Sir John Eccles, expert neuroscientist and collaborator with Karl Popper delivered two series of lectures at the University of Edinburgh from 1978–79. The first series of lectures was published under the title The Human Mystery, followed by this second volume. After developing a strong theory of dualist interactionism and using this to explore human self-consciousness in the first volume, this volume moves to discuss this idea of dualist interaction in relation to developments in neuroscience.