EFFECTS OF BLUE LIGHT ON TRANSCUTANEOUS AURICULAR VAGUS NERVE STIMULATION-INDUCED PUPIL DILATION RESPONSE

Details

Supervisors

El Tahry, Riëm

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

Epilepsy ranks as the second most prevalent neurological disorder worldwide, yet one-third of the patients is resistant to anti-seizure medications (ASMs). Vagus Nerve Stimulation (VNS) is a neuromodulation approach to treat refractory patients, using a pulse generator implanted under the left clavicle. VNS activates an afferent network linked to the noradrenergic system in the brain and the locus coeruleus (LC), which plays a key role in antiepileptogenesis. This project investigates transcutaneous auricular VNS (taVNS), a non-invasive technique stimulating the au-ricular branch of the vagus nerve via the left ear. Another focus is blue light, which is also thought to activate the noradrenergic system. We hypothesise that blue light enhances taVNS physiological biomarkers, such as pupil dilation. To test this, pupil-lometry with active and sham taVNS was conducted on 25 healthy adults exposed to four light conditions: dim (DL), low-intensity blue (lBL), blue (BL), and orange (OL). Our results showed a greater taVNS-induced pupil dilation response (PDR) compared to sham across all light conditions. The PDR under low blue light was significantly larger than under blue or dim light. Persisting effects were observed in the post-stimulation phase, with taVNS-induced PDR in lBL being significantly larger than in DL. Notably, the results supported our hypothesis, as the largest pupil dilation was observed under taVNS and lBL, suggesting that lBL optimally enhances the effects of taVNS. In contrast, higher-intensity blue light could be too intense, potentially lead-ing to a saturation effect. We propose an inverted U-shaped model to explain the correlation between the phasic and tonic activity of the LC, where different light conditions modulate LC tonic activity and influence the phasic response to taVNS. Future experiments in this laboratory will be conducted in VNS-implanted patients to assess in-depth this potentiation effect, with low blue light particularly. If con-firmed, additional markers could be explored to better understand this interaction between low blue light and PDR, potentially paving the way for blue luminotherapy as an adjunctive treatment for patients.