Authors :
Presenting Author: Inci Cakiroglu, MSc – Université Catholique de Louvain
Venethia Danthine, MD – Université Catholique de Louvain
Raphaël Vicini, MSN – UCLouvain
Ana Marta Dias, MSc – Université Catholique de Louvain
Enrique Germany Morrison, PhD – Université catholique de Louvain
Antoine Nonclercq, PhD – Université Libre de Bruxelles
Riëm El Tahry, MD, PhD – Université Catholique de Louvain, Clinique Universitaire ST Luc
Rationale:
This study aims to characterize how intermittent photic stimulation (IPS) and vagus nerve stimulation (VNS) modulate occipital EEG synchronicity in patients with drug-resistant epilepsy. We investigated FC differences between resting state (RS) and IPS under VNS ON versus OFF conditions, and tracked their evolution from pre-implantation (V1) to six months post-implantation (V5). We hypothesized that brain connectivity in response to IPS differs between VNS responders (R) and non-responders (NR), and that VNS may progressively modulate this connectivity over time.
Methods:
EEG data from twelve patients (5R, 7NR) were collected at four time points (V1, V3, V4, V5) under standardized conditions (eyes closed/open, RS vs PS at 3, 6, 9, 18, and 30 Hz, VNS ON vs OFF). We calculated occipital weighted phase lag index (wPLI)1 across typical EEG frequency bands and we compared values using a linear mixed model across visits between groups (R vs NR) and state (RS vs PS). Results:
Before implantation (V1), NR exhibited higher occipital wPLI during 30 Hz IPS compared to RS, particularly in the high-beta EEG band (p = 0.0017). They also showed significantly higher wPLI during IPS than R (p = 0.010), who displayed similar levels of synchronicity between IPS and RS at V1 and across visits. Interestingly, this increased IPS-induced synchronicity in NR persisted after six months of VNS implantation (V5; p = 0.022). However, the significant difference in synchronicity during IPS between NR and R seen at V1 was no longer present at V5.Conclusions:
These findings suggest that IPS reveals significant hypersynchronicity in VNS non-responders in occipital regions, potentially reflecting a photosensitive-like EEG profile2. In contrast, responders display a more stable occipital network, with limited reactivity to IPS, similar to a healthy brain2-4. Notably, the absence of group differences after 6 months suggests that chronic VNS modulates IPS induced hypersynchrony in non-responders, however, this modulation does not appear to be associated with clinical outcome. These results support the potential of IPS-induced EEG responses as a pre-implantation predictive biomarker of VNS treatment efficacyFunding:
This work was funded by Innoviris, the public agency supporting research and innovation in the Brussels-Capital Region.