Transcutaneous vagus nerve stimulation - A brief introduction and overview

Area of Science:

• Neurology
• Biomedical Engineering
• Neuroscience

Background:

• Invasive vagus nerve stimulation (VNS) is clinically approved for epilepsy, depression, obesity, and stroke rehabilitation but involves surgery, side effects, and high costs.
• Transcutaneous VNS (tVNS) emerged as a non-invasive, cost-effective, and accessible alternative approximately 20 years ago.
• The ear's outer acoustic canal is a potential site for tVNS due to the vagus nerve's accessibility and observed reflex responses to auricular stimulation.

Purpose of the Study:

• To explore the potential and challenges of transcutaneous vagus nerve stimulation (tVNS) as a non-invasive therapeutic modality.
• To investigate the complexities of auricular nerve innervation and its implications for effective tVNS.
• To elucidate the central pathways and brain structures modulated by tVNS.

Main Methods:

• Review of existing literature on invasive and transcutaneous VNS, auricular anatomy, and neurophysiological responses.
• Analysis of the innervation patterns of the outer ear, including the auricular branch of the vagus nerve (ABVN) and other sensory nerves.
• Examination of the central nervous system pathways activated by tVNS, including the nucleus of the solitary tract and the locus-coeruleus-norepinephrine system.

Main Results:

• The outer ear presents a complex innervation landscape with multiple sensory nerves, including the ABVN, which has fewer Aβ-fibers compared to the cervical vagus nerve, necessitating optimized stimulation parameters.
• tVNS activates specific central pathways, such as the nucleus of the solitary tract and the locus-coeruleus-norepinephrine system.
• VNS, including tVNS, influences various brain areas within the central autonomic network and limbic system.

Conclusions:

• Optimal stimulation sites, parameters, and algorithms for tVNS require further investigation due to the ear's complex sensory nerve distribution.
• Understanding the central pathways mediating tVNS effects is crucial for its therapeutic application.
• tVNS holds significant promise for enhancing autonomic balance and treating a wide range of autonomic, neurological, psychiatric, and rheumatologic conditions, potentially becoming a standard therapeutic tool.