Anatomo-Physiologic Basis for Auricular Stimulation

Abstract

Introduction: Stimulation of cranial nerves modulates central nervous system (CNS) activity via the extensive connections of their brainstem nuclei to higher-order structures. Clinical experience with vagus-nerve stimulation (VNS) demonstrates that it produces robust therapeutic effects, however, posing concerns related to its invasiveness and side-effects. Discussion: Trigeminal nerve stimulation (TNS) has been recently proposed as a valid alternative to VNS. The ear presents afferent vagus and trigeminal-nerve distribution; its innervation is the theoretical basis of different reflex therapies, including auriculotherapy. An increasing number of studies have shown that several therapeutic effects induced by invasive VNS and TNS, can be reproduced by noninvasive auricular-nerve stimulation. However, the sites and neurobiologic mechanisms by which VNS and TNS produce their therapeutic effects are not clear yet. Conclusions: Accumulating evidence suggests that VNS and TNS share multiple levels and mechanisms of action in the CNS.

Keywords: auricular stimulation; brainstem; central nervous system; forebrain; neuromodulation; trigeminal nerve stimulation; vagus nerve stimulation.

Conflict of interest statement

No competing financial interests exist.

Figures

FIG. 1.

Schematic representation of the innervation of the external ear.

FIG. 2.

Schematic representation of the main areas in the central nervous system areas possibly influenced by external ear stimulation via vagal and trigeminal nerves. VPM, ventral posterior medial nucleus; ILN, intralaminar nuclei; En, endopiriform nucleus; BNST, bed nucleus stria terminalis; PAG, periacquductal gray matter; PBN, nucleus parabrachialis; RN, raphe nucleus; LC, locus coeruleus; NST, nucleus of the solitarii tract; ABVN, auricular branch of the vagus nerve; ATN, auricular temporal branch of the trigeminal nerve.