The Neurology of Consciousness

Cognitive Neuroscience and Neuropathology

Steven Laureys, Olivia Gosseries, Giulio Tononi

• Publisher: Academic Press
• Year: 2015
• eBook ISBN: 9780128011751
• Edition: 2
• Topic: Psychology
• Subtopic: Neurology
• Index: Psychology

The second edition of The Neurology of Consciousness is a comprehensive update of this ground-breaking work on human consciousness, the first book in this area to summarize the neuroanatomical and functional underpinnings of consciousness by emphasizing a lesional approach offered by the study of neurological patients. Since the publication of the first edition in 2009, new methodologies have made consciousness much more accessible scientifically, and, in particular, the study of disorders, disruptions, and disturbances of consciousness has added tremendously to our understanding of the biological basis of human consciousness. The publication of a new edition is both critical and timely for continued understanding of the field of consciousness. In this critical and timely update, revised and new contributions by internationally renowned researchers—edited by the leaders in the field of consciousness research—provide a unique and comprehensive focus on human consciousness. The new edition of The Neurobiology of Consciousness will continue to be an indispensable resource for researchers and students working on the cognitive neuroscience of consciousness and related disorders, as well as for neuroscientists, psychologists, psychiatrists, and neurologists contemplating consciousness as one of the philosophical, ethical, sociological, political, and religious questions of our time. - New chapters on the neuroanatomical basis of consciousness and short-term memory, and expanded coverage of comas and neuroethics, including the ethics of brain death - The first comprehensive, authoritative collection to describe disorders of consciousness and how they are used to study and understand the neural correlates of conscious perception in humans. - Includes both revised and new chapters from the top international researchers in the field, including Christof Koch, Marcus Raichle, Nicholas Schiff, Joseph Fins, and Michael Gazzaniga

Part I

Basics

Outline

Chapter 1 Neuroanatomical Basis of Consciousness

Chapter 2 Functional Neuroimaging Techniques

Chapter 3 Neuronal Oscillations, Coherence, and Consciousness

Chapter 4 Neural Correlates of Visual Consciousness

Chapter 5 The Relationship Between Consciousness and Top-Down Attention

Chapter 1

Neuroanatomical Basis of Consciousness

Hal Blumenfeld, Departments of Neurology, Neurobiology, and Neurosurgery, Yale University School of Medicine, New Haven, CT, USA

Neurology utilizes a localization-based approach that has firmly established the functional neuroanatomy of consciousness. Clinical disorders can either impair the specific contents of consciousness, such as language or visual processing; or can interfere with the overall level of consciousness. The specialized brain networks controlling the level of consciousness are called the “consciousness system,” and include cortical components, consisting mainly of bilateral frontoparietal association cortex, as well as subcortical components comprising multiple parallel arousal systems in the upper brainstem, thalamus, hypothalamus, and basal forebrain. Subcortical arousal systems include widespread projections acting through glutamate, gamma amino butyric acid, acetylcholine, epinephrine, dopamine, serotonin, histamine, and orexin. The bilateral higher-order heteromodal association cortex acts together with the subcortical components of the consciousness system to control the level of alertness, attention, and awareness. Cortical anatomy is also crucial for other aspects of consciousness including hemispheric specialization, emotional drive, feature binding, top-down, bottom-up, task-positive and task-negative (default mode) attention systems, voluntary action, self-awareness, and memory encoding for the report of conscious experience.

Keywords

Consciousness; neuroanatomy; association cortex; thalamus; brainstem; arousal; attention; ascending reticular activating system; frontal lobe; parietal lobe

Outline

Introduction 3

The Consciousness System 5

Subcortical Networks and Consciousness 6

The Thalamus and Consciousness 8

Glutamatergic and Related Arousal Systems 9

Cholinergic Arousal Systems 9

GABAergic Arousal Systems 12

Noradrenergic Arousal Systems 12

Serotoninergic Arousal Systems 13

Dopaminergic Arousal Systems 13

Histaminergic Arousal Systems 14

Orexinergic Arousal Systems 15

Adenosine and Arousal 15

Amygdala and Arousal 15

Attention and Awareness: Roles of Subcortical Arousal Systems, Tectal Region, Basal Ganglia, Claustrum, and Cerebellum 15

Cortical Networks and Consciousness 16

The Cortex and Arousal 16

Attention and Consciousness 16

Hemispheric Dominance of Attention 17

Affect, Motivation, and Attention 18

The Binding Problem 18

Top-Down and Bottom-Up Attention Networks 19

Task-Positive and Task-Negative Networks 19

Memory Systems and Consciousness 20

Volition and Conscious Free Will 21

Self-Awareness and Embodiment 22

Awareness: Conscious Report and Contrastive Analysis 22

Acknowledgments 23

References 23

Introduction

Consciousness is of great importance to normal human quality of life. The nature of consciousness and the best way to understand and define it have long generated lively debate among scientists, philosophers, clinicians, and the general public. From a neurological perspective, consciousness is classically described as emerging from brain systems that make up the content of consciousness, regulated by distinct systems that control the level of consciousness (Plum and Posner, 1982).

The content of consciousness is the substrate upon which levels of consciousness act. This content includes all the various types of information processed by hierarchically organized sensory, motor, emotional, and memory systems in the brain (Figure 1.1). Much of neuroscience is dedicated to understanding the normal functioning of these systems. Selective deficits in contents of consciousness, such as loss of a portion of one’s visual field, or sudden impairment in spoken language, are also the main subject matter of clinical neurology.

Figure 1.1 The content of consciousness. Parallel interconnected and hierarchically organized sensory and motor systems receive inputs, generate outputs, and perform internal processing on multiple levels, from relatively simple to highly abstract. Three additional special systems—mediating memory, emotions and drives, and consciousness itself—act on the other systems in a widely distributed manner, especially at the highest levels of processing. Source: Modified with permission from Blumenfeld (2010).

However, level of consciousness can affect all of these specific functions. The level of consciousness is controlled by specialized cortical and subcortical systems that determine the amount of alertness, attention, and awareness (mnemonic, AAA) (Blumenfeld, 2002). Basic alertness (arousal, wakefulness) is necessary for any meaningful responses to occur. Attention enables selective or sustained information to be processed. Finally, awareness is the ability to form experiences that can potentially be reported later. This chapter will review the neuroanatomical basis of brain systems that control the level of consciousness. In analogy with other cortical-subcortical systems such as the sensory, motor or limbic systems, the brain networks dedicated to regulating the level of consciousness can be referred to as the “consciousness system” (Blumenfeld, 2010, 2012). This chapter begins with an overview of the main cortical and subcortical structures that constitute the consciousness system. Next, the major subcortical networks that regulate level of consciousness are each discussed in turn, including the thalamus and subcortical arousal nuclei acting through multiple neurotransmitters (glutamate, acetylcholine, gamma amino butyric acid (GABA), norepinephrine, serotonin, dopamine, histamine, orexin) that arise from the upper brainstem, basal forebrain, and hypothalamus. The second half of the chapter reviews important cortical networks for controlling the level of alertness, attention, and awareness, including systems that select and encode conscious experiences into memories for subsequent report. This neuroanatomical review of the cortical and subcortical systems that control level of consciousness will serve as a general introduction to the normal functions as well as disorders of consciousness discussed in the remaining chapters in this book.

The Consciousness System

The specialized brain networks controlling the level of consciousness can be referred to as the “consciousness system” (Blumenfeld, 2009, 2010) (Figure 1.2). It has long been recognized through studies based on human brain disorders (Penfield, 1950; Plum and Posner, 1972; Von Economo, 1930) as well as experimental animal models (Bremer, 1955; Moruzzi and Magoun, 1949; Steriade and McCarley, 2010) that the level of consciousness depends critically on both cortical and subcortical structures. Here we provide a brief overview of the cortical and subcortical networks comprising the consciousness system, which will be discussed in greater detail in the remaining sections of the chapter.

Figure 1.2 The consciousness system. Anatomical structures involved in regulating the level of consciousness, specifically controlling the level of alertness, attention and awareness. (A) Medial view showing cortical (blue) and subcortical (red) components of the consciousness system. (B) Lateral cortical components of the consciousness system. Note that other circuits not pictured here, such as the anterior insula, claustrum, basal ganglia, amygdala, and cerebellum, may also play a role in attention and other aspects of consciousness. Source: Reproduced with permission from Blumenfeld (2010).

Cortical components of the consciousness system include the major regions of the higher-order “heteromodal” (Mesulam, 2000) association cortex (Figure 1.2; see also Figure 1.11). On the medial brain surface, important components are the medial frontal, anterior cingulate, posterior cingulate, and medial parietal (precuneus, retrosplenial) cortex (Figure 1.2A). On the lateral surface, major consciousness system networks include the lateral frontal, anterior insula, orbital frontal, and lateral temporal-parietal association cortex (Figure 1.2B).

It is important to recognize that individual components of the higher-order association cortex play important and well-studied roles in specific cognitive functions in the dominant and non-dominant hemispheres as described in the behavioral neurology literature (Heilman and Valenstein, 2003; Mesulam, 2000). Recently these same association cortex regions have also been described as participating in either so-called task-positive networks based on their activation during externally oriented attention (Asplund et al., 2010; Buschman and Miller, 2007; Dosenbach et al., 2007; Vanhaudenhuyse et al., 2011) or task-negative networks, also known as the “default mode” based on activity at rest (Fox et al., 2005; Raichle et al., 2001). Regardless of the heterogeneous functions of individual regions or networks, it is the collective activity of widespread areas of bilateral association cortex that determines the level of consciousness. Taken as a whole, the higher-order association cortex interacts with subcortical arousal systems (Steriade and McCarley, 2010) to exert powerful control over the overall level of arousal, attention, and awareness.

Subcortical components of the consciousness system include the upper brainstem activating systems, thalamus, hypothalamus, and basal forebrain (Figure 1.2A). It is likely that other subcortical structures (not shown) also participate, including portions of the basal ganglia, cerebellum, amygdala, and claustrum. Multiple parallel neurotransmitter systems participate in subcorti...

Table of contents

• Cover image
• Title page
• Table of Contents
• Dedication
• Copyright
• Foreword
• Preface
• List of Contributors
• Part I: Basics
• Part II: Waking, Sleep, and Anaesthesia
• Part III: Severe Brain Injury and Related Conditions
• Part IV: Seizures, Splits, Neglects, and Assorted Disorders
• Index