Abstract
The vagus nerve constitutes a significant element of the autonomic nervous system, serving a
crucial function in maintaining metabolic homeostasis and playing a pivotal role in the
neuroendocrine-immune axis (The three different systems that contribute to development and
maintenance of homeostasis, the nervous, endocrine and immune systems are closely
interrelated [the neuroendocrine-immune axis(1)]) to uphold equilibrium via its afferent and
efferent pathways. Vagus nerve stimulation (VNS) encompasses various methods of
stimulating the vagus nerve, involving both manual and electrical techniques. The vagus nerve
(tenth cranial nerve) plays a significant role in regulating various physiological functions,
including heart rate, respiratory activity, and digestive processes. In this study, we will
examine the applications of VNS and taVNS and their differences. taVNS is a non-intrusive
version of VNS which in turn makes it easier to use and it is more affordable. It also doesn’t
need a specialist to be used, thus patients could take it home and learn to use it by themselves.
Keywords: Vagus Nerve Stimulation, VNS, Modern Medicine, Medicine
Mohammadamin Yarahmadi
Tehran International School, Tehran, Iran
Introduction
James Leonard Corning, born on November 27, 1855, was an American
neurologist and surgeon who made significant contributions to medical science.
He conducted pioneering work in the late 19th century related to the potential
therapeutic applications of electrical stimulation of the vagus nerve. His
experiments demonstrated how such stimulation could potentially influence
bodily functions, laying the groundwork for future research in neurostimulation
and its therapeutic benefits.
Corning’s early work on vagus nerve stimulation (VNS) showcased the
nerve’s role in regulating various bodily functions, including heart rate,
digestion, and mood. Despite not receiving widespread recognition during his
lifetime, Corning’s experiments and insights have since influenced the field of
neurostimulation. His work has had profound effects on the development of
VNS as a therapeutic modality, especially in the treatment of epilepsy and
neuropsychiatric disorders.
Furthermore, Corning’s pioneering efforts have also sparked interest in
transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive
technique that stimulates the vagus nerve through the skin of the outer ear. This
approach has shown potential in various medical domains, including pain
management, mood disorders, and inflammatory conditions.
He designed an “electrocompressor” for the carotid (2, 3), a fork-shaped tool
documented in the archives of the National Library of Medicine. Corning
hypothesized that irregular cerebral blood flow was a trigger for seizures, and
his apparatus aimed to both bilaterally compress and electrically stimulate the
carotid sheath (4).
As mentioned before, after Corning, his work was under-appreciated until
1938, in which Bailey and Bremer gave out “A sensory cortical representation of
the vagus nerve with a note on the effects of low blood pressure on the cortical
electrogram”. In the study, Bailey and Bremer investigated the activation of the
cortical neurons using a electrogram within a feline model. Similar studies were
done on the topic by Zanchetti and colleagues (6), and Professor Jacob
Zabara(Who is considered the creator of the VNS we know of today, he did
seminal work in the 1980s). Jacon Zabara was able to inhibit experimental
seizures in canines by repetitive vagal stimulation (7).
The inception of VNS trials paved the way for the first human implantation of
a VNS device in 1988, carried out by Penry and Dean. Notably, their
magnificent work revealed a reduction in seizure frequencies in three out of four
patients initially implanted with VNS systems (8). The U.S. Food and Drug
Administration (FDA) granted approval for the marketing of VNS for epilepsy
in 1997, following a pivotal trial involving 310 patients that demonstrated a
notable 23% reduction in seizures after three months of VNS treatment (9, 10).
Subsequent to this milestone, FDA approval expanded to encompass the
marketing of the VNS device for depression in 2005, and later for morbid
obesity in 2015 (as not covered in this review). Having gained acceptance as a
long-term treatment for epilepsy, VNS is currently utilized by more than 15,000
patients globally. The exploration of VNS efficacy has prompted inquiries into
its potential application in addressing various neuropsychiatric disorders (11).