Interictal high-frequency oscillations (80-500 Hz) in the human epileptic brain: entorhinal cortex.

TitleInterictal high-frequency oscillations (80-500 Hz) in the human epileptic brain: entorhinal cortex.
Publication TypeJournal Article
Year of Publication2002
AuthorsBragin, A, Wilson CL, Staba RJ, Reddick M, Fried I, Engel J
JournalAnnals of neurology
Volume52
Issue4
Pagination407-15
Date Published2002 Oct
ISSN0364-5134
KeywordsElectrodes, Implanted, Electroencephalography, Entorhinal Cortex, Epilepsy, Temporal Lobe, Humans, Periodicity
Abstract

Unique high-frequency oscillations of 250 to 500 Hz, termed fast ripples, have been identified in seizure-generating limbic areas in rats made epileptic by intrahippocampal injection of kainic acid, and in patients with mesial temporal lobe epilepsy. In the rat, fast ripples clearly are generated by a different neuronal population than normally occurring endogenous ripple oscillations (100-200 Hz), but this distinction has not been previously evaluated in humans. The characteristics of oscillations in the ripple and fast ripple frequency bands were compared in the entorhinal cortex of patients with mesial temporal lobe epilepsy using local field potential and unit recordings from chronically implanted bundles of eight microelectrodes with tips spaced 500 microm apart. The results showed that ripple oscillations possessed different voltage versus depth profiles compared with fast ripple oscillations. Fast ripple oscillations usually demonstrated a reversal of polarity in the middle layers of entorhinal cortex, whereas ripple oscillations rarely showed reversals across entorhinal cortex layers. There was no significant difference in the amplitude distributions of ripple and fast ripple oscillations. Furthermore, multiunit synchronization was significantly increased during fast ripple oscillations compared with ripple oscillations (p < 0.001). These data recorded from the mesial temporal lobe of epileptic patients suggest that the cellular networks underlying fast ripple generation are more localized than those involved in the generation of normally occurring ripple oscillations. Results from this study are consistent with previous studies in the intrahippocampal kainic acid rat model of chronic epilepsy that provide evidence supporting the view that fast ripples in the human brain reflect localized pathological events related to epileptogenesis.

DOI10.1042/AN20110027
Alternate JournalAnn. Neurol.