The physiology, anatomy and stimulation of the vagus nerve in epilepsy

The vagus nerve is the longest cranial nerve, with much of its territory residing outside the head, in the neck, chest and abdomen. Although belonging to the parasympathetic division of the autonomic nervous system, it is dominated by sensory axons originating in the heart, lungs and airways and the gastrointestinal tract. Electrical stimulation of the cervical vagus nerve via surgically implanted cuff electrodes has been used clinically for the treatment of drug-resistant epilepsy for three decades but has also shown efficacy in the treatment of drug-resistant depression and certain gastrointestinal disorders. Through consideration of the anatomical composition of the vagus nerve, its physiology and its distribution throughout the body, we review the effects of vagus nerve stimulation in the context of drug-resistant epilepsy. This narrative review is divided into two sections: part one surveys the anatomy and physiology of the vagus nerve, and part two describes what we know about how vagus nerve stimulation works.