Background: Chronic vagus nerve stimulation (VNS) is a recognized treatment for refractory epilepsy and depression. The vagus nerve projects to several brainstem autonomic structures. As pupillary measures are an easy and non-invasive method to evaluate autonomic functioning, we used resting diameter and light reflex measures to investigate the influence of VNS on the human central autonomic nervous system.
Method: We studied 21 patients (7 with major depression, 14 with epilepsy) treated with chronic VNS (30s ON, 5 min OFF stimulation trains). Resting pupil size and light reflex measures were compared in consecutive intervals with (ON) and without stimulation (OFF).
Results: Compared to the OFF condition, the ON condition was associated with a significant increase in resting pupil diameter, but did not affect light reflex measures. There was no group difference between the two populations of patients (depression and epilepsy) on any of the pupil measures.
Conclusion: VNS at clinically significant levels increases resting pupil diameter.
Keywords: Autonomic nervous system; Locus coeruleus; Neuromodulation; Pupillary light reflex; Pupillography.
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