Pain and the Conscious Brain

摘要

Pain and the Conscious Brain is a new paperback, part of a series from the International Association for the Study of Pain, that brings together some of the world’s leading neuroscientists to offer their thoughts on the relationships between the brain, pain, and human consciousness. When asked to review this book, I happily agreed; I am always ready to learn. A few days later, the small paperback arrived: It was 240 pages in length, spanned 16 chapters, and covered topics such as “Pain and Spatial Boundaries of the Bodily Self” and “The Neuroevolutionary Sources of Consciousness and Affect.” What was I thinking? Perhaps I should return the text and beg forgiveness for even thinking I could offer potential readers any insights about such abstract material. I then began to read. What had the authors set out to accomplish? Garcia-Larrea in Lyon, France, and Jackson in Quebec City, Canada, have dedicated their careers to gaining a better understanding of pain and its relationship to the structure and function of the human brain. They tell us, “Consciousness is a unique achievement of the human brain. Sensory receptors in the body convert physical stimuli in to patterns of nerve impulses that are projected to specific areas of the brain. In those areas an extraordinary event occurs: The continuous flow of nerve impulses is transformed into our perception of our body and the environment we live in.” Nicely stated, but I am still not sure why they wrote this text or how I might relate this to the clinical treatment of patients with pain. “One of the perceptions is pain,” they continue. “Some pains are generated by observable physical events…other pains such as phantom limb pain…are generated in the brain…this unique book [is] devoted to understanding the brain mechanisms that generate the conscious experience of pain.” Maybe, just maybe, there is something here for the clinician to learn. Section 1 is dedicated to providing readers with a better understanding of consciousness, from being awake to being aware. Topics include the neurobiology of coma, vegetative and minimally conscious states, and a chapter that fully explores the neuroanatomy and the neurobiology of consciousness. The section ends with an outstanding chapter on the current state of using neuroimaging to understand pain in humans, summarizing the wealth of evidence showing that pain experiences require coordinated activity across many regions in the brain and emphasizing that there is no single “pain center” within the brain. Section 2 focuses on how the experience of pain can be altered by modulating consciousness. There are detailed and easily understandable discussions of pain perception during sleep and the intersection of consciousness, the placebo effect, and the perception of pain. The scientific underpinnings of how mindfulness and meditative practices can alter the conscious perception of pain are explained. Of notable interest to anesthesiologists is a lucid summary of studies using functional neuroimaging to tease out the changes in cortical activity that accompany loss of consciousness during induction of general anesthesia. Similar techniques may prove useful in identifying analgesic drugs and their cortical targets in drug discovery. Section 3 is a fascinating tour through various neurologic disorders and their relative effects on the perception of pain. These essays are a stern reminder that pain processing often is largely intact, even in extremely premature infants and those in minimally conscious states or with dementia. For the clinician, this section is particularly informative, reviewing how development of functional pain perception occurs in the fetus and how to assess pain in those who cannot communicate verbally. “Behind and Beyond Consciousness of Pain,” Section 4, begins with a discussion of the link between attention, emotions, and pain. It turns out that unpleasant odors increase the perceived intensity and unpleasantness of reported pain. E