Abstracts

Neocortical epilepsy represents a large and heterogeneous group. Within this group patients with lesions, whether temporal or extratemporal, may have better post-surgical seizure control than patients with nonlesional neocortical seizures. It is often easier to identify the seizure focus in lesional patients, in part guided by the MRI abnormality. We applied advanced time-frequency analysis to characterize seizure dynamics for this sub-group of neocortical epilepsy, and especially to assess the occurrence of organized rhythmic activity (ORA) pattern.
We analyzed data from 42 complex partial seizures from 5 different patients with lesional lateral temporal or extratemporal epilepsy monitored in the epilepsy monitoring unit for pre-surgery evaluation with intracranial subdural grid arrays in 2002-2003. We applied the matching pursuit (MP) method developed by Mallat and Zhang (1993) which allows for continuous time-frequency decomposition of rapidly changing signals without requiring linear or nonlinear assumptions. The Gabor atom density (GAD) method (Jouny et al. 2003) derived from the MP method provides a value that represents the number of atoms necessary to represent the signal. It can be interpreted as the complexity of the EEG during that period.
Seizures from each of our 5 patients exhibit pattern of rhythmic activity clearly shown by MP analysis. Among the 42 seizures, 34 exhibit patterns of organized rhythmic activity ([gt] 5 sec). MP reconstruction for multiple seizures revealed reproducible harmonic content between seizures from the same patient but different between patients. [table1]In addition, for 32 seizures out of 42, there is a slow propagation pattern, where seizures stay focal with limited spread or with only a late involvement of remote areas.
MP and GAD analysis of the seizures of these patients with neocortical lesions revealed ORA patterns in some ways similar to the patterns observed in patients with mesial temporal onset seizures. Nevertheless, patterns in these neocortical seizures may occur earlier in the seizure, eg. during initiation. Their frequency is typically above the frequency of ORA in mesial temporal onset seizures (Franaszczuk et al. 1998). These periods of ORA were not observed in nonlesional patients. These dynamics may provide insights about the link between the seizure type and the lesions from which they originate, and also their more favorable surgical outcomes. These results are being extended and further compared to patterns of ictal dynamics in nonlesional neocortical epilepsy.
[Supported by: NS 33732]