Figure 1.

The Vagal Cortical Pathways model: overall four consecutive pathways of the transcutaneous auricular vagal nerve stimulation. By stimulating the auricular branch of the vagus nerve, it leads to (A) the activation of the trigeminal nucleus and tractus of the solitarius nucleus located in the lower brainstem (gold arrows). Their activation leads to (B) the activation of the locus coeruleus and the raphe nuclei localized in the upper brainstem (red arrows). Then, (C) the locus coeruleus produces norepinephrine and modulates global brain activity (pink arrows). Finally, (D) the raphe nuclei produce serotonin, which also targets the brain, especially some structures of the limbic system and the frontal cortex (blue arrows).