The unforeseen future: Impacts of the COVID-19 pandemic on home video-EEG telemetry.

The coronavirus disease 2019 (COVID-19) pandemic had widespread impact on health care systems globally-particularly services arranged around elective admission and attendance such as epilepsy monitoring units and home video-EEG telemetry (HVET). Here, we review the ongoing impacts of the pandemic on HVET services among several different providers who used different initial models of HVET. We discuss the features of HVET that led to success in providing continued diagnostic services to patients with epilepsy and related disorders and through retrospective audit of our services demonstrate the high diagnostic yield of HVET. We reflect on this unforeseen future and its implications for other diagnostic techniques and approaches.

A Continuous Clustering Algorithm for Detection of Local Sleep in Humans.

OBJECTIVE: Research in animal models has shown that many EEG sleep features reflect local conditions, which is a consequence of relative inactivity of neuronal clusters. In humans, the authors previously reported that focal sleep patterns appear on the cortex during the wake state and suggested that this underlies the condition described as drowsiness. The focal changes at individual electrodes appeared as a combination of increased instantaneous amplitude in the delta band and decreased instantaneous frequency in the theta-alpha band during non-REM sleep, with the opposite occurring during the wake state, permitting their categorization as "active" and "inactive." A limitation of the previous work was the use of a binary k-means clustering algorithm, which created the possibility that the findings were biased toward a predominantly inactive state while the study subject was still awake. The present study tested the hypothesis that analyzing the same data by using a continuous rather than binary classifier would overcome this limitation. METHODS: An analysis was performed on records from six patients with refractory epilepsy who were undergoing video-electrocorticographic monitoring with implanted subdural grid electrodes. A fuzzy c-means clustering algorithm was utilized after feature extraction from the recordings to create state classifications for each moment in each recording. A subsequent analysis was performed to determine the relative contributions of instantaneous amplitude versus instantaneous frequency to the classification. RESULTS: Localized state changes consistent with the hypothesis were observed. The contributions from instantaneous frequency and amplitude appeared roughly equal. CONCLUSIONS: This study reveals evidence of local sleep during the wake state in humans.

Focal Changes to Human Electrocorticography With Drowsiness: A Novel Measure of Local Sleep.

Drowsiness may be defined as the progressive loss of cortical processing efficiency that occurs with time passing while awake. This loss of cortical processing efficiency is reflected in focal changes to the electroencephalogram, including islands of increased delta power concurrent with drop-offs in neuronal activity (i.e., focal cortical inactivity). The authors hypothesized that these focal changes are evidenced at individual electrodes by combination of increased instantaneous amplitude in delta band and decreased instantaneous frequency in theta-alpha band, permitting their categorization as "active" and "inactive." An analysis of records from six patients with refractory epilepsy undergoing video-electrocorticographic monitoring was conducted. Feature extraction and state classification on multiple recordings revealed focal changes consistent with the hypothesis, as well as progressively increased numbers of inactive electrodes with time awake. The implications of these findings on the study of sleep, and particularly local sleep, are discussed.

A simple clinical score for prediction of nonepileptic seizures.

Psychogenic nonepileptic seizures (PNES), often mistaken for epilepsy in community practice, require inpatient video-EEG (VEEG) monitoring for diagnostic confirmation. We developed a simple score designed for use in an outpatient setting to predict the subsequent VEEG diagnosis of PNES. We retrospectively compared fifty-five consecutive patients with VEEG-proven PNES (N1=55) with a group of randomly selected patients with VEEG-proven epilepsy (N2=55). Patients were divided into two groups: I) a 'truly retrospective' group of 27 patients with PNES and 27 patients with epilepsy whose data served to develop the score, and II) a 'pseudoprospective' group of 28 patients each with PNES and epilepsy to whom the score was applied. Six features in the history of the Group I cohort appeared more prominent in patients with PNES than patients with epilepsy and were assigned escalating numerical values as follows: number of declared drug allergies (0, 0.5, 1), number of declared comorbidities (0, 0.5, 1), number of previous invasive medical interventions of any type (0, 0.5, 1), and a history of significant psychological or physical trauma (0 or 1). In addition, a score was assigned to verbal description of the seizures themselves as being consistent (=0), atypical (=1), or indeterminate (=0.5) for epilepsy. The values were added to yield an omnibus score ranging from 0 to 6. Scoring of Group II subjects in a blinded fashion revealed that in general patients with PNES had higher scores, and the majority obtained a score >2; most patients with epilepsy scored <1.5. Group difference in the mean between the PNES and epilepsy cohort was highly significant (p<0.0001, Wilcoxon rank-sum test). Our score is a simple clinical instrument based on the patient history that may find use in the triage of patients awaiting hospitalization for VEEG and in pre-VEEG counseling.

Reactivation of visual-evoked activity in human cortical networks.

In the absence of sensory input, neuronal networks are far from being silent. Whether spontaneous changes in ongoing activity reflect previous sensory experience or stochastic fluctuations in brain activity is not well understood. Here we demonstrate reactivation of stimulus-evoked activity that is distributed across large areas in the human brain. We performed simultaneous electrocorticography recordings from occipital, parietal, temporal, and frontal areas in awake humans in the presence and absence of sensory stimulation. We found that, in the absence of visual input, repeated exposure to brief natural movies induces robust stimulus-specific reactivation at individual recording sites. The reactivation sites were characterized by greater global connectivity compared with those sites that did not exhibit reactivation. Our results indicate a surprising degree of short-term plasticity across multiple networks in the human brain as a result of repeated exposure to unattended information.

Temporal lobe white matter asymmetry and language laterality in epilepsy patients.

Recent studies using diffusion tensor imaging (DTI) have advanced our knowledge of the organization of white matter subserving language function. It remains unclear, however, how DTI may be used to predict accurately a key feature of language organization: its asymmetric representation in one cerebral hemisphere. In this study of epilepsy patients with unambiguous lateralization on Wada testing (19 left and 4 right lateralized subjects; no bilateral subjects), the predictive value of DTI for classifying the dominant hemisphere for language was assessed relative to the existing standard-the intra-carotid Amytal (Wada) procedure. Our specific hypothesis is that language laterality in both unilateral left- and right-hemisphere language dominant subjects may be predicted by hemispheric asymmetry in the relative density of three white matter pathways terminating in the temporal lobe implicated in different aspects of language function: the arcuate (AF), uncinate (UF), and inferior longitudinal fasciculi (ILF). Laterality indices computed from asymmetry of high anisotropy AF pathways, but not the other pathways, classified the majority (19 of 23) of patients using the Wada results as the standard. A logistic regression model incorporating information from DTI of the AF, fMRI activity in Broca's area, and handedness was able to classify 22 of 23 (95.6%) patients correctly according to their Wada score. We conclude that evaluation of highly anisotropic components of the AF alone has significant predictive power for determining language laterality, and that this markedly asymmetric distribution in the dominant hemisphere may reflect enhanced connectivity between frontal and temporal sites to support fluent language processes. Given the small sample reported in this preliminary study, future research should assess this method on a larger group of patients, including subjects with bi-hemispheric dominance.

Seizure symptoms and ambulatory EEG findings: incidence of epileptiform discharges.

AIMS: Ambulatory video-EEG monitoring has been utilized as a cost-effective alternative to inpatient video-EEG monitoring for non-surgical diagnostic evaluation of symptoms suggestive of epileptic seizures. We aimed to assess incidence of epileptiform discharges in ambulatory video-EEG recordings according to seizure symptom history obtained during clinical evaluation. METHODS: This was a retrospective cohort study. We queried seizure symptoms from 9,221 consecutive ambulatory video-EEG studies in 35 states over one calendar year. We assessed incidence of epileptiform discharges for each symptom, including symptoms that conformed to a category heading, even if not included in the ILAE 2017 symptom list. We report incidences, odds ratios, and corresponding p values using Fisher's exact test and univariate logistic regression. We applied multivariable logistic regression to generate odds ratios for the six symptom categories that are controlled for the presence of other symptoms. RESULTS: History that included motor symptoms (OR=1.53) or automatisms (OR=1.42) was associated with increased occurrence of epileptiform discharges, whereas history of sensory symptoms (OR=0.76) predicted lack of epileptiform discharges. Patient-reported symptoms that were associated with increased occurrence of epileptiform discharges included lip-smacking, moaning, verbal automatism, aggression, eye-blinking, déjà vu, muscle pain, urinary incontinence, choking and jerking. On the other hand, auditory hallucination memory deficits, lightheadedness, syncope, giddiness, fibromyalgia and chronic pain predicted absence of epileptiform discharges. The majority of epileptiform discharges consisted only of interictal sharp waves or spikes. CONCLUSIONS: Our study shows that the use of ILAE 2017 symptom categories may help guide ambulatory video-EEG studies.

The real-world economic impact of home-based video electroencephalography: the payer perspective.

Aims: Electroencephalography (EEG) is an established method to evaluate and manage epilepsy; video EEG (VEEG) has significantly improved its diagnostic value. This study compared healthcare costs and diagnostic-related outcomes associated with outpatient vs inpatient VEEG among patients with epilepsy in the US. Materials and methods: This study used Truven MarketScan Commercial and Medicare Supplemental claims databases. Patients with a VEEG between July 1, 2013 and December 31, 2016 were identified. Index event was the first VEEG claim, which was used to determine inpatient and outpatient cohorts. Continuous health plan enrollment 6 months pre- and 12 months post-index VEEG was required. Primary outcomes were costs during the index event and 12 months post index. A generalized linear model with gamma distribution and a log link was used to estimate adjusted index and post-index costs. Results: Controlling for baseline differences, epilepsy-related cost of index VEEG was significantly lower for the outpatient ($4,098) vs the inpatient cohort ($13,821; p < 0.0001). The cost differences observed at index were maintained in the post-index period. The 12-month post-index epilepsy-related costs were lower in the outpatient cohort ($6,114 vs $12,733, p < 0.0001). Time from physician referral to index VEEG was significantly shorter in the outpatient cohort (30.6 vs 42.5 days). Patients in the inpatient cohort were also more likely to undergo an additional subsequent follow-up inpatient VEEG (p < 0.0001). Limitations: Administrative claims data have limitations, including lack of data on clinical presentation, disease severity, and comprehensive health plan information. Generalizability may be limited to a US insured population of patients who met study criteria. Conclusions: Index VEEG was less costly in an outpatient vs inpatient cohort, and costs were lower during the follow-up period of 12 months, suggesting that outpatient VEEG can be provided to appropriate patients as a less costly option. There were fewer follow-up tests in the outpatient cohort with similar pre- and post-index diagnoses.

Analysis of Morbidity and Outcomes Associated With Use of Subdural Grids vs Stereoelectroencephalography in Patients With Intractable Epilepsy.

Importance: A major change has occurred in the evaluation of epilepsy with the availability of robotic stereoelectroencephalography (SEEG) for seizure localization. However, the comparative morbidity and outcomes of this minimally invasive procedure relative to traditional subdural electrode (SDE) implantation are unknown. Objective: To perform a comparative analysis of the relative efficacy, procedural morbidity, and epilepsy outcomes consequent to SEEG and SDE in similar patient populations and performed by a single surgeon at 1 center. Design, Setting and Participants: Overall, 239 patients with medically intractable epilepsy underwent 260 consecutive intracranial electroencephalographic procedures to localize their epilepsy. Procedures were performed from November 1, 2004, through June 30, 2017, and data were analyzed in June 2017 and August 2018. Interventions: Implantation of SDE using standard techniques vs SEEG using a stereotactic robot, followed by resection or laser ablation of the seizure focus. Main Outcomes and Measures: Length of surgical procedure, surgical complications, opiate use, and seizure outcomes using the Engel Epilepsy Surgery Outcome Scale. Results: Of the 260 cases included in the study (54.6% female; mean [SD] age at evaluation, 30.3 [13.1] years), the SEEG (n = 121) and SDE (n = 139) groups were similar in age (mean [SD], 30.1 [12.2] vs 30.6 [13.8] years), sex (47.1% vs 43.9% male), numbers of failed anticonvulsants (mean [SD], 5.7 [2.5] vs 5.6 [2.5]), and duration of epilepsy (mean [SD], 16.4 [12.0] vs17.2 [12.1] years). A much greater proportion of SDE vs SEEG cases were lesional (99 [71.2%] vs 53 [43.8%]; P < .001). Seven symptomatic hemorrhagic sequelae (1 with permanent neurological deficit) and 3 infections occurred in the SDE cohort with no clinically relevant complications in the SEEG cohort, a marked difference in complication rates (P = .003). A greater proportion of SDE cases resulted in resection or ablation compared with SEEG cases (127 [91.4%] vs 90 [74.4%]; P < .001). Favorable epilepsy outcomes (Engel class I [free of disabling seizures] or II [rare disabling seizures]) were observed in 57 of 75 SEEG cases (76.0%) and 59 of 108 SDE cases (54.6%; P = .003) amongst patients undergoing resection or ablation, at 1 year. An analysis of only nonlesional cases revealed good outcomes in 27 of 39 cases (69.2%) vs 9 of 26 cases (34.6%) at 12 months in SEEG and SDE cohorts, respectively (P = .006). When considering all patients undergoing evaluation, not just those undergoing definitive procedures, favorable outcomes (Engel class I or II) for SEEG compared with SDE were similar (57 of 121 [47.1%] vs 59 of 139 [42.4%] at 1 year; P = .45). Conclusions and Relevance: This direct comparison of large matched cohorts undergoing SEEG and SDE implantation reveals distinctly better procedural morbidity favoring SEEG. These modalities intrinsically evaluate somewhat different populations, with SEEG being more versatile and applicable to a range of scenarios, including nonlesional and bilateral cases, than SDE. The significantly favorable adverse effect profile of SEEG should factor into decision making when patients with pharmacoresistant epilepsy are considered for intracranial evaluations.

Outcome of ambulatory video-EEG monitoring in a ˜10,000 patient nationwide cohort.

PURPOSE: We evaluate outcome of in-home diagnostic ambulatory video-EEG monitoring (AVEM) performed on a nationwide cohort of patients over one calendar year, and we compare our findings with outcomes of inpatient adult and pediatric VEM performed during the same year at two academic epilepsy centers. METHODS: This is a retrospective cohort study. We obtained AVEM outcome data from an independent ambulatory-EEG testing facility. Inpatient VEM data from a 4-bed adult epilepsy center and an 8-bed pediatric epilepsy center were also included. Primary outcome measure was composite percentage of VEM records with epileptiform activity on EEG tracings or at least one video-recorded pushbutton event. We assessed patient-reported symptoms documented in AVEM event diaries. RESULTS: Of 9221 AVEM recordings performed across 28 states, 62.5% attained primary outcome. At least one patient-activated pushbutton event was captured on video in 54% of AVEM recordings (53.6% in adults, 56.1% in children). Epileptiform activity was reported in 1657 (18.0%) AVEM recordings (1473 [88.9%] only interictal, 9 [0.5%] only ictal, 175 [10.6%] both interictal and ictal). Most common patient-reported symptomatology during AVEM pushbutton events was behavioral/autonomic/emotional in adults and children. Compared to AVEM, inpatient VEM captured more confirmed representative events in adult and pediatric samples. CONCLUSIONS: AVEM is useful for non-urgent diagnostic evaluation of events.

A definition of drowsiness: one purpose for sleep?

While significant research has been done into the physiological mechanisms that underlie sleep and the sleep/wake cycle, the available data regarding the nature of drowsiness is far more limited. An objective measurement of drowsiness would have clinical utility, and a precise definition of the drowsy state could offer insights into the nature and purpose of sleep. Studies utilizing fMRI have demonstrated increased area of central nervous system involvement with tasks of increasing complexity. Preliminary data from studies of magnetoencephalography (MEG) with a receptive language task have demonstrated a progressive increase in global coherence of activity between MEG sensors with increasing drowsiness. The relationship between global coherence and the level of drowsiness suggests that the former may serve as an objective measurement of the latter. If true, the relationship suggests the hypothesis that drowsiness may be defined as a progressive loss of cortical network processing efficiency, requiring the recruitment of greater amounts of cortical tissue to perform the same task.

Partial agenesis of the corpus callosum in a patient with juvenile myoclonic epilepsy.

We describe a patient who presented at our epilepsy-monitoring unit with myoclonic jerks, and was diagnosed with juvenile myoclonic epilepsy (JME). Imaging of his brain revealed partial agenesis of the corpus callosum (ACC). We discuss the known genetic basis of both JME and ACC, as well as the role of the corpus callosum (CC) in primary generalized epilepsy. Both JME and ACC are associated with gene loci on chromosome 15q14. Structural brain abnormalities other than ACC, such as atrophy of the corpus callosum have been reported in patients with JME. ACC has been associated with seizures, suggesting an anti-epileptogenic role of the corpus callosum. On the other hand, corpus callosotomy is used to treat refractory idiopathic generalized epilepsy, which shows that the corpus callosum may play an epileptogenic role. The occurrence of both these conditions in one patient raises the question of whether they are purely coincidental or if there is a common basis for both. Several issues need to be addressed: the mechanism of seizure generalization in the setting of partial ACC, the possible role of other structures in generalization, and whether the ACC contributes to epileptogenesis as a result of the lack of a normal CC inhibitory effect.

A unified statistical model for the human electrocorticogram.

OBJECTIVE: Extracellular field potentials (ECFs) generated in the cerebral cortex span a vast range of spatiotemporal scales. The process(es) leading to this large dynamic range remain debatable. Here we propose a novel statistical description of the amplitude spectrum of the human electrocorticogram (ECoG). METHODS: Spectral analysis was performed on long-term recordings from epilepsy patients undergoing pre-surgical evaluation with intracranial electrodes. Amplitude spectra were fit with a multi-component Gaussian model on semi-logarithmic axes. RESULTS: The Gaussian formulation provided excellent fits to the data. It also suggested how the changes accompanying the sleep-wake cycle and certain epileptiform transitions could be understood by variation in the parameters of the model. CONCLUSIONS: The proposed continuum model synthesizes several previous observations regarding the statistical structure of the resting human ECoG. It offers a conceptual platform for understanding the EEG changes accompanying the sleep-wake cycle and pathologically hypersynchronous behaviour. SIGNIFICANCE: Statistical characterisation of the spectral distribution of field potentials yield insight into the cortico-cortical interactions that underlie the summated cortical ECFs comprising the ECoG. Such insight is relevant for a synoptic understanding of major state changes in the brain that are diagnosed in clinical practice by visual inspection of the ECoG.

Periodic Lateralized Epileptiform Discharges and Afterdischarges: Common Dynamic Mechanisms.

PURPOSE: No neurophysiological hypothesis currently exists addressing how and why periodic lateralized epileptiform discharges (PLEDs) arise in certain types of brain disease. Based on spectral analysis of clinical scalp EEG traces, the authors formulated a general mechanism for the emergence of PLEDs. METHODS: The authors retrospectively analyzed spectra of PLED time series and control EEG segments from the opposite hemisphere in 25 hospitalized neurological patients. The observations led to the development of a phenomenological model for PLED emergence. RESULTS: Similar to that observed in our previous work with afterdischarges, an analytic relationship is found between the spectrum of the baseline EEG and the PLED EEG, characterized by "condensation" of the main baseline spectral cluster, with variable inclusion of higher harmonics of the condensate. CONCLUSIONS: Periodic lateralized epileptiform discharges may arise by synchronization of preexisting local field potentials, through a variable combination of enhancement of excitatory neurotransmission and inactivation of inhibitory neurotransmission provoked by the PLED-associated disease process. Higher harmonics in the PLED spectrum may arise by recurrent feedback, possibly from entrained single units. A mechanism is suggested for PLED emergence in certain diseased brain states and the association of PLEDs with EEG seizures. The framework is a spatially extended version of that, which the authors proposed, underlies afterdischarge and analogous to the cooperative behavior seen in a variety of natural multi-oscillator systems.

Dynamic mechanisms underlying afterdischarge: a human subdural recording study.

OBJECTIVE: No synoptic understanding exists of how and why afterdischarges (ADs) occur following electrical stimulation of the cerebral cortex. Based on human observations, we formulated a general mechanism for the emergence of ADs. METHODS: We retrospectively analysed spectra of AD time-series and control segments of the resting electrocorticogram (ECoG) in 15 epilepsy patients who underwent cortical stimulation mapping. The observations led to the development of phenomenological models for AD emergence and morphology. RESULTS: An analytical relationship exists between the spectrum of the baseline ECoG and the ensuing AD, characterised by 'condensation' of the main baseline spectral cluster, with variable inclusion of higher harmonics of the condensate. CONCLUSIONS: ADs arise by synchronisation of pre-existing local field potentials, likely through temporary inactivation of inhibitory interneurons from repetitive stimulation-induced depolarization. The appearance of higher harmonics indicates that ADs are further modulated by recurrent feedback, likely from the entrained activity of single units. SIGNIFICANCE: For the first time, a putative mechanism is suggested for AD emergence following electrical stimulation of the cerebral cortex. Insight is also offered into several empirical observations regarding ADs, detailed in the main text. More generally, a novel conceptual synthesis emerges between the behaviour of electrically-excited cortex and the physics of nonlinearly coupled multi-oscillator systems.

An interictal EEG spectral metric for temporal lobe epilepsy lateralization.

OBJECTIVE: Visually-obvious abnormalities in the resting baseline EEG--slowing, spiking and high-frequency oscillations (HFOs)--are cardinal, though incompletely understood, features of the seizure onset zone in focal epilepsy. We hypothesized that evidence of cortical network dysfunction in temporal lobe epilepsy (TLE) would persist in the absence of visually-classifiable abnormalities in the baseline EEG recorded within the conventional passband, and that metrics of such dysfunction could serve as a lateralizing diagnostic in TLE. METHODS: Epochs of resting EEG without significant abnormalities in light sleep over several days were compared between a group of 10 patients with proven TLE and 10 subjects without epilepsy. A novel laterality metric computed from the line length of normalized power spectra from the temporal channels was compared between the two groups. RESULTS: Significant group differences in spectral line length laterality metric were found between the TLE and control group. At the individual level, seven of 10 TLE patients had highly significant laterality metrics, all concordant with the known laterality of their disease. SIGNIFICANCE: Detailed spectral analysis offers novel insight into TLE network behavior, independent of the orthodox abnormalities of EEG slowing, spikes or HFOs. The results may be deployed in a practical diagnostic manner, offer insight into the EEG manifestations of disordered cellular network architecture in TLE, and maybe understood through simple analogy with the theory of linear time-invariant physical systems.

Stereotactic laser ablation of epileptogenic periventricular nodular heterotopia.

Periventricular nodular heterotopia (PVNH) is a neuronal migrational disorder often associated with pharmacoresistant epilepsy (PRE). Resective surgery for PVNH is limited by its deep location, and the overlying eloquent cortex or white matter. Stereotactic MR guided laser interstitial thermal therapy (MRgLITT) has recently become available for controlled focal ablation, enabling us to target these lesions. We here demonstrate the novel application and techniques for the use of MRgLITT in the management of PVNH epilepsy. Comprehensive presurgical evaluation, including intracranial EEG monitoring in two patients revealed the PVNH to be crucially involved in their PRE. We used MRgLITT to maximally ablate the PVNH in both cases. In the first case, seizure medication adjustment coupled with PVNH ablation, and in the second, PVNH ablation in addition to temporal lobectomy rendered the patient seizure free. A transient visual deficit occurred following ablation in the second patient. MRgLITT is a promising minimally invasive technique for ablation of epileptogenic PVNH, a disease not generally viewed as surgically treatable epilepsy. We also show here the feasibility of applying this technique through multiple trajectories and to create lesions of complex shapes. The broad applicability and long term efficacy of MRgLITT need to be elaborated further.

Characterization of interictal epileptiform discharges with time-resolved cortical current maps using the helmholtz-hodge decomposition.

Source estimates performed using a single equivalent current dipole (ECD) model for interictal epileptiform discharges (IEDs) which appear unifocal have proven highly accurate in neocortical epilepsies, falling within millimeters of that demonstrated by electrocorticography. Despite this success, the single ECD solution is limited, best describing sources which are temporally stable. Adapted from the field of optics, optical flow analysis of distributed source models of MEG or EEG data has been proposed as a means to estimate the current motion field of cortical activity, or "cortical flow." The motion field so defined can be used to identify dynamic features of interest such as patterns of directional flow, current sources, and sinks. The Helmholtz-Hodge Decomposition (HHD) is a technique frequently applied in fluid dynamics to separate a flow pattern into three components: (1) a non-rotational scalar potential U describing sinks and sources, (2) a non-diverging scalar potential A accounting for vortices, and (3) an harmonic vector field H. As IEDs seem likely to represent periods of highly correlated directional flow of cortical currents, the U component of the HHD suggests itself as a way to characterize spikes in terms of current sources and sinks. In a series of patients with refractory epilepsy who were studied with magnetoencephalography as part of their evaluation for possible resective surgery, spike localization with ECD was compared to HHD applied to an optical flow analysis of the same spike. Reasonable anatomic correlation between the two techniques was seen in the majority of patients, suggesting that this method may offer an additional means of characterization of epileptic discharges.

Quality assessment of electroencephalography obtained from a "dry electrode" system.

This study examines the difference in application times for routine electroencephalography (EEG) utilizing traditional electrodes and a "dry electrode" headset. The primary outcome measure was the time to interpretable EEG (TIE). A secondary outcome measure of recording quality and interpretability was obtained from EEG sample review by two blinded clinical neurophysiologists. With EEG samples obtained from 10 subjects, the average TIE for the "dry electrode" system was 139s, and for the conventional recording 873s (p<0.001). The results support the hypothesis that such a "dry electrode" system can be applied with more than an 80% reduction in the TIE while still obtaining interpretable EEG.