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Abstract

The auricular branch of the vagus nerve is responsible for the transmission of sensory information from the ear's cymba concha to homeostatic brainstem nuclei and thalamic
nuclei as well as the insular cortex. These centers are crucial for the representation and processing of interoceptive afferents. In a study using ultra-high-field fMRI, the auricular branch of the vagus nerve was transcutaneously stimulated using a current-source
device supplying a pulse train of 30s stimulation (0.2-0.5mA) on followed by 30s stimulation off. Pulses were delivered to bipolar titanium electrode contacts positioned on the ear. A high frequency noise blocker was added to each electrode channel, facilitating greater signal-to-noise functional echo-planar imaging. The data were modeled to obtain activation maps related to the nerve stimulation and also the periods before and after stimulation. A contrast between stimulation on and off periods primarily elucidates correlated activity of the contralateral posterior primary interoceptive cortex. Comparing periods of stimulation and post-stimulation to the resting-state, the anterior insular and cingulate cortices as well as the thalamus and brainstem nuclei responsible for viscerosensory information processing were invariably activated. Such spatial-temporal patterns
of subcortical activity may reflect the recruitment of high-order cortical centers and autonomic system modulation over periods of time exceeding that of stimulation.