Within the depth-psychology corpus, the autonomic nervous system is treated not as a peripheral physiological convenience but as the very substrate of psychological life — the biological architecture through which safety, danger, attachment, and trauma are registered, encoded, and expressed. Stephen Porges’ Polyvagal Theory dominates the field’s engagement with this term, recasting the classical two-branch (sympathetic/parasympathetic) model into a three-tier phylogenetic hierarchy: the ancient dorsal vagal circuit governing immobilization and collapse, the intermediate sympathetic system enabling fight-or-flight mobilization, and the uniquely mammalian ventral vagal circuit supporting social engagement, co-regulation, and felt safety. Deb Dana extends this neurophysiological framework into clinical practice, treating autonomic state as the ground from which narrative, behavior, and relational capacity emerge — not the other way around. Damasio’s somatic-marker hypothesis adds a complementary axis, using autonomic responses (particularly skin conductance) to demonstrate that visceral signaling is constitutive of rational decision-making, not merely its accompaniment. Across these voices, a productive tension persists between top-down cognitive accounts of emotion regulation and the polyvagal insistence on bottom-up, body-first, evolutionarily conserved dynamics. The stakes are high: how one theorizes the autonomic nervous system determines one’s entire model of trauma, therapy, and relational healing.