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Exploration of lateralization of Vagus Nerve Stimulation induced pupillary responses on refractory epileptic patients

Boughaba, Najoua
(2025)

Files

BOUGHABA_Najoua_97752000_2024-2025.pdf
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Details

Supervisors
El Tahry, Riëm
Faculty
Faculté de pharmacie et des sciences biomédicales
Degree label
Master [120] en sciences biomédicales, à finalité approfondie
Abstract
Vagus nerve stimulation (VNS), a neurostimulation technique used for over 30 years in epilepsy patients resistant to pharmacological treatments, relies on mechanisms of action that have yet to be elucidated. In around 30% of implanted patients, this stimulation proves ineffective. To date, no biomarker for assessing the efficacy of VNS is used in clinical practice, and no “optimal dose” has been defined. Biomarker development is essential and could also provide more per- sonalized titration, currently performed empirically. Although the mechanisms of VNS are still partially understood, they appear to involve the LC- NA system. Indeed, VNS is thought to activate the locus coeruleus, a brain structure that is the main source of noradrenergic neurons, leading to the release of noradrenaline. This system can be assessed by a variety of measures, including variations in pupillary size, which is the focus of our study. In order to better understand the mechanisms underlying VNS and identify poten- tial biomarkers, we explored the existence of lateralization of pupillary dilation between the two eyes, an observation previously reported in rats. To this end, we measured variations in pupillary size in responders VNS implant patients, whom we stimulated repeatedly, in the form of several stimulation blocks during the experiment. Alt- hough a difference in pupillary dilation was perceived visually, this was not statistically signif- icant, making it impossible to conclude that lateralization was present in these patients. We also knew that stimulation intensity influences pupillary dilatation. However, the effect of frequency had not yet been explored. In the experiment, patients were stimulated at different intensities and frequencies. An influence of intensity was confirmed, in line with previous stud- ies. However, frequency also appeared to have an impact. Contrary to our initial hypotheses, an increase in frequency caused a decrease in pupillary dilation. Further studies will be needed to confirm these latest observations and deepen our understanding of them.