The mammalian vagus nerve is neuroanatomically linked to the cranial nerves controlling facial expression and vocal intonation.
"the nerves that control the face, the smile, nerves that control the intonation of our voice were linked to how that mammalian vagus was working." (said at 0:23:39)
The speaker is describing a core tenet of Stephen Porges's 'Polyvagal Theory', which posits an integrated mammalian 'social engagement system' linking the myelinated ventral vagal motor pathways (nucleus ambiguus) with cranial nerves controlling facial expression (cranial nerve VII) and vocalization (cranial nerves IX and X). While brainstem motor nuclei for these cranial nerves do anatomically co-exist in the medulla and pons and share central autonomic network connections, the specific polyvagal hypothesis of a uniquely mammalian, phylogenetically distinct 'face-heart' functional circuit is heavily contested in comparative neuroanatomy and autonomic physiology.
- context: The polyvagal theory: new insights into adaptive reactions of the autonomic nervous system… (Cleveland Clinic journal of medicine 2009)
"As the source nuclei of the primary vagal efferent pathways regulating the heart shifted from the dorsal motor nucleus of the vagus in reptiles to the nucleus ambiguus in mammals, a face-heart connection evolved with emergent properties of a social engagement system that would enable social interactions to regulate visceral state." (abstract, results, passage verified)
pubmedfull study (doi) - context: Functional anatomy of the vagus system: How does the polyvagal theory comply? (Biological psychology 2022)
"In particular, the widespread use of heart rate variability as an index of autonomic cardiac control and a proposed central role of the vagus in biopsychological concepts, e.g., the polyvagal theory, provide a good opportunity to recall basic features of vagal anatomy." (abstract, results, passage verified)
pubmedfull study (doi) - contradicts: Fundamental challenges and likely refutations of the five basic premises of the polyvagal … (Biological psychology 2023)
"Polyvagal conjectures rest on a primary assumption that brainstem ventral and dorsal vagal regions in mammals each have their own unique mediating effects upon control of heart rate. The polyvagal hypotheses link these putative dorsal- vs. ventral-vagal differences to socioemotional behavior... I will here briefly document how each of these basic premises have been shown to be either untenable or highly implausible based on the available scientific literature." (abstract, results, passage verified)
pubmedfull study (doi)