Epilepsy is a common neurological disease which affects people's tremendously. It affects peoples lives in many ways, not only by causing seizures, but also by disturbing the normal brain to function at 100%. If the origin of epileptic activity in the brain is focal, it can be cured by epilepsy surgery. This is currently successful in 50-70%, but this number can increase if we would be able to define the focus of epilepsy more precisely. The goal of our project was to delineate the focus of epilepsy with intra-operative recordings of the electrical brain activity, and look for small vibrations in the signal: high frequency oscillations (HFOs). The project objectives were to improve both the recording methods and the signal analysis methods to better define the core of epilepsy and to understand the effect of epileptic activity on the rest of the healthy brain.
We built a database of previous invasive EEG and innovated the recordings themselves. We used advanced signal analysis methods including machine learning to better recognize the epileptic activity and found several complementary signal biomarkers. We used high-density electrode grids and found that this improved detecting the small HFOs and potentiated more precise recognition of epileptic tissue by advanced signal analysis. We developed flexible electrode that can record from within a resection cavity to check if all diseased tissue has been removed. We used short stimulations to find the diseased tissue which responds differently to stimulation than healthy tissue. We found ways to recognize the position of the electrode grids during surgery, which is needed for to directly guide the neurosurgeon by projecting the signal analysis results.
The project gained us insight into the pathophysiology of epilepsy. We found that removing tissue producing epileptic activity has a positive effect on cognition. We studied people with brain tumors and epilepsy and found that the invasive EEG recordings recognizes infiltrative tumor growth and inflammation. This shows that understanding and optimal recording of the epileptic brain signal can improve not only the direct effects of epilepsy surgery to stop seizures, but also aids optimal effects on cognition and tumor removal.
The next step that is needed is to build a system that combines optimal recording, analysis and feedforward projection of results on the brain surface to guide neurosurgeons.
