A computational biomarker of photosensitive epilepsy from interictal EEG

Abstract

People with photosensitive epilepsy (PSE) are prone to seizures elicited by visual stimuli. The possibility of inducing epileptiform activity in a reliable way makes PSE a useful model to understand epilepsy, with potential applications for the development of new diagnostic methods and new treatments for epilepsy. A relationship has been demonstrated between PSE and both occipital and more widespread cortical hyperexcitability using various types of stimulation. Here we aimed to test whether hyperexcitability could be inferred from resting interictal electroencephalographic (EEG) data without stimulation. We considered a cohort of 46 individuals with idiopathic generalised epilepsy (IGE) that underwent EEG during intermittent photic stimulation (IPS): 26 had a photoparoxysmal response (PPR), the PPR group, and 20 did not, the non-PPR group. For each individual, we computed functional networks from the resting EEG data prior to stimulation. We then placed a computer model of ictogenicity into the networks and simulated the network’s propensity to generate seizures in silico (the brain network ictogenicity, BNI). Furthermore, we computed the node ictogenicity, NI, a measure of how much each brain region contributes to the overall ictogenic propensity. We used the BNI and NI as proxies for testing widespread and occipital hyperexcitability, respectively. We found that the BNI was not higher in the PPR group relative to the non-PPR group. However, we observed that the (right) occipital NI was significantly higher in the PPR group relative to the non-PPR group. Other regions did not have significant difference in NI values between groups.

Significance Statement

We used a computational framework to assess widespread and occipital hyperexcitability in people with epilepsy from apparently normal EEG. We aimed at distinguishing individuals with photosensitivity from individuals without this susceptibility to seizures provoked by visual stimuli. Our results suggest that either widespread hyperexcitability did not differ between the two groups of individuals, or that our methods were not appropriate to measure this hyperexcitability. Conversely, we observed higher occipital hyperexcitability in the photosensitive group compared to the other group. This finding suggests that occipital hyperexcitability is an enduring feature in the brain activity of people with photosensitivity. Thus, our results suggest that our methods based on resting-state EEG may aid the diagnosis of photosensitive epilepsy without requiring stimulation.