Neurobehavioral Anatomy, Third Edition

Christopher M. Filley, Christopher M Filley

• Publisher: University Press of Colorado
• Year: 2011
• Print ISBN: 9781607320982
• eBook ISBN: 9781607320999
• Topic: Biological Sciences
• Subtopic: Physiology
• Index: Biological Sciences

Thoroughly revised and updated to reflect key advances in behavioral neurology, Neurobehavioral Anatomy, Third Edition is a clinically based account of the neuroanatomy of human behavior centered on a consideration of behavioral dysfunction caused

CHAPTER ONE

BEHAVIOR AND THE BRAIN

Human behavior has an enduring appeal. Who among us has not reflected from time to time on how it is that a memory is formed, a sentence produced, or an emotion experienced? What is the origin of the thoughts and feelings that seem so distinctively to characterize the human species? Despite the enormous interest of this subject, however, our knowledge of human behavior is remarkably limited. The principle that the brain is the source of behavior has been acknowledged—with some notable exceptions—since the time of Hippocrates in ancient Greece, but the study of this relatively small organ encased in the skull presents challenges like none other in human biology. Many scientific investigators are deterred by the extraordinary complexity of brain-behavior relationships and, thus, select other areas of inquiry in which meaningful advances—and research grants—are assumed to be more easily attainable. Much of the formal study of behavior is descriptive, and even at this level there are formidable difficulties in the reliable characterization of the observed phenomena. Correlating the vast expanse of human behavior with the intricate neurobiology of the brain in health and disease is still more imposing. This state of relative ignorance is particularly regrettable since a better understanding of behavior could provide limitless benefits both in enhancing the achievements of our species and in reducing its destructiveness. Indeed, a more complete view of behavior as a function of the brain would have important implications for every realm of human activity.

By way of introduction to the core information presented in this book, it will be useful first to consider some philosophical and historical background that influences the study of behavior. Then follows a discussion of selected features of brain anatomy that pertain to neurobehavioral function in general. A brief digression into the intriguing but discredited area of phrenology is then presented as an illustration of the perils of simplistic thinking. Finally, we consider behavioral neurology and its unique viewpoint, hoping to demonstrate how knowledge of brain structure and function is critical to a comprehensive understanding of human behavior.

THE MIND-BRAIN PROBLEM

Traditionally, philosophers have taken a primary role in considering the phenomena of human behavior. The introspective method of thinking about one’s own thoughts and feelings was the sole available technique throughout most of human history. Scientific investigation of how and why people act as they do has a rather short history. Only in recent times has there been the development of a systematic empirical approach to the study of behavior, first with the rise of psychology in the nineteenth century (James 1890), and then with the explosive growth of neuroscience in the twentieth (Corsi 1991). These two traditions can be seen as “top down” and “bottom up” to signify their different approaches, and both have made major contributions to our understanding of behavior. Yet it hardly need be stated that these empirical endeavors have not laid to rest ancient philosophical issues. Science has by no means provided answers to all questions about the nature of the mind, and some would maintain that it never can (Horgan 1994). Biology can, however, provide provocative information with which to explore these issues. Although it may seem imprudent for a clinical neuroscientist to indulge in the discussion that follows, there is good reason to suppose that old philosophical problems can be more clearly addressed in the light of new biological knowledge (Young 1987).

One of the oldest and most difficult questions in philosophy is that of the relation of mind to body, commonly known as the mind-body problem. Human beings can reasonably assume that there exists, by virtue of daily experience, a conscious mind and, because of equally evident physical realities, an entity known as the body Of all body parts, it is also apparent that the brain very likely has the most to do with the mind, and the issue is therefore more precisely called the mind-brain problem. The difficulty arises when one realizes that mental states are clearly subjective, whereas the brain is an objective reality. Consciousness, to most people an obvious, albeit mysterious, human characteristic, does not readily appear to spring from the physical object we recognize as the brain. Many question whether a collection of nerve cells and chemicals can explain the ineffable phenomenon of consciousness, which is often equated with or regarded as akin to such concepts as the soul or spirit. As the philosopher John Searle bluntly poses the mind-brain problem: “How, for example, could this grey and white gook inside my skull be conscious?” (Searle 1984, 15). Consciousness does indeed appear to be the most mystifying feature of the human mind, and establishing it as a property of the brain is by no means straightforward.

Two fundamental solutions have dominated philosophical inquiry into this dilemma. For the sake of simplicity, these may be termed dualism and materialism. Dualism, most notably propounded by René Descartes in the seventeenth century, holds that mind and brain are independent; the famous Cogito ergo sum (”I think, therefore I am”) asserts the primacy of mind over matter (Descartes 1637) and implies that mental activities are divorced from physical events. Descartes did imagine there to be a point of intersection between the mind and the body and suggested the unpaired pineal gland as the site where the mind receives sensory traffic and acts upon the brain. But his steadfast separation of the immaterial mind from the material brain has exerted enormous influence for hundreds of years.

Materialism, advanced in various ways by thinkers as diverse as John Locke, Bertrand Russell, and Francis Crick, contends in general that mind and body are inseparable; as a result, mental events are nothing more than the expression of the brain’s physical activities. Advocates of this “identity theory” argue that the Cartesian division between mental and physical substances is no more than an assertion, in the trenchant phrase of Gilbert Ryle, that there exists a “ghost in the machine” (Ryle 1949). An extreme variant of materialism is B. F. Skinner’s behaviorism, an influential movement in twentieth-century American psychology emphasizing the manipulation of behavior by environmental conditions (Skinner 1971), and which, in effect, holds the concept of mind to be irrelevant to the scientific study of behavior.

The mind-brain problem continues to be pursued with vigor. Among modern philosophers who have continued the debate are Karl Popper (Popper and Eccles 1977), an advocate of dualist interactionism, and those who reject dualism, such as Searle (1984, 2004), Patricia Churchland (1986), and Daniel Dennett (1991). In particular, Churchland and Dennett have embraced neuroscience to the extent that they employ the term “mind-brain” to express complete acceptance of the identity of mind and brain (Churchland 1986; Dennett 1991).

At first glance, the dualist position may seem untenable in view of modern conceptions of neuroscience, but difficult problems remain nonetheless. Prominent among them is the question of free will. Do people act “freely” or under strictly determined laws of physics and chemistry? This dilemma can be more precisely posed as follows: If the mind and brain are in fact identical, and the actions of the brain can eventually be understood and predicted, then where is an escape from the determinist trap into which materialism must fall? Will not all behavior be governed by physical forces, and thus free will be impossible? Here are other questions to which science has not yet offered an answer. Arguments such as these continue to pose for some a significant obstacle to an enthusiastic acceptance of the materialist position.

Notwithstanding the lingering uncertainties raised by dualism, it is difficult to deny the practical utility of the materialist perspective. Advances in science are no less impressive if they pertain to the neural basis of behavior than if they lead to the discovery of penicillin for the treatment of bacterial pneumonia. It is undeniable that investigation of the brain has informed the understanding of a wide range of human behaviors that were previously inexplicable as physical phenomena. In clinical practice, experience with stroke, dementia, or traumatic brain injury patients leaves little doubt that activities of the mind are reliably and often dramatically affected by physical alterations in the brain. The fact that uncertain or inconsistent relationships between brain and behavior continue to challenge neuroscientists—as they clearly do—is testimony to the extraordinary complexity of the brain, not evidence that such relationships do not exist. Although occasional neuroscientists can be found who adopt a dualist position (Penfield 1975; Popper and Eccles 1977), the great majority find that physical events are providing increasingly complete and satisfying explanations for the activities of the mind. As a heuristic principle, the notion that brain events underlie and are directly correlated with mental events has been remarkably productive to date. Without necessarily presuming to answer the thorny philosophical questions introduced above, neuroscience has nevertheless assembled an impressive body of data indicating that the mind’s activities are an unequivocal result of the brain’s structure and function. In this sense, scientific advances shed light on old problems that, while not solved, at least seem less imposing.

The position taken in these pages derives from an unhesitating embrace of the methods and findings of neuroscience, and therefore follows in the materialist tradition. Although neuroscience cannot comment on a nonphysical reality, there seems little to gain by postulating a spiritual or mystical essence that cannot be reduced to the level of scientific analysis, especially when such complex human capacities as memory, language, and emotion are already yielding to this kind of inquiry. Indeed, as we will see in Chapter 9, a neurology of religion is a plausible approach to understanding a human experience that has traditionally been seen as representing divine influence (Saver and Rabin 1997). In this respect, the dualist tradition does remind us that many mental events have been interpreted as dissociated from any apparent physical basis. Because the task ahead requires developing an understanding of how these mental events are organized by the brain, Searle has recently proposed the idea of “biological naturalism” as a perhaps more harmonious solution to the mind-brain problem (Searle 2004). Whatever the terminology preferred, the proposition that mental events are in fact caused by neurobiological processes in the brain has a compelling rationale and much empirical support (Geschwind 1985; Churchland 1986; Dennett 1991; Searle 2004), and there is ample reason to expect that continuing explication of the brain’s operations will also unravel the secrets of the mind.

GENERAL FEATURES OF BRAIN ANATOMY

Neuroanatomy has been a foundation of behavioral neurology and continues to provide many insights into the neural organization of human behavior. Just as the elemental motor and sensory functions of the nervous system can be understood as emanating from the operations of brain neurons, so too can the myriad phenomena of cognition and emotion (Mesulam 2000; Kandel, Schwartz, and Jessell 2000). This book is concerned with the anatomy of higher functions, and clinically relevant regions of the brain will be covered in the chapters that follow. As an introduction, however, it will be helpful to begin with some general neuroanatomic features of the brain as they bear upon neurobeh...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Dedication
• CONTENTS
• PREFACE TO THE THIRD EDITION
• CHAPTER ONE: BEHAVIOR AND THE BRAIN
• CHAPTER TWO: MENTAL STATUS EVALUATION
• CHAPTER THREE: DISORDERS OF AROUSAL AND ATTENTION
• CHAPTER FOUR: MEMORY DISORDERS
• CHAPTER FIVE: LANGUAGE DISORDERS
• CHAPTER SIX: APRAXIA
• CHAPTER SEVEN: AGNOSIA
• CHAPTER EIGHT: RIGHT HEMISPHERE SYNDROMES
• CHAPTER NINE: TEMPORAL LOBE SYNDROMES
• CHAPTER TEN: FRONTAL LOBE SYNDROMES
• CHAPTER ELEVEN: TRAUMATIC BRAIN INJURY
• CHAPTER TWELVE: DEMENTIA
• EPILOGUE
• GLOSSARY OF NEUROBEHAVIORAL TERMS
• INDEX