Abstracts

Rationale: Intracranial video EEG (IVEEG) records high-frequency oscillations (HFOs) in the epileptic zone during focal seizures. Their localization at seizure onset may indicate the ictal onset zone. HFOs propagate during ictal semiological changes, which may indicate the ictal symptomatogenic zone. To make visible their propagation pattern and the difference between different frequencies, we evaluated spatiotemporal changes in ictal HFOs by topographic map movie of ictal HFOs integrated with ictal IVEEG. Methods: We recorded IVEEGs in two patients with focal sensory seizures and secondary generalization (sampling rate, 1 kHz) before resection surgery. We used Multiple Band Frequency Analysis to calculate power spectra of ictal EEGs with temporal window of 50 or 100 ms and frequency window of 2 Hz. We averaged power values within gamma (40-80 Hz), ripple (80-200 Hz) and fast ripple frequencies (200-300 Hz) to obtain the time course of ictal HFO power values at all electrodes. We made movies of topographic HFO power synchronized to IVEEG. Case #1: 17-year-old right-handed boy with paresthesia in the left hand followed by secondary generalization. Case #2: 17-year-old right-handed girl with numb or tingling sensation in the right arm with secondary generalization. Results: In Case #1, left hand sensory seizure onset was associated with EEG attenuation and gamma, ripple and fast ripple activity over the middle portion of the right postcentral gyrus corresponding to the left hand sensory area. Thereafter HFOs spread to the precentral gyrus and with concomitant left arm tonic contraction. As the HFOs increased in power and spread to adjacent area, the seizure became secondarily generalized. Gamma activities, ripples and fast ripples distribution and propagation pattern were similar during ictal evolution. In Case #2, ictal onset with abnormal right arm sensation was associated with EEG attenuation and gamma activity and ripples at the middle portion of the left postcentral gyrus corresponding to the right hand sensory area. During right arm and face tonic contraction, ripples were seen over the upper and middle portions of the precentral gyrus, while gamma power was reduced. With secondary generalization, gamma and ripple power increased and spread to the upper portion of the pre- and postcentral gyri and the middle and inferior portions of the precentral gyrus. Scattered fast ripples also appeared in the same region. Conclusions: This integrated topographic map movie depicts ictal HFOs propagating from focal onset in the sensory cortex to adjacent areas in secondary generalization. It revealed evolution of ictal HFOs from the ictal onset zone to the ictal symptomatogenic zone. The propagation pattern of ictal gamma, ripple and fast ripple frequency HFOs differs. The significance of this difference will be clarified by collecting further data of intracranial ictal HFOs and time-locked seizure semiology.