Chronic Pain and Brain Abnormalities

By Carl Y. Saab

It is only natural for someone in pain to attend to the body part that hurts. Yet this book tells the story of persistent pain having negative effects on brain function. The contributors, all leading experts in their respective fields of pain electrophysiology, brain imaging, and animal models of pain, strive to synthesize compelling and, in some ways, connected hypotheses with regard to pain-related changes in the brain. Together, they contribute their clinical, academic, and theoretical expertise in a comprehensive overview that attempts to define the broader philosophical context of pain (disentangling sensical from nonsensical claims), list the changes known to take place in the brains of individuals with chronic pain and animal models of pain, address the possible causes and mechanisms underlying these changes, and detail the techniques and analytical methods at our disposal to "visualize" and study these changes.

• Philosophical and social concepts of pain; testimonials of chronic-pain patients
• Clinical data from pain patients’ brains
• Advances in noninvasive brain imaging for pain patients
• Combining theoretical and empirical approaches to the analysis of pain-related brain function
• Manipulation of brain function in animal models
• Emerging neurotechnology principles for pain diagnostics and therapeutics

• Language: English
• Publisher: Academic Press
• Release date: Jun 28, 2013
• ISBN: 9780124058965

Book preview

1

Introduction

Carl Y. Saab,    Brown University, Providence, RI, USA

We are all bitched from the start and you especially have to be hurt like hell before you can write seriously. But when you get the damned hurt use it—don’t cheat with it. Be as faithful to it as a scientist.

Ernest Hemingway to F. Scott Fitzgerald.

Pain is the question mark turned like a fishhook in the human heart.

Peter De Vries.

Rationale and Scope of this Book

This book focuses on the neurophysiological mechanisms of pain in the brain, in particular chronic pain conditions. Chronic pain is broadly defined as a myriad of long-lasting, poignantly unpleasant sensations, in addition to a host of cognitive, behavioral and emotional comorbidities that are not alleviated by standard pharmacotherapy. It is a state of consciousness that deviates from common painful experiences in ways that profoundly threaten the patient’s wellbeing and quality of life. A more elaborate definition of chronic pain is discussed below, and the authors have each attempted to articulate the specific chronic pain condition in question, as there are many that manifest with different etiologies, symptomatology and, arguably, physiological mechanisms.

Certain forms of chronic pain such as neuropathic pain, are classified as neurological disorders, begging the question where in the nervous system is the pathology? Can one speak of pathogenesis and etiology of chronic pain in classical terms such as the pathogenesis of cancer or the etiology of cystic fibrosis? Restricted lesions in the brain have been known to lead to central pain, for example thalamic pain syndrome due to a stroke in the thalamus. However, the authors of this book do not wish to generalize that the brain is the target organ of pathology in patients suffering from all sorts of chronic pain, the same way for example that joint pathology is the ubiquitous cause for arthritis. Rather, we endorse the view that brain mechanisms associated with chronic pain could provide valuable clues to the underlying neural circuitry that is required for the pain experience. This perspective should not be construed as pointing fingers at pain centers in the brain that set off a host of feelings and emotions intimately entwined with pain.

Accordingly, my main goal as Editor was to engage leading clinicians and scientists in the pain field to reconcile the wealth of clinical and laboratory data in one book, to place these data within a coherent hypothetical framework, and to discuss up-to-date therapeutic options that target the brain exclusively. In my opinion, the authors have done an excellent job in identifying a set of measurable neurophysiological phenomena that are highly correlated with the pain experience (i.e. predictive of pain), and phenomena whose modulation could alter the pain experience (i.e. of potential therapeutic value).

With these disclaimers in mind, it would be presumptuous (even non-sensical) to claim that, one day, given the right technology, we’ll be able to visualize what pain looks like in the brain. What we are prepared to say, instead, is that we are now closer to predicting pain in others with a high degree of confidence based on empirical measures. Moreover, we hope that similar approaches might, at the very least, help guide future diagnostics, and also, in the best case scenario, inform novel therapies.

What is Pain?

Can pain be accurately defined? Several authoritative books on pain have only partially succeeded in defining the pain experience in a fully comprehensive manner.¹–⁷ Even one of the most widely-used definitions of pain among medical and academic professionals (which was formulated by the International Association for the Study of Pain, IASP⁸) falls short of grasping the pain experience in its entirety from the genealogy, etiology, epistemology and phenomenology perspectives* (see below). It is not surprising that linguists and philosophers across ages have been fascinated with the human experience of pain as a subject of study. Unless the reader is born with a genetic predisposition for pain insensitivity,⁹ they will unequivocally understand what pain means without further elaboration. This concept of perfectly understanding (or relating to) a phenomenon, yet not being able to reach universal agreement over its definition using communicable language, is not unique to pain. Consider for example the word game. Try as you may to reach a consensus on a definition of what game is (or what it is not), even among your closest friends, game will still mean different things to different people. Yet, call on someone to play a game, the person would likely engage in that specific activity (knowing the rules governing that game) without invoking a philosophical conundrum. It is argued that terms such as game, love and pain are understood because of community agreement about what these terms refer to, irrespective of our inability to confine them within the boundaries of common language. Therefore they are said to be representations of knowledge only partially anchored in language, and can only be conveyed most sincerely and gracefully by showing rather than by saying: "There are, indeed, things that cannot be put into words. They make themselves manifest. They are what is mystical¹⁰ (p. 89); What we cannot speak about we must pass over in silence¹⁰(p. 89*). This is why, it is assumed, when two individuals communicate their pain experiences to one another, they can be said to play a language game whose rules follow popular votes far from being rigid (see Private Language and Rule-Following Arguments).¹¹ Accordingly, one expects the qualifiers of the human pain experience to change dramatically with time and across cultures. Indeed, chilling accounts of pain insensitivity based on race portray a disturbing cultural bias and a racial rapport to pain (Negresses will bear cutting with nearly, if not quite, as much impunity as dogs and rabbits"⁵, p. 40). Furthermore, the rising epidemic of pain hints at a possible shift in the collective pain barometer in modern days. Compare our daily moaning and groaning about back pain and joint pain with anecdotal accounts of Greek and Trojan wartime injuries, which are described with anatomical precision in The Iliad, however, with no hint of suffering or agony that live up to the traumatic atrocities they endured.⁵ It seems that the boundary of language cowers to pain, and one is inclined, thereof, to accept Wittgenstein’s position, that the genuine definition of a word lies in its use (Don’t Think but Look! aphorism