Inclusion Criteria:  Healthy participants (defined as those without pre-existing medical comorbidity that makes them take medications or go to hospitals regularly), aged 18-65, from staff, students and the local population of Queen Mary, University of London  Exclusion Criteria:  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) Pregnant or breastfeeding females History of drug or alcohol abuse Participants who have cardiovascular condition problems or epilepsy Participants with cochlear implants Participants who are using pain killers Not meeting any of the inclusion criteria above