Abstracts

Partial seizures are transient periods of abnormal network excitation of focal origin with regional propagation. The duration of a partial seizure can be operationally defined as either the duration of abnormal activity at the focus or at more remote regions. Intracranial recordings allow for accurate determination of seizure duration. Interestingly in many complex partial seizures, seizure termination occurs simultaneously in all sampled regions even after regional propagation. We have begun to study these patterns of seizure termination using visual analysis aided by quantitative measures of signal complexity., Thus far 43 partial seizures have been analyzed from 6 patients who were admitted to the epilepsy monitoring unit for presurgical evaluation with intracranial subdural arrays. These initial analyses included a selection of patients with mesial temporal onset epilepsy (MTLE, n=2), neocortical lesional epilepsy (NCLE, n=2), and neocortial nonlesional epilepsy (NCNLE, n=2). Visual determination of electrographic duration of the seizures was supplemented with measures of the duration of signal complexity changes derived from time-frequency analyses. The Gabor atom density (GAD) index provides a composite measure of signal complexity and has been shown to correlate with ictal changes in the EEG. The duration of ictal changes at the focus of seizure onset (focal duration) was compared to the duration of ictal changes (epileptiform activity) from all sampled channels. Synchronous termination was operationally defined as the cessation of seizure activity in all recorded channels within 5 seconds and asynchronous termination was operationally defined as cessation of seizure activity at site of seizure initiation but continuation at other electrodes for more than 5 seconds., Visual and GAD analyses of the 43 seizures from six patients show that the termination pattern of seizures in all the six patients appears to depend upon the duration of the seizure. Seizures that are shorter in duration (22.9-98.8 seconds) typically have synchronous termination but seizures that are longer in duration (91.6-229.3 seconds) are more likely to have asynchronous termination. This is true of both temporal and neocortical seizures, whether they are lesional or non-lesional., Synchronous termination of partial seizures appears independent of the symptomatic cause or location of seizure onset but is dependent on seizure duration. Seizures with shorter duration are more likely to have synchronous termination; seizures of longer duration are more likely to have asynchronous termination. This may reflect more extensive propagation. In addition, network feedback may be an important contributing factor to synchronous seizure cessation. Patterns of seizure termination may have implications for treatment involving medications or surgical resection. Additional analyses are ongoing., (Supported by NIH grant NS 48222.)