Our understanding of the functioning of the brain has grown rapidly over the last decade or two. So has our recognition of the possible role of brain dysfunction in diseases considered earlier to be of peripheral or somatic origin. This culminates naturally in a focus on the nature of the influence of the brain on other systems such as the autonomic, neuroendocrine and immune systems. And we must come full circle and question the nature of the influence of these systems on the function of the brain. Thus, we gain a picture of a complex regulatory interaction, fine tuned in normal...