# Feeding, Emotion, and the Brain Stem: The Interesting Case of the Mesencephalic Trigeminal Nucleus

## TL;DR

This paper explores the mesencephalic trigeminal nucleus, a brainstem structure involved in jaw control and possibly linked to emotional states.

## Contribution

The paper highlights the anatomical proximity of the mesencephalic trigeminal nucleus to the peri-acqueductal gray, suggesting a potential role in emotion.

## Key findings

- The mesencephalic trigeminal nucleus is adjacent to the peri-acqueductal gray, a key area for emotion.
- Behavioral evidence suggests the jaw and oral cavity are linked to emotional states like pleasure and aggression.
- Direct connections between the trigeminal nucleus and PAG are not well-supported by current findings.

## Abstract

Background: Our growing understanding of the brain basis of mind has seen an interest in evolutionarily ancient structures, most notably the brainstem. This paper offers an interesting example of this underexplored territory, by considering the mesencephalic component of the trigeminal nucleus. This largely uncelebrated brainstem structure is central to control of the jaw, and for the foundational acts of eating, oral exploration, and biting. Objectives: This paper explores the interesting anatomy of the mesencephalic trigeminal: unique in the nervous system as a centrally located sensory ganglion, which combines sensory and motor function for the jaw. An unexplored aspect of its anatomy is that the mesencephalic component of the nucleus lies directly adjacent to the brain’s core system for the experience of emotion, the peri-acqueductal gray (PAG). Results: The data suggest a role for the jaw, and more broadly the oral cavity, in relation to a range of feeling states, from pleasure to aggression. This is supported by behavioural and classic neuropsychological findings, such as the Klüver-Bucy syndrome. However, the proposal is not well-supported by findings of direct connections between the trigeminal nucleus and the PAG. Conclusions: While these contrasting findings present a conundrum, there may be a role for non-synaptic signalling, of the sort increasingly understood to be important for interoception and homeostasis.