Abstracts

Rationale: Mesial temporal lobe epilepsy is a condition which can cause a wide range of morbidity. Central to this is the variation between simple partial (SP) and complex partial (CP) seizures. Prior work has shown that there is qualitative neocortical slowing in areas distant to the seizure focus during partial seizures. This neocortical slow activity consists of an increase in delta and theta waves observed during seizures, similar to that seen in sleep, coma and encephalopathy. To date, there have been limited studies that examined the differences between SP and CP seizures using quantitative techniques. Methods: Pre-operative intracranial EEG was obtained for 37 seizures in 14 patients with confirmed mesial temporal lobe epilepsy. Two evaluators described behavior on video recordings to determine verbal responsiveness, which served as a marker of consciousness. EEGs were then evaluated by power spectral analysis to determine amplitudes in the classic frequency bands (delta, theta, alpha, beta, and gamma) in nine cortical regions. Ictal and post-ictal amplitudes were compared to the average baseline activity of the 60 seconds prior to onset. Individual changes were then averaged with all seizures of the same type (SP versus CP). Results: As reported previously, both SP and CP seizures showed marked increases in alpha, beta and gamma frequencies in the ipsilateral medial and lateral temporal lobes. Frontal cortical regions showed greatest increases in delta and theta bands. This frontal slowing disappeared immediately post-ictally in SP seizures, but persisted in CP seizures. The most notable differences between SP and CP seizures were in the subset of patients with contralateral electrodes. In these patients, SP seizures showed no contralateral medial temporal lobe changes, while CP showed nearly identical patterns to the ipsilateral side. Bilateral frontal cortical slowing also appeared more marked in CP than SP seizures, although there were insufficient lateral frontal electrodes to make a definitive assessment. Conclusions: These quantitative analyses confirm past visual assessments showing bilateral temporal involvement during complex, but not simple partial seizures. Additionally, contralateral frontal association cortex showed increased amplitude slow waves during CP seizures, which did not appear as evident during SP seizures. Delineating the electroencephalographic changes associated with changes in consciousness may help to better understand the networks involved in one of the more disabling aspects of this type of epilepsy. Ultimately, this will ideally be useful in developing more refined and targeted treatments for mesial temporal lobe epilepsy. Supported by grants from The Donaghue Foundation and the Betsy and Jonathan Blattmachr Family.