Continuous Transcutaneous Auricular Vagus Nerve Stimulation Increases Long-Latency Neural Processing in Multiple...

Area of Science:

• Neuroscience
• Psychophysiology
• Noninvasive Neuromodulation

Background:

• Transcutaneous auricular vagus nerve stimulation (taVNS) is a noninvasive method targeting vagal afferent fibers, with potential applications in neurological and mental health disorders.
• The proposed mechanism involves activating the locus coeruleus (LC) and subsequent noradrenergic activation (NA), enhancing arousal and attention, though evidence remains mixed.
• Limited research exists on taVNS effects across different sensory modalities and its impact on specific neural markers.

Purpose of the Study:

• To investigate if continuous taVNS enhances noradrenergic activation (NA) markers and neural processing across auditory, respiratory, and somatosensory modalities.
• To examine the effects of taVNS on evoked potentials, neural gating, salivary alpha-amylase (sAA), and resting-state EEG alpha power.
• To assess taVNS's influence on subjective arousal, stimulus intensity, and unpleasantness.

Main Methods:

• A 2-day, sham-controlled crossover study involving 45 healthy adults.
• Participants received either taVNS (cymba concha) or sham stimulation (earlobe) while undergoing auditory, respiratory, and somatosensory tasks with concurrent EEG recording.
• Measurements included salivary alpha-amylase (sAA), subjective arousal ratings, resting-state EEG alpha power, and event-related potentials (P50, N1, P2) for neural gating assessment.

Main Results:

• Self-reported arousal significantly increased during taVNS compared to sham.
• P2 component amplitudes in auditory and somatosensory evoked potentials were enhanced during taVNS.
• No significant effects were observed on neural gating (S2-S1 difference), sAA levels, resting-state alpha power, or subjective stimulus intensity/unpleasantness.

Conclusions:

• Continuous taVNS can enhance subjective arousal and specific neural responses (P2 component) in auditory and somatosensory processing.
• The study did not find evidence supporting the LC-NA hypothesis through standard markers like sAA or resting-state alpha power.
• Limitations in combining taVNS with EEG were highlighted, emphasizing the need for further research into the mechanisms of taVNS.