THE VAGUS NERVE

vagus-nerve

They call me the wanderer! The Vagus Nerve and Psychobiotics.

In human anatomy, when we talk about the Vagus Nerve, we are not describing what happens somewhere in the Nevada desert. No, the 10th cranial nerve is named after the latin for ‘Wandering’. As are the words vague and vagabond. The reason this particular nerve is described as such is because it is the longest of the cranial nerves and stretches from the paired roots in the brainstem to the lowest part of the viscera, connecting with the heart along the way.vagus-nerve-connectionThe vagus nerve is part of the autonomic nervous system, responsible for functions we normally do not consciously control, although, by means of biofeedback and certain yogic and other mindfulness practices, we can learn to regulate them. The autonomic nervous system is divided into a sympathetic (‘fight/ flight’) division and a parasympathetic (‘rest/ digest’) division. The vagus nerve is part of this latter functional division and so is vitally important when it comes to controlling the vegetative, relaxation and healing/ repair processes of the body.

There is constant activity in the vagus nerve which we term ‘Vagal Tone’. So, for example, when the heart rate needs to slow down our vagal tone increases to enable this. When our gut needs to process a meal, again, vagal tone increases to facilitate digestion. Conversely, when our heart rate needs to speed up or our gut function can idle, the vagal tone decreases. This happens during the acute stress response (‘fight/ flight’) to produce the necessary physiological changes required for dealing with the situation. All perfectly healthy and normal. However, if the stressor persists (or is perceived to still be there) the stress response becomes chronic and inappropriate which is characterised by a sustained low vagal tone. This, in turn, can lead to problems such as heart beat irregularities (‘palpitations’, racing heart rate), gut disorders (IBS, acid reflux, ulcers), and inflammation.

So, one of the best ways of monitoring how stressed we are would be to measure vagal tone. But how do we do this? With the development of wearable technology and applications on devices such as the smartphone, we can now do this accurately and non-invasively. The metric used is something called ‘Heart Rate Variability’, or HRV for short, and there are several apps that can measure this. A high HRV means high vagal tone which is desirable over the long term. Individuals with low HRV (low vagal tone) over time are vulnerable to the dysfunctions associated with chronic stress (dis-stress). For example, a low vagal tone is associated with chronic inflammatory changes, including the release of chemicals called cytokines, which are fundamental to diseases such as the rheumatic conditions and atheroma as well as psychological conditions such as depression and hyper-anxiety. Recent research has shown that stimulating the vagus nerve actually secretes anti-inflammatory factors (‘Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis’ by Koopman et al in PNAS, July 2016) and this has exciting implications for interventions in these disease processes, for example with surgically implanted vagus nerve stimulators (VNS).

Another feature of vagal tone is its role in the so-called ‘Gut-Brain’ relationship. The vagus nerve not only communicates the status of our gut to the nervous system and vice-versa but also integrates information about what is going on in the immune, endocrine, and nervous systems. We know that the ecology of the gut has profound effects on overall body physiology and the mechanisms for this are being elucidated. One of the key developments in our understanding of our relationship with gut flora has been the discovery of communicating factors produced by the commensal microbes (microbiomes) in our gut. The vagus nerve responds to these and, in turn, can transmit information to and from the gut/ brain. Those ‘gut feelings’ really are profound! A new book by Dr. Emeran Mayer, professor of medicine and psychiatry at UCLA, called ‘The Mind Gut Connection’ explores this new science of ‘Psychobiotics’.

Can we influence this without impacting a vagal stimulator or applying a Vulcan nerve pinch?

nerve-punch

Yes, we can, and it’s not especially difficult. Vagal nerve stimulation occurs when we take a few deep breaths and breathe out slowly and forcefully to exercise the diaphragm. It also gets stimulated when we hum or speak due to the resonant frequencies (a reason, perhaps, for the efficacy of the ‘OM’ chant or singing and chanting in religious ceremonies). Splashing cold water on the face is another way of triggering a parasympathetic (vagal) response and may be linked to the so-called mammalian dive reflex. Loving-kindness meditation has been shown to induce higher vagal tone (‘How Positive Emotions Build Physical Health: Perceived Positive Social Connections Account for the Upward Spiral Between Positive Emotions and Vagal Tone’, Fredrickson and Kok 2010). Also, given the importance of the reciprocal gut/ brain connection, maintaining a healthy gut ecology is vital for good parasympathetic/ sympathetic balance.

At Calmer Clinics we are proud to have a range of clinical approaches that can address these issues, helping to restore a healthy vagal tone.