Spikes analysis before and after stimulation of the vagus nerve: a case study.

Epilepsy is one of the most common and serious neurological conditions worldwide. It affects people of all ages, genders and backgrounds. Thirty-five percent of patients with epilepsy are drug-resistant, meaning they do not fully respond to medication. For selected patients, epilepsy surgery — involving either resective procedures or the implantation of neurostimulators — represents a valid therapeutic option. Neuromodulatory approaches involving direct or induced electrical currents have been developed to reduce seizure frequency and duration. One such approach is vagus nerve stimulation (VNS), which sends regular, mild electrical pulses to the brain via the vagus nerve to prevent or reduce seizures. Once the electrical charge reaches the brainstem, it is discharged to different areas of the brain, modulating neural networks. This thesis reports a case study of a pediatric patient with drug-resistant epilepsy undergoing VNS therapy, with high-density EEG recordings collected before implantation and four months after. The aim was to provide neurologists with further quantitative information to support the interpretation of EEG signals, identification of epileptic foci and evaluation of treatment efficacy. Epileptiform discharges were annotated by a neurologist. Spikes were processed using an automated algorithm to extract morphology, duration, amplitude and sharpness and to estimate the presumptive onset channel. Moreover, scalp topographies and spectral analysis were performed to investigate both spatial distribution and background rhythms. Results showed a marked reduction in spike frequency after VNS (from ~15 to ~3 events per minute), particularly during wakefulness, with residual discharges more focal and spatially restricted. Morphological analysis indicated that post-VNS spikes during wakefulness had shorter duration and higher sharpness, whereas during sleep amplitudes and sharpness decreased, with more stable temporal features. Topographical maps confirmed a shift from diffuse frontal–central activity to more localized frontal discharges. Spectral analysis demonstrated a reduction of pathological delta activity during wakefulness and a shift of rhythms to the expected distribution during wakefulness and sleep. These findings suggest that VNS modulates both quantitative and qualitative aspects of epileptiform discharges and background activity, supporting its role as an effective neuromodulatory treatment. Despite the limitations of a single-case design, this study highlights methodological strategies and provides evidence of VNS-induced electrophysiological improvements in a pediatric drug-resistant epileptic patient.