Inclusion Criteria:  Generally healthy  Exclusion Criteria:  Age under 18 years Pregnancy Acute illnesses/fever Any medication that interferes with the autonomic nervous system (e.g., beta blockers) Any medication that interferes with glucose metabolism (e.g., antidiabetic drugs) Any medication that interferes with lipid metabolism (e.g., statins) Any medical conditions that interfere with the autonomic nervous system Type 1 or Type 2 diabetes Epilepsy Cardiac conditions, including arrhythmia Vestibulocochlear neuronitis or nerve damage (e.g., hearing loss or tinnitus) Skin irritation/inflammation at the stimulation site at the ear Current drug or alcohol abuse