This article contains a summary of the findings of are search study that was conducted by a group of independent researchers. For information about the group of researchers and the full study manuscript, see the information at the bottom of this article.
Snapshot of Findings
Short bursts of noninvasive vagus nerve stimulation:
- Increased activation in the left dorsolateral pre-frontal cortex, which may explain the mechanism behind the anti-depressant effect of VNS
- Increased bilateral activation of the anterior cingulate cortex (ACC), a brain region involved in cognition and emotional processing.
- Activated the same regions in the brain as implantable vagus nerve stimulation devices.
- Should be applied for at least 6-7 minutes to get activation in the emotional command centers in the brainstem and maximize the mood benefits of the treatment.
Title of Research Study
"Neurophysiologic effects of transcutaneous auricular vagus nerve stimulation via electrical stimulation of the tragus: a concurrent taVNS/fMRI study and review."
Published in Brain Stimulation in 2018.
Noninvasive vagus nerve stimulation applied to vagal afferents around the ear. Device used was a custom-built ear-clip electrode.
The researchers measured brain activity after noninvasively stimulating the vagus nerve. Brain activity was measured using a functional MRI machine.
- Does stimulating auricular branches of the vaugs nerve around the ear area actually activate regions in the brain known to be connected to the vagus nerve?
- Is noninvasive vagus nerve stimulation around the ear area a potential supplement or replacement to its invasive counterpart?
The patient population was with healthy patients with an average age of 25.8 years.
Vagal Nerve Stimulation Parameters
- Active Stimulation: Ear clip on the left tragus
- Control Stimulation: Ear clip on the left ear lobe
Waveform Frequency: 25 Hz
Pulse Width: 500 µs
Intensity: 200% of the perception threshold, meaning double of whatever the intensity was where a patient could begin feeling the stimulation.
Duration of Stimulation: 60 seconds of stimulation delivered 3 times over the course of 6 minutes for a total of 3 minutes of stimulation.
Frequency of Stimulation: A single stimulation session
Active Stimulation: Increased activity or blood oxygenation in the right postcentral gyrus, bilateral insula, frontal cortex, right operculum, and left cerebellum.
Control Stimulation: Increased activity or blood oxygenation in the right postcentral gyrus only.
Between Active and Control Groups: significantly higher activity in right caudate, bilateral anterior cingulate, cerebellum, left prefrontal cortex, and mid-cingulate.
The authors concluded that applying electrical stimulation to the auricular branch of the vagus nerve in and around the ear area does indeed activate cerebral afferents of the vagal pathway, suggesting that noninvasive auricular vagus nerve stimulation could be a promising alternative to implantable vagus nerve stimulation.
The researchers in this study stimulated the auricular vagus nerve for 60s at a time and did not find any activation in the brainstem. The authors cited other researchers who stimulated the auricular vagus nerve for 6-7 minutes and did find activation in the brainstem, suggesting that longer stimulation sessions are necessary to activate regions in the brainstem and improve one’s ability to process emotions more efficiently.
The researchers also found that vagus nerve stimulation activated the right dorsolateral pre-frontal cortex (DLPFC). The DLPFC has been known to be under activated in depressed patients, and vagus nerve stimulation may improve depression symptoms by increasing DLPFC activation.
It concluded that stimulating the afferent branches around the ear area activates the regions in your brain that the vagus nerve has been anatomically shown to communicate with, indicating that products like VeRelief actually do stimulate the vagus nerve.
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Authors and Affiliations
Bashar W. Badran et al., 2018
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC, 29425, United States
Background: Electrical stimulation of the auricular branch of the vagus nerve (ABVN) via transcutaneous auricular vagus nerve stimulation (taVNS) may influence afferent vagal networks. There have been 5 prior taVNS/fMRI studies, with inconsistent findings due to variability in stimulation targets and parameters.
Objective: We developed a taVNS/fMRI system to enable concurrent electrical stimulation and fMRI acquisition to compare the effects of taVNS in relation to control stimulation.
Methods: We enrolled 17 healthy adults in this single-blind, crossover taVNS/fMRI trial. Based on parameters shown to affect heart rate in healthy volunteers, participants received either left tragus (active) or earlobe (control) stimulation at 500 μs 25 HZ for 60 s (repeated 3 times over 6 min). Whole brain fMRI analysis was performed exploring the effect of active stimulation, control stimulation, and the comparison. Region of interest analysis of the midbrain and brainstem was also conducted.
Results: Active stimulation produced significant increased BOLD signal in the contralateral postcentral gyrus, bilateral insula, frontal cortex, right operculum, and left cerebellum. Control stimulation produced BOLD signal activation in the contralateral postcentral gyrus. In the active vs. control contrast, tragus stimulation produced significantly greater BOLD increases in the right caudate, bilateral anterior cingulate, cerebellum, left prefrontal cortex, and mid-cingulate.
Conclusion: Stimulation of the tragus activates the cerebral afferents of the vagal pathway and combined with our review of the literature suggest that taVNS is a promising form of VNS. Future taVNS/fMRI studies should systematically explore various parameters and alternative stimulation targets aimed to optimize this novel form of neuromodulation.
Badran BW, Dowdle LT, Mithoefer OJ, LaBate NT, Coatsworth J, Brown JC, DeVries WH, Austelle CW, McTeague LM, George MS. Neurophysiologic effects of transcutaneous auricular vagus nerve stimulation (taVNS) via electrical stimulation of the tragus: A concurrent taVNS/fMRI study and review. Brain Stimul. 2018 May-Jun;11(3):492-500. doi: 10.1016/j.brs.2017.12.009. Epub 2017 Dec 29. PMID: 29361441; PMCID: PMC6487660.