This single-center randomized controlled trial aims to investigate the effects of transcutaneous auricular vagus nerve stimulation on the acute stress responses.

The primary aim of this study is to assess the efficacy of taVNS in mitigating the acute stress response induced by the Maastricht Acute Stress Task (MAST) among healthy subjects, measured by cortisol levels in saliva samples.

Secondary objectives include:

• Evaluating taVNS's potential to counteract stress-induced sympathetic activation and thereby alleviate stress-related effects, including negative affect, as measuring using the I-PANAS-SF questionnaire, and feelings of stress, pain, and unpleasantness, as measured with 0-100 Visual Analog Scales (VAS)
• Assessing its impact on autonomic outflow parameters, using a blood pressure monitor for blood pressure, and a FitBit smartwatch for heart rate variability, and Shimmer3 GSR sensor for heart rate variability and skin conductance.
• Evaluating the relationship between stress responses and affective symptoms and personality traits, utilizing the Generalized Anxiety Disorder 7-Item Scale (GAD-7), Patient Health Questionnaire (PHQ-9), and the Big Five Inventory (BFI).

Participants will be randomly assigned to either the taVNS or sham stimulation group, administered 30 minutes before the MAST.

Inclusion Criteria:

• Healthy participants (defined as those without a pre-existing medical comorbidity)
• Aged between 18-65 years
• Ability to understand and speak the Dutch language.

Exclusion Criteria:

• Medical history or condition affecting the cardiovascular, respiratory, urogenital, gastrointestinal/hepatic, haematologic/immunologic, HEENT (head, ears, eyes, nose, throat), dermatological/connective tissue, musculoskeletal, metabolic/nutritional, endocrine, neurological/psychiatric systems, as well as prior major surgeries or ongoing laboratory abnormalities that could potentially limit participation or completion of the study protocol;
• Any use of medication, especially those that may influence the autonomic nervous system or the hypothalamus-pituitary-adrenal axis (e.g., beta-agonists or corticosteroids), with the exception of contraceptives and paracetamol;
• Current or lifetime psychopathology (including PHQ-9 and GHD-7 scores > 10);
• Substance abuse (including excessive alcohol consumption);
• Smoking;
• Pregnancy, lactation, or intention to become pregnant during the study period;
• Use of devices (e.g., cochlear implants) or other reasons (e.g. wounds, permanent ear-piercing) which complicate the use of the tVNS device;
• Participation in another clinical study in which the MAST was used;
• Administration of investigational drugs or participation in any scientific intervention study that might interfere with this study (to be determined by the principal investigator) within 180 days preceding the commencement of the study;
• Students and employees of Maastricht University are not precluded from participation, unless they have a direct personal, professional or hierarchical position with regards to any of the study team members or their department.