Pain has many valuable functions. It can be a warning or force us to rest our bodies. Yet most ongoing chronic pain, such as unrelenting backache or headache, has no discernable cause and diminishes countless lives. Over the years a scientific revolution has taken place in chronic pain research and therapy. A major catalyst for this was the introduction of the "gate theory" by Professor Ronald Melzack and Professor Patrick D. Wall, which argued that pain is a unified stream of experience generated by the brain, incorporating a whole host of psychological functions. Their now-classic book,...