Vagus nerve stimulation: from neurology and beyond!
The vagus nerve is one of 12 pairs of nerves that come off the lower part of the brain called the brainstem. It is the tenth in line and therefore also called the tenth cranial (or X) nerve.
It is an interesting nerve for various reasons. Unlike other cranial nerves, it travels way beyond the head and neck. It has a very long course through the neck to the chest and abdomen. Furthermore it regulates a wide variety of organ functions such as heart, respiratory and gut activities. An important branch of the vagus nerve is the recurrent laryngeal nerve which innervates the larynx (voice box).
Due to a quirk of the embryonic development of the aorta, this nerve gets pulled down into the chest before it makes a U-turn back to the neck. It is therefore easily damaged in operations of the neck or chest, and therefore the bane of surgeons.
Scientists have recognised this characteristic feature of the vagus nerve and have tried to manipulate it for therapeutic reasons. The most well-recognised is the stimulation of the vagus nerve to control epileptic seizures. This vagus nerve stimulation (VNS) requires implanting a stimulator under the skin on the chest, and this is connected to the vagus nerve with wires. Somehow or the other, this stimulation modulates seizures. The Epilepsy Society has detailed information on the technical aspects of VNS, and below is a video showing how VNS works.
The American Academy of Neurology guidelines on VNS, published in the journal Neurology, help Neurologists decide when to use VNS. Below are the main indications for VNS in epilepsy:
- Refractory partial onset seizures in adults >12 years not suitable for surgery
- Partial or generalised seizures in children
- Lennox-Gastaut syndrome (LGS)
- Mood improvement in adult epilepsy
There are however several non-neurological diseases that may benefit from VNS including arthritis, diabetes, hiccups and heart failure. Science News explores these indications further in an article interestingly titled Viva Vagus: Wandering Nerve Could Lead to Range of Therapies. Like opening a can of worms, VNS may extend it’s tentacles far and wide; imagine for example that there is a study looking at the benefit of VNS in bulimia.