Chronic Electrocorticography Research Articles

Usefulness of Intraoperative Electrocorticography for the Localization of Epileptogenic Zones.

Intraoperative electrocorticography (iECoG) is widely performed to identify irritative zones in the cortex during brain surgery; however, several limitations (e.g., short recording times and the effects of general anesthesia) reduce its effectiveness. The present study aimed to evaluate the utility of iECoG for localizing epileptogenic zones. We compared the results of iECoG and chronic electrocorticography (cECoG) in 25 patients with refractory epilepsy. Subdural electrodes were implanted with iECoG under general anesthesia (2% sevoflurane). cECoG recordings were performed for 3-14 days. The distribution of iECoG spikes was compared with cECoG spike, seizure onset zone, and resection areas. The concordance patterns of each distribution were classified into four patterns: Group 1: No spike in iECoG, Group 2: concordant (2a: iECoG smaller, 2b: iECoG larger, Group 3: discordant >50%). The concordance rate of interictal spikes, seizure onset zones, and resection areas were 88.0% (Group 2a: 72.0%, Group 2b: 16.0%), 70.0% (Group 2a: 25.0%, Group 2b: 45.0%), and 81.0% (Group 2a: 42.9%, Group 2b: 38.1%), respectively. The resection of iECoG spike areas significantly correlated with good surgical outcomes. The indication and limitations of iECoG need to be realized, and the complementary use of iECoG and cECoG may enhance clinical utility.

Bilateral temporal lobe epilepsy: How many seizures are required in chronic ambulatory electrocorticography to estimate the laterality ratio?

This study was undertaken to measure the duration of chronic electrocorticography (ECoG) needed to attain stable estimates of the seizure laterality ratio in patients with drug-resistant bilateral temporal lobe epilepsy (BTLE). We studied 13 patients with drug-resistant BTLE who were implanted for at least 1year with a responsive neurostimulation device (RNS System) that provides chronic ambulatory ECoG. Bootstrap analysis and nonlinear regression were applied to model the relationship between chronic ECoG duration and the probability of capturing at least one seizure. Laterality of electrographic seizures in chronic ECoG was compared with the seizure laterality ratio from Phase 1scalp video-electroencephalographic (vEEG) monitoring. The Kaplan-Meier estimator was used to evaluate time to seizure laterality ratio convergence. Seizure laterality ratios from Phase 1scalp vEEG monitoring correlated poorly with those from RNS chronic ECoG (r=.31, p=.30). Across the 13 patients, average electrographic seizure frequencies ranged from 1.4seizures/month to 5.1seizures/day. A 50% probability of recording at least one electrographic seizure required 9.1days of chronic ECoG, and 90% probability required 44.3days of chronic ECoG. A median recording duration of 150.9days (5months), corresponding to a median of 16seizures, was needed before confidence intervals for the seizure laterality ratio reliably contained the long-term value. The median recording duration before the point estimate of the seizure laterality ratio converged to a stationary value was 236.8days (7.9months). RNS chronic ECoG overcomes temporal sampling limitations intrinsic to inpatient Phase 1 vEEG evaluations. In patients with drug-resistant BTLE, approximately 8months of chronic RNS ECoG are needed to precisely estimate the seizure laterality ratio, with 75% of people with BTLE achieving convergence after 1 year of RNS recording. For individuals who are candidates for unilateral resection based on seizure laterality, optimized recording duration may help avert morbidity associated with delay to definitive treatment.

Machine Learning to Classify Relative Seizure Frequency From Chronic Electrocorticography.

Brain responsive neurostimulation (NeuroPace) treats patients with refractory focal epilepsy and provides chronic electrocorticography (ECoG). We explored how machine learning algorithms applied to interictal ECoG could assess clinical response to changes in neurostimulation parameters. We identified five responsive neurostimulation patients each with ≥200 continuous days of stable medication and detection settings (median, 358 days per patient). For each patient, interictal ECoG segments for each month were labeled as "high" or "low" to represent relatively high or low long-episode (i.e., seizure) count compared with the median monthly long-episode count. Power from six conventional frequency bands from four responsive neurostimulation channels were extracted as features. For each patient, five machine learning algorithms were trained on 80% of ECoG, then tested on the remaining 20%. Classifiers were scored by the area-under-the-receiver-operating-characteristic curve. We explored how individual circadian cycles of seizure activity could inform classifier building. Support vector machine or gradient boosting models achieved the best performance, ranging from 0.705 (fair) to 0.892 (excellent) across patients. High gamma power was the most important feature, tending to decrease during low-seizure-frequency epochs. For two subjects, training on ECoG recorded during the circadian ictal peak resulted in comparable model performance, despite less data used. Machine learning analysis on retrospective background ECoG can classify relative seizure frequency for an individual patient. High gamma power was the most informative, whereas individual circadian patterns of seizure activity can guide model building. Machine learning classifiers built on interictal ECoG may guide stimulation programming.

Evidence of state-dependence in the effectiveness of responsive neurostimulation for seizure modulation

BackgroundAn implanted device for brain-responsive neurostimulation (RNS® System) is approved as an effective treatment to reduce seizures in adults with medically-refractory focal epilepsy. Clinical trials of the RNS System demonstrate population-level reduction in average seizure frequency, but therapeutic response is highly variable. HypothesisRecent evidence links seizures to cyclical fluctuations in underlying risk. We tested the hypothesis that effectiveness of responsive neurostimulation varies based on current state within cyclical risk fluctuations. MethodsWe analyzed retrospective data from 25 adults with medically-refractory focal epilepsy implanted with the RNS System. Chronic electrocorticography was used to record electrographic seizures, and hidden Markov models decoded seizures into fluctuations in underlying risk. State-dependent associations of RNS System stimulation parameters with changes in risk were estimated. ResultsHigher charge density was associated with improved outcomes, both for remaining in a low seizure risk state and for transitioning from a high to a low seizure risk state. The effect of stimulation frequency depended on initial seizure risk state: when starting in a low risk state, higher stimulation frequencies were associated with remaining in a low risk state, but when starting in a high risk state, lower stimulation frequencies were associated with transition to a low risk state. Findings were consistent across bipolar and monopolar stimulation configurations. ConclusionThe impact of RNS on seizure frequency exhibits state-dependence, such that stimulation parameters which are effective in one seizure risk state may not be effective in another. These findings represent conceptual advances in understanding the therapeutic mechanism of RNS, and directly inform current practices of RNS tuning and the development of next-generation neurostimulation systems.

Plug-and-play control of a brain-computer interface through neural map stabilization.

Brain-computer interfaces (BCIs) enable control of assistive devices in individuals with severe motor impairments. A limitation of BCIs that has hindered real-world adoption is poor long-term reliability and lengthy daily recalibration times. To develop methods that allow stable performance without recalibration, we used a 128-channel chronic electrocorticography (ECoG) implant in a paralyzed individual, which allowed stable monitoring of signals. We show that long-term closed-loop decoder adaptation, in which decoder weights are carried across sessions over multiple days, results in consolidation of a neural map and 'plug-and-play' control. In contrast, daily reinitialization led to degradation of performance with variable relearning. Consolidation also allowed the addition of control features over days, that is, long-term stacking of dimensions. Our results offer an approach for reliable, stable BCI control by leveraging the stability of ECoG interfaces and neural plasticity.

The Potential for a Speech Brain-Computer Interface Using Chronic Electrocorticography.

A brain-computer interface (BCI) is a technology that uses neural features to restore or augment the capabilities of its user. A BCI for speech would enable communication in real time via neural correlates of attempted or imagined speech. Such a technology would potentially restore communication and improve quality of life for locked-in patients and other patients with severe communication disorders. There have been many recent developments in neural decoders, neural feature extraction, and brain recording modalities facilitating BCI for the control of prosthetics and in automatic speech recognition (ASR). Indeed, ASR and related fields have developed significantly over the past years, and many lend many insights into the requirements, goals, and strategies for speech BCI. Neural speech decoding is a comparatively new field but has shown much promise with recent studies demonstrating semantic, auditory, and articulatory decoding using electrocorticography (ECoG) and other neural recording modalities. Because the neural representations for speech and language are widely distributed over cortical regions spanning the frontal, parietal, and temporal lobes, the mesoscopic scale of population activity captured by ECoG surface electrode arrays may have distinct advantages for speech BCI, in contrast to the advantages of microelectrode arrays for upper-limb BCI. Nevertheless, there remain many challenges for the translation of speech BCIs to clinical populations. This review discusses and outlines the current state-of-the-art for speech BCI and explores what a speech BCI using chronic ECoG might entail.

Running-down phenomenon captured with chronic electrocorticography.

SummaryThe running‐down phenomenon refers to 2 analogous but distinct entities that may be seen after epilepsy surgery. The first is clinical, and denotes a progressive diminution in seizures after epilepsy surgery in which the epileptogenic zone could not be completely removed (Modern Problems of Psychopharmacology 1970;4:306, Brain 1996:989). The second is electrographic, and refers to a progressive deactivation of a secondary seizure focus after removal of the primary epileptogenic zone. This progressive decrease in epileptiform activity may represent a reversal of secondary epileptogenesis, where a primary epileptogenic zone is postulated to activate epileptiform discharges at a second site and may become independent.3 The electrographic running‐down phenomenon has been reported in only limited numbers of patients, using serial postoperative routine scalp electroencephalography (EEG) (Arch Neurol 1985;42:318). We present what is, to our knowledge, the most detailed demonstration of the electrographic running‐down phenomenon in humans, made possible by chronic electrocorticography (ECoG). Our patient's left temporal seizure focus overlapped with language areas, limiting the resection to a portion of the epileptogenic zone, followed by implantation of a direct brain‐responsive neurostimulator (RNS System, NeuroPace Inc.) to treat residual epileptogenic tissue. Despite the limited extent of the resection, the patient remains seizure‐free more than 2 years after surgery, with the RNS System recording ECoG without delivering stimulation. We reviewed the chronic recordings with automated spike detection and inspection of electrographic episodes marked by the neurostimulator. These recordings demonstrate progressive diminution in spiking and rhythmic discharges, consistent with an electrographic running‐down phenomenon.

Three- and four-dimensional mapping of speech and language in patients with epilepsy.

We have provided 3-D and 4D mapping of speech and language function based upon the results of direct cortical stimulation and event-related modulation of electrocorticography signals. Patients estimated to have right-hemispheric language dominance were excluded. Thus, 100 patients who underwent two-stage epilepsy surgery with chronic electrocorticography recording were studied. An older group consisted of 84 patients at least 10 years of age (7367 artefact-free non-epileptic electrodes), whereas a younger group included 16 children younger than age 10 (1438 electrodes). The probability of symptoms transiently induced by electrical stimulation was delineated on a 3D average surface image. The electrocorticography amplitude changes of high-gamma (70-110 Hz) and beta (15-30 Hz) activities during an auditory-naming task were animated on the average surface image in a 4D manner. Thereby, high-gamma augmentation and beta attenuation were treated as summary measures of cortical activation. Stimulation data indicated the causal relationship between (i) superior-temporal gyrus of either hemisphere and auditory hallucination; (ii) left superior-/middle-temporal gyri and receptive aphasia; (iii) widespread temporal/frontal lobe regions of the left hemisphere and expressive aphasia; and (iv) bilateral precentral/left posterior superior-frontal regions and speech arrest. On electrocorticography analysis, high-gamma augmentation involved the bilateral superior-temporal and precentral gyri immediately following question onset; at the same time, high-gamma activity was attenuated in the left orbitofrontal gyrus. High-gamma activity was augmented in the left temporal/frontal lobe regions, as well as left inferior-parietal and cingulate regions, maximally around question offset, with high-gamma augmentation in the left pars orbitalis inferior-frontal, middle-frontal, and inferior-parietal regions preceded by high-gamma attenuation in the contralateral homotopic regions. Immediately before verbal response, high-gamma augmentation involved the posterior superior-frontal and pre/postcentral regions, bilaterally. Beta-attenuation was spatially and temporally correlated with high-gamma augmentation in general but with exceptions. The younger and older groups shared similar spatial-temporal profiles of high-gamma and beta modulation; except, the younger group failed to show left-dominant activation in the rostral middle-frontal and pars orbitalis inferior-frontal regions around stimulus offset. The human brain may rapidly and alternately activate and deactivate cortical areas advantageous or obtrusive to function directed toward speech and language at a given moment. Increased left-dominant activation in the anterior frontal structures in the older age group may reflect developmental consolidation of the language system. The results of our functional mapping may be useful in predicting, across not only space but also time and patient age, sites specific to language function for presurgical evaluation of focal epilepsy.

Reductions in cortical alpha activity, enhancements in neural responses and impaired gap detection caused by sodium salicylate in awake guinea pigs.

Tinnitus chronically affects between 10–15% of the population but, despite its prevalence, the underlying mechanisms are still not properly understood. One experimental model involves administration of high doses of sodium salicylate, as this is known to reliably induce tinnitus in both humans and animals. Guinea pigs were implanted with chronic electrocorticography (ECoG) electrode arrays, with silver‐ball electrodes placed on the dura over left and right auditory cortex. Two more electrodes were positioned over the cerebellum to monitor auditory brainstem responses (ABRs). We recorded resting‐state and auditory evoked neural activity from awake animals before and 2 h following salicylate administration (350 mg/kg; i.p.). Large increases in click‐evoked responses (> 100%) were evident across the whole auditory cortex, despite significant reductions in wave I ABR amplitudes (in response to 20 kHz tones), which are indicative of auditory nerve activity. In the same animals, significant decreases in 6–10 Hz spontaneous oscillations (alpha waves) were evident over dorsocaudal auditory cortex. We were also able to demonstrate for the first time that cortical evoked potentials can be inhibited by a preceding gap in background noise [gap‐induced pre‐pulse inhibition (PPI)], in a similar fashion to the gap‐induced inhibition of the acoustic startle reflex that is used as a behavioural test for tinnitus. Furthermore, 2 h following salicylate administration, we observed significant deficits in PPI of cortical responses that were closely aligned with significant deficits in behavioural responses to the same stimuli. Together, these data are suggestive of neural correlates of tinnitus and oversensitivity to sound (hyperacusis).

Ratio Ictal SPECT Co-registered with MRI visualizes a greater extent of the ictal onset zone in focal refractory epilepsy

Background: Until recently, the main non-invasive technique to evaluate the ictal onset zone has been Subtraction ictal SPECT coregistered with MRI (SISCOM). While SISCOM provides useful information about the ictal onset zone, the case we report herein suggests the possibility that multiple regions are involved in a more complex network 7 , whose identification can improve the patient’s prospects for resective epilepsy surgery. Case: The 23 year old right handed female case under discussion illustrates how Ratio Ictal SPECT coregistered with MRI (RISCOM) findings better guided the invasive evaluation with a more precise targeting of the subdural grids. Here, the concordance between the noninvasive technique (RISCOM) and the invasive evaluation (chronic electrocorticography) allowed a better determination of the seizure onset zone for resective epilepsy surgery. In turn, the resected tissue included a more extended area (orbitofrontal), which was not seen by SISCOM. Importantly, the case also allows for a better understanding of the relationship between the epileptogenic lesion and the ictal onset zone, and their role in the postsurgical outcome. The patient achieved seizure freedom (Engel 1A). Conclusion: A more accurate determination of the ictal onset zone by this novel noninvasive technique not only greatly impact in the postsurgical outcome of patients with focal refractory epilepsy. It may also indicate that the ictal onset zone can be the expression of interlobar connections that does not necessarily include the epileptogenic lesion of patients with malformations of cortical development.

The Effects of Cognitive Control and Time on Frontal Beta Oscillations.

Frontal beta oscillations are associated with top-down control mechanisms but also change over time during a task. It is unclear whether change over time represents another control function or a neural instantiation of vigilance decrements over time, the time-on-task effect. We investigated how frontal beta oscillations are modulated by cognitive control and time. We used frontal chronic electrocorticography in monkeys performing a trial-and-error task, comprising search and repetition phases. Specific beta oscillations in the delay period of each trial were modulated by task phase and adaptation to feedback. Beta oscillations in this same period showed a significant within-session change. These separate modulations of beta oscillations did not interact. Crucially, and in contrast to previous investigations, we examined modulations of beta around spontaneous pauses in work. After pauses, the beta power modulation was reset and the cognitive control effect was maintained. Cognitive performance was also maintained whereas behavioral signs of fatigue continued to increase. We propose that these beta oscillations reflect multiple factors contributing to the regulation of cognitive control. Due to the effect of pauses, the time-sensitive factor cannot be a neural correlate of time-on-task but may reflect attentional effort.

Chronic Recording Electrocorticography Guided Resective Epilepsy Surgery: Overview and Future Directions

Sensing, modeling, and neuromodulation technologies are profoundly advancing the practice of epilepsy surgery. Chronically implanted neural monitoring technologies developed for seizure termination and seizure prediction have each been found to be useful in unintended applications, specifically for the planning of resective surgery. We review and summarize the use of chronic monitoring in an unanticipated context in which it was found to be invaluable in the planning of surgery; this was observed in a pivotal study of a seizure detection and termination system. Monitoring of patients chronically in their normal ambulatory setting, as facilitated by this technology, allows unperturbed assessment of patients while on outpatient medication regimens and without the time and space constraints imposed by cost and infection risk inherent in subacute inpatient invasive monitoring. Five patients in the NeuroPace US pivotal trial underwent resective surgery which was subsequent to and enabled by chronic recordings from the implanted monitoring system. These resective surgeries were independent from the primary intended function of the implanted neural monitoring device. Chronic monitoring facilitated greater anatomical localization of the sources and allowed for a deeper understanding of the dynamic network behavior of interconnected seizure foci, thereby facilitating a substantially more sophisticated approach to resective surgery. In the NeuroPace trial, monitoring and analysis of chronic unlimited recording electrocorticography (CURE) from chronically implanted subdural and depth electrodes facilitated planning of resective surgery that resulted in near or complete seizure freedom in 4 patients. This series suggests that chronic recording of electrocorticographic signals is a therapeutic modality meritorious of further investigation. Note: This was analysis and study was performed on patients previously enrolled in the NeuroPace® RNS® Ststem Pivotal trial: http://clinicaltrials.gov/show/NCT00572195

Quantitative peri-ictal electrocorticography and long-term seizure outcomes in temporal lobe epilepsy

We analyzed peri-ictal electrocorticography below 70 Hz by a semiautomatic quantitative method. Thirty-four patients with medically intractable temporal lobe epilepsy underwent chronic electrocorticography using subdural electrodes. The resection extent of cortices with maximum amplitude activities were compared between seizure outcome groups. In detected activity significantly related to seizure outcome, we analyzed waveforms with automated waveform amplitude analysis. Mann-Whitney U tests were used. Mean follow-up duration was 49.7 ± 18.2 months. The resection extents of maximum amplitude activities in theta bands during the period between -10 and -5s from the ictal onset were significantly different between seizure outcome groups (adjusted p=0.01, the Benjamini-Hochberg correction). Delta, alpha and beta bands were related to seizure outcome only without multiple comparison corrections (unadjusted p=0.02, 0.03 and 0.04). Waveform peak amplitudes greater than 200 μV tended to be more common in the seizure free group than in the non-seizure-free group (unadjusted p=0.06). Waveform peak amplitudes greater than 350 μV were significantly more common in the cortical dysplasia type I group than in the hippocampal sclerosis group (unadjusted p=0.03). The resection of theta band activities during the preictal period was most important for good seizure outcome in temporal lobe epilepsy.

The value of intraoperative electrocorticography in surgical decision making for temporal lobe epilepsy with normal MRI

We hypothesized that acute intraoperative electrocorticography (ECoG) might identify a subset of patients with magnetic resonance imaging (MRI)-negative temporal lobe epilepsy (TLE) who could proceed directly to standard anteromesial resection (SAMR), obviating the need for chronic electrode implantation to guide resection. Patients with TLE and a normal MRI who underwent acute ECoG prior to chronic electrode recording of ictal onsets were evaluated. Intraoperative interictal spikes were classified as mesial (M), lateral (L), or mesial/lateral (ML). Results of the acute ECoG were correlated with the ictal-onset zone following chronic ECoG. Onsets were also classified as "M,""L," or "ML." Positron emission tomography (PET), scalp-EEG (electroencephalography), and Wada were evaluated as adjuncts. Sixteen patients fit criteria for inclusion. Outcomes were Engel class I in nine patients, Engel II in two, Engel III in four, and Engel IV in one. Mean postoperative follow-up was 45.2 months. Scalp EEG and PET correlated with ictal onsets in 69% and 64% of patients, respectively. Wada correlated with onsets in 47% of patients. Acute intraoperative ECoG correlated with seizure onsets on chronic ECoG in all 16 patients. All eight patients with "M" pattern ECoG underwent SAMR, and six (75%) experienced Engel class I outcomes. Three of eight patients with "L" or "ML" onsets (38%) had Engel class I outcomes. Intraoperative ECoG may be useful in identifying a subset of patients with MRI-negative TLE who will benefit from SAMR without chronic implantation of electrodes. These patients have uniquely mesial interictal spikes and can go on to have improved postoperative seizure-free outcomes.

ECoG studies of valproate, carbamazepine and halothane in frontal-lobe epilepsy induced by head injury in the rat

The use of electrocorticography (ECoG) with etiologically realistic epilepsy models promises to facilitate the discovery of better anti-epileptic drugs (AEDs). However, this novel approach is labor intensive, and must be optimized. To this end, we employed rostral parasagittal fluid percussion injury (rpFPI) in the adolescent rat, which closely replicates human contusive closed head injury and results in posttraumatic epilepsy (PTE). We systematically examined variables affecting the power to detect anti-epileptic effects by ECoG and used a non-parametric bootstrap strategy to test several different statistics, study designs, statistical tests, and impact of non-responders. We found that logarithmically transformed data acquired in repeated-measures experiments provided the greatest statistical power to detect decreases in seizure frequencies of preclinical interest with just 8 subjects and with up to ∼40% non-responders. We then used this optimized design to study the anti-epileptic effects of acute exposure to halothane, and chronic (1week) exposures to carbamazepine (CBZ) and valproate (VPA) 1month post-injury. While CBZ was ineffective in all animals, VPA induced, during treatment, a progressive decrease in seizure frequency in animals primarily suffering from non-spreading neocortical seizures, but was ineffective in animals with a high frequency of spreading seizures. Halothane powerfully blocked all seizure activity. The data show that rpFPI and chronic ECoG can conveniently be employed for the evaluation of AEDs, suggest that VPA may be more effective than CBZ to treat some forms of PTE, and support the theory that pharmacoresistance may depend on the severity of epilepsy. The data also demonstrate the utility of chronic exposures to experimental drugs in preclinical studies and highlight the need for greater attention to etiology in clinical studies of AEDs.

Post-traumatic epilepsy following fluid percussion injury in the rat

The lack of an adequate model of post-traumatic epilepsy (PTE), in which, similarly to the human condition, chronic spontaneous focal seizures follow a single episode of traumatic brain injury, has hampered the identification of clinically relevant epileptogenic mechanisms and the development of effective therapies. We studied the electrophysiological, behavioural and structural consequences of a clinically relevant model of closed head injury, the lateral fluid percussion injury (FPI), in the rat. We found that a single episode of severe FPI is sufficient to cause PTE. Chronic electrocorticography (ECoG) demonstrated spontaneous chronic seizures that were partial, originated from the neocortex at the site of injury, and progressively worsened and spread over time. The cases of epilepsy in the post-traumatic population increased over time following injury. Post-FPI epileptic rats exhibited pauses in their behaviour, facial automatisms and myoclonus at the time of epileptiform ECoG events. In vitro local field potential recordings demonstrated persistent hyperexcitability of the neocortex at and around the site of injury that was associated with intense glial reactivity. These results for the first time demonstrate persistent hyperexcitability of the injured neocortex and define a useful model for pathophysiological studies of basic mechanisms of spontaneous epileptogenesis and for preclinical screening of effective antiepileptogenic drugs.

Pilomotor seizures in frontal lobe epilepsy: case report

We report a 27-year-old man with pilomotor seizures originating in the right frontal lobe. Subtracted ictal SPECT coregistered with MRI showed multifocal hyperperfused areas in the anterior medial frontal area, mainly involving the cingulate gyrus. Chronic electrocorticography with subdural electrode arrays during the piloerection demonstrated that the pilomotor seizures were originating in the anterior medial frontal region. After resection of the focus, the patient became seizure free.

Pilomotor seizures in frontal lobe epilepsy: case report

We report a 27-year-old man with pilomotor seizures originating in the right frontal lobe. Subtracted ictal SPECT coregistered with MRI showed multifocal hyperperfused areas in the anterior medial frontal area, mainly involving the cingulate gyrus. Chronic electrocorticography with subdural electrode arrays during the piloerection demonstrated that the pilomotor seizures were originating in the anterior medial frontal region. After resection of the focus, the patient became seizure free.

Cerebral ganglioglioma with epilepsy: neuroimaging features and treatment.

Gangliogliomas are an increasingly recognized cause of epilepsy in children. In this study the clinical, neuroimaging, and neurophysiological data of five patients with cerebral ganglioglioma and epilepsy are reviewed retrospectively. The average age of these patients was 4.4 years at onset and the average duration of seizures before diagnosis was 11 months. Tumors were located in the frontal (3), parietal (1), and occipital (1) lobes. While one cystic and four solid tumors showed various densities on CT and MRI, one frontal lesion was not demonstrated by CT scan but clearly shown by MRI. Scalp electroencephalography (EEG) showed neither localized nor epileptiform abnormalities in three patients, while the remaining two had these abnormalities. In one patient, invasive chronic electrocorticography (ECoG) recordings with subdural electrodes revealed an ictal onset zone located in the hand motor area. In all patients, intraoperative ECoG failed to reveal any epileptiform activities, and tumor removal alone was performed. For a mean of 3.4 years after surgery, all patients are alive and seizure-free, with stable imaging findings. Tumor resection may be the most important factor for optimal seizure control and prevention of tumor recurrence despite the fact that EEG and ECoG findings may conflict on tumor location.

Temporal lobectomy for intractable epilepsy: Correlation of ictal onset determined by chronic electrocorticography and seizure outcome with degree of hippocampal sclerosis

This study sought to determine whether hippocampal sclerosis (HS) can be predicted from the results of electrocorticography (ECoG). One hundred seven patients underwent anterior temporal lobectomy (ATL) (44 R, 63 L) for epilepsy in the absence of a structural lesion and had the degree of HS graded pathologically from 0 to 4. Preoperative evaluation included ictal chronic ECoG with subdural strip electrodes, which showed a temporal onset in each case. Twenty-seven (25%) specimens were grade 0, 15 (14%) were grade 1–2, and 65 (61%) were grade 3–4. ECoG showed a unilateral mesial temporal seizure onset in 70% of grade 0, 73% of grade 1–2, and 78% of grade 3–4 patients ( p > 0.5). A unilateral regional onset, i.e., involving all temporal electrodes, occurred in 15% of grade 0, 13% of grade 1–2, and 12% of grade 3–4 patients ( p > 0.5). Bilateral independent onset occurred in 11% of grade 0, 13% of grade 1–2 ( p > 0.5), and none of grade 3–4 patients ( p p p p