Abstracts

High frequency oscillations ([gt]= 40 Hz) in epileptogenic brain are not yet understood, but are a recognized phenomenon in a large proportion of patients with epilepsy. DC potential shifts have been noted in animal models of seizure but are not routinely recorded in humans with epilepsy. The physiologic effect of extracellularly mediated DC potentials on transmembrane voltage-gated ion channels suggests itself as a potential contributor to ictogenesis, and thus worthy of investigation., To investigate the potential relationship between high and low frequency oscillations in epilepsy we recorded continuous unfiltered EEG from from 15 patients implanted with intracranial electrodes as part of their evaluation for epilepsy surgery. The acquistion system used had a dynamic range of +132 to -132 mV, no hardware filtering, and a per channel digitization rate of 32556 Hz. The data were recorded from Pt/Ir clinical intracranial electrodes in both depth and grid/strip configurations. Nine of the patients had mesial temporal onset, the remaining 6 had neocortical onset seizures., High frequency oscillations, defined here as [gt]= 40Hz, were observed in the clinically determined seizure onset leads in all 15 patients. The seizure onset frequency ranged from 45 to 143 Hz. In 14 of the 15 patients the high frequency discharge was cotemporaneous with a large scale DC shift ranging from 0.6 to 1.7 mV. The shift occasionally preceded the high frequency discharge by many seconds as shown in the accompanying figure, however in some cases the high frequency discharge appeared to precede the DC shift., There is high degree of association between the DC shifts and high frequency oscillations during seizure. Further investigations into the cause of this association may lead to a better understanding of ictogenesis and open novel avenues for treatment.[figure1], (Supported by: Salary support for Dr. Stead was provided by the Epilepsy Foundation of America.)