This study investigated whether transcutaneous auricular vagus nerve stimulation (taVNS) enhances reversal learning and augments noradrenergic biomarkers (i.e., pupil size, cortisol, and salivary alpha-amylase [sAA]). We also explored the effect of taVNS on respiratory rate and cardiac vagal activity (CVA). Seventy-one participants received stimulation of either the cymba concha (taVNS) or the earlobe (sham) of the left ear. After learning a series of cue-outcome associations, the stimulation was applied before and throughout a reversal phase in which cue-outcome associations were changed for some (reversal), but not for other (distractor) cues. Tonic pupil size, salivary cortisol, sAA, respiratory rate, and CVA were assessed at different time points. Contrary to our hypothesis, taVNS was not associated with an overall improvement in performance on the reversal task. Compared to sham, the taVNS group performed worse for distractor than reversal cues. taVNS did not increase tonic pupil size and sAA. Only post hoc analyses indicated that the cortisol decline was steeper in the sham compared to the taVNS group. Exploratory analyses showed that taVNS decreased respiratory rate but did not affect CVA. The weak and unexpected effects found in this study might relate to the lack of parameters optimization for taVNS and invite to further investigate the effect of taVNS on cortisol and respiratory rate.

中文翻译：

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经皮耳迷走神经刺激对逆转学习、强直瞳孔大小、唾液α-淀粉酶和皮质醇的影响

本研究调查了经皮耳迷走神经刺激 (taVNS) 是否能增强逆向学习和增加去甲肾上腺素能生物标志物（即瞳孔大小、皮质醇和唾液 α-淀粉酶 [sAA]）。我们还探讨了 taVNS 对呼吸频率和心脏迷走神经活动 (CVA) 的影响。71 名参与者接受了左耳的 cymba concha (taVNS) 或耳垂 (sham) 的刺激。在学习了一系列线索-结果关联后，在反转阶段之前和整个过程中都应用了刺激，其中一些（反转）的线索-结果关联发生了变化，但对于其他（干扰）线索则没有。在不同时间点评估强直瞳孔大小、唾液皮质醇、sAA、呼吸频率和 CVA。与我们的假设相反，taVNS 与逆转任务性能的整体改进无关。与 sham 相比，taVNS 组在干扰项方面的表现比逆转线索更差。taVNS 没有增加强直性瞳孔大小和 sAA。只有事后分析表明，与 taVNS 组相比，假手术组的皮质醇下降幅度更大。探索性分析表明，taVNS 降低了呼吸频率，但不影响 CVA。本研究中发现的微弱和意外影响可能与 taVNS 缺乏参数优化有关，并邀请进一步研究 taVNS 对皮质醇和呼吸频率的影响。只有事后分析表明，与 taVNS 组相比，假手术组的皮质醇下降幅度更大。探索性分析表明，taVNS 降低了呼吸频率，但不影响 CVA。本研究中发现的微弱和意外影响可能与 taVNS 缺乏参数优化有关，并邀请进一步研究 taVNS 对皮质醇和呼吸频率的影响。只有事后分析表明，与 taVNS 组相比，假手术组的皮质醇下降幅度更大。探索性分析表明，taVNS 降低了呼吸频率，但不影响 CVA。本研究中发现的微弱和意外影响可能与 taVNS 缺乏参数优化有关，并邀请进一步研究 taVNS 对皮质醇和呼吸频率的影响。