Investigating Safety and Effectiveness of a Peripheral Stimulation Device

Participants will be seated in a comfortable chair with their feet on a foot stool. Stimulation will be applied to the soles of the feet or toes. During stimulation, brain activity will be recorded using a non-invasive brain imaging technique such as electroencephalography (EEG) or functional near-infrared spectroscopy (fNIRS) to ensure stimulation is targeting the appropriate somatosensory receptors and carrying information to the brain. Participants will be asked about perception of stimulation (whether they perceive it or not), and the level of discomfort using a visual analogue scale. Participants will complete a single visit lasting 2-3 hours. During their visit, they will undergo two types of stimulation (electrical and vibrotactile) with a 30-minute wash out period in-between. Each stimulation type will be applied in pulses for 30-45 minutes. The order of which stimulation type (i.e., electrical or vibrotactile) a participant receives first is counterbalanced. Further details of the stimulation hardware and brain imaging is provided below. Stimulation & brain imaging: The stimulation devices will be programmed to achieve stimulation with certain patterns and parameters (e.g., pulse width and frequency) reported in studies such as those using coordinated reset stimulation (CRS) applied to the fingers. a) For electrical stimulation, a custom-built device will be used to deliver electrical pulses via electrodes attached to the participant's skin. The current delivered will be up to a maximum of 4.5 mA (depending on the level perceived by participants). This is less than the currents delivered by commercially available transcutaneous electrical nerve stimulation (TENS) devices, which apply electrical stimulation for management of pain. b) For vibrotactile stimulation, a commercial device, manufactured by Engineering Acoustics, with individual vibrators and a controller, will be used to deliver brief vibrations (similar to the notifications delivered by smartphones). Both forms of stimulation will be delivered at a level that is perceivable, with pulses in the range of 50-300ms delivered every 0.3-7 seconds. Individual motors (for vibrotactile stimulation) or electrodes (for electrical stimulation) will be placed on 4 separate sites on one foot. Each site is stimulated one at a time. The order of stimulation is randomised. Brain activity during stimulation will be recorded using fNIRS or EEG to ensure that stimulation generates a cortical response. Both systems, with fNIRS applied first and EEG second, will be used on 3-5 healthy participants to determine which system better detects brain responses to vibrotactile stimulation. Participants will be given a 30-minute break in-between recordings. The preferred system will then be used on the remaining healthy participants. Both EEG and fNIRS recordings involve participants wearing a cap which is fitted based on a person's head circumference. EEG measures brain electrical activity using electrodes placed on the cap. fNIRS includes light sources and detectors placed on the cap and uses near-infrared light to measure changes in blood oxygen levels, from which brain activity is inferred. The Bionics Institute has both an Biosemi ActiveTwo EEG system (Biosemi, Netherlands) and a NIRScout fNIRS system (NIRx, Germany) which will be used in this study. Data from healthy participants will be used to determine which stimulation patterns generate clear cortical responses and are comfortable for the participants. This will assist in developing a future protocol for use with individuals with Parkinson’s Disease if indicated.