Transcutaneous vagal nerve stimulation (tVNS) has been applied to a number of disease areas including visceral pain, depression, cluster headache and Alzheimer's disease. However, there is marked heterogeneity in these studies pertaining to i) the anatomical site of stimulation (neck, inner concha or tragus of ear), and ii) the waveform parameters of the stimulating impulse. This exploratory cross-sectional study will address these knowledge gaps by comparative functional neuroimaging of the neural correlates of tVNS with disparate anatomical sites and electrical waveform characteristics during rest in healthy participants.

Inclusion criteria:

• Of female sex;
• Healthy participants (defined as those without a pre-existing medical comorbidity)
• Age between 18 and 40 years;
• BMI between 18 and 30 kg/m2;
• Women on oral contraceptives only
• All subjects should be right-handed.
• Inclusion will be determined on the basis of availability. Subjects should be able to attend for 2 scanning sessions.

Exclusion criteria

• Presence of metallic prostheses, pacemakers, metal clips on blood vessels, metal parts in the eye, an intrauterine device, metal braces, tattoos and/or other metal objects;
• History of major head trauma or head/brain surgery;
• History of claustrophobia;
• History of severe or chronic cardiovascular, respiratory, urogenital, gastrointestinal/ hepatic, haematological/immunologic, HEENT (head, ears, eyes, nose, throat), dermatological/connective tissue, musculoskeletal, metabolic/nutritional, endocrine, neurological/psychiatric diseases, major surgery and/or laboratory assessments which might limit participation in or completion of the study protocol;
• Use of regular medication, including vitamin and iron supplementation, except oral contraceptives, within 14 days prior to start of the study;
• Pregnancy, lactation, wish to become pregnant;
• High alcohol consumption (>15 alcoholic units consumed per week);
• Using drugs of abuse;
• Administration of investigational drugs or participation in any scientific intervention study which may interfere with this study (to be decided by the principle investigator), in the 180 days prior to the study;
• Participants unable to provide informed consent
• Participants with any systemic disease or medications that may influence the autonomic nervous system (e.g. beta-agonists or Parkinson's disease)
• Current smokers or current use of nicotine in any other way (including E-cigarettes and patches)
• History of clinical anxiety or depression, or a hospital anxiety or depression score >8
• Participants whom score 8 or more on the HADS-questionnaire at study commencement
• Patient whom have cardiovascular conduction problems
• Patient with cochlear implants
• Not meeting any of the inclusion criteria above
• Any evidence of structural brain abnormalities examined by anatomical MRI will lead to exclusion

Females only (in order to limit confounding)

Female healthy volunteers aged between 18-40 years