As the topic of mental health has gained attention over the past several years, you've no doubt heard a couple of related phrases you're not familiar with. One is the vagus nerve. The other is heart rate variability. Here, we'll delve into the vagus nerve and what it's all about.



What is the Vagus Nerve?



The vagus nerve, also known as the 10th cranial nerve or cranial nerve X, is the longest and most complex of the cranial nerves. It is also known as the "wanderer nerve" due to its long, winding course through the body, connecting various organs and systems. It is a key part of the parasympathetic nervous system, which controls involuntary body functions such as digestion, heart rate, and immune response.“Vagus Nerve: What It Is, Function, Location & Conditions.” Cleveland Clinic, https://my.clevelandclinic.org/health/body/22279-vagus-nerve. Accessed 6 Feb. 2024.



The vagus nerve originates in the medulla oblongata, a part of the brain that connects to the spinal cord, and extends down through the neck to the vital abdominal organs.Segal, Dayva. “Vagus Nerve: What to Know.” WebMD, https://www.webmd.com/brain/vagus-nerve-what-to-know. Accessed 6 Feb. 2024. It contains both motor and sensory fibers, which means it can send and receive information.Kenny BJ, Bordoni B. Neuroanatomy, Cranial Nerve 10 (Vagus Nerve) [Updated 2022 Nov 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537171/



The vagus nerve carries signals between the brain, heart, and digestive system. It is responsible for various bodily functions, including digestion, heart rate, and breathing. It also plays a role in controlling mood, immune response, and the regulation of food intake, satiety, and energy homeostasis.Breit S, Kupferberg A, Rogler G, Hasler G. Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Front Psychiatry. 2018 Mar 13;9:44. doi: 10.3389/fpsyt.2018.00044. PMID: 29593576; PMCID: PMC5859128.



Vagus nerve stimulation (VNS) is a treatment method that uses electrical impulses to stimulate the nerve. It's used to treat some cases of epilepsy and depression that don't respond to other treatments.



Damage to it can lead to conditions like gastroparesis, where food does not move into the intestines, and vasovagal syncope, a condition where people faint from low blood pressure.



Vagal Tone



Vagal tone is often used to assess heart function, emotional regulation, and other processes that alter or are altered by changes in parasympathetic activity. A higher resting vagal tone means you have a reserve capacity for stress. You're more stress resilient.Laborde S, Mosley E, Thayer JF. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research - Recommendations for Experiment Planning, Data Analysis, and Data Reporting. Front Psychol. 2017 Feb 20;8:213. doi: 10.3389/fpsyg.2017.00213. PMID: 28265249; PMCID: PMC5316555.



Vagal tone is typically measured indirectly by heart rate variability (HRV), which is the variation in time between each heartbeat. HRV is considered a marker of the body's resilience and adaptability to stress, with higher HRV (indicating greater variability in the intervals between heartbeats) generally associated with better health and fitness, greater resilience to stress, and lower risk of disease.



The Vagus Nerve and the Gut-Brain Axis



The vagus nerve plays a pivotal role in the gut-brain axis, a complex communication network that links the central nervous system (CNS) with the gastrointestinal (GI) tract. This bidirectional pathway allows for the exchange of signals between the gut and the brain, influencing a wide range of bodily functions, including mood, immune response, digestion, and heart rate. Here's how the vagus nerve affects the gut-brain axis:



Direct and Indirect Sensing



The vagus nerve can directly or indirectly sense a variety of signals from t...