EEG biomarkers to guide epilepsy surgery

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.

Even more complex signal analysis may potentiate recognizing the true high-frequency electrographic signature of epilepsy. Also, the recording could be improved by using electrical stimulation and high-density electrode grids. We started a large study (in collaboration with UMCU) which combines improved steps for recording, analysing and projection of the typical EEG signature intra-operatively on the brain, to directly guide the neurosurgeon.

The study intends to better find the core of epilepsy, but also to understand the effect of epileptic activity on the rest of the brain that might lead to possible changes in cognition or mood.

Neurosurgical projection device

Principal Investigator: