What is the vagus nerve?

And what’s it got to do with yoga?

Yoga makes us feel good. And scientific research is just beginning to discover why. Over the next few posts I’ll introduce you to the vagus nerve, which is a key player in balancing the calming and activating sides of our nervous system. Read on to find out how this single nerve can help us with health, emotional wellbeing, happiness, memory, digestion, and social relationships. It’s fascinating, even if you’re not a science geek like me!

What is the vagus nerve?

Many of us live in a state of ‘fight or flight’. We react instinctively to the stressors around us – the daily commute, an important meeting or deadline, interpersonal problems, health concerns, financial worries, and so on. Our bodies respond by getting ready for action in much the same way as our ancestors would have responded to a life threatening danger. The breath gets shallow, heart rate increases, blood travels to our extremities, and our mental and visual focus becomes fixed and tense. But although the stress response is vital in some situations, we simply weren’t built to function in a state of constant activation and this can lead to physical and emotional health issues.

Yoga helps us find balance by encouraging the calming parasympathetic nervous system to take over, and giving the activating sympathetic nervous system a much-needed break. And the major player in the parasympathetic nervous system is the vagus nerve, or ‘wandering nerve’. The vagus nerve is the longest of all the nerves and is the only cranial nerve to leave the skull, venturing into the body to regulate and calm the activity of the heart, lungs and all the abdominal organs, as well as our facial muscles.

The vagus nerve has two branches in mammals. One branch is responsible for our ‘rest and digest’ mode when we’re feeling calm and safe, and the ‘freeze’ response to trauma (that’s a topic for another day). The other is responsible for the ‘tend and befriend’ response – our positive social interactions.

So how does the vagus nerve work? Here comes the science bit…

When we feel safe, the vagus nerve calms the activity of our organs and promotes healing, wellbeing, digestion and compassionate communication through the release of neurotransmitters and hormones.

• Calming: Acetylcholine is released directly from the vagus nerve, causing the heart rate and breathing to slow down.
• Reducing inflammation: In turn, acetylcholine stops the production of cytokines that cause inflammation in the body in response to stress. Too much inflammation weakens the immune system, making it more susceptible to illnesses like rheumatoid arthritis, Crohn’s disease, Alzheimer’s and Parkinson’s.
• Emotional wellbeing: The vagus nerve stimulates the release of GABA (Gamma-Aminobutyric Acid), which has a calming effect on the brain. High GABA levels are associated with emotional wellbeing, but GABA levels are often low in people with depression, anxiety, post-traumatic stress disorder, or negative self-image.
• Memory: The vagus nerve helps to increase brain-derived neurotrophic factor (BDNF) levels in the brain. BDNF helps nerves and brain tissue to regenerate, creating new neural pathways and improving our memory. Many antidepressants work to increase BDNF levels, because they are often low in people with chronic stress and depression.
• Digestion: The vagus nerve sends signals to the stomach, gut and gallbladder to promote healthy and effective digestion.
• Human connection: The vagus nerve also causes the release of ‘feel-good’ hormones oxytocin and vasopressin. These hormones stop the stress hormone cortisol from being released and promote our emotional connection and bond with other people.
• Compassionate communication: When the vagus nerve is active, it’s reflected in your face – smiling and eye contact come easily, and your tone of voice is smooth and warm, making it more likely that you’ll have positive interactions with the people around you.

This long list shows how important it is to have a strong and active vagus nerve for our overall physical health and emotional and social wellbeing. But keep reading, there’s more…

The body-mind connection

Here’s another amazing fact about the vagus nerve: only 10-20% of the nerve fibres take information from the brain to the body to initiate all the activities listed above. The remaining 80-90% of nerve fibres actually take information from the body to the brain.

Why is this is amazing? Well, it tells us how working with the body and breath can affect our minds, rather than relying solely on the mind to try to control our stress levels. Because, let’s face it, the mind is notorious for taking us down rabbit holes of negativity and self-criticism. It also means we don’t have to wait until we’re in a candlelit yoga class or a health spa for the vagus nerve to work its magic – we can find a calm state of mind at any time using our body and breath.

Here are some examples of the body-mind connection:

• In a stressful situation, consciously deepening and slowing the breath sends signals, via the vagus nerve to the brain, that we are safe. The brain responds by telling the body and mind to relax, strengthening the message that we can deal calmly with this situation. This is why we are often advised to ‘take a deep breath’ in difficult situations.
• Our ‘gut feelings’ are taken seriously by the nervous system – if we’re feeling anxiety in our gut, the vagus nerve sends a message to the brain to put the sympathetic nervous system on high alert. In contrast, if digestion is effective this tells the brain we are safe, contributing to a positive feedback loop that promotes further healthy digestion and a sense of wellbeing.
• The vagus nerve is also known as the nerve of compassion. When it is active, positive social interactions come more easily. But it also works the other way around – when we decide to smile, make eye contact and interact with people (even if we don’t feel like it) this activates the vagus nerve, making us feel good and making these interactions easier and even more likely.

These findings begin to explain how yoga can help us cope with stress, anxiety, or over-stimulation through activating the vagus nerve, and remind us that yoga is not just about getting strong and flexible in our bodies. In the next blog post I’ll tell you more about how to strengthen the vagus nerve over time through yogic practices like asana (yoga poses), pranayama (breathing), meditation, and how we treat ourselves and others.

Namaste,

Beth x

Acknowledgements:
This blog post is based on my elective research for my yoga teacher training in 2016.
In addition to the references below, the content is informed by training and information from the following teachers: Heather Mason; Mieke Kreeftenberg; and Charlotte Watts.

References:
– Carter, C. S. (2014) Oxytocin Pathways and the Evolution of Human Behavior. Annual Review of Psychology, 65, 17-39. doi: 10.1146/annurev-psych-010213-115110.
– Furmaga, H. et al. (2012) Vagal Nerve Stimulation Rapidly Activates Brain-Derived Neurotrophic Factor Receptor TrkB in Rat Brain. PLoS ONE 7(5): e34844. doi:10.1371/journal.pone.0034844
– Goyal, M.D., and Hirano, I. (1996) The Enteric Nervous System. The New England Journal of Medicine, 334, 1106-1115. doi: 10.1056/NEJM199604253341707
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– Koopman, F.A. et al. (2016) Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis. Proceedings of the National Academy of Sciences of the United States of America, 113(29), 8284-9. doi: 10.1073/pnas.1605635113.
– Pavlov, V.A. and Tracey, K.J. (2012) The vagus nerve and the inflammatory reflex—linking immunity and metabolism. Nature Reviews: Endocrinology, 8(12): 743–754. doi: 10.1038/nrendo.2012.189
– Porges, S.W. (2011) The Polyvagal Theory: Neurophysiological Foundations of Emotions, Attachment, Communication, and Self-Regulation. Norton Series on Interpersonal Neurobiology.
– Porges, S.W. (2013) Interview with Stephen Porges on Polyvagal Theory. https://www.youtube.com/watch?v=8tz146HQotY.
– Streeter, C. et al. (2012) Effects of yoga on the autonomic nervous system, gamma-aminobutyric-acid, and allostasis in epilepsy, depression, and post-traumatic stress disorder. Medical Hypotheses, 78(5), 571–579. doi: 10.1016/j.mehy.2012.01.021.
– Weinstein, G. et al. (2014) Serum Brain-Derived Neurotrophic Factor and the Risk for Dementia: The Framingham Heart Study. JAMA Neurology, 71(1), 55-61. doi:10.1001/jamaneurol.2013.4781.