disorder. The research is ongoing where the performance is evaluated with different classifier and features.

P.121 Memantine inhibits cortical spreading depolarization and improves neurovascular function following traumatic brain injury: results of a randomized pre-clinical trial

Background: Cortical spreading depolarization (CSD) is associated with poor outcomes following traumatic brain injury (TBI). Here we aimed to: (1) determine the effect of NMDA-receptor antagonism on CSDs in healthy and TBI animals in vivo; and (2) conduct a randomized pre-clinical trial (RCT) of memantine for prevention neurological decline following repetitive mild TBI (rmTBI). Methods: Rodents received either one moderate (n = 23) or four daily mild (rmTBI; n = 30) head impacts (weight drop). Sham animals received brief anesthetic without TBI (n = 40). 93 animals underwent cranial window surgery with electrocorticographic (ECoG) monitoring and electrically triggered CSDs. Ketamine (100uM topical or 25 mg/kg IP) and memantine (10 mg/kg IP) were tested in vivo. An RCT was conducted (N=31) using memantine (10 mg/kg) or saline (2.5 cc/kg) for rmTBI with daily neurobehavioural testing. Results: In TBI animals, ketamine or memantine inhibited CSDs in 44-88%, and 50-67% of cases, respectively. Near-DC/AC-ECoG amplitude was reduced by 44-75% and 52-67%, and duration by 39-87% and 61-78%, respectively. RCT animals that received memantine had higher mean neurological scores (9.27 (SD 3.08) vs. 5.56 (SD 3.05), p< 0.001) vs. saline. Conclusions: Memantine suppressed CSDs following TBI, in vivo. In a pre-clinical RCT of rmTBI, memantine prevented neurological decline.

Increased Perirolandic Cortical Excitability May Facilitate Sensory Motor Mapping in Children (P13-1.003)

<h3>Objective:</h3> We are hereby describing a case of refractory pediatric epilepsy where resection of perirolandic seizure foci was performed successfully under neurophysiologic guidance. <h3>Background:</h3> Pediatric neurophysiologic sensory-motor mapping is frequently unsuccessful, due to inability to localize central sulcus (CS) and primary motor cortex (M1). These shortcomings result from poor somatosensory evoked potentials (SSEP) and high M1 depolarization thresholds respectively, both reflections of the immaturity of the central nervous system. <h3>Design/Methods:</h3> Case report <h3>Results:</h3> An 8-year-old boy with developmental delay, debilitating focal epilepsy and epileptic encephalopathy underwent phase 2 video EEG monitoring. The recordings showed seizures with early involvement of several depth electrodes located within the right parieto-frontal regions, and an early motor semiology involving the left arm. The patient underwent neurophysiologically guided resection of the seizure foci under general anesthesia. Pre-resection electrocorticography (ECoG) via a 64 contact grid showed abundant perirolandic epileptiform discharges (ED), maximal postcentrally. Cortical recordings of high amplitude median SSEP and a low depolarization threshold led to successful CS localization and identification of M1, respectively. A subdural strip electrode placed over the precentral gyrus and secured in position, allowed simultaneous ECoG and motor monitoring during the resection of the postcentral foci. Initially, ECoG showed near continuous runs of ED, unchanged by cortical electrical stimulation. Under steady state anesthesia, at a constant propofol infusion rate, this activity decreased in frequency and stopped altogether towards the end stages of the resection, as the M1 threshold increased by 7 mA. Post-resection fronto-parietal ECoG recordings were quiet. Post-operatively, the patient became seizure free, showed cognitive improvement and no motor deficits. <h3>Conclusions:</h3> Increased cortical excitability may lead to successful functional mapping in children. Under steady anesthetic conditions, increases in the M1 threshold during resection of nearby epileptic foci may be an early sign of decrease in the abnormal regional cortical excitability. <b>Disclosure:</b> Dr. Alzahrany has nothing to disclose. Dr. Simon has received personal compensation in the range of $500-$4,999 for serving as an Expert Witness for Risk Management Foundation of the Harvard Institutions Incorporated. Dr. Simon has received personal compensation in the range of $5,000-$9,999 for serving as an Expert Witness for MCIC Vermont. Dr. Simon has received personal compensation in the range of $5,000-$9,999 for serving as an Expert Witness for Aaronson, Rappaport, Feinstein&amp; Deutch. Dr. Simon has received publishing royalties from a publication relating to health care. Dr. Simon has received personal compensation in the range of $0-$499 for serving as a Speaker with American Clinical Neurophysiology Society . Dr. Simon has a non-compensated relationship as a Speaker with International Society of Intraoperative Neurophysiology that is relevant to AAN interests or activities. Dr. Simon has a non-compensated relationship as a Speaker with Brazilian Congress of Neurology that is relevant to AAN interests or activities.

Less-invasive subdural electrocorticography for investigation of spreading depolarizations in patients with subarachnoid hemorrhage.

Wyler-strip electrodes for subdural electrocorticography (ECoG) are the gold standard for continuous bed-side monitoring of pathological cortical network events, such as spreading depolarizations (SD) and electrographic seizures. Recently, SD associated parameters were shown to be (1) a marker of early brain damage after aneurysmal subarachnoid hemorrhage (aSAH), (2) the strongest real-time predictor of delayed cerebral ischemia currently known, and (3) the second strongest predictor of patient outcome at 7 months. The strongest predictor of patient outcome at 7 months was focal brain damage segmented on neuroimaging 2 weeks after the initial hemorrhage, whereas the initial focal brain damage was inferior to the SD variables as a predictor for patient outcome. However, the implantation of Wyler-strip electrodes typically requires either a craniotomy or an enlarged burr hole. Neuromonitoring via an enlarged burr hole has been performed in only about 10% of the total patients monitored. In the present pilot study, we investigated the feasibility of ECoG monitoring via a less invasive burrhole approach using a Spencer-type electrode array, which was implanted subdurally rather than in the depth of the parenchyma. Seven aSAH patients requiring extraventricular drainage (EVD) were included. For electrode placement, the burr hole over which the EVD was simultaneously placed, was used in all cases. After electrode implantation, continuous, direct current (DC)/alternating current (AC)-ECoG monitoring was performed at bedside in our Neurointensive Care unit. ECoGs were analyzed following the recommendations of the Co-Operative Studies on Brain Injury Depolarizations (COSBID). Subdural Spencer-type electrode arrays permitted high-quality ECoG recording. During a cumulative monitoring period of 1,194.5 hours and a median monitoring period of 201.3 (interquartile range: 126.1-209.4) hours per patient, 84 SDs were identified. Numbers of SDs, isoelectric SDs and clustered SDs per recording day, and peak total SD-induced depression duration of a recording day were not significantly different from the previously reported results of the prospective, observational, multicenter, cohort, diagnostic phase III trial, DISCHARGE-1. No adverse events related to electrode implantation were noted. In conclusion, our findings support the safety and feasibility of less-invasive subdural electrode implantation for reliable SD-monitoring.

Transcranial focused ultrasound and electrocorticography-based closed-loop epilepsy control system for an awake rat model

Abstract Neurostimulation with closed-loop interaction is one of the clinical solutions for patients with drug-resistant epilepsy. However, there are growing demands for an epilepsy control system with minimal invasiveness. Transcranial focused ultrasound (tFUS) is a promising non-invasive neuromodulation technique for controlling epileptic seizures due to its superior spatial specificity and depth penetrability. Here, we demonstrated a tFUS-based closed-loop system in combination with electrocorticography (ECoG), which provides precise monitoring of epileptic discharge for epileptic patients. In-house built 16-ch ECoG electrodes were attached to the Sprague-Dawley rat’s dura for detecting seizure spike-wave proceeding high-frequency oscillations (HFO) and monitoring epileptic discharges. After recovery from the surgery, kainic acid (5 mg/kg) was injected to generate a temporal lobe epilepsy rat model. An ultrasonic transducer operating at a fundamental frequency of 300 kHz was attached to the scalp for tFUS stimulation, which was automatically controlled by the system based on the HFO detection algorithm with real-time ECoG monitoring. The closed-loop tFUS stimulation on the right hippocampus with 40 Hz pulse-repetition frequency (PRF) and 5 % duty cycle induced the diminution of the duration of seizure spike-wave and the suppression of the power of brain oscillations such as theta, gamma bands from the bilateral hemisphere, compared to sham stimulation. Furthermore, the developed system is able to adjust the sonication protocol by monitoring seizure spike-wave. We therefore could provide optimized control of tFUS stimulation for seizure suppression. We demonstrated an ultrasound-based closed-loop system inhibiting epileptiform activity by providing tFUS stimulation before the generation of an epileptic spike-wave. The proposed system in this study shows the potential for developing a system that provides non-invasive seizure control without additional surgical burden for patients who are wearing medical brain implants such as ECoG or other types of intracranial EEG electrodes. Research Category and Technology and Methods Basic Research: 6. Pulsed Ultrasound (pUS) Keywords: transcranial focused ultrasound, closed-loop control, epilepsy, ECoG

Synchronization clusters located on epileptic onset zones in neocortical epilepsy

BackgroundBrain function is thought to rely on complex interactions of dynamic neural systems, which depend on the integrity of structural and functional networks. Focal epilepsy is considered to result from excessive focal synchronization in the network. Synchronization analysis of multichannel electrocorticography (ECoG) contributes to the understanding of and orientation of epilepsy. The aim of this study was to explore the synchronization in multichannel ECoG recordings from patients with neocortical epilepsy and characterize neural activity inside and outside the onset zone.MethodsFour patients with neocortical epilepsy, who became seizure-free for more than 1 year after surgery guided by ECoG monitoring, were included in this study. ECoG data recorded during pre-surgical evaluation were analyzed. Synchronizations in phase and amplitude of different frequency bands between ECoG channels was analyzed using MATLAB. We generated 100 surrogate data from the original ECoG data using Amplitude Adjusted Fourier Transform to calculate the enhanced synchronization. The relationship between synchronization characteristics and seizure onset zone was analyzed.ResultsWe found synchronization clusters in the 14–30 Hz and 30–80 Hz bands around the onset areas during both interictal and the beginning of ictal periods in all four patients.ConclusionsThe enhanced-synchronization clusters play a central role in epilepsy, and may activate the onset areas and contribute to the spreading of epileptiform activity.

Mapping spreading depolarisations after traumatic brain injury: a pilot clinical study protocol

IntroductionCortical spreading depolarisation (CSD) is characterised by a near-complete loss of the ionic membrane potential of cortical neurons and glia propagating across the cerebral cortex, which generates a transient suppression...

The Relationship Between Seizures and Spreading Depolarizations in Patients with Severe Traumatic Brain Injury.

Both seizures and spreading depolarizations (SDs) are commonly detected using electrocorticography (ECoG) after severe traumatic brain injury (TBI). A close relationship between seizures and SDs has been described, but the implications of detecting either or both remain unclear. We sought to characterize the relationship between these two phenomena and their clinical significance. We performed a post hoc analysis of a prospective observational clinical study of patients with severe TBI requiring neurosurgery at five academic neurotrauma centers. A subdural electrode array was placed intraoperatively and ECoG was recorded during intensive care. SDs, seizures, and high-frequency background characteristics were quantified offline using published standards and terminology. The primary outcome was the Glasgow Outcome Scale-Extended score at 6months post injury. There were 138 patients with valid ECoG recordings; the mean age was 47 ± 19years, and 104 (75%) were men. Overall, 2,219 ECoG-detected seizures occurred in 38 of 138 (28%) patients in a bimodal pattern, with peak incidences at 1.7-1.8days and 3.8-4.0days post injury. Seizures detected on scalp electroencephalography (EEG) were diagnosed by standard clinical care in only 18 of 138 (13%). Of 15 patients with ECoG-detected seizures and contemporaneous scalp EEG, seven (47%) had no definite scalp EEG correlate. ECoG-detected seizures were significantly associated with the severity and number of SDs, which occurred in 83 of 138 (60%) of patients. Temporal interactions were observed in 17 of 24 (70.8%) patients with both ECoG-detected seizures and SDs. After controlling for known prognostic covariates and the presence of SDs, seizures detected on either ECoG or scalp EEG did not have an independent association with 6-month functional outcome but portended worse outcome among those with clustered or isoelectric SDs. In patients with severe TBI requiring neurosurgery, seizures were half as common as SDs. Seizures would have gone undetected without ECoG monitoring in 20% of patients. Although seizures alone did not influence 6-month functional outcomes in this cohort, they were independently associated with electrographic worsening and a lack of motor improvement following surgery. Temporal interactions between ECoG-detected seizures and SDs were common and held prognostic implications. Together, seizures and SDs may occur along a dynamic continuum of factors critical to the development of secondary brain injury. ECoG provides information integral to the clinical management of patients with TBI.

To Analyze the Application Value of Perioperative Nursing Care in Patients with Resected Brain Tumor Accompanied with Epileptic Symptoms under Cortical Electrocorticography Monitoring

Objective To explore the application value of perioperative nursing for patients with brain tumors with epilepsy symptoms under the cortical electrocorticography (EEG) monitoring. Methods A total of 86 patients with brain tumor complicated with epilepsy admitted to the department of brain surgery of our hospital from January 2018 to December 2019 were selected as the research objects, and all underwent resection under cortical EEG monitoring. According to different nursing methods, they were divided into the control group and observation group, each with 43 cases. The control group was given perioperative basic nursing, and the observation group was given perioperative comprehensive nursing. The EEG image of the patient during the operation was observed by a portable EEG monitor. Anxiety and depression were assessed by self-rating anxiety scale (SAS) and self-rating depression scale (SDS) scores. The self-made satisfaction questionnaire was used to investigate the nursing satisfaction. A visual analogue (VAS) score is used to assess pain degree. A multiparameter monitor was used to detect the patient's heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP). The quality of life was assessed by the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-30). The complication rate and recurrence rate were also counted. Results Eighty-six patients with epileptic brain tumor developed spikes in 35 cases, including 7 meningiomas, 22 gliomas, and 6 cholesteatomas; 27 cases of sharp waves, including 14 meningiomas, 12 gliomas, and 1 case of cholesteatomas; and 24 cases of complex wave, including 9 cases of meningioma, 13 cases of glioma, and 2 cases of cholesteatoma. There was no significant difference in the scores of SAS, SDS, VAS, HR, SBP, DBP, and quality of life between the two groups at T0. The VAS score increased at T1 and T2, and the increase in the control group was greater than that in the observation group. At T3 and T4, the SAS, SDS, and VAS scores of the two groups decreased, and the observation group decreased more than the control group. HR, SBP, and DBP of the two groups showed an upward trend at T1 and T2, and the increase in the control group was more significant than that in the observation group. At T3, the three indicators of the two groups decreased, and the observation group decreased more significantly than the control group. At T4, the scores of all indicators of the quality of life of the two groups increased, and the observation group increased more significantly than the control group. The nursing satisfaction of the observation group was higher than that of the control group. The complication rate and recurrence rate in the observation group were decreased compared with the control group. Conclusion Perioperative comprehensive nursing intervention for patients with epileptic brain tumor undergoing resection under cortical EEG monitoring can reduce or even eliminate the recurrence rate of epilepsy, reduce the patient's pain and stress response, and improve the patient's quality of life. It can also reduce the occurrence of complications, improve nursing satisfaction, thereby improving patient compliance, and has a high clinical application value.

Spreading Depolarization After Chronic Subdural Hematoma Evacuation: Associated Clinical Risk Factors and Influence on Clinical Outcome.

Chronic subdural hematoma (cSDH) is a common neurosurgical condition responsible for excess morbidity, particularly in the geriatric population. Recovery after evacuation is complicated by fluctuating neurological deficits in a high proportion of patients. We previously demonstrated that spreading depolarizations (SDs) may be responsible for some of these events. In this study, we aim to determine candidate risk factors for probable SD and assess the influence of probable SD on outcome. We used two cohorts who underwent surgery for cSDH. The first cohort (n = 40) had electrocorticographic monitoring to detect SD. In the second cohort (n = 345), we retrospectively identified subjects with suspected SD based on the presence of transient neurological symptoms not explained by structural etiology or ictal activity on electroencephalography. We extracted standard demographic and outcome variables for comparisons and modeling. Of 345 subjects, 80 (23%) were identified in the retrospective cohort as having probable SD. Potential risk factors included history of hypertension, worse clinical presentation on the Glasgow Coma Scale, and lower Hounsfield unit density and volume of the preoperative subdural hematoma. Probable SD was associated with multiple worse-outcome measures, including length of stay and clinical outcomes, but not increased mortality. On a multivariable analysis, probable SD was independently associated with worse outcome, determined by the Glasgow Outcome Scale score at the first clinic follow-up (odds ratio 1.793, 95% confidence interval 1.022-3.146) and longer hospital length of stay (odds ratio 7.952, 95% confidence interval 4.062-15.563). Unexplained neurological deficits after surgery for cSDH occur in nearly a quarter of patients and may be explained by SD. We identified several potential candidate risk factors. Patients with probable SD have worse outcomes, independent of other baseline risk factors. Further data with gold standard monitoring are needed to evaluate for possible predictors of SD to target therapies to a high-risk population.

Invasive Multimodal Neuromonitoring in Aneurysmal Subarachnoid Hemorrhage: A Systematic Review.

Aneurysmal subarachnoid hemorrhage is a devastating disease leaving surviving patients often severely disabled. Delayed cerebral ischemia (DCI) has been identified as one of the main contributors to poor clinical outcome after subarachnoid hemorrhage. The objective of this review is to summarize existing clinical evidence assessing the diagnostic value of invasive neuromonitoring (INM) in detecting DCI and provide an update of evidence since the 2014 consensus statement on multimodality monitoring in neurocritical care. Three invasive monitoring techniques were targeted in the data collection process: brain tissue oxygen tension (ptiO2), cerebral microdialysis, and electrocorticography. Prospective and retrospective studies as well as case series (≥10 patients) were included as long as monitoring was used to detect DCI or guide DCI treatment. Forty-seven studies reporting INM in the context of DCI were included (ptiO2: N=21; cerebral microdialysis: N=22; electrocorticography: N=4). Changes in brain oxygen tension are associated with angiographic vasospasm or reduction in regional cerebral blood flow. Metabolic monitoring with trend analysis of the lactate to pyruvate ratio using cerebral microdialysis, identifies patients at risk for DCI. Clusters of cortical spreading depolarizations are associated with clinical neurological worsening and cerebral infarction in selected patients receiving electrocorticography monitoring. Data supports the use of INM for the detection of DCI in selected patients. Generalizability to all subarachnoid hemorrhage patients is limited by design bias of available studies and lack of randomized trials. Continuous data recording with trend analysis and the combination of INM modalities can provide tailored treatment support in patients at high risk for DCI. Future trials should test interventions triggered by INM in relation to cerebral infarctions.

Pitfalls of Commonly Used Ischemic and Dementia Models Due to Early Seizure by Carotid Ligation.

While the bilateral common carotid artery (CCA) ligation model is widely used in cerebrovascular disease and dementia studies, it can frequently cause seizures. We examined the validity of seizure as an experimental model of ischemia. Eight-week-old male Wistar and Sprague-Dawley (SD) rats were implanted with electrocorticography (ECoG) electrodes and bilateral CCA ligation was performed and compared to the sham groups. ECoG monitoring was used to confirm the seizure discharge and count the number of spikes in the interictal phase 2 h after ligation, followed by power spectral analysis. Magnetic resonance imaging (MRI) was performed 6 h after bilateral CCA ligation to assess fractional anisotropy (FA), apparent diffusion coefficient (ADC), and cerebral blood flow (CBF) values. Magnetic resonance spectroscopy (MRS) was also performed and the ischemic parameters and electrophysiological changes were compared. The Wistar rat group had significantly higher mortality, frequency of seizures, incidence of non-convulsive seizures, and number of spikes in the interictal period compared to those in the SD rat group. Power spectral analysis showed increased power in the delta band in both Wistar and SD rat groups. MRI, after CCA ligation, showed significantly lower ADC values, lower glutamine and glutamate levels, and higher lactate values in Wistar rats, although there was no difference in FA values. Metabolic and electrophysiological changes after CCA ligation differed according to the rat strain. Wistar rats were prone to increased lactate and decreased glutamine and glutamate levels and the development of status epilepticus. Seizures can affect the results of ischemic experiments.

Early Findings of Intracortical Depth Electrocorticography Monitoring in Traumatic Brain Injury Patients

Early Findings of Intracortical Depth Electrocorticography Monitoring in Traumatic Brain Injury Patients

Electrocorticography in patients with severe traumatic brain injury

Introduction. The frequency of adverse outcomes in patients with severe traumatic brain injury (TBI) exceeds 25%. Epileptic seizures and vasospasm, in the absence of pathogenetic treatment, cause irreversible brain damage and thus complicate the course of severe TBI. Bedside electroencephalography (EEG) is traditionally used to diagnose these conditions. However, its low spatial resolution when recording from the scalp and a large number of artefacts that make it challenging to analyse the data. Materials and methods. Electrocorticography (ECoG) monitoring was performed using subdural electrodes implanted in the traumatic brain lesion during TBI surgery in 11 patients during the acute period of severe TBI. All patients were concurrently monitored using scalp EEG with subdermal needle electrodes. Results. Analysis of scalp recordings showed frequency disturbances and oscillation asymmetry in all patients, while sporadic epileptiform activity and rhythmic and periodic patterns were detected in 18% and 64% of subjects, respectively. Analysis of invasive EEG showed sporadic epileptiform activity in 27% of patients, while rhythmic and periodic patterns were present in 91%. Moreover, epileptiform activity was registered only by the subdural leads in 3 patients. The total percentage of subjects in whom we registered clinical and electrographic signs of convulsive and non-convulsive status epilepticus using EEG and ECoG was 55%. We found indirect EEG signs of slow-spreading cortical depolarization in one patient whose level of consciousness was coma, followed by an electrographic pattern of status epilepticus on ECoG. Conclusion. ECoG recording, while patients with severe TBI are in the intensive care unit, increases the diagnostic capabilities of this method, allowing electrographic seizures to be recorded more often and more accurately, but also to detect indirect signs of slow-spreading cortical depolarization using standard EEG amplifiers. Electrode implantation during TBI surgery is safe and does not significantly change the surgical approach.

Electrocorticographic events from long-term ambulatory brain recordings can potentially supplement seizure diaries

PurposeTo determine the feasibility of using epileptiform events detected by continuous electrocorticographic monitoring via a brain-responsive neurostimulation system to supplement patient-maintained seizure diaries. MethodsData were retrospectively analyzed from a randomized controlled trial of brain-responsive neurostimulation (RNS® System) for adjunctive treatment of medically intractable focal onset seizures in 191 subjects. The long-term (≥3 months) correspondence between daily counts of diary-reported seizures and device-recorded “long epileptiform events” (LEs), a proxy for electrographic seizures (ESs), was assessed using cross-correlation and logistic generalized estimating equation models. ResultsDiary-reported seizures and LEs significantly co-varied across days in 124 patients whose detection settings were held constant, with a significantly higher correlation in 54 patients (44 %) whose LEs were usually ESs (high concordance patients). There were more days in which LEs were detected than days in which patients reported a seizure (positive predictive value (PPV): 34 %). On days when there were no LEs, there were typically no diary-reported seizures (negative predictive value (NPV): 90 %). In patients with a high concordance between LEs and ESs, the PPV and NPV were both slightly higher, 43 % (35–52 %) and 93 % (95 % CI: 86–97 %) respectively. ConclusionAlthough LEs can substantially outnumber diary reported seizures, the high across-day correlation and strong NPV between LEs and diary seizures suggests that LEs recorded by the RNS® System could potentially supplement seizure diaries by providing an objective biomarker for relative seizure burden.

Effect of sevoflurane on high-frequency brain electrical activity

Background. In 30 % of cases with epilepsy, it qualifies as medically intractable and requires surgical treatment. The need for improvement of epilepsy surgery effectiveness demands updating of the preoperative assessment protocols. Intraoperative wide-range electrocorticography is a novel technique for defining resection volume in focal structural epilepsy. Combined analysis of high-frequency and epileptiform activity provides additional information and allows prognosticating of surgery outcome. However, consistent evaluation of intraoperative monitoring results is only possible when general anesthetic effect on brain electrical activity is taken into account.Objective. This study was aimed at evaluation of anesthetic gas sevoflurane effect on high-frequency brain electrical activity, recorded directly from the cortex or deep brain structures.Design and methods. Eight patients were included in this study (2 females, 6 males), aged 19 to 47, with a long-term epilepsy (disease duration 15 to 38 years). Prolonged electrocorticographic monitoring was indicated to these patients, combined with eloquent zones mapping in some cases. Patients were implanted with grid electrodes on frontal and temporal cortex, and deep brain Spencer electrodes into the mesial temporal lobe. Wide-range electrocorticography was recorded during slow-wave sleep and intraoperatively under sevoflurane anesthesia. Pathological high-frequency oscillations (pHFOs) rate was counted.Results. In seven patients pHFOs were recorded extraoperatively. Pathological HFO rate varied between 13 and 30 % (mean — 19 %). Distribution of pHFO did not change due to anesthesia effects. Mean background noise amplitude was significantly decreased intraoperatively (z = 2.45; p = 0.014). This effect facilitated visual marking of pHFOs. There were no trends in comparison between extraoperative and intraoperative pHFO rate.Conclusion. Well-controlled levels of general anesthesia obtained with sevoflurane (0,9-1,1 MAC) showed minimal effect on high-frequency brain electrical activity. This allows thorough analysis of wide-range electrocorticogiaphy without waking the patient and provides more information about the extension of the epileptogenic zone and its resection rate intraoperatively.

Phase-dependent modulation of cortical and thalamic sensory responses during spike-and-wave discharges.

The neuronal underpinnings of impaired consciousness during absence seizures remain largely unknown. Spike-and-wave (SW) activity associated with absences imposes two extremely different states in cortical neurons, which transition from suprathreshold synaptic depolarizations during spike phases to membrane hyperpolarization and electrical silence during wave phases. To investigate whether this rhythmic alternation of neuronal states affects the processing of sensory information during seizures, we examined cortical and thalamic responsiveness to brief sensory stimuli in the different phases of the epileptic cycle. Electrocorticographic (ECoG) monitoring from the primary somatosensory cortex combined with intracellular recordings of subjacent pyramidal neurons, or extracellular recordings of somatosensory thalamic neurons, were performed in the Genetic Absence Epilepsy Rat From Strasbourg. Sensory stimuli consisted of pulses of compressed air applied to the contralateral whiskers. Whisker stimuli delivered during spike phases evoked smaller depolarizing synaptic potentials and fewer action potentials in cortical neurons compared to stimuli occurring during wave phases. This spike-related attenuation of cortical responsiveness was accompanied by a reduced neuronal membrane resistance, likely due to the large increase in synaptic conductance. Sensory-evoked firing in thalamocortical neurons was also decreased during ECoG spikes as compared to wave phases, indicating that time-to-time changes in the thalamocortical volley may also contribute to the variability of cortical responses during seizures. These findings demonstrate that thalamocortical sensory processing during absence seizures is nonstationary and strongly suggest that the cortical impact of a given environmental stimulus is conditioned by its exact timing relative to the SW cycle. The lack of stability of thalamic and cortical responses along seizures may contribute to impaired conscious sensory perception during absences.

Somatosensation Evoked by Cortical Surface Stimulation of the Human Primary Somatosensory Cortex.

Electrical stimulation of the primary somatosensory cortex using intracranial electrodes is crucial for the evocation of artificial somatosensations, typically tactile sensations associated with specific regions of the body, in brain-machine interface (BMI) applications. The qualitative characteristics of these artificially evoked somatosensations has been well documented. As of yet, however, the quantitative aspects of these evoked somatosensations, that is to say the quantitative relationship between intensity of electrical stimulation and perceived intensity of the resultant somatosensation remains obscure. This study aimed to explore this quantitative relationship by surface electrical stimulation of the primary somatosensory cortex in two human participants undergoing electrocorticographic monitoring prior to surgical treatment of intractable epilepsy. Electrocorticogram electrodes on the primary somatosensory cortical surface were stimulated with varying current intensities, and a visual analogue scale was employed to provide a quantitative measure of intensity of the evoked sensations. Evoked sensations included those of the thumb, tongue, and hand. A clear linear relationship between current intensity and perceived intensity of sensation was observed. These findings provide novel insight into the quantitative nature of primary somatosensory cortex electrical stimulation-evoked sensation for development of somatosensory neuroprosthetics for clinical use.

Correlates of Spreading Depolarization, Spreading Depression, and Negative Ultraslow Potential in Epidural Versus Subdural Electrocorticography.

Spreading depolarizations (SDs) are characterized by near-complete breakdown of the transmembrane ion gradients, neuronal oedema and activity loss (=depression). The SD extreme in ischemic tissue, termed ‘terminal SD,’ shows prolonged depolarization, in addition to a slow baseline variation called ‘negative ultraslow potential’ (NUP). The NUP is the largest bioelectrical signal ever recorded from the human brain and is thought to reflect the progressive recruitment of neurons into death in the wake of SD. However, it is unclear whether the NUP is a field potential or results from contaminating sensitivities of platinum electrodes. In contrast to Ag/AgCl-based electrodes in animals, platinum/iridium electrodes are the gold standard for intracranial direct current (DC) recordings in humans. Here, we investigated the full continuum including short-lasting SDs under normoxia, long-lasting SDs under systemic hypoxia, and terminal SD under severe global ischemia using platinum/iridium electrodes in rats to better understand their recording characteristics. Sensitivities for detecting SDs or NUPs were 100% for both electrode types. Nonetheless, the platinum/iridium-recorded NUP was 10 times smaller in rats than humans. The SD continuum was then further investigated by comparing subdural platinum/iridium and epidural titanium peg electrodes in patients. In seven patients with either aneurysmal subarachnoid hemorrhage or malignant hemispheric stroke, two epidural peg electrodes were placed 10 mm from a subdural strip. We found that 31/67 SDs (46%) on the subdural strip were also detected epidurally. SDs that had longer negative DC shifts and spread more widely across the subdural strip were more likely to be observed in epidural recordings. One patient displayed an SD-initiated NUP while undergoing brain death despite continued circulatory function. The NUP’s amplitude was -150 mV subdurally and -67 mV epidurally. This suggests that the human NUP is a bioelectrical field potential rather than an artifact of electrode sensitivity to other factors, since the dura separates the epidural from the subdural compartment and the epidural microenvironment was unlikely changed, given that ventilation, arterial pressure and peripheral oxygen saturation remained constant during the NUP. Our data provide further evidence for the clinical value of invasive electrocorticographic monitoring, highlighting important possibilities as well as limitations of less invasive recording techniques.