Transcutaneous Auricular Vagus Nerve Stimulation Facilitates Cortical Arousal and Alertness


. 2023 Jan 12;20(2):1402.


doi: 10.3390/ijerph20021402.

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Yuxin Chen et al.


Int J Environ Res Public Health.


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Abstract

Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising noninvasive technique with potential beneficial effects on human emotion and cognition, including cortical arousal and alertness. However, it remains unclear how taVNS could improve cortical arousal and alertness, which are crucial for consciousness and daily task performance. Here, we aimed to estimate the modulatory effect of taVNS on cortical arousal and alertness and to reveal its underlying neural mechanisms. Sixty subjects were recruited and randomly assigned to either the taVNS group (receiving taVNS for 20 min) or the control group (receiving taVNS for 30 s). The effects of taVNS were evaluated behaviorally using a cue-target pattern task, and neurologically using a resting-state electroencephalogram (EEG). We found that taVNS facilitated the reaction time for the targets requiring right-hand responses and attenuated high-frequency alpha oscillations under the close-eye resting state. Importantly, taVNS-modulated alpha oscillations were positively correlated with the facilitated target detection performance, i.e., reduced reaction time. Furthermore, microstate analysis of the resting-state EEG when the eyes were closed illustrated that taVNS reduced the mean duration of microstate C, which has been proven to be associated with alertness. Altogether, this work provided novel evidence suggesting that taVNS could be an enhancer of both cortical arousal and alertness.


Keywords:

alertness; alpha oscillations; attention; cortical arousal; microstates; transcutaneous auricular vagus nerve stimulation (taVNS).

Conflict of interest statement

The authors declare no conflict of interest.

Figures


Figure 1



Figure 1

Experimental procedure and behavioral results. (a) Description of the experimental procedure; (b) Description of the single trial procedure in the dot-probe task; (c) Schematic of the taVNS stimulator and the stimulating sites; (d) The comparison of RT difference (post–pre) for left- and right-hand responses between the two groups. * p < 0.05; taVNS, transcutaneous auricular vagus nerve stimulation; RT, reaction time; ns, non-significant.


Figure 2



Figure 2

The high-α oscillation PSD under the close-eye resting state. (a) PSD topographies in the pre-test and post-test phases and the post–pre PSD difference topographies of high-α oscillations for the taVNS group and control group; (b) Topography of the t-value obtained from independent sample t-tests at each electrode for high-α oscillation PSD difference; (c) High-α oscillation PSD difference for the taVNS group and the control group; (d) Group average spectra and their post–pre differences at the C3 and CP5 electrodes for the taVNS group and the control group. Red asterisks in (b) represents significant differences between the taVNS group and the control group; the shadow region in (d, right panel) represents the frequency range of high-α oscillations; *** p ≤ 0.001.


Figure 3



Figure 3

Microstate analysis procedure and mean duration difference of each microstate under the close-eye resting state. (a) EEG data after preprocessing; (b) GFP of signals marked by red dashed box in (a) and topographies at the latencies of GFP peaks; (c) Four microstates (i.e., microstates A–D) obtained by integrating all subjects’ EEG data after AAHC and sorting; (d) Single subject sequence obtained by back fitting from global microstate templates; (e) Mean duration difference for each microstate (i.e., microstates A–D, respectively, marked in different colors) under the close-eye resting state was extracted and calculated by single subject sequence. GFP, global field power; AAHC, atomize and agglomerate hierarchical clustering. * p < 0.05.


Figure 4



Figure 4

Partial correlation between the RT difference and the PSD difference of high-α oscillations in the taVNS group under the close-eye resting state. ** p < 0.01.

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