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. 2023 May 16;20:64. doi: 10.1186/s12984-023-01187-8

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© The Author(s) 2023

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 3 — Emotion-to-motor transformation loop. Contraction of facial muscles relays proprioceptive (magenta) and interoceptive (purple) afferent signals to the amygdala (AMYG) via the trigeminal, glossopharyngeal, and vagus nerves and corresponding brainstem nuclei. AMYG forms a feedback loop with the anterior face area of the midcingulate cortex (M3). The AMYG-M3 connectivity establishes the processing center responsible for decision-making to select and produce a facial expression in response to a particular emotional context. These limbic inputs further calibrate the final motor output of the corticobulbar motor system, where the contraction of the upper (green) and lower (orange) face muscles is modulated via two separate anatomical pathways and the facial nerve. Dashed arrows represent afferent inputs, dotted arrows represent the processing center, and solid arrows represent efferent outputs. Abbreviations: AMYG, amygdala; CN V, cranial nerve V (trigeminal); CN VII, cranial nerve VII (facial); CN IX, cranial nerve IX (glossopharyngeal); CN X, cranial nerve X (vagus); INS, insula; LC, locus coeruleus; LFN, lateral facial nucleus; M1, primary motor cortex; M3, anterior face area of the midcingulate cortex; M4, caudal face area of the midcingulate cortex; MFN, medial facial nucleus; MTN, mesencephalic trigeminal nucleus; NTS, nucleus tractus solitarius; PBN, parabrachial nuclei; PMCvl, ventrolateral regions of the premotor cortex; SMA, supplementary motor area. Created with BioRender.com, RRID:SCR_018361.