The wandering nerve

As the tenth cranial nerve, it originates in your brainstem and extends downward through your neck, into your chest and abdomen. Also referred to as the ‘wandering nerve’ due to its extensive reach, the vagus nerve is continuously part of scientific studies exploring, amongst others, treatments for neurological and gastrointestinal disorders.

Playing a major role in promoting relaxation, digestion and recovery, it branches out to multiple organs, including your heart, lungs, liver, spleen, stomach, intestines and kidneys. It is a critical component of your autonomic nervous system (ANS) which regulates involuntary physiologic processes like heart rate, blood pressure and respiration.

Our ANS has two parts - the sympathetic nervous system (SNS) which owns the "fight or flight" response that prepares your body to respond to perceived threats by increasing heart rate, redirecting blood flow to muscles and releasing stress hormones. The parasympathetic nervous system (PNS) is associated with the "rest and digest" response and helps your body return to a state of calm after a stressful event. The vagus nerve plays a major role in promoting relaxation, digestion and recovery.

The impact of the vagus nerve on various bodily functions has been the subject of extensive research, writes Lisa Keer of Mass General, the largest hospital-based research program in the United States of America, which leads to a better understanding of how vagal tone – a measure of vagus nerve active – can affect you physically. In her in-depth review, The Vagus Nerve: A Key Player in Your Mental Health and Well-being, she refers to certain key areas which include amongst others cardiovascular and digestive health.

The vagus nerve helps to regulate heart rate and blood pressure, with a high vagal tone associated with a lower resting heart rate, reduced blood pressure, and increased heart rate variability (HRV), which is the variation in time between heartbeats.



Key indicator

HRV is a key indicator of autonomic nervous system balance and cardiovascular health. It is also essential for proper digestive function, as it regulates the release of digestive enzymes, gastric acid and bile. It also controls the contractions of the stomach and intestines, which move food through the digestive tract.

Impaired vagal function can lead to various gastrointestinal issues, including acid reflux, gastroparesis (delayed stomach emptying), and irritable bowel syndrome (IBS).

Keer also describes the vagus nerve’s role in modulating inflammation, a crucial aspect of its impact on your physical health. Chronic inflammation is a common underlying factor in many diseases, including autoimmune disorders, metabolic syndrome, and neurodegenerative conditions like Alzheimer's disease. By regulating the production of pro-inflammatory cytokines, the vagus nerve helps prevent excessive inflammation and supports your body's ability to fight off infections and heal from injuries.

The influence of the vagus nerve and its connection to the brain, particularly through the gut-brain axis, plays a significant role in mood regulation, stress response, and cognitive function, says Keer.

Vagal tone plays a role in your mental health specifically around stress and anxiety, with a high vagal tone associated with a greater ability to recover from stress, as it promotes the activation of the PNS.

Low vagal tone which has been linked to an increased risk of depression, on the other hand, is associated with heightened stress reactivity, a reduced ability to cope with stress, as well as with chronic stress.



Functions

According to Keer the vagus nerve's influence on cognitive function is an emerging area of research related to cognitive processes like attention, memory, and executive function, with high vagal tone being linked to better cognitive performance, particularly in tasks that require self-regulation and decision-making.

Currently, there are two pathways to promote vagal nerve tone, the non-medical and the medical. The non-medical pathway includes deep breathing, meditation and mindfulness practices, regular physical activity as well as brief exposure to cold, such as taking cold showers.

The medical pathway relies on vagus nerve stimulation (VNS), where a device that delivers electrical impulses to the vagus nerve is implanted in two places near the left side of your collarbone. A VNS device can help to regulate mood and improve depressive symptoms.

VNS devices have been approved for treatment-resistant depression, particularly in cases where traditional antidepressant medications and therapies have not been effective.

The Food and Drug Administration (FDA) has approved VNS for adults who have difficulty responding to traditional treatments for depression, while research suggests it may help the brain become more adaptable and resilient by promoting new connections.

Regarding the immune system, studies suggest that stimulating the vagus nerve may help regulate the immune system, with VNS being investigated as a potential treatment for autoimmune diseases like rheumatoid arthritis and multiple sclerosis.

Studies have also identified a clear pathway for communication between the gut and the brain, where gut microbiota can regulate vagal activity. VNS is also being explored to regulate blood pressure, lower blood sugar and even be a helpful tool to combat long Covid.



Reflexivity

Neural signals can reflexively control aspects of the immune system nobody had thought about before, says Dr Kevin Tracey, president of the Feinstein Institutes for Medical Research at Northwell Health and cofounder of SetPoint Medical, a company that hopes to market a vagus nerve stimulation system for autoimmune diseases.

A neurosurgeon at the University of Washington in Seattle who implanted SetPoint stimulators in patients with rheumatoid arthritis as part of a study, Dr Andrew Ko, however, says it is still not clear whether vagus nerve stimulation will be as effective as drug treatment, with VNS devices already approved for certain patients with epilepsy and depression.

Devices that stimulate the brains of people with Parkinson's disease have proved, according to Ko, better than medication at reducing symptoms. Another study in an animal model provides direct evidence for the role of the vagus nerve in gut microbiome-brain communication, addressing a critical gap in the field. The research found a clear causal relationship between gut microbiota and vagal nerve activity.

While the potential benefits of VNS bring hope for many sufferers, more research is still needed to fully understand its effects and to develop safe and effective treatment strategies.