Quantitative visualization of ictal subdural EEG changes in children with neocortical focal seizures

Abstract

Objective-To quantify the ictal subdural electroencephalogram (EEG) changes using spectral analysis, and to delineate the quantitatively defined ictal onset zones on high-resolution 3D MR images in children with intractable neocortical epilepsy.Methods-Fourteen children with intractable neocortical epilepsy (age: 1-16 years) who had subsequent resective surgery were retrospectively studied. The subjects underwent a high-resolution MRI and prolonged subdural EEG recording. Spectral analysis was applied to 3 habitual focal seizures. After fast Fourier transformation of the EEG epoch at ictal onset, an amplitude spectral curve (square root of the power spectral curve) was created for each electrode. The EEG magnitude of ictal rhythmic discharges was defined as the area under the amplitude spectral curve within a preset frequency band including the ictal discharge frequency, and calculated for each electrode. The topography mapping of ictal EEG magnitude was subsequently displayed on a surface-rendered MRI. Finally, receiver operating characteristic (ROC) analysis was performed to evaluate the consistency between quantitatively and visually defined ictal onset zones.Results-The electrode showing the maximum of the averaged ictal EEG magnitude was part of the visually defined ictal onset zone in all cases. ROC analyses demonstrated that electrodes showing >30% of the maximum of the averaged ictal EEG magnitude had a specificity of 0.90 and a sensitivity of 0.74 for the concordance with visually defined ictal onset zones.Significance-Quantitative ictal subdural EEG analysis using spectral analysis may supplement conventional visual inspection in children with neocortical epilepsy by providing an objective definition of the onset zone and its simple visualization on the patient's MRI.

Cortical glucose metabolism positively correlates with gamma-oscillations in nonlesional focal epilepsy

“…ECoG spectral amplitudes at 100–200 Hz were not assessed in our previous study where ECoG data were obtained with a sampling frequency at 200 Hz (Nishida et al, 2007). The ECoG spectral amplitude of 32–64 Hz was calculated without a 58–62 Hz component, if visual inspection revealed a 60 Hz artifact peak on the amplitude spectral curve for all subdural electrodes (Asano et al, 2004); similarly, the spectral amplitude at 100–200 Hz was calculated without components at 118–122 Hz and 178–182 Hz, as needed.…”

Effect of sleep on interictal spikes and distribution of sleep spindles on electrocorticography in children with focal epilepsy

“…Medial temporal spindles were intermittently noted during the seizure (arrows), but did not participate in the ictal discharges. (D) The topography of central spindles was delineated on his own three-dimensional reconstructed surface MR image, using a method similar to that previously described (Asano et al, 2004b). To obtain referencefree topographic maps of spectral measures, all signals were re-montaged to an average reference (Hart et al, 1998;Asano et al, 2005).…”

Cortical abnormalities in epilepsy revealed by local EEG synchrony

“…Extending interictal ICEEG interpretation using quantitative techniques, however, have disclosed critical background features relevant to surgical decisionmaking that are not apparent to visual inspection. For example, very high frequency (> 100 Hz), low amplitude activity (< 5 μV) has been associated with the epileptogenic zone (Worrell, Parish et al 2004;Alarcon, Binnie et al 1995;Allen, Fish et al 1992), as has neuronal synchrony recorded from hippocampal microelectrodes (Colder, Wilson et al 1996) and spectrogram measurements of EEG amplitude (Asano, Muzik et al 2004). Such techniques may be used to detect signatures of cortical abnormality that are not necessarily associated with the well known paroxysmal features, and that may be linked to seizures.…”