EEG and invasive EEG record seizures to understand where the source of epilepsy is. The EEG between seizures also shows abnormalities, which are called epileptiform discharges (spikes). Recently, a new biomarker has been discovered: high frequency oscillations (HFOs). These HFOs could be seen after high-pass filtering the EEG at 80 Hz (ripples of 80-250 Hz and fast ripples of 250-500 Hz). These HFOs seem more specific than spikes and we are evaluating if they might be used directly during surgery with intra-operative invasive EEG recordings.
Example of HFO: regular EEG (0-80 Hz), filtered (>80 Hz and >250 Hz) and a wavelet map showing all frequencies. The second trace shows a ripple and the third trace shows a fast ripple.