Different Frequency Applications of Transcutaneous Auricular Vagus Nerve Stimulation in Healthy Individuals

Inclusion Criteria: * Healthy adults aged 18 to 40 years * No known neurological, cardiovascular, respiratory, or metabolic disease * Able to understand study procedures and provide written informed consent * No active infection, open wound, or dermatological lesion in the ear region that would interfere with taVNS application * Willing and able to attend all study visits Exclusion Criteria: * History of cardiac arrhythmia, pacemaker, or any implanted electronic medical device History of hypertension, diabetes, chronic pulmonary disease, epilepsy, or systemic disease affecting autonomic nervous system function * Regular use of medications that may affect autonomic function (e.g., beta-blockers, antidepressants, antiarrhythmics) * Intense physical exercise within the previous 24 hours * High caffeine or alcohol intake within 12 hours prior to assessment * Active smoking on the assessment day * Pregnancy or suspected pregnancy * Severe discomfort during stimulation (VAS \>= 7), dizziness, nausea, or unwillingness to continue * Any condition judged by the investigators to make participation unsuitable'