Pain mechanisms and their disorders

The purpose of this article is to summarise how functional imaging techniques have changed our understanding of normal and abnormal pain mechanisms, how they inform a change in clinical practice and to speculate on possible future clinical uses. The experience of pain can only be defined in terms of human consciousness. Functional imaging techniques have made it possible to identify the main cerebral components of the human nociceptive system. These comprise at least two main human nociceptive systems working in parallel called the medial and lateral pain systems (Fig. 1). This has provided a physical construct for the concept of the human pain matrix1. We are just beginning to understand the division of function within these systems, providing the possibility of establishing a more rational framework for pain therapy. There is a spectrum of pain experience from pain that may closely reflect physical events in tissue (e.g. leading to excitation of nociceptors