Abstracts

Prior studies suggest that temporal lobe seizures cause impaired function in widespread neocortical areas in addition to mesial temporal lobe regions. A recent study by Blumenfeld et al. (NEUROLOGY, 2004) found increased low voltage fast and polyspike ictal activity in ipsilateral mesial and lateral temporal regions, with simultaneous large amplitude ictal slowing in frontoparietal regions. However, these observations were based on subjective ratings of the intracranial EEG recordings and were not correlated with behavior. In the present study we employ quantitative analyses to more accurately describe ictal and post-ictal changes associated with various brain regions during complex and simple partial seizures. 12 Patients with surgically confirmed mesial temporal lobe epilepsy who underwent intracranial EEG monitoring and had no seizures during a follow-up period of at least 1 year after temporal lobe resection were selected for analysis. Seizures that secondarily generalized were excluded. Electrode contacts were assigned to one of nine cortical regions based on MRI surface reconstructions. Power measurements for classically defined spectral bands were calculated with the Fourier transform for the ictal and peri-ictal time periods for each EEG signal. A small, brief increase in beta (13-25 Hz) and gamma (25-50 Hz) frequency power was seen in ipsilateral mesial temporal regions immediately following seizure onset. This was followed by a much larger increase in alpha (8-13 Hz), beta, gamma, and particularly theta (4-8 Hz) power in ipsilateral mesial and lateral temporal regions. Simultaneously, a large increase in delta (0-4 Hz) power was seen in lateral, medial, and orbital frontal regions, which sometimes persisted throughout the post-ictal period. Subclinical seizures involved transient changes confined to the ipsilateral mesial temporal contacts. Although considerable between-patient variability was found, individual patients showed remarkable consistency in EEG patterns across their seizures. Quantitative power analysis showed increased high frequency activity in temporal regions and low frequency activity in frontal regions during partial seizures of temporal lobe origin. These results support and expand upon previous studies of EEG activity positing that neocortical slowing represents a form of [quot]surround inhibition[quot] during such seizures. Further analyses may reveal specific differences between EEG signals in complex and simple partial seizures, and contribute to an understanding of behavioral manifestations of temporal lobe seizures.