Abstracts

Multiple band frequency analysis (MBFA), a new frequency analysis method, provides better frequency and temporal resolutions than fast Fourier or wavelet transform. We evaluated dynamic changes of high frequency oscillations (HFOs) on brain surface maps using MBFA to localize epileptogenic zones in neocortical epilepsy. We studied 2 children with intractable neocortical epilepsy by subdural EEG (SDEEG) at 1 KHz sampling rate. We performed MBFA for 1-5 second ictal EEG using the software [italic]Short Spectrum Eye[/italic] (Gram, Saitama, Japan). We identified HFOs, determined the frequency range, and calculated averaged powers at every 10 ms for all electrodes. We imported the averaged powers into a topographic mapping program [italic]Prism[/italic] and [italic]Insight[/italic] (Persyst, Prescott, AZ) to visualize HFO powers on the brain surface picture. To analyze temporal interrelationships of regions with HFOs, we arranged HFO power maps at every 20 ms to project movies of ictal HFOs on the brain surface.
Case 1: A 17 year old right handed girl presented with simple partial seizures consisting of numbness and tingling sensations in the right arm followed by clonic movements and secondary generalization.
Case 2: A 14 year old left handed boy with asymmetric epileptic spasms in clusters. Case 1; During partial seizures, MBFA of 25-channel SDEEG showed 80-130 Hz HFOs over the middle portion of the left postcentral gyrus and upper portion of the left post- and pre-central gyri. Sequential power maps of 80-130 Hz HFOs revealed high powers over these 2 regions, and reverberating power changes between them with a maximum at the middle portion of postcentral gyrus. We resected the upper and middle portions of left postcentral gyrus. She has rare and brief partial motor seizures without sensory aura and secondary generalization 9 months after surgery.
Case 2; During spasms, MBFA of 106-channel SDEEG showed extensive but noncontiguous 60-150 Hz HFOs over the right superior and inferior frontal, and middle temporal gyri. Sequential power maps of 80-120 Hz HFOs revealed initial high power over the right superior frontal gyrus and subsequent activations over other 2 regions. We performed partial right frontal lobectomy, cortical excisions of the superior and inferior frontal gyri, and middle temporal gyrus where predominant HFOs existed. He is seizure free 6 months after surgery. The combination of MBFA and sequential brain surface HFO power mapping enabled us to recognize the localization and dynamic changes of ictal HFOs. This spatial and temporal analysis of HFO cortical mapping may disclose the behavior of ictal networks in the cortical epileptogenic zones.