An investigation into the effect of skin stimulation on smell function

INTERVENTION: Transcutaneous Electrical Nerve Stimulation (TENS) will be applied under the pain threshold with CE approved home use TENS device by a researcher who is a medical doctor. Different dilutions of smell sticks (scientifically validated and medically approved) will be used to determine the smell function of the participants before and after the TENS interventions by an odour researcher. The number of the smell sticks that will be used may differ 4 to 10 because of the interindividual smell threshold differences. In all sessions, frontal cortex activation will be monitored for olfactory function responses with FDA approved near infrared monitoring device (NIRS). In each arm, there will be two streams: low(10Hz) and high frequency(80Hz) stimulation. 24 participants of each Arm will be allocated into two streams: 12 participants for low frequency stimulation stream and the other 12 participants for high frequency stimulation stream. Each stream will also have their own placebo group in which the same 12 participants will be enrolled. There is no evidence that 10 minutes of a single stimulation have prolonged effects. In addition, each session will be performed on a different day(active or placebo) so that the participants will be participating in different days for each session to eliminate the possible overlapping effects of the previous session. Each session duration will take 1 hour (baseline tests+stimulation+after stimulation tests) and each participant will be participating for a total of 2 hours in two different days(one day for active and one day for placebo session). All sessions will take place in the live human research/ultrasound room in Otago University, Department of Anatomy, Dunedin. Arm1 : TENS will be applied to ear skin(direct vagus nerve stimulation) with ear specific TENS electrode under pain threshold to 24 healthy volunteers for 10 minutes. This is a within designed study, therefore each participant will be participating both to an active and a placebo. 12 of the participants will be allocated to low frequency active stimulation stream and the other 12 of the participants will be allocated to high frequency active stimulation stream.Each stream will also have their own placebo group in which the same 12 participants will be enrolled. Arm2: TENS will be applied to wrist skin(indirect vagus nerve stimulation) with body specific TENS electrode under pain threshold to 24 healthy volunteers for 10 minutes. This is a within designed study, therefore each participant will be participating both to active and placebo groups. 12 of the participants will be allocated to low frequency active stimulation stream and the other 12 of the participants will be allocated to high frequency active stimulation stream. Each stream will also have their own placebo group in which the same 12 participants will be enrolled. CONDITION: Alzheimer disease Appetite disorders Dementia Parkinson's Disease PRIMARY OUTCOME: Change in Sniff‐stick threshold test results (statistical difference in detection odours based on detection of the same odour after the electrostimulation). ; SECONDARY OUTCOME: % Change in Near Infrared Monitoring score of Frontal Cortex perfusion INCLUSION CRITERIA: * 22‐39 years old male * NZ European * In good health, and not on any regular medication * A non‐smoker