Have you ever wondered why the same social situation that feels energising to one person leaves another completely depleted? Or why certain environments, like a busy open-plan office or a difficult conversation, seem to cost some people so much more than others? Part of the answer may lie less in personality or willpower and more in something more fundamental: the state of the nervous system. What is polyvagal theory? Developed by neuroscientist Stephen Porges, polyvagal theo