John Chrysostom often presented himself as a physician of the soul. He performed psychic therapy through consolation, encouragement to overcome the passions, and instruction in ascetic discipline. He also drew regularly upon his medical learning to provide detailed metaphors of sickness and healing. Like many preachers of his generation, he was steeped in classical learning, which included the naturalistic medical tradition. This chapter examines the attention that Chrysostom pays to the brain and the nervous system. Largely neglected in studies of the late-antique body, the brain and nerves were, as primary instruments of the rational and governing part of the soul, central to fourth-century anthropology, and also to the political imagination. Using a framework adopted from history and philosophy of medicine, this chapter argues that Chrysostom appropriates a medical model of the brain and nervous system in order to situate himself as a physician not only of the individual soul, but of the ecclesial body as a whole. Interpreting Christ as the “brain,” which distributes spirit to the members through the nerves, Chrysostom destabilises the boundaries of individual bodies in order to emphasise their mutual interdependence, while at the same time reinforcing the boundaries of the church. The nervous system supplies a model of organic hierarchy, through which Chrysostom might establish a norm, as well as a category of deviance, with regard to participation in the body of the church.