Polyvagal Theory - The Ventral Vagal Complex

The Ventral Vagal Complex

With increased neural complexity seen in mammals (due to phylogenetic development) evolved a more sophisticated system to enrich behavioral and affective responses to an increasingly complex environment. The ventral branch of the vagus originates in the nucleus ambiguus and is myelinated to provide more control and speed in responding. This branch is also known as the “smart vagus” because it is associated with the regulation of sympathetic “fight or flight” behaviors in the service of social affiliative behaviors. These behaviors include social communication and self-soothing and calming. In other words, this branch of the vagus can inhibit or disinhibit defensive limbic circuits, depending on the situation. The VVC provides primary control of supradiaphragmatic visceral organs, such as the esophagus, bronchi, pharynx, and larynx. The VVC also exerts important influence on the heart. When vagal tone to the heart’s pacemaker is high, a baseline or resting heart rate is produced. In other words, the vagus acts as a restraint, or brake, limiting heart rate. However, when vagal tone is removed, there is little inhibition to the pacemaker, and so rapid mobilization (“fight/flight”) can be activated in times of stress, but without having to engage the sympathetic-adrenal system, as activation comes at a severe biological cost.

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