In an Unspoken Voice: How the Body Releases Trauma and Restores Goodness

by Peter A. Levine

fish species.† The function of this primitive system is immobilization, metabolic conservation, and shutdown. Its target of action is the internal organs. Next in evolutionary development is the sympathetic nervous system. This global arousal system has evolved from the reptilian period about 300 million years ago. Its function is mobilization and enhanced action (as in fight or flight); its target in the body is the limbs. Finally, the third, and phylogenetically most recent, system (deriving from about 80 million years ago) exists only in mammals. This neural subsystem shows its greatest refinement in the primates, where it mediates complex social and attachment behaviors. It is the branch of the parasympathetic nervous system that regulates the so-called mammalian or “smart” vagus nerve, which is neuroanatomically linked to the cranial nerves that mediate facial expression and vocalization. This most recently acquired system animates the unconsciously mediated muscles in throat, face, middle ear, heart and lungs, which together communicate our emotions, both to others and to ourselves.