The vagus nerve has multiple branches that innervate many of our organs, including the heart, lungs and stomach, and much more. However, a new Swiss study by Melanie Klarer et al published in May this year in the Journal of Neuroscience, has shown how afferent vagus pathways are able to modulate our fear and anxiety response, and also affect our ability to ‘un-learn’ previously conditioned fear responses.
Around 80% or more of the vagus nerve fibres are dedicated to sending signals to the brain about the state of the viscera and it is known that healthy vagus nerve communication from gut to brain helps to slow down the fear response, by using neurotransmitters such as acetylcholine and GABA – lowering heart rate and blood pressure and encouraging the parasympathetic response of ‘rest and digest’.
So, for this study, the team at ETH Zurich dissected these afferent nerve fibres to the stomach, to study how interrupting this feedback loop might affect brain and cognitive function.
The researchers were especially interested in the link between innate anxiety and ‘learned’ or ‘conditioned’ fear – in the tests the brain was still able to send signals to the stomach but the brain could not ‘hear’ the stomach’s vagal response.
In anxiety-behaviour experiments, rats without vagal feedback from the gut demonstrated two main findings – a reduced innate fear (e.g. to bright lights, open spaces etc) but also a longer retention of previously learned fears. This confirms the importance of healthy vagal tone to overcome fear conditioning.
Furthermore, the loss of the gut vagus signal altered the production of adrenaline and GABA in the brain, meaning that the rats took much longer to re-associate sounds previously associated with a negative stimulus with a new ‘safe’ or neutral situation.
The Implications for PTSD
Hence these new findings may eventually shine a light on developing new treatments for PTSD (post-traumatic stress disorder) – stimulation or normalisation of the vagus nerve may help people to reassociate non-threatening stimuli which became traumatically associated with triggering fear/anxiety, with a new neutral or non-traumatic experience/response. Vagus nerve stimulation (VNS) is currently used to treat epilepsy and depression, but its efficacy remains controversial.
In a press release Urs Meyer stated:
“We were able to show for the first time that the selective interruption of the signal path from the stomach to the brain changed complex behavioural patterns. This has traditionally been attributed to the brain alone. The study shows clearly that the stomach also has a say in how we respond to fear; however, what it says, i.e. precisely what it signals, is not yet clear.”
This short video from 2011 also discusses the possible use of VNS for patients with PTSD:
Read here, from half way down the page ‘Activating the Vagus Nerve Without Machinery‘ for a quick run-down of some ways to improve vagus function or to stimulate the vagus pathway:
Insightful Nutrition – Orthomolecular Health and Nutrition – ‘Activating the Vagus Pathway’
1. Klarer, M. et al. Gut Vagal Afferents Differentially Modulate Innate Anxiety and Learned Fear. J. Neurosci. 34 , 7067–7076 (2014).