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Neural Plasticity
Volume 7 (2000), Issue 1-2, Pages 49-63
http://dx.doi.org/10.1155/NP.2000.49

Functional and Anatomic Correlates of Two Frequently Observed Temporal Lobe Seizure-Onset Patterns

1Medical Research Unit in Neurophysiology, National Medical Center, IMSS Mexico City, Mexico
2Department of Neurology, UCLA Center for the Health Sciences, Los Angeles, CA 90095, USA
3Department of Neurobiology, UCLA Center for the Health Sciences, Los Angeles, CA 90095, USA
4The Brain Research Institute, UCLA Center for the Health Sciences, Los Angeles, CA 90095, USA
5Department of Neuroscienes NC-30 Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA

Copyright © 2000 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Intracranial depth electrode EEG records of 478 seizures, recorded in 68 patients undergoing diagnostic monitoring with depth electrodes, were evaluated to investigate the correlates of electrographic onset patterns in patients with temporal lobe seizures. The seizure onsets in 78% of these patients were identified as either hypersynchronous onsets, beginning with low-frequency, high-amplitude spikes, or low-voltage fast (LVF) onsets, increasing in amplitude as the seizure progressed. The number of patients (35) having hypersynchronous seizure onsets was nearly twice that of patients (18) having LVF onsets. Three major differences were seen among patients with the two seizure-onset patterns. When compared with patients having LVF onsets, patients with hypersynchronous seizure onsets had a significantly greater probability of having (1) focal rather than regional seizure onsets (p<0.01), (2) seizures spreading more slowly to the contralateral mesial temporal lobe (p<0.003), and (3) cell counts in resected hippocampal tissue showing greater neuronal loss (p<0.001). The results provide evidence that the most frequent electrographic abnormality associated with mesial temporal seizures is local hypersynchrony, a condition associated with major neuronal-loss in the hippocampus. The results also indicate that LVF seizure onsets more frequently represent widely distributed discharges, which interact with and spread more rapidly to surrounding neocortical areas.