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Intracranial Electrodes (intracranial + electrode)
Selected AbstractsIntrinsic Ictal Dynamics at the Seizure Focus: Effects of Secondary Generalization Revealed by Complexity MeasuresEPILEPSIA, Issue 2 2007Christophe C. Jouny Summary:,Purpose: Partial seizures (PSs) may be self-limited regional events or propagate further and secondarily generalize. The mechanisms and dynamics of secondarily generalized tonic,clonic seizures (GTCSs) are not well understood. Methods with which to assess the dynamic of those events are also limited. Methods: Seizures were analyzed from patients with intractable partial seizures undergoing monitoring with intracranial electrodes. Inclusion in this study required patients to have at least one PS and one GTCS. From >120 patients, seven patients fulfilled these criteria, three with mesial temporal (MTLE) onset seizures and four with neocortical lesional (NCLE) onset seizures. In total, 50 seizures were analyzed by using the matching pursuit (MP) method and the Gabor atom density (GAD), a measure of signal complexity derived from the MP method. Results: The GAD complexity pattern at the seizure focus for the initial ictal period is remarkably consistent in a given patient, regardless of whether secondary generalization occurs. Secondary generalization produces greater modification of seizure activity at the focus in patients with NCLE than in patients with MTLE. In seizures from four patients with NCLE, secondary generalization resulted in an average increase of 115% in complexity at the focus compared to PSs. Conclusions: GAD shows that seizure dynamics of PSs are often very stereotyped from seizure to seizure in a given patient, particularly during early ictal evolution. Secondary generalization is more likely to produce changes in the duration and dynamics at the seizure focus in NCLE patients compared with MTLE patients. These observations suggest distinct mechanisms (e.g., feedback) that are operational during secondary generalization. [source] The Role of Intracranial Electrode Reevaluation in Epilepsy Patients After Failed Initial Invasive MonitoringEPILEPSIA, Issue 5 2000Adrian M. Siegel Summary: Purpose: Intracranial electrode recording often provides localization of the site of seizure onset to allow epilepsy surgery. In patients whose invasive evaluation fails to localize seizure origin, the utility of further invasive monitoring is unknown. This study was undertaken to explore the hypothesis that a second intracranial investigation is selected patients warrants consideration and can lead to successful epilepsy surgery. Methods: A series of 110 consecutive patients with partial epilepsy who had undergone intracranial electrode evaluation (by subdural strip, subdural grid, and/or depth electrodes) between February 1992 and October 1998 was retrospectively analyzed. Of these, failed localization of seizure origin was thought to be due to sampling error in 13 patients. Nine of these 13 patients underwent a second intracranial investigation. Results: Reevaluation with intracranial electrodes resulted in satisfactory seizure-onset localization in seven of nine patients, and these seven had epilepsy surgery. Three frontal, two temporal, and one occipital resection as well as one multiple subpial transection were performed. Six patients have become seizure free, and one was not significantly improved. The mean follow-up is 2.8 years. There was no permanent morbidity. Conclusions: In selected patients in whom invasive monitoring fails to identify the site of seizure origin, reinvestigation with intracranial electrodes can achieve localization of the region of seizure onset and allow successful surgical treatment. [source] Contrasting roles of neural firing rate and local field potentials in human memoryHIPPOCAMPUS, Issue 8 2007Arne Ekstrom Abstract Recording the activity of neurons is a mainstay of animal memory research, while human recordings are generally limited to the activity of large ensembles of cells. The relationship between ensemble activity and neural firing rate during declarative memory processes, however, remains unclear. We recorded neurons and local field potentials (LFPs) simultaneously from the same sites in the human hippocampus and entorhinal cortex (ERC) in patients with implanted intracranial electrodes during a virtual taxi-driver task that also included a memory retrieval component. Neurons increased their firing rate in response to specific passengers or landmarks both during navigation and retrieval. Although we did not find item specificity in the broadband LFP, both ,- and ,-band LFPs increased power to specific items on a small but significant percent of channels. These responses, however, did not correlate with item-specific neural responses. To contrast item-specific responses with process-specific responses during memory, we compared neural and LFP responses during encoding (navigation) and retrieval (associative and item-specific recognition). A subset of neurons also altered firing rates nonspecifically while subjects viewed items during encoding. Interestingly, LFPs in the hippocampus and ERC increased in power nonspecifically while subjects viewed items during retrieval, more often during associative than item-recognition. Furthermore, we found no correlation between neural firing rate and broadband, ,-band, and ,-band LFPs during process-specific responses. Our findings suggest that neuronal firing and ensemble activity can be dissociated during encoding, item-maintenance, and retrieval in the human hippocampal area, likely relating to functional properties unique to this region. © 2007 Wiley-Liss, Inc. [source] EEG-fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium-enhanced MR angiogramsHUMAN BRAIN MAPPING, Issue 3 2004Andrew P. Bagshaw Abstract Combined EEG-fMRI has recently been used to explore the BOLD responses to interictal epileptiform discharges. This study examines whether misspecification of the form of the haemodynamic response function (HRF) results in significant fMRI responses being missed in the statistical analysis. EEG-fMRI data from 31 patients with focal epilepsy were analysed with four HRFs peaking from 3 to 9 sec after each interictal event, in addition to a standard HRF that peaked after 5.4 sec. In four patients, fMRI responses were correlated with gadolinium-enhanced MR angiograms and with EEG data from intracranial electrodes. In an attempt to understand the absence of BOLD responses in a significant group of patients, the degree of signal loss occurring as a result of magnetic field inhomogeneities was compared with the detected fMRI responses in ten patients with temporal lobe spikes. Using multiple HRFs resulted in an increased percentage of data sets with significant fMRI activations, from 45% when using the standard HRF alone, to 62.5%. The standard HRF was good at detecting positive BOLD responses, but less appropriate for negative BOLD responses, the majority of which were more accurately modelled by an HRF that peaked later than the standard. Co-registration of statistical maps with gadolinium-enhanced MRIs suggested that the detected fMRI responses were not in general related to large veins. Signal loss in the temporal lobes seemed to be an important factor in 7 of 12 patients who did not show fMRI activations with any of the HRFs. Hum. Brain Mapp. 22:179,192, 2004. © 2004 Wiley-Liss, Inc. 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