In previous posts we’ve pointed out that there is some evidence that the brain and body response to invasive and non-invasive vagus nerve stimulation appears to be very similar. Now scientists from Israel have added further evidence to support this idea.
In a pre-print version of the paper published in the online biology research archive (bioRxiv) the three researchers reported on a study in which they tested participant response to transcutaneous vagus nerve stimulation (tVNS) using measures of pupil dilation and electroencephalography (EEG). The study found that tVNS applied to the ear resulted in robust pupil dilation (within a few seconds of trial onset) and modulated alpha wave EEG activity in the occipital lobe at the back of the brain.
Importantly, these bodily responses are comparable to responses from invasive vagus nerve stimulation, indicating that non-invasive methods are a viable alternative in scientific research and in clinical applications; while obviously being far safer to administer.
Previous studies have also shown that there are comparable responses, but this is the first to focus attention on pupillometry and ongoing EEG activity in the occipital lobe. Most other studies have focused instead on changes to reaction times which also show up in brain wave signals.
The researchers noted that the measured responses between invasive and non-invasive vagus nerve stimulation were not completely identical however, speculating that this is due to slight differences in stimulation protocols.
The auricular tVNS (sometimes abbreviated to taVNS) was also compared to sham stimulation. The sham did not elicit the responses observed in the non-sham stimulation, clearly indicating that the observations were elicited by the stimulation.