Abstracts

RATIONALE: Neuronal oscillations are recently the most remarkable topics in epilepsy. Wavelet-frequency analysis, one of the computational non-stationary analysis of EEG signals, has been used to investigate the synchronization property to cause intractable epilepsy. Focal cortical dysplasia (FCD) is known to be intrinsically epileptogenic. We applied wavelet-frequency analysis to evaluate the specific frequency patterns on ictal subdural EEG in patients with FCD.
METHODS: We reviewed five patients with FCD who underwent cortical excision following subdural EEG recording. For wavelet analysis, we selected paired-subdural electrodes located to the center of the MRI lesion. We analyzed three phases (pre-ictal, ictal onset and peri-ictal) in the most prominent EEG seizures with Gaussian wavelet analysis (1-12, 5-20, 10-35, and 30-60 Hz for 20 seconds).
RESULTS: We found various frequency patterns at each phase. Pre-ictal phase showed wide-ranged (1-60 Hz) frequency activities associated with interictal spike discharges. During ictal onset phase, two patients had brief high-intensity gamma activities, consisting of wide-ranged high-frequency (30-60 Hz) lasting less than 2 seconds. The other three patients did not have any explicit high-intensity activities. Peri-ictal phase showed various prolonged high-intensity activities lasting longer than 10 seconds, the gamma range (around 50 Hz) in one, the beta range (around 20 Hz) in one and the alpha range (around 10 Hz) in three patients.
CONCLUSIONS: Wavelet-frequency analysis can differentiate the ictal transitional phases by dynamic changes of frequency. We found brief high-intensity gamma activities and prolonged high-intensity activities in various frequency during the ictal time course in patients with FCD. We need further investigation to understand neuronal oscillations in the intrinsically epileptogenic FCD.