Brain Star Award winner Chifaou Abdallah

Identification of two brain signal features that guide surgery in drug-resistant epilepsy

Epilepsy is one of the most common neurological conditions, affecting individuals across all age groups, social classes, and geographical locations. For patients whose seizures remain uncontrolled despite optimal medical therapy, epilepsy surgery represents the most effective treatment option and offers the highest chance of long-term seizure freedom. Surgical success, however, critically depends on the accurate identification of the seizure generating (epileptogenic) tissue, as its complete removal is a major determinant of postoperative outcome.

Despite extensive presurgical evaluations including advanced imaging and invasive stereo-electroencephalography (SEEG), which remains the clinical gold standard, precise delineation of the epileptogenic network remains challenging. In this study, Chifaou Abdallah, working in the laboratories of Birgit Frauscher and Christophe Grova at McGill University, identified a fundamentally new, biologically grounded approach to defining epileptogenic tissue using invasive SEEG. They demonstrated that the spatial co-localisation of gamma spikes and pre-seizure (preictal) spikes provides a robust marker of region where seizure start that predicts surgical outcome more accurately than conventional seizure-onset zone.

Using a large, multicenter SEEG cohort, they showed that patients in whom regions defined by overlapping gamma and preictal spike activity are removed are significantly more likely to achieve seizure freedom. In contrast, partial or absent removal of these biomarker-defined regions is associated with substantially poorer outcome. Importantly, neither gamma spikes nor preictal spikes alone achieved comparable predictive performance, highlighting that their co-localisation was essential.

Seizures persist in up to 40% of epilepsy patients, despite the use of optimal antiseizure medications, and this study has important implications for the clinical management of these patients with drug-resistant epilepsy. By validating this marker against post-operative seizure outcome in a large multicenter SEEG cohort, the study provides strong evidence that epileptogenicity is more accurately captured by the convergence of both processes than by either feature alone. This addresses a critical challenge in epilepsy surgery, where incomplete identification of epileptogenic tissue remains a leading cause of surgical failure.

The results have direct clinical relevance as these features can be quantified and mapped at the individual-patient level, offering a concrete approach to support surgical planning and to assess whether key epileptogenic regions have been adequately targeted.

Beyond surgical decision-making, the findings advance a network-level understanding of epileptogenicity, which has implications for SEEG implantation strategies, marker-based monitoring, and future approaches to personalized epilepsy care.

About Dr. Chifaou Abdallah

Dr. Chifaou Abdallah is a neurologist and clinical researcher specializing in epilepsy, with expertise in intracranial EEG analysis (SEEG), magnetoencephalography (MEG), high-density EEG (HD-EEG) and epilepsy surgery. She completed her medical training in France, including her neurology residency and clinical fellowship, before pursuing a PhD in Neuroscience at McGill University. Her doctoral work was conducted at the Montreal Neurological Institute and Hospital, in collaboration with the laboratories of Drs. Birgit Frauscher and Christophe Grova. Her research focuses on identifying reliable electrophysiological biomarkers of the epileptogenic zone to improve surgical outcomes in patients with drug-resistant epilepsy. Her work integrates invasive electrophysiology, multimodal neuroimaging, and clinically oriented outcome analyses, with the goal of developing practical tools that can be implemented across epilepsy centers.

Sources of funding

Funding for this research was provided by the Canadian Institutes of Health Research (CIHR), Fonds de Recherche du Québec—Santé (FRQS) and the Savoy Foundation.