One of the primary connections between neuroscience and psychotherapy is the understanding of the autonomic nervous system. For decades therapists have been taught that there are two sides—the sympathetic (stressors) and parasympathetic (restoration)—complementing each other.

But according to Stephen Porges, developer of the Polyvagal Theory, this teaching is off the mark. He has found that these two systems are not equivalent, but are actually hierarchical, and that there is a third system to consider—the vagal circuit.

Watch the clip to hear him talk about the sympathetic and parasympathetic systems, and why trying to control behaviors independently of physiological states doesn’t work.