Electrical Stimulation of the Vagus Nerve is a Novel Approach to Treating Depression
New technology wearable on the ear may provide relief from the most debilitating symptoms of depression
Traditional vagus nerve stimulation(VNS) has been studied as a possible treatment for depression, but it is not ideal due to invasiveness, costliness, and the risk associated with surgery. Transcutaneous vagus nerve stimulation(tVNS), on the other hand, is safe, non-invasive, and well-tolerated by the body. tVNS stimulates the nerve endings of the vagus nerve through the skin and is used to treat epilepsy and depression.
Electrical Stimulation of Nerve Endings in the Ear
A specific type of tVGS called transcutaneous auricular vagus nerve stimulation(taVGS) stimulates nerve endings in certain parts of the ear called the auricular concha. The device is wearable sort of like headphones, but it stimulates the endings of nerve fibers of the vagus nerve. This is thought to alter the regulation of various systems of the body and brain causing changes in mood.
Transcutaneous auricular vagus nerve stimulation device stimulates the ends of vagus nerve fibers found in the locations of the ear colored red. Image Credit
The “Wandering” Nerve
The name vagus comes from the Latin word for wandering, a reference to the pathway that travels from the brain to organs in the throat and chest. It is the longest and most complex cranial nerve of the body. Acting as a bi-directional communication system between the brain and viscera, nearly 80% of the fibers of the vagus nerve provide information to the central nervous system about the internal state of the body. It is part of the parasympathetic branch of the autonomic nervous system which is responsible for unconscious activity such as breathing and heartbeat. Specifically, the parasympathetic nervous system is associated with energy conservation and is colloquially called the ‘rest and digest’ system.
Modulating Neural Activity in the Limbic System
Stimulation of the vagus nerve alters areas of the brain associated with depression through direct and indirect connections. In neural anatomy terms, the auricular branch of the vagus nerve sends pathways to the nucleus tractus solitarii, which is further connected to areas of the limbic system such as the hypothalamus, amygdala, and hippocampus.
The limbic system is a structure involved in regulating an array of experiences including emotion, memory, and learning. Abnormalities in the limbic system are theorized to underlie depression, so modulation of this system through electrical stimulation alters the structure and functioning of these areas, bringing about changes in mood and depressive symptoms. This may be helpful for people in managing the symptoms of depression and anxiety.
Reducing Chronic Inflammation
Chronic stress can make depression worse, and many people with depression have comorbid anxiety disorders. Overactivation of the stress response for long periods of time causes a chronic inflammatory response that increases the ‘wear and tear’ of the body called allostatic load. The vagus nerve attenuates the stress response, deactivating the ‘fight or flight’ branch of the autonomic nervous system called the sympathetic nervous system. This leads to reductions in the inflammatory response, helping to manage this symptom of depression.
Interacting with the Gut Microbiome
The gut microbiota is the collection of bacterial organisms that live within the digestive tract. Studies of the bacteria that exist in the gut have discovered the importance of the gut microbiota in modulating the stress response. Bacterial interactions with the brain are mediated through neural, immune, and endocrine pathways. The vagus nerve is known to regulate the gastrointestinal, endocrine, and immune systems. Therefore, taVNS may be effective in treating depression through adjustment of the communication between the gut and the brain.
Final Thoughts on The Therapeutic Value in Treating Depression
Depression is a debilitating disease affecting a large percentage of the population. Some people do not respond to treatments leaving more options to be desired. taVNS offers a novel therapeutic potential giving people more control of their nervous system’s flow of electrical energy, so it likely will be value of value to people as an adjunct to traditional methods of treating depression such as talk therapy. Current research looks promising and suggests taVNS helps to manage symptoms such as chronic stress, insomnia, and inflammation.
Sources:
Fang, J., Egorova, N., Rong, P., Liu, J., Hong, Y., Fan, Y., … Kong, J. (2017). Early cortical biomarkers of longitudinal transcutaneous vagus nerve stimulation treatment success in depression. NeuroImage: Clinical, 14, 105–111. https://doi.org/10.1016/j.nicl.2016.12.016
Mas-Herrero, E., Dagher, A., & Zatorre, R. J. (2018). Modulating musical reward sensitivity up and down with transcranial magnetic stimulation. Nature Human Behaviour, 2(1), 27–32. https://doi.org/10.1038/s41562-017-0241-z
