Non-invasive Vagus Nerve Stimulation and Sleep in Healthy Volunteers.

The Transcutaneous Electrical Nerve Stimulator (TENS) creates electrical impulses from a 9VDC-battery whose continuous intensity rate can be controlled by the user. The alligator clip with 2 electrodes is placed on the tragus part of the ear (shown to be 45% innervated via auricular vagus nerve) to stimulate the vagus nerve with an adjustable peak intensity (0-80mA), a frequency of 2 - 250Hz and a pulse width of 30-260 µsec. The vagus nerve contains a mixture of different types of nerve fibres, which are organized into bundles (fascicles). The fibres vary in diameter and conduction velocity, with A-type fibres the largest and fastest and C-type fibres the smallest and slowest, with B-type fibres intermediate. During nerve stimulation, fibres are activated in order of size from the largest (A-type) to the smallest (C-type). It has been suggested that A-type fibres are mainly activated during the stimulation via auricular vagus nerve.