Can stimulating the vagus nerve be an effective treatment for spinal cord injury recovery?
The vagus nerve is the tenth cranial nerve, and it plays a role in many of our major involuntary body functions.
This article will explore how spinal cord injury affects the vagus nerve and explain why electrical stimulation of the vagus nerve can boost recovery outlook.
What is the Vagus Nerve?
The vagus nerve is the largest of the twelve pairs of cranial nerves that stem from the brain.
“Vagus” means wanderer in Latin, which perfectly embodies the way the nerve affects various organs and essential body functions.
Primary functions of the vagus nerve include:
- Decreasing heart rate, blood pressure, and breathing rate
- Reducing inflammation
- Improving motivation
- Boosting plasticity
- Reducing depression and anxiety
- Relaying messages between the gut and brain
The vagus nerve plays a significant role in regulating your parasympathetic nervous system, which is responsible for your ‘rest and digest’ or relaxation functions.
It branches off in many different directions and innervates the throat, larynx (voice box), heart, tongue, external ears, lungs, and gastrointestinal tract.
When the vagus nerve is stimulated, its tone increases. High vagal tone allows you to relax by decreasing alertness, slowing down your heart rate, speeding up digestion, and relaxing your bladder and bowel muscles.
What Happens to the Vagus Nerve After Spinal Cord Injury?
The vagus nerve is not directly affected by spinal cord injury because it is not part of the spinal column.
The cranial nerves are located above the spinal cord and branch out separately.
However, many organs and muscles are dually innervated by sensory neurons from the spinal cord and vagus nerve.
Throughout the day, your body switches off between a state of “rest and digest” (parasympathetic response) and “fight or flight” (sympathetic response).
After a spinal cord injury (typically at level T6 and higher), people are at risk for experiencing autonomic dysreflexia. This is when the body overreacts when it encounters noxious stimuli to areas below your level of injury.
Your “fight or flight” response is activated, causing a spike in blood pressure, sweating, and anxiety.
In individuals without SCI, the message about the noxious stimuli would be sent to the brain, and the brain would send a signal back to the body telling it to move away from the stimuli, in turn allowing the parasympathetic system to take over and relax your body. But since this communication cannot occur properly in individuals with SCI, the typical relaxation responses are unable to bring your body back to a “restful” state (where blood pressure comes back down, etc.).
Can Vagus Nerve Stimulation Promote Spinal Cord Injury Recovery?
Vagus nerve stimulation (VNS) involves using a biomedical device that transmits mild electrical currents to the brain via the vagus nerve.
While it won’t treat your spinal cord injury, VNS can boost your mental and physical health so that your body is in the best condition to pursue recovery.
Clinical trials on animal models of spinal cord injury have shown that electrical stimulation of the vagus nerve helps with recovery.
While there are limited human studies on the effectiveness of VNS for spinal cord injury, VNS is an FDA-approved treatment for depression (a condition commonly experienced after SCI).
By lowering heart rate, blood pressure, inflammation, and increasing deep breathing, VNS can reduce stress and depression.
Additionally, it increases the release of neurotransmitters like norepinephrine, serotonin, and dopamine to improve motivation, mood, and reward perception.
Side Effects of Vagus Nerve Stimulation
Because the vagus nerve affects so many body functions, stimulation of this nerve comes with many potential side effects.
Side effects of vagus nerve stimulation include:
- Voice changes or hoarseness
- Sore throat
- Shortness of breath
- Changes in heart rate, breathing
- Stomach discomfort
- Difficulties swallowing
The Importance of the Vagus Nerve After Spinal Cord Injury
The vagus nerve helps regulate the autonomic nervous system, which is crucial after a spinal cord injury.
Vagus nerve stimulation can help improve mental and physical health, which helps keep secondary complications like depression in check.
Health is holistic, and by adjusting physical factors like heart rate, blood pressure, and digestion, spinal cord injury patients can feel more relaxed and motivated to work on recovery.
image credits: ©iStock.com/Ergin Yalcin/ttsz