How Does the Vagus Nerve Convey Gut Instincts to the Brain?
New research offers an exciting possibility for the treatment of PTSD.
Posted May 23, 2014
What situations make you feel nervous, fearful, or anxious to the point that you get butterflies and feel sick to your stomach? Are there people, places, or situations in your life that evoke a “fear-conditioned” response? Scientists in Switzerland recently identified how the vagus nerve conveys threatening “gut feelings” to the brain.
The vagus nerve is known as the "wandering nerve" because it has multiple branches that diverge from two thick stems rooted in the cerebellum and brainstem that wander to the lowest viscera of your abdomen touching your heart and most major organs along the way. Vagus means "wandering" in Latin. The words vagabond, vague, and vagrant are all derived from the same Latin root.
In a fascinating new study, researchers at ETH Zurich have identified how “gut instincts” coming up to the brain via the vagus nerve are linked to different responses to fear. The team of scientists was led by Urs Meyer, a researcher in Professor Wolfgang Langhans' group at ETH Zurich.
The study is titled, “Gut Vagal Afferents Differentially Modulate Innate Anxiety and Learned Fear” and was published on May 21, 2014, in the Journal of Neuroscience.
The Vagus Nerve Conveys Messages Between the Brain and Gut
The vagus nerve constantly sends updated sensory information about the state of the body's organs "upstream" to your brain via afferent nerves. In fact, 80 to 90 percent of the nerve fibers in the vagus nerve are dedicated to communicating the state of your viscera up to your brain.
The terms “afferent” and “efferent” typically refer to nerves that lead into or out of the brain. Afferent signals are sent from a nerve receptor into the brain while efferent signals are sent from the brain to the peripheral body.
Visceral feelings and gut instincts are literally emotional intuitions transferred up to your brain via the vagus nerve. In previous studies, signals from the vagus nerve traveling from the gut to the brain have been linked to modulating mood and distinctive types of fear and anxiety.
As with any mind-body feedback loop, messages also travel "downstream" from your conscious mind through the vagus nerve (via efferent nerves) signaling your organs to create an inner-calm so you can “rest-and-digest” during times of safety or to prepare your body for “fight-or-flight” in dangerous situations.
For this study, the Swiss scientists snipped the afferent nerve fibers of the vagus nerve going from the gut to the brain. Cutting the vagus nerve turned the usual feedback loop between gut instincts and the brain from a two-way communication into a one-way street. This allowed the researchers to hone in on the role that the vagus nerve plays in conveying gut instincts up to the brain.
In particular, the researchers were interested in identifying the link between innate anxiety and conditioned or “learned” fear. In test animals, the brain was still able to send signals down to the stomach, but the brain couldn’t receive signals coming up from the stomach.
Healthy vagus nerve communication between your gut and your brain helps to slow you down like the brakes on your car by using neurotransmitters such as acetylcholine and GABA. These neurotransmitters literally lower heart rate, blood pressure, and help your heart and organs slow down so that you can rest-and-digest.
The Vagus Nerve Is Linked to Fear Conditioning
The new Swiss study explored the consequences of a complete disconnection of signals from the vagus nerve coming up from the gut to the brain and how this affected innate anxiety, conditioned fear, and subsequent neurochemical changes in the brain.
In a fear conditioning experiment on rats, the researchers in Zurich linked an unpleasant experience to a specific sound. Interestingly, the gut instinct signal from the vagus nerve was necessary for unlearning a conditioned response of fear. Through a variety of behavioral studies, the researchers determined that the rats without a fully functioning vagus nerve were less afraid of open spaces and bright lights compared with controlled rats with an intact vagus nerve.
However, without the two-way communication of the vagus nerve between the brain and gut the rats showed a lower level of innate fear, but a longer retention of learned fear. From this discovery, the researchers concluded that an innate response to fear appears to be influenced significantly by “gut instinct” signals sent from the stomach to the brain. This confirms the importance of a healthy vagal tone to maintain grace under pressure and to overcome fear conditioning.
Mark Twain addressed the backlash of conditioned fear when he said, “We should be careful to get out of an experience only the wisdom that is in it and stop, there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well; but also she will never sit down on a cold one anymore.”
In my book, The Athlete’s Way, I write extensively about ways to overcome learned fear and innate anxiety. If you’d like to read a sample from the book with some practical tips on how to overcome conditioned fear responses click here.
A simple mantra I've used as an athlete to engage my vagus nerve when faced with a threatening challenge is to take a few deep breaths and recite a line by Corra Harris, author of I'd Climb the Highest Mountain: "The bravest thing you can do when you are not brave is to profess courage and act accordingly."
The most exciting discovery of this study is that under closer scrutiny of the rats' brains, the researchers found that the loss of signals coming up from the abdomen via the vagus nerve altered the production of both adrenaline and GABA in the brain.
When the researchers switched from a negative to a neutral stimulus, the rats without gut instincts coming up to the brain via the vagus nerve required significantly longer to re-associate the sound with the new, “safe” and neutral situation. The researchers point out that this finding is congruent with other recently published studies, which found that stimulation of the vagus nerve can facilitate learning.
Conclusion: The Vagus Nerve Has Powerful Psychological Influences
Stimulation of the vagus nerve might be able to speed up the process by which people with PTSD can learn to reassociate a non-threatening stimulus which triggers anxiety with a neutral and non-traumatic experience. Vagus nerve stimulation (VNS) is currently used to treat epilepsy and depression, although the psychologcial benefits of VNS remain controversial.
In a press release, Meyers concluded, "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 behavioral 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."
The researchers intend to do more research to better understand the exact dialogue between the vagus nerve and the brain which will hopefully lead to more effective treatments for PTSD and other anxiety disorders.
If you’d like to read more on this topic, check out my Psychology Today blog posts:
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