Surface EEG (surface + eeg)

Distribution by Scientific Domains

Selected Abstracts

Electrical source imaging for presurgical focus localization in epilepsy patients with normal MRI

EPILEPSIA, Issue 4 2010
Verena Brodbeck
Summary Purpose:, Patients with magnetic resonance (MR),negative focal epilepsy (MRN-E) have less favorable surgical outcomes (between 40% and 70%) compared to those in whom an MRI lesion guides the site of surgical intervention (60,90%). Patients with extratemporal MRN-E have the worst outcome (around 50% chance of seizure freedom). We studied whether electroencephalography (EEG) source imaging (ESI) of interictal epileptic activity can contribute to the identification of the epileptic focus in patients with normal MRI. Methods:, We carried out ESI in 10 operated patients with nonlesional MRI and a postsurgical follow-up of at least 1 year. Five of the 10 patients had extratemporal lobe epilepsy. Evaluation comprised surface and intracranial EEG monitoring of ictal and interictal events, structural MRI, [18F]fluorodeoxyglucose positron emission tomography (FDG-PET), ictal and interictal perfusion single photon emission computed tomography (SPECT) scans. Eight of the 10 patients also underwent intracranial monitoring. Results:, ESI correctly localized the epileptic focus within the resection margins in 8 of 10 patients, 9 of whom experienced favorable postsurgical outcomes. Discussion:, The results highlight the diagnostic value of ESI and encourage broadening its application to patients with MRN-E. If the surface EEG contains fairly localized spikes, ESI contributes to the presurgical decision process. [source]

Spindles-Inducing Mechanism Modulates Sleep Activation of Interictal Epileptiform Discharges in the Landau,Kleffner Syndrome

EPILEPSIA, Issue 2 2000
L. Nobili
Summary: Purpose: Landau,Kleffner syndrome (LKS) is characterized by a marked increase of interictal epileptiform discharges (IEDs) during sleep. During nonrapid eye movement (NREM) sleep, neuronal membrane potential oscillations lead to the appearance of spindles and delta waves in the surface EEG and might develop into paroxysmal synchronization. Spectral analysis allows the quantitative description of the dynamics of delta (slow-wave activity, SWA, 0.5-4.5 Hz) and sigma activity (SA, 12.0,16.0 Hz) and can be used to assess the relation between SA, SWA, and IEDs during sleep. Methods: We performed six overnight continuous EEG-polysomnographic studies in three patients with LKS. The temporal series of SWA and SA were obtained from a spike-free derivation lead. The IEDs count was performed on the most active lead. Relations between sigma and SWA and time series of lEDs were tested by means of correlation techniques after data normalization. Results: Our results revealed a significantly higher correlation between IEDs and SA with respect to SWA in all the subjects, in total sleep time. The same analysis limited to NREM sleep highlights the better correlation between SA and IEDs. Conclusions: Our data suggest that neural mechanisms involved in the generation of sleep spindles facilitate IEDs production in LKS. [source]

Task-related gamma-band dynamics from an intracerebral perspective: Review and implications for surface EEG and MEG

Karim Jerbi
Abstract Although non-invasive techniques provide functional activation maps at ever-growing spatio-temporal precision, invasive recordings offer a unique opportunity for direct investigations of the fine-scale properties of neural mechanisms in focal neuronal populations. In this review we provide an overview of the field of intracranial Electroencephalography (iEEG) and discuss its strengths and limitations and its relationship to non-invasive brain mapping techniques. We discuss the characteristics of invasive data acquired from implanted epilepsy patients using stereotactic-electroencephalography (SEEG) and electrocorticography (ECoG) and the use of spectral analysis to reveal task-related modulations in multiple frequency components. Increasing evidence suggests that gamma-band activity (>40 Hz) might be a particularly efficient index for functional mapping. Moreover, the detection of high gamma activity may play a crucial role in bridging the gap between electrophysiology and functional imaging studies as well as in linking animal and human data. The present review also describes recent advances in real-time invasive detection of oscillatory modulations (including gamma activity) in humans. Furthermore, the implications of intracerebral findings on future non-invasive studies are discussed. Hum Brain Mapp, 2009. 2009 Wiley-Liss, Inc. [source]

Intracortical electroencephalography in acute brain injury,

Allen Waziri MD
Objective Continuous electroencephalography (EEG) is used in patients with neurological injury to detect electrographic seizures and clinically important changes in brain function. Scalp EEG has poor spatial resolution, is often contaminated by artifact, and frequently demonstrates activity that is suspicious for but not diagnostic of ictal activity. We hypothesized that bedside placement of an intracortical multicontact electrode would allow for improved monitoring of cortical potentials in critically ill neurological patients. Methods Sixteen individuals with brain injury, requiring invasive neuromonitoring, underwent implantation of an eight-contact minidepth electrode. Results Intracortical EEG (ICE) was successfully performed and compared with scalp EEG in 14 of these 16 individuals. ICE provided considerable improvement in signal-to-noise ratio compared with surface EEG, demonstrating clinically important findings in 12 of 14 patients (86%) including electrographic seizures (n = 10) and acute changes related to secondary neurological injury (n = 2, 1 ischemia, 1 hemorrhage). In patients with electrographic seizures detected by ICE, scalp EEG demonstrated no concurrent ictal activity in six, nonictal-appearing rhythmic delta in two, and intermittently correlated ictal activity in two. In two patients with secondary neurological complications, ICE demonstrated prominent attenuation 2 to 6 hours before changes in other neuromonitoring modalities and more than 8 hours before the onset of clinical deterioration. Interpretation ICE can provide high-fidelity intracranial EEG in an intensive care unit setting, can detect ictal discharges not readily apparent on scalp EEG, and can identify early changes in brain activity caused by secondary neurological complications. We predict that ICE will facilitate the development of EEG-based alarm systems and lead to prevention of secondary neuronal injury. Ann Neurol 2009;66:366,377 [source]