A Comparison of EEG Seizure Patterns Recorded with Surface and Depth Electrodes in Patients with Temporal Lobe Epilepsy

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Abstract
Surface and depth EEG seizure patterns were compared in 34 patients with intractable temporal lobe epilepsy in whom depth EEG electrodes were chronically implanted to localize epileptogenic sites with a view to surgery. EEG records, accompanied by clinical seizures, auras, no behavioral changes and records for which no behavioral observations were made, were judged with respect to the manner in which seizure activity originating unilaterally in the depth of one of the temporal lobes spread to the surface. For each EEG record, the onset of seizure activity in depth was classified as being focal or regional in form, and seizure activity was judged as: not spreading to the surface, spreading bilaterally and synchronously to the surface, spreading initially to the surface ipsilateral to the depth site(s) in which the electrographic seizure first appeared or spreading initially to the surface contralateral to the depth site(s) in which the seizure activity initially occurred. EEG seizure activity was less likely to propagate to the surface for those records that were either unaccompanied by behavior changes or accompanied only by auras than for those records accompanied by clinical seizures. In records accompanied by clinical seizures, seizure activity commonly propagatd to the surface in a bilateral and synchronous fashion and spread initially to the ipsilateral but not to the contralateral surface. Anatomical and electrophysiological data accounting for the occurrence of ipsilateral spread were discussed. Diagnostic usefulness of surface recordings during clinical seizures in temporal lobe epilepsy was discussed.