Subdural Grid Research Articles

Increased nationwide use of stereoencephalography for intracranial epilepsy electroencephalography recordings

Intracranial electroencephalography (iEEG) can be performed using minimally invasive stereo-electroencephalography (SEEG) or by implanting subdural electrodes via a craniotomy or multiple burr holes. There is anecdotal evidence that SEEG is becoming more common in the United States, though this has yet to be quantified. To address this question, all SEEG and burr hole/craniotomy subdural iEEG procedures were extracted from the Centers for Medicare and Medicaid Services Part B data files for the years 2000–2016. National trends were compared over time. In 2016, SEEG became the most frequently performed intracranial monitoring procedure in the Medicare population, increasing from 28.8% of total cases in 2000 to 43.1% in 2016 (p = 0.02). The proportion of strip electrode cases (through burr holes) significantly declined, while the frequency of craniotomies for subdural grid placement did not significantly change. These data are consistent with a nationwide increase in the utilization of SEEG with a concomitant decline in burr hole placement of subdural strip electrodes in the United States. The factors driving these changes are unknown, but are likely due in part to the desire for minimally invasive surgical options.

Representation of steady-state visual evoked potentials elicited by luminance flicker in human occipital cortex: An electrocorticography study

Despite the widespread use of steady-state visual evoked potentials (SSVEPs) elicited by luminance flicker in clinical and research settings, their spatial and temporal representation in the occipital cortex largely remain elusive. We performed intracranial-EEG recordings in response to targets flickering at frequencies from 11 to 15 Hz using a subdural electrode grid covering the entire right occipital cortex of a human subject, and we were able to consistently locate the gazed stimulus frequency at the posterior side of the primary visual cortex (V1). Peripheral flickering, undetectable in scalp-EEG, elicited activations in the interhemispheric fissure at locations consistent with retinotopic maps. Both foveal and peripheral activations spatially coincided with activations in the high gamma band. We detected localized alpha synchronization at the lateral edge of V2 during stimulation and transient post-stimulation theta band activations at the posterior part of the occipital cortex. Scalp-EEG exhibited only a minor occipital post-stimulation theta activation, but a strong transient frontal activation.

Promises and limitations of human intracranial electroencephalography.

Intracranial electroencephalography (iEEG), also known as electrocorticography when using subdural grid electrodes or stereotactic EEG when using depth electrodes, is blossoming in various fields of human neuroscience. In this article, we highlight the potentials of iEEG in exploring functions of the human brain while also considering its limitations. The iEEG signal provides anatomically precise information about the selective engagement of neuronal populations at the millimeter scale and the temporal dynamics of their engagement at the millisecond scale. If several nodes of a given network are monitored simultaneously with implanted electrodes, the iEEG signals can also reveal information about functional interactions within and across networks during different stages of neural computation. As such, human iEEG can complement other methods of neuroscience beyond simply replicating what is already known, or can be known, from noninvasive lines of research in humans or from invasive recordings in nonhuman mammalian brains.

Mapping face categorization in the human ventral occipitotemporal cortex with direct neural intracranial recordings.

The neural basis of face categorization has been widely investigated with functional magnetic resonance imaging (fMRI), identifying a set of face-selective local regions in the ventral occipitotemporal cortex (VOTC). However, indirect recording of neural activity with fMRI is associated with large fluctuations of signal across regions, often underestimating face-selective responses in the anterior VOTC. While direct recording of neural activity with subdural grids of electrodes (electrocorticography, ECoG) or depth electrodes (stereotactic electroencephalography, SEEG) offers a unique opportunity to fill this gap in knowledge, these studies rather reveal widely distributed face-selective responses. Moreover, intracranial recordings are complicated by interindividual variability in neuroanatomy, ambiguity in definition, and quantification of responses of interest, as well as limited access to sulci with ECoG. Here, we propose to combine SEEG in large samples of individuals with fast periodic visual stimulation to objectively define, quantify, and characterize face categorization across the whole VOTC. This approach reconciles the wide distribution of neural face categorization responses with their (right) hemispheric and regional specialization, and reveals several face-selective regions in anterior VOTC sulci. We outline the challenges of this research program to understand the neural basis of face categorization and high-level visual recognition in general.

Utilizing neuronavigation for virtual electrode representation and safe resection following SEEG; a technical report

Purpose: One of the most effective treatments for epilepsy is resection, but it remains underutilized. Efforts must be made to increase the ease, safety, and efficacy of epilepsy resection to improve utilization. Studies have shown an improved risk profile of stereoelectroencephalography (SEEG) over subdural grids (SDG) for invasive monitoring. One limitation to increased adoption of SEEG at epilepsy centers is the theoretical difficulty of planning a delayed resection once electrodes are removed. Our objective was to develop and present a technique using readily available neuronavigation technology to guide a cortical, non-lesional epilepsy resection with co-registration of imaging during invasive monitoring to imaging in an explanted patient, allowing for virtual visualization of electrodes.Methods: An example case taking advantage of the technique described above as an adjunct for an anatomically guided resection is presented with technical details and images.Results: Intraoperative neuronavigation was successfully used to virtually represent previously removed SEEG electrodes and accuracy could be easily verified by examining scars on the scalp, bone, dura and pia.Conclusions: The simple technique presented can be a useful adjunct to resection following SEEG. This may help increase the adoption of SEEG, even when resection is planned.

Facing the hidden wall in mesial extratemporal lobe epilepsy.

Refractory extratemporal lobe epilepsy (ETLE) tends to have a less favourable surgical outcome in comparison to temporal lobe epilepsy. ETLE poses specific diagnostic and therapeutic challenges, particularly in cases where seizures develop from the midline. This review focuses on the diagnostic challenges and therapeutic strategies in mesial ETLE. The great diversity of interhemispheric functional areas and extensive connectivity to extramesial structures results in very heterogeneous seizure semiology. Specific signs, such as ictal body turning, can suggest a mesial onset. The hidden cortex of the mesial wall furthermore gives rise to specific diagnostic difficulties due to the low localizing value of scalp EEG. Advanced imaging, as well as targeted intracranial studies, can substantially contribute to depict the seizure onset zone since electroclinical findings are difficult to interpret in most cases. Surgical accessibility of the interhemispheric space can be challenging, both for the placement of subdural grids, as well as for resective surgery. When facing the hidden cortex on the mesial wall of the hemispheres, targeted intra- or extra-operative intracranial recordings can lead to satisfactory outcomes in properly selected cases.

Comparing Measures of Active and Passive Field Spread between non-, partially, and fully invasive human brain recordings

Event Abstract Back to Event Comparing Measures of Active and Passive Field Spread between non-, partially, and fully invasive human brain recordings Mansoureh Fahimi Hnazaee1*, Benjamin Wittevrongel1, Evelien Carrette2, Ine Dauwe2, Alfred Meurs2, Paul Boon2, Dirk Van Roost2 and Marc Van Hulle1 1 Faculty of Medicine, KU Leuven, Belgium 2 Ghent University Hospital, Belgium BACKGROUND Precise details of the propagation of neural activity on remote cortical areas are still poorly understood; this propagation refers to both electric diffusion as a result of physiological propagation of action potentials along axons (active spread) and the passive spread of the electric field over the cortical surface, also referred to as field spread, or as more commonly known, electrical volume conduction. Principles of volume conduction is of significant interest for researchers interested in solving the M/EEG inverse problem and increasing the accuracy of source localization. Therefore we need measures that can separate instantaneous signal propagation from genuine causal and functional interactions, such as methods that can reveal the temporal delay. However, no study has yet attempted to compare the influence of volume conduction for different levels of invasiveness. In this study, by using measures of phase-based and amplitude based correlations both on actual data and reconstructed sources obtained from the data for each recording modality, we try to quantify the level of volume conduction, comparing between subcortical, cortical, and scalp recordings. METHODS We recorded 3 minutes of resting state (with eyes fixating) and a rich stimuli task in 5 patients (2 female and 3 male patients) from simultaneously implanted subdural grids, depth electrodes, and scalp EEG. Areas of subdural recording were spread over left and right temporal and frontal cortex, and depth electrodes were implanted in left and/or right hippocampus in 4 patients and left insula in 1 patient. The data is decomposed into traditional frequency bands using Morlet wavelet function. Phase-based connectivity measures were used to quantify the interactions include Phase Locking Value (PLV), and imaginary part of Phase Locking Value (iPLV) whereas for Amplitude-based we used Spearman correlation coefficient. The connectivity analysis is done on both the data and on the estimated sources obtained using Independent Components Analysis (ICA). The independent sources were estimated with statistical and algorithmic reliability with the help of bootstrapping and random initialization using the Icasso software package. The calculated measures from both the original data and on the estimated independent sources are then analyzed statistically using ANOVA. CONCLUSION Our study provides a comprehensive account of the spatial spread between SEEG, ECoG and EEG. As can be expected, IPLV consistently decreases for higher frequency bands. Additionally, the lower PLV and Spearman correlation for ECoG compared to SEEG can probably be attributed to the larger average distances (larger spatial coverage) spanned by ECoG. Using ICA analysis on partially invasive and fully invasive brain recording we consistently found between 4 and 7 cortical generators, which is in accordance with previous studies on functional networks during resting state. Similar overall trends in connectivity can be seen for both raw data and reconstructed sources, however PLV and Spearman are now higher for SEEG compared to ECoG, which is likely attributed to a higher number of cortical generators discovered from ECoG. FUTURE WORK - Current results show the analysis of a single subject, further analysis would include normalizing and pooling results from all subjects in order to investigate connectivity as a function of anatomical location. When pooling results we can also account for inter-electrode distances and control these for modalities. - It has been shown that correlations are more variable and on average higher during rest than when the patient is engaged in a listening task. In this study data has been recorded from the same patients engaged during a rich stimuli task (an audio-visual movie to ensure engagement of multi-sensory and higher-level cognitive functions). A future step would be to compare task and non-task connectivity measures.

Disconnection of the pathological connectome for multifocal epilepsy surgery.

OBJECTIVERecent neuroimaging studies suggest that intractable epilepsy involves pathological functional networks as well as strong epileptogenic foci. Combining cortico-cortical evoked potential (CCEP) recording and tractography is a useful strategy for mapping functional connectivity in normal and pathological networks. In this study, the authors sought to demonstrate the efficacy of preoperative combined CCEP recording, high gamma activity (HGA) mapping, and tractography for surgical planning, and of intraoperative CCEP measures for confirmation of selective pathological network disconnection.METHODSThe authors treated 4 cases of intractable epilepsy. Diffusion tensor imaging-based tractography data were acquired before the first surgery for subdural grid implantation. HGA and CCEP investigations were done after the first surgery, before the second surgery was performed to resect epileptogenic foci, with continuous CCEP monitoring during resection.RESULTSAll 4 patients in this report had measurable pathological CCEPs. The mean negative peak-1 latency of normal CCEPs related to language functions was 22.2 ± 3.5 msec, whereas pathological CCEP latencies varied between 18.1 and 22.4 msec. Pathological CCEPs diminished after complete disconnection in all cases. At last follow-up, all of the patients were in long-term postoperative seizure-free status, although 1 patient still suffered from visual aura every other month.CONCLUSIONSCombined CCEP measurement, HGA mapping, and tractography greatly facilitated targeted disconnection of pathological networks in this study. Although CCEP recording requires technical expertise, it allows for assessment of pathological network involvement in intractable epilepsy and may improve seizure outcome.

Precision surgery of rolandic glioma and insights from extended functional mapping

ObjectivesElectrical cortical stimulation mapping (ECSM) is the current gold standard functional mapping technique; however, it is burdened by several limitations. Our objective in this study is to show that extended functional mapping modalities can (1) allow neurosurgeons to map and preserve eloquent regions that are inaccessible by the traditional ECSM technique and (2) factor into the operative decision-making process and surgical trajectory during resection of Rolandic brain tumors. Patients and methodsA 55year old patient having a right Rolandic glioblastoma underwent subdural grid implantation followed by surgical resection. Multimodal functional mapping including electrical stimulation, high gamma power mapping, functional magnetic resonance imaging, and diffusion tensor imaging were performed to define the location of the patient’s eloquent cortex and white matter tracts in relation to the tumor and determine the optimal surgical trajectory prior to resection. ResultsThe patient tolerated a safe surgical resection without any new postoperative deficits. ECSM mapping successfully delineated safe areas for resection as well as eloquent areas related to motor control and speech production. High gamma power analysis successfully mapped areas involved in arm reach. Functional MRI showed the regions related to finger tapping. DTI demonstrated the corticospinal tract and its relation to the hand motor cortex and the tumor. ConclusionAdjunct mapping techniques used to supplement the data offered by ECSM can help advance the field of functional mapping and Rolandic surgery via broadening our accessibility to the human brain and providing a comprehensive map of eloquent grey and white matter structures and their relation to the tumor.

Higher-order motor cortices actively engage in motor inhibition: Cortical stimulation and event-related potentials as an evidence from subdural grid electrodes

Higher-order motor cortices actively engage in motor inhibition: Cortical stimulation and event-related potentials as an evidence from subdural grid electrodes

350 Stereoelectroencephalography for Refractory Localization-related Epilepsy

Abstract INTRODUCTION Patients with pharmacotherapy-resistant localization-related epilepsy (LRE) may be candidates for surgical intervention if the seizure onset zone can be well localized. Long used in Europe, intracranial recording with stereoelectroencephalography (sEEG) is emerging as an alternative to subdural strip and grid techniques in North American centers. METHODS We reviewed our initial experience in a consecutive cohort of patients who underwent sEEG for extraoperative monitoring of LRE between May 2014 and September 2016. RESULTS >Fifty patients (37 adult, 13 pediatric) were implanted with 536 depth electrodes (mean 10.7 per patient, 7.9 per implanted hemisphere). Among 18 patients with suspected lesional epilepsy (including 3 with bilateral and 4 with multiple unilateral lesions), sEEG identified lesional foci in 16 (89%) cases (15 unifocal, 1 bitemporal). Two patients required further localization with subdural grids. Of 20 patients with nonlesional epilepsy, sEEG localized foci in 16 (80%) cases (13 unifocal, 2 bitemporal, 1 multifocal). Two patients had foci near eloquent cortex requiring grid placement for further mapping and two could not be focally localized. Finally, of 12 patients who had previous resections or ablations, sEEG localized foci in 11 (92%) cases (10 peri-cavity, 1 multifocal) and 1 was not focally localized. Complications were minor and rare. In 536 electrodes, there were no (0.0%) infections or symptomatic hemorrhages and 3 (0.6%) small, asymptomatic hemorrhages. One electrode was deflected into the subdural space during placement and 1 patient required replacement of 2 electrodes that were broken during seizures in the monitoring unit. CONCLUSION Robot-assisted sEEG is a safe and useful method for localizing epileptogenic foci in patients with lesional, nonlesional, and previously treated LRE. The success of seizure onset localization and safety compare favorably with invasive subdural monitoring. Longer clinical follow up will be required to determine whether sEEG monitoring improves long-term seizure freedom in these challenging epilepsy patients.

209 Surgical Outcomes with Insular and Insular-Plus Pediatric Epilepsy

Abstract INTRODUCTION It has been increasingly recognized that the insular cortex plays an important role in frontotemporal-parietal epilepsy (FTPE) in children. The insula, however, cannot be properly interrogated with conventional subdural grids, and its anatomy makes it difficult to implicate the insula with semiology or non-invasive modalities. At last year's meeting, we reported on the safety and utility of insular-depth electrode placement for interrogation of the insula. Here, we report post-surgical outcomes on 31 patients with insular-depth electrode confirmed refractory epilepsy. METHODS We used Current Procedural Terminology (CPT) billing records to identify cases of depth electrode insertion performed at our institution. Clinical information, operative reports, and pathology data from patients undergoing operative intervention was then retrospectively collected. RESULTS >Thirty-one patients underwent direct invasive sampling implicating the insula in seizure onset and prompted either thermoablation or surgical resection of some portion of the insula. Fourteen patients had biopsy-proven cortical dysplasia, Fourteen patients had suspected cortical dysplasia, two patients had tuberous sclerosis and one patient had a primary brain tumor. Fourteen patients had prior intracranial operations. Fourteen patients underwent thermoablation of the insula and seventeen underwent resection of some portion of the insula. 31% of patients who underwent thermoablation of the insular had an Engel Class outcome of I compared to 63% of patients who underwent open insular resection. Thus, in our cohort, insular resection was superior to thermoablation in achieving superior functional outcomes as measured by Engel Class. CONCLUSION Surgical resection and thermoablation of the insula are both acceptable treatments for insular and insular-plus epilepsy. In our cohort, outcomes with surgical resection were improved, although the reasons for this are unclear. Further study is required to delineate optimal operative care in patients with insular and insular-plus epilepsy.

P370 The thalamo-cortical generators of sleep spindles as revealed by laminar analysis of neocortex

Introduction Sleep spindles are generated in thalamo-cortical networks. Thalamo-cortical projections include core projections to middle and matrix projections to superficial cortical layers. It has been proposed that sleep spindles can be generated in either of these networks. Materials and methods We used electrophysiological data recorded with subdural grid and intracortical multielectrodes in five therapy-resistant epileptic patients undergoing invasive monitoring. Spindles were detected automatically in electrocorticography channels and detection-triggered laminar microelectrode recordings were analyzed. The second spatial derivative of spindle-band filtered (band pass 10–16 Hz, 96 dB) local field potential data allowed to approximate the laminar distribution of the transmembrane generators (current source density, CSD) of spindles. The information regarding the concurrent population cellular activity was obtained by applying a high frequency band filter (500–5000 Hz, 48 dB) on epoched data. Based on the histological reconstructions of laminar electrode tracks, we could identify the precise laminar localization of current sources and sinks. Results Results indicate highly heterogeneous intracortical local field potentials during sleep spindles, and maximum CSD in layer I, II and IV. Multi-unit activity was increased in spindle troughs as it was identified based on the spindle band filtered local field potentials. The single unit analyis revealed preferential firing of most neurons during the positive-negative phase transition of spindles. Conclusions The results confirm that both core and matrix thalamocortical projections contribute to spindle generation, but most spindles appear to be generated by a combination of the two and only a small minority by only one or the other. Neuronal firing tracks the phase of spindles in corticographic channels. Supported by KTIA_NAP_13-1-2013-0001.

S45 Invasive EEG investigation of insular cortex epilepsy

Introduction The possible involvement of the insular cortex in the constitution of the epileptogenic zone can sometimes be suspected thanks to pre-surgical phase 1 non-invasive investigations. Electrophysiological abnormalities largely consist of indirect signs, and the suspected diagnosis relies on the clinical description of seizures and on metabolic imaging. This is due to the deepness of the insular cortex and this explains why invasive phase II investigations are necessary in most cases. Invasive pre-surgical investigations are based on, either Subdural Grid Electrodes (SGE), or Stereo-ElectroEncephaloGraphy (SEEG). Methods We systematically reviewed the literature about phase II insular investigation. Results In addition to a significantly lower complication rate, when compared to SGE, SEEG appears to be more suitable to explore a deep structure like insula. SGE offers a good electrophysiological sampling of the superficial cortex but cannot accurately investigate, neither the deep parts of the sulci, nor the cortex of the insula itself. Conversely, SEEG allows direct and precise investigation of the insula. Trans-opercular trajectories allow to reach almost any part of the insula, while recording the operculum at the same time. Last, SEEG makes it possible to perform SEEG-guided radiofrequency thermo-coagulations. Discussion The anatomical proximity of the sylvian vessels requires to use a robust stereotactic methodology for SEEG: namely a frame-based procedure associated with X-ray vascular investigation. Moreover, SEEG may offer a therapeutic option when resective surgery, for any reason, is not feasible. Conclusion SEEG with trans-sylvian trajectory is the most appropriate technique for intracranial insular investigation.

P243 Functional connectivity analysis of cortico-cortical evoked potentials

Objectives The electrical stimulation of the cortical tissue can evoke early (N1) and late (N2) cortico-cortical evoked potential (CCEP) components. In this study, we applied functional connectivity analysis to investigate the attenuation and network topology induced by electrical stimulation. We also compared the synchronization and network topology in case of stimulations inside and outside the epileptic zone (EZ). Methods 16 presurgery epileptic patients were analyzed with subdural grid positions. The CCEP mapping was performed by injecting current pulses (10 mA, 0.2 ms pulse width, 25 trials) into all adjacent electrode contacts. Phase synchronization across trials was applied on the N1 (10–50 ms; filtered to 10–40 Hz) and N2 (50–500 ms; filtered to 1–4 Hz) evoked potentials to measure functional connectivity. We applied Minimum Spanning Tree analysis to express topological parameters of the networks. Results N1 had higher local synchrony than N2 and N1 had faster attenuation from the stimulation point toward more distant electrodes than N2. Furthermore, N1 was characterized by a more star-like network topology than N2. N1 synchrony was higher and the network became more centralized when the current was injected to the EZ. Conclusion The neural mechanism of N1 is based on direct cortico-cortical connections while N2 is thought to be the result of more complex processes. This can explain our more distributed N2 network compared to the local N1 network. Significance The extensive synchrony and centralized topology of the N1 network in case of EZ stimulation supports the increased excitability of the epileptogenic zone.

Frontal Fibers Connecting the Superior Frontal Gyrus to Broca Area: A Corticocortical Evoked Potential Study.

The frontal aslant tract is a deep frontal pathway connecting the superior frontal gyrus (SFG) to Broca area. This fiber is assumed to be associated with language functions, especially speech initiation and spontaneity. The aim of this study was to electrophysiologically investigate this network using corticocortical evoked potentials (CCEPs). This study enrolled 8 patients with brain tumors or medically intractable focal epilepsies who underwent frontal craniotomy over the language-dominant side. All patients underwent CCEP recordings during tumor resection or during invasive evaluation for epilepsy surgery. Alternating 1-Hz electrical stimuli were delivered to pars opercularis (pO) and pars triangularis (pT), corresponding to Broca area, and SFG via the subdural grid electrodes with intensity of 10 mA. Electrocorticograms from SFG and pO/pT time-locked to 50 stimuli were averaged in each trial to obtain CCEP responses. In all patients, stimulation of pO/pT induced CCEP responses in SFG. CCEP responses were recorded in lateral SFG in 5 patients and in supplementary motor areas in 4 patients. Reciprocality was observed in 7 patients in the stimulation of SFG. CCEP responses were significantly faster at SFG from pO/pT than at pO/pT from SFG (Wilcoxon signed rank test, P= 0.028). The present study demonstrated a corticocortical network connecting Broca areas and SFG in a reciprocal manner. Our findings might provide new insight into language and motor integration.

Trans-falcine and contralateral sub-frontal electrode placement in pediatric epilepsy surgery: technical note.

Phase II monitoring with intracranial electroencephalography (ICEEG) occasionally requires bilateral placement of subdural (SD) strips, grids, and/or depth electrodes. While phase I monitoring often demonstrates a preponderance of unilateral findings, individual studies (video EEG, single photon emission computed tomography [SPECT], and positron emission tomography [PET]) can suggest or fail to exclude a contralateral epileptogenic onset zone. This study describes previously unreported techniques of trans-falcine and sub-frontal insertion of contralateral SD grids and depth electrodes for phase II monitoring in pediatric epilepsy surgery patients when concern about bilateral abnormalities has been elicited during phase I monitoring. Pediatric patients with medically refractory epilepsy undergoing stage I surgery for phase II monitoring involving sub-frontal and/or trans-falcine insertion of SD grids and/or depth electrodes at the senior author's institution were retrospectively reviewed. Intra-operative technical details of sub-frontal and trans-falcine approaches were studied, while intra-operative complications or events were noted. Operative techniques included gentle subfrontal retraction and elevation of the olfactory tracts (while preserving the relationship between the olfactory bulb and cribriform plate) to insert SD grids across the midline for coverage of the contralateral orbito-frontal regions. Trans-falcine approaches involved accessing the inter-hemispheric space, bipolar cauterization of the anterior falx cerebri below the superior sagittal sinus, and sharp dissection using a blunt elevator and small blade scalpel. The falcine window allowed contralateral SD strip, grid, and depth electrodes to be inserted for coverage of the contralateral frontal regions. The study cohort included seven patients undergoing sub-frontal and/or trans-falcine insertion of contralateral SD strip, grid, and/or depth electrodes from February 2012 through June 2015. Five patients (71%) experienced no intra-operative events related to contralateral ICEEG electrode insertion. Intra-operative events of frontal territory venous engorgement (1/7, 14%) due to sacrifice of anterior bridging veins draining into the SSS and avulsion of a contralateral bridging vein (1/7, 14%), probably due to prior anterior corpus callosotomy, each occurred in one patient. There were no intra-operative or peri-operative complications in any of the patients studied. Two patients required additional surgery for supplemental SD strip and/or depth electrodes via burr hole craniectomy to enhance phase II monitoring. All patients proceeded to stage II surgery for resection of ipsilateral epileptogenic onset zones without adverse events. Trans-falcine and sub-frontal insertion of contralateral SD strip, grid, and depth electrodes are previously unreported techniques for achieving bilateral frontal coverage in phase II monitoring in pediatric epilepsy surgery. This technique obviates the need for contralateral craniotomy and parenchymal exposure with limited, remediable risks. Larger case series using the method described herein are now necessary.

Electrocorticography of Spatial Shifting and Attentional Selection in Human Superior Parietal Cortex.

Spatial-attentional reorienting and selection between competing stimuli are two distinct attentional processes of clinical and fundamental relevance. In the past, reorienting has been mainly associated with inferior parietal cortex. In a patient with a subdural grid covering the upper and lower bank of the left anterior and middle intraparietal sulcus (IPS) and the superior parietal lobule (SPL), we examined the involvement of superior parietal cortex using a hybrid spatial cueing paradigm identical to that previously applied in stroke and in healthy controls. In SPL, as early as 164 ms following target onset, an invalidly compared to a validly cued target elicited a positive event-related potential (ERP) and an increase in intertrial coherence (ITC) in the theta band, regardless of the direction of attention. From around 400–650 ms, functional connectivity [weighted phase lag index (wPLI) analysis] between SPL and IPS briefly inverted such that SPL activity was driving IPS activity. In contrast, the presence of a competing distracter elicited a robust change mainly in IPS from 300 to 600 ms. Within superior parietal cortex reorienting of attention is associated with a distinct and early electrophysiological response in SPL while attentional selection is indexed by a relatively late electrophysiological response in the IPS. The long latency suggests a role of IPS in working memory or cognitive control rather than early selection.

Surgical outcome of MRI-negative refractory extratemporal lobe epilepsy

ObjectiveThe aim of this study is to determine outcome of resective epilepsy surgery in MRI-negative extratemporal lobe epilepsy (MNETLE) patients who underwent invasive evaluations and to determine factors governing outcome. MethodsWe studied 28 patients who underwent resective epilepsy surgery for MNETLE from August 2006 to November 2015, in whom complete follow-up information was available. Electro-clinical, pathological and surgical data were evaluated. 24 patients (82.8%) were explored with intracranial EEG (9 stereoelectroencephalography (SEEG), 7 subdural grids and 8 both). All patients were followed for at least 6 months. ResultsDuring a mean follow up period of 32 [6–113] months, 13 (46.4%) patients became seizure-free (ILAE 1) and 18 (64.3%) had a good (ILAE 1, 2, 3) outcome. 21 (75.0%) patients had focal cortical dysplasia (FCD). Univariate analysis showed that more restricted (regional) interictal and ictal epileptiform discharges in surface EEG were significantly associated with seizure freedom (P=0.016 and P=0.024). Multivariate analysis confirmed that having ≥120 electrode contacts in the evaluation is an independent variable predicting seizure freedom (HR=4.283, 95% CI=1.342–13.676, P=0.014). ConclusionInvasive EEG is a powerful tool in the pre-surgical evaluation of patients with MNETLE. Invasive EEG implantation that include the irritative zone and EEG onset zone as indicated by surface EEG, as well as wider brain coverage predict seizure freedom, contingent upon a sound anatomo-electro-clinical hypothesis for implantation.

Extratemporal resections in pediatric epilepsy surgery-an overview.

Despite optimized medical treatment, approximately one third of all patients with epilepsy continue to have seizures and by definition have medically resistant epilepsy (MRE). For these patients, surgical disruption of the epileptogenic network may enable freedom or great improvement in control of their seizures. The success of surgery is dependent on accurate localization of the epileptogenic zone and network. Epilepsy arising from regions of cortical dysplasia within the neocortex of the frontal, parietal, and occipital lobes show a propensity for reorganization and progressive decline in seizure freedom and consequent poorer surgical outcome. These procedures often require staged investigation with intracranial electrodes via subdural grids or stereoelectroencephalography (SEEG) and are considered extratemporal resections (ETRs). Central concepts include the following: (1) localization of epileptogenic and eloquent functional regions, (2) safe and effective placement of intracranial electrode arrays, (3) resection of epileptogenic cortex, and (4) avoidance of complications. Each of these concepts is summarized and developed in this summary paper.