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Michael Kogan, David J. Caldwell, Shahin Hakimian, Kurt E. Weaver, Andrew L. Ko and Jeffery G. Ojemann

E valuation of the seizure resection area relies on identifying the irritative zone based on interictal spikes and/or specific ictal patterns in the ictal onset zone. More recently, high-frequency oscillations (HFOs), defined as transient focal increases in amplitude within the frequency range between 80 and 500 Hz, 15 have been observed as a more specific marker for the epileptogenic zone 6 , 14 , 15 , 24 , 26 , 36 , 37 , 39 independent of interictal spikes. 14 However, their clinical application remains to be fully implemented because of limitations in

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Howard M. Eisenberg, Andrew C. Papanicolaou, Stephen B. Baumann, Robert L. Rogers and Linda M. Brown

These two basic properties facilitate the task of relating the recorded magnetic field to its intracranial source. The MEG has been used with considerable success in modeling and localizing sources of normal EEG, of components of sensory evoked responses, 1, 8–11, 13, 17–20 and of interictal discharges in patients with focal epilepsy. 3–5, 14–16, 21 While surface EEG provides information about the general vicinity of interictal spike sources, MEG can be employed to estimate the location, strength, and orientation of the same sources with a greater degree of

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Lilly Tang, Mary Mantle, Paul Ferrari, Hagen Schiffbauer, Howard A. Rowley, Nicholas M. Barbaro, Mitchel S. Berger and Timothy P. L. Roberts

require a two-stage operation. Additionally, intraoperative ECoG, by far considered to be the gold standard of intraoperative functional mapping, prolongs operation and anesthesia time and does not offer information prior to surgery. Magnetoencephalography has been shown to be a useful technique for localizing ictal and interictal spike events 10, 28 as well as for functional preoperative mapping of the language 21, 29 and somatosensory cortices. 6, 7, 13, 22, 26 Moreover, MEG is noninvasive and has excellent temporal resolution, which are needed to determine spike

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Makoto Oishi, Hiroshi Otsubo, Koji Iida, Yasuhiro Suyama, Ayako Ochi, Shelly K. Weiss, Jing Xiang, William Gaetz, Douglas Cheyne, Sylvester H. Chuang, James T. Rutka and O. Carter Snead III

M agnetoencephalography has been used in the presurgical evaluation of neocortical epilepsy patients to noninvasively localize the sources of interictal discharges and the functional cortices. 15 , 18 , 20 , 21 , 24 An ECD model is an accepted method for analysis of MEG interictal epileptiform discharge data in spite of the lack of a unique solution for the inverse problem for MEG. 8 , 30 Data analysis using a single ECD is based upon the assumption that there is only one compact neuronal source in the activated cortex. But when the actual neurons

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Alain Rougier, Dominique Lurton, Bouchaib El Bahh, Véronique Lespinet, Anne-Marie Bidabé, Martine Guillot and Jean-Marie Caillé

T he value of regional cerebral blood flow (rCBF) assessment during the interictal period to determine the lateralization of the focus in temporal lobe epilepsy (TLE) is limited. Interictal 99m Tc-hexamethylpropyleneamine oxime (HMPAO)—single-photon emission computerized tomography (SPECT) scanning correctly identifies the side of the brain containing the epileptic focus in approximately 50% of cases. 13, 21, 37, 43 Only visual or numerical side-to-side comparison can be obtained using this method, but rCBF measurement by 15 O-butanol positron emission

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Hideaki Ishibashi, Panagiotis G. Simos, Eduardo M. Castillo, William W. Maggio, James W. Wheless, Howard L. Kim, Vijay Venkataraman, Daniel K. Sanders, Joshua I. Breier, Wenbo Zhang, Robert N. Davis and Andrew C. Papanicolaou

T he primary objective of preoperative evaluation for epilepsy surgery is accurate localization of the epileptogenic zone. To meet this objective, localization data are obtained from a variety of diagnostic modalities, including electrophysiological monitoring, anatomical imaging, and physiological imaging. Even in patients with focal epilepsy, however, interictal paroxysmal activity and electrographic onset of seizures can appear widespread or bilateral on scalp EEG recordings. In such cases, the analysis of focal abnormalities of background rhythmic activity

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Cuiping Xu, Tao Yu, Guojun Zhang, Gary B. Rajah, Yuping Wang and Yongjie Li

analysis. Inclusion criteria were 1) the occurrence of ESs with or without other seizure types and 2) video-EEG (VEEG) recording capturing the spasms. Presurgical Evaluation All patients in the study had undergone comprehensive evaluation including detailed history, long-term scalp VEEG, MRI, magnetoencephalography (MEG), interictal single-photon emission computed tomography (SPECT), and invasive intracranial monitoring with subdural electrodes or depth electrodes, when necessary. Long-term scalp VEEG (Micromed) with electrodes in the international 10-20 position

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William T. Couldwell

The origin and mechanisms of human interictal epileptic discharges remain unclear. Here, we describe a spontaneous, rhythmic activity initiated in the subiculum of slices from patients with temporal lobe epilepsy. Synchronous events were similar to interictal discharges of patient electroencephalograms. They were suppressed by antagonists of either glutamatergic or gamma-aminobutyric acid (GABA)-ergic signaling. The network of neurons discharging during population events comprises both subicular interneurons and a subgroup of pyramidal cells. In these pyramidal cells, GABAergic synaptic events reversed at depolarized potentials. Depolarizing GABAergic responses in neurons downstream to the sclerotic CA1 region contribute to human interictal activity.

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Hiroshi Otsubo, Atsushi Shirasawa, Shiro Chitoku, James T. Rutka, Scott B. Wilson and O. Carter Snead III

The method we describe here entails computerized voltage topographic mapping directly onto a digital image of the brain surface and shows the dynamics of the ictal and interictal ECoG features on this image. No change in the electrode montage is required. To our knowledge, this is the first report of the use of this procedure. Mapping Procedures Functional Mapping and IVEEG Monitoring We studied 12 children who had extrahippocampal epilepsy refractory to multiple antiepileptic medications by using IVEEG monitoring with placement of a subdural grid. Time

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Odeya Bennett-Back, Ayako Ochi, Elysa Widjaja, Shohei Nambu, Akio Kamiya, Cristina Go, Sylvester Chuang, James T. Rutka, James Drake, O. Carter Snead III and Hiroshi Otsubo

epilepsy, congenital hemiparesis, and/or cognitive impairments. 15 Localization of ictal and interictal electroencephalography (EEG) discharges is challenging in patients with PC/E because the fluid-filled cavity and atrophic cortical tissue distort electrical fields and reduce the amplitude of scalp EEG. Therefore, patients with intractable focal epilepsy secondary to PC/E, which is associated with dense hemiparesis, are frequently subjected to a hemispherectomy due to difficulty in localization with ictal and interictal EEG. 4 , 12 , 20 , 25 For patients with m ild h