MULTI-ELECTRODE TRANSCUTANEOUS ELECTRICAL STIMULATION OF THE HUMAN EXTERNAL EAR

This article reviews the development of a new concept for crafting and testing a multi-electrode set-up for selective transcutaneous auricular nerve stimulation (tANS) using particular superficial regions of the external ear (EE). The purpose of the work is to assess the mechanical properties of the set-up to ensure the optimum conditions for the users, and to test the ability to affect vital physiological functions. The set-up consisted of eight cap-like platinum simulating cathodes (S = 14.58 mm2) that were embedded in the left and right silicone ear plugs. The plugs were mounted onto the frame of dummy headphones and inserted into the EE, while a common anode (anode) (S = 4500 mm2) was placed at the nape of the neck. The mechanical performance was assessed by measuring the axial force Fx acting on each cathode against the bending of the dummy headphone frame while simulating the conditions of the set-up being mounted onto the head. The functionality was tested by applying stimuli onto four predefined sites at the EE to modify particular vital physiological functions of female volunteers. The preliminary results show that during the tANS, the bi-nasal respiration became shorter but more frequent with steeper inspiration and a lower airflow. The results also show that during the tANS, the heart rate was slightly diminished along with the respiratory sinus arrhythmia. Finally, a dicrotic notch within the toe photoplethysmogram was masked by the waves with a frequency of approximately 300 min–1. The presented work has implications for the multi-electrode set-up design and the prediction of efficient tANS used to modify physiological functions.