Introduction to Clinical Neuropsychology PDF

1 쎱 INTRODUCTION TO CLI...

1 쎱 INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY A Definition of Clinical Neuropsychology and Its Aims This book is concerned with the lives of real people whose behavior, emotions, or thinking abilities have become disordered, disrupted, or unusual as a result of some type of brain disorder or damage. The study of human behaviors, emotions, and thoughts and how they relate to the brain, particularly the damaged brain, is the subject matter of clinical neuropsychology. Clinical neuropsychology has both applied and academic aims. Applied aims in- clude learning more about neurological disorders and diseases so that we can more accurately and usefully diagnose, treat, and rehabilitate people who suffer such dis- orders and, along with other disciplines, ultimately find ways to prevent their occur- rence. The primary academic aim is to learn more about how the undamaged or “normal” human brain and mind work by carrying out experiments, usually in the form of cognitive tests, on brain-damaged people. Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. This introductory chapter describes the similarities and differences between clin- ical neuropsychology and other related disciplines. It then touches on functional neu- roanatomy, important neuropsychological terms and concepts, the interaction of clin- ical practice and research, the roles of a clinical neuropsychologist, and cross-cultural issues in neuropsychology. Each of these topics demands a chapter or book to itself, and a few paragraphs on each will act only as a reminder of knowledge you already have or provide just enough material to help you understand most of the information in the case studies. To provide a general sense of the basic tools the neuropsychologist uses to understand what is going on in the minds of brain-damaged patients or clients, Chapter 2 describes the different aspects of the neuropsychological assessment. Chap- ters 3 to 19 each present one or two case studies chosen to illustrate particular neu- ropsychological disorders, such as aphasia, visual agnosia, and dementia. A number of other issues important to the clinical neuropsychologist are raised throughout the case studies. At the end of this introductory chapter is a list of topics keyed to the chapters that provide further information about them. 3 Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  4 FRACTURED MINDS Relationship of Clinical Neuropsychology to Other Disciplines A number of disciplines are closely related to clinical neuropsychology and overlap with it (Fig. 1-1). The main ones can best be conceptualized as a continuum with the brain at one end (neurology) and the mind at the other (cognitive psychology). Neu- rology is the study of the medical aspects of central nervous system disorders and treatments. Compared with neuropsychologists, neurologists tend to be more con- cerned with clinical symptoms and signs as indications of underlying neuropathology in the brain, spinal cord, and peripheral nervous system and less concerned with the details of the higher behaviors and cognitions mediated by the brain and how the detailed study of their breakdown can inform us about normal higher cognitive pro- cesses. At the other, more academic, end of the spectrum lies cognitive psychology, a popular subdiscipline of academic psychology. Its aim is to understand the workings of the human mind by analyzing the higher cognitive functions and their components. Participants in cognitive psychology experiments are unimpaired people (usually un- dergraduate university students) rather than brain-damaged patients, and cognitive psy- chologists have developed many important experimental paradigms that allow mea- surement of minute differences in cognitive performance under controlled conditions. For example, the time required to perform different tasks or a single task under dif- ferent conditions might be measured in milliseconds, and from these results inferences can be made about the cognitive processes underlying the behaviors. Cognitive neuropsychology is a relatively recent label for a type of research that many neuropsychologists have been conducting for years. It is, as the name suggests, a hybrid of cognitive psychology and clinical neuropsychology. It concentrates on the detailed analysis of higher cognitive functions, often using similar paradigms to those used in cognitive psychology, but it studies brain-damaged patients rather than “nor- mals” (McCarthy and Warrington 1990). In their hypotheses and analyses of deficits Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. and their implications for the normal functioning of the brain, cognitive neuropsy- Figure 1-1 The discipline of clinical neuropsychology in relation to neu- rology and psychology. Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 5 chologists, although certainly not ignoring the brain entirely, tend to be less interested than clinical neuropsychologists in where the damage is and how it might be related to the impairment. Similarly, they are not interested in brain pathology, disease, and treatment on their own per se, but only as a means to the end of understanding the workings of the normal mind. Thus, clinical neuropsychology positions itself between neurology and cognitive neuropsychology. It has a neurological interest in brain pathology and the resulting symptoms and a psychological interest in the analysis of higher cognitive functions, both to understand the workings of the normal mind and to develop better rehabili- tation methods for patients. In practice, all the disciplines in Figure 1-1 overlap con- siderably, and many practitioners and researchers straddle two or more of these. Some neurologists specialize in clinical neuropsychology, and they are often known as be- havioral neurologists. Clinical neuropsychologists who have an affiliation with a uni- versity psychology department as well as a hospital often carry out research that would best fit into the cognitive neuropsychology category. This is well illustrated by some of the case studies in this book that are more closely aligned with cognitive neuro- psychology than clinical neuropsychology (see Chapters 3, 6, 8, and 19). Other important areas that contribute to clinical neuropsychology include animal psychology and neuroscience, neuropharmacology, and human neurophysiology. This latter discipline measures the electrical brain waves of patients using electroenceph- alographs (EEG) and evoked potentials. In recent years rapidly developing neuroim- aging technology has changed the face of neuroscience, and clinical neuropsychology has been one of the greatest beneficiaries. Computed tomography (CT) (see Chapters 6, 7, and 19 for examples) and magnetic resonance imaging (MRI) (see Chapter 8 and 14 for examples) permit us to visualize the anatomic structures and damage in the living brain, while cerebral blood flow techniques, positron emission tomography (PET), and functional MRI allow us to visualize the changing metabolism of the working brain. The relevance of these latter techniques lies in their potential to confirm Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. and extend our hypotheses about brain–behavior relations. That is, when a non-brain- damaged person is speaking, does Broca’s area (hypothesized to mediate speech) “light up” on a PET scan? Alternatively, when a patient has a large lesion in Broca’s area (as confirmed on a CT brain scan) but still manages to speak, what area of the brain “lights up” when a PET scan is carried out on this patient? Finally, but importantly, a practicing clinical neuropsychologist should first be an accomplished clinical psychologist, as will become evident in many of the case studies that follow. Even clinical neuropsychologists who restrict themselves to assessment and do not take an active part in rehabilitation and therapy require some clinical skills to enable them to build the rapport necessary to achieve a valid and useful assessment and to discuss in a sensitive manner the often distressing information about a patient’s performance. In addition, patients often express strong emotions about their illness and their wider situation during their assessment, especially during the initial inter- view, and the clinical neuropsychologist should be able to respond professionally and sensitively. People with stable, long-term lesions who have volunteered as research Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  6 FRACTURED MINDS subjects are also entitled to sensitive treatment that does not exploit or disempower them. Functional Neuroanatomy The human brain is the most complex system in the animal kingdom, and it is well beyond the scope of this book to cover neuroanatomy in any detail. This section provides a brief, simplistic overview of the cortical areas and other neuroanatomical structures that are most closely related to the disorders of higher cortical functioning covered in this book. This section should serve as a reminder for readers who have studied neuroanatomy and provide some background for those who have not. For readers who wish to learn more about this important area, the neuropsychology texts by Lezak (1995) and Walsh (1994) have excellent, easy-to-read sections on neuro- atomy for neuropsychologists; more detailed descriptions of neuroanatomy can be found in Mesulam (1985). Gross Structure of the Brain The brain has three major divisions: the cerebral hemispheres, the cerebellum, and the brain stem. Neuropsychology is most concerned with the cerebral hemispheres. Figure 1-2 shows lateral (from the side) and medial (split down the middle from front to back) views of the human brain. The brain stem, an upward extension of the spinal cord, consists of four parts: the medulla oblongata, pons, midbrain, and diencephalon. It is the life-support part of the brain as it controls respiration, cardiovascular function, and gastrointestinal function. It also contains the nuclei for the cranial nerves con- nected with the special senses, but it is not directly concerned with higher cognitive function. The cerebellar hemispheres are paired structures at the base of the cerebral hemispheres and are concerned mainly with motor coordination, muscle tone, and Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. balance. The cerebral hemispheres are paired structures above the midbrain and pons. They are covered by a highly convoluted layer of nerve cells called the cerebral cortex, or grey matter. The “hills” of the cortex are called gyri (singular, gyrus) and the “valleys” are called sulci (singular, sulcus). The axons or fiber tracts that connect the nerve cells to the rest of the brain form a layer directly below the cortex called the white matter. Deep within the hemispheres are further paired structures of grey matter called the basal ganglia. Chapter 15, which describes Parkinson’s disease, provides more detail about the basal ganglia and their connections. The two hemispheres are separated by the longitudinal fissure, a deep groove that runs from the anterior frontal lobes to the posterior occipital lobes. The other main fissures are the central (or rolandic) fissure or sulcus, which separates the frontal from the parietal lobe, and the lateral (or sylvian) fissure or sulcus, which separates the temporal lobe from the frontal and parietal lobes. A tough band of interhemispheric fibers called the corpus callosum forms the major Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07. Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. Figure 1-2 The upper figure is a lateral view of the left hemisphere; the lower figure a medial view of the right hemisphere of the human brain. 7 Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  8 FRACTURED MINDS functional connection between the two hemispheres. Within each hemisphere, fiber tracts connect different parts of the hemisphere. A system called the ascending reticular formation (RF) controls the overall arousal level of the cortex. The RF is a diffuse system of multisynaptic neuron chains traveling up through the brain stem. All the major sensory pathways send impulses via collateral axons to the RF, which relays them to a group of nuclei in the thalamus, paired grey matter structures deep in the brain on either side of the midline at the upper end of the brain stem. The thalamus serves as a relay center for motor pathways, many sensory pathways, and the RF. On reaching the thalamus, the impulses are relayed to the cerebral cortex, where they influence the level of mental alertness or sleep. Within the brain lies the limbic system, which includes the hippocampus and amyg- dala, which lie medially to the temporal lobes; the cingulate gyrus, which lies along the medial surface of the frontal and parietal lobes; and some deep, midline structures in the brain, including the mamillary bodies. The limbic system is involved in emotion, motivation, and memory. The brain has three coverings, called the meninges. The outermost thick, tough, covering is called the dura mater (“tough mother”), which adheres to the inner surface of the skull. The delicate, filamentous middle membrane, called the arachnoid mater (“spider mother”), is attached by cobweb-like strands of tissue to the fine pia mater (“little mother”), which adheres closely to the cortex. The subarachnoid space lies between the arachnoid mater and the pia mater and is filled with cerebrospinal fluid (CSF). Blood vessels also lie within the subarachnoid space and dip down in the sulci to supply deeper parts of the brain. An inflammation of the meninges is called meningitis; one symptom of meningitis is a stiff neck, caused by the muscles of the neck contracting strongly (called guarding) to prevent bending of the neck and the subsequent painful stretching of the inflamed meninges. The ventricles are lakes of CSF located deep within the hemispheres. The lateral Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. ventricles, large paired structures in the center of each hemisphere, connect in the middle to form the third ventricle and, below that, the fourth ventricle. The CSF is continually formed by the choroid plexus within the ventricles and circulates through the ventricles and around the outside of the brain and spinal cord within the subar- achnoid space. Excess CSF drains into the venous system from the subarachnoid space. If one of the small apertures between the ventricles becomes blocked, the CSF cannot flow out and the ventricles increase in size, causing increased intracranial pressure. This condition, known as hydrocephalus, can be corrected by a neurosurgeon placing a valve, or shunt, into the blocked ventricle to allow the CSF to flow through a tube into a body cavity. The cerebrovascular system is too complex to describe in detail here, but in simple terms it involves two pairs of cerebral arteries: the internal carotid arteries, which supply the anterior parts of the brain, and the vertebral arteries, which supply the posterior parts of the brain. The two internal carotid arteries enter the skull and ascend on either side of the optic chiasm, where each artery branches to form the anterior Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 9 cerebral arteries (ACA) and middle cerebral arteries (MCA), one set in each hemi- sphere. The ACAs sweep forward to supply the medial and lower (inferior) surfaces of the frontal lobes, the medial surfaces of the parietal lobes, and the corpus callosum. The MCAs travel laterally within the lateral fissure and branch to supply much of the lateral surfaces of the frontal, temporal, and parietal lobes as well as parts of the in- ferior surfaces of the frontal lobes and medial surfaces of the temporal lobe. The MCA also branches to form the striate arteries, which supply the deeply situated internal capsule, the main passageway for the fiber tracts between the motor cortex and the spine (the corticospinal tract or pyramidal tract). The tiny diameter of the striate arteries makes them vulnerable to blockage, resulting in damage to the corticospinal tract and subsequent paralysis of the opposite side of the body. The MCA supplies 75% or more of the blood supply to the cerebral hemispheres. The paired vertebral arteries enter the skull at the point where the spinal cord becomes continuous with the brain stem and join to form the single basilar artery on the undersurface of the brainstem; the basilar artery then divides to form paired pos- terior cerebral arteries, which supply the occipital lobes and parts of the medial and inferior surfaces of the temporal lobes, including the hippocampus. The internal ca- rotid and vertebral arterial systems are linked at the base of the brain by a single anterior communicating artery and two posterior communicating arteries, forming a ring of vessels lying in the subarachnoid space, called the Circle of Willis. If one of the main arteries becomes blocked, the blood can pass around the circle to reach the deprived area. The Circle of Willis is a frequent site of weakenings on the artery wall, called aneurysms. If an aneurysm bursts, it expels blood around the brain in the subarachnoid space, causing a subarachnoid hemorrhage (see Chapter 12). A blockage in a vessel away from the Circle of Willis can result in the blood and oxygen supply being cut off to the part of the brain that vessel supplies, resulting in an area of brain death, called a stroke (see Chapter 5). The venous system involves superficial veins, which drain the lateral and lower Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. (inferior) surfaces of the hemispheres, and deep veins, which drain the internal area of the brain. The cerebral veins empty into channels within the dura mater called venous sinuses, which in turn empty into the large internal jugular vein. Cerebral Cortex Cortical zones The cortex of each hemisphere can be divided in various ways, two of which are particularly useful for neuropsychologists. By dividing the cerebral hemi- spheres into primary, secondary, and tertiary cortical zones, as illustrated in Figure 1-3, the anatomical-functional relationships of the cortex can be conceptualized (Luria 1973; Mesulam 1985). The parietal, temporal, and occipital lobes lying behind the central sulcus constitute the posterior cortex and are involved mainly in a person’s awareness of what is happening in the world. Each of these lobes can be divided into three zones. The primary zones are primary projection areas in which incoming sensory in- Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  10 FRACTURED MINDS Figure 1-3 A diagram of a lateral view of the left hemisphere of the human brain divided into primary, secondary, and tertiary cortical zones. CS, central (rolandic) sulcus; LF, lateral (sylvian) fissure; M, motor strip; PM, premotor cortex; PF, prefrontal cortex; PS, primary sensory cortex; SS, secondary sensory cortex; PA, primary auditory cortex; SA, secondary auditory cortex; PV, primary visual cortex; SV, secondary visual cortex; TC, tertiary (multimodal) cortex. formation is projected to sense-modality-specific neurons. Each side of the body is Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. mapped topographically onto the primary sensory strip of the opposite (contralateral) hemisphere. Thus, a touch on the index finger of the right hand is projected to specific neurons in the primary sensory cortex of the left parietal lobe (the postcentral gyrus lying directly behind the central sulcus). The position of the finger would be projected to other specific neurons in the primary zone. The topographic pattern of neurons within the primary sensory strip of the parietal lobe can be conceptualized as a person hanging upside down with his foot hanging over the longitudinal fissure into the medial side of the hemisphere, with the trunk and hand represented on the lateral surface of the hemisphere and the face represented at the lower edge of the lateral surface at the edge of the lateral or sylvian fissure. The primary zone of the temporal lobes is concerned with sounds, and different frequencies are represented in different parts of the primary zone. Similarly, the primary zone of the occipital lobes represents specific parts of the visual field. Damage to specific areas of the primary cortex results in highly specific deficits of sensation in the topographically related body part or sense organ. Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 11 The secondary zones (also called the association cortex) lie adjacent to the primary zones. The neurons in these zones, unlike those in the primary zones, do not have a direct topographic relationship with sensory information relayed from a particular body part or sense organ. Instead, they receive the modality-specific information from their primary cortex and integrate it into meaningful wholes. Thus, the secondary cortex is concerned with perception and meaning within a single-sense modality. Dam- age to parts of the secondary cortex can therefore result in an inability to perceive or comprehend what one is touching or hearing or seeing, depending on whether the damage is in the parietal, temporal, or occipital secondary zones. The tertiary zones lie at the inner borders of each lobe so that the parietal, tem- poral, and occipital tertiary zones overlap. At this level, modality specificity disap- pears, and integration of information across sense modalities occurs. Damage to the tertiary zones can lead to complex higher cognitive disorders that involve transmodal integration (e.g., writing to dictation). The tertiary zones also have links with the limbic system, which is involved in emotion and memory; therefore, disorders result- ing from damage to the tertiary cortex may also involve abnormal emotional com- ponents. The frontal lobes lie anterior to the central sulcus and are concerned mainly with acting on knowledge relayed to the posterior part of the cerebral cortex from the outside world. The frontal lobes can also be divided into three zones. The primary zone, or motor strip, is on the precentral gyrus, immediately anterior to the central sulcus, and parallels the sensory strip in that each side of the body is mapped topo- graphically (like a person hanging upside down) onto the primary motor strip of the opposite (contralateral) hemisphere. The secondary zone (association cortex), also called the premotor cortex, mediates the organization of motor patterns, such as riding a bicycle. The tertiary zone, also called the prefrontal cortex, is a large area situated at the anterior pole of the brain; it includes both the lateral cortex and the basomedial (or Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. orbitomedial) cortex, which lies between the two hemispheres and extends to the underside of the frontal lobes above the eyes. The tertiary cortex is involved in ex- ecutive functions, including planning, organization, and abstract thinking. Because they also have rich connections with the limbic system, the prefrontal lobes are inti- mately involved with mood, motivation, and emotion, and damage to them can result in many and varied impairments involving the interactions of motivational and emo- tional states and executive functions. Cortical lobes The division of the cortex of each hemisphere into four lobes is the most often used concept in clinical neuropsychology. Although the lobes are often viewed as separate areas and are frequently linked to specific functions, they are in fact divisions of convenience rather than true anatomic divisions. Nevertheless, these divisions serve a useful purpose in discussions of brain–behavior relations. The four cortical lobes of the left hemisphere are labeled in Figure 1-2, and the right hemisphere is divided up in the same way. The large frontal lobes form the anterior part of the Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  12 FRACTURED MINDS brain, and the parietal, temporal, and occipital lobes make up the portion posterior to the central sulcus. All three posterior lobes (in each hemisphere) are involved in the awareness, per- ception, and integration of information from the outside world, although their con- nections with the limbic system ensure that the way the world is experienced is influ- enced by the individual’s mood, motivation, and past experiences. Generally, the parietal lobe is involved in functions involving tactile sensations, position sense, and spatial relations. The left parietal lobe has a bias toward sequential and logical spatial abilities, such as perceiving the details within a spatial pattern, whereas the right parietal lobe is more involved with the holistic appreciation of spatial information. The left parietal lobe also appears to mediate the ability to calculate, which involves both logical and spatial concepts. The right parietal lobe is especially good at con- ceptualizing complex spatial relations, and people with right parietal lesions often have extreme difficulty copying complex patterns or working out how to put jigsaw puzzles together. The temporal lobes are concerned primarily with auditory and olfactory abilities, but they are involved in integrating visual perceptions with other sensory information. They also mediate some memory functions, especially those involved in new learning. Their intimate connections with the hippocampus, a part of the limbic system, allow the integration of emotion and motivation with the sensory information relayed from the outside world to the posterior lobes of the hemispheres. The left temporal lobe is concerned more with verbal and sequential functions; it includes the language com- prehension area and is involved in new verbal learning and memory. The right tem- poral lobe tends to be more concerned with nonverbal functions, such as the interpre- tation of emotional voice tone and emotional facial expression and the appreciation of music and nonlanguage sounds. It also appears to play a part in nonverbal learning and memory, although this role is not as clear as the left temporal lobe’s role in verbal memory. Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. The occipital lobes are the visual lobes, and they mediate sight, visual perception, and visual knowledge. A patient with a large lesion of the right occipital lobe may have a complete left-visual-field defect (loss of vision) in the visual fields of both eyes (called a homonymous hemianopia), and a patient with bilateral lesions of the primary visual cortex at the very pole of the occipital lobes will be unable to see although his eyes function normally. This condition is termed cortical blindness. Visual-field defects can also occur if the visual pathways are damaged at other points. A lesion in the right temporal lobe that damages the optic radiation as it travels from the optic chiasma to the occipital cortex will result in a visual-field defect in the upper left quadrant of both eyes. A lesion of the right parietal lobe that damages the optic tract will result in a visual-field defect in the lower left quadrant of both eyes. Visual-field defects are straightforward sensory defects resulting from damage to the primary projection cortex and the optic fibers traveling to them. Lesions of the occipital secondary or association cortex can result in a number of strange disorders, particularly when the lesions are bilateral. For example, the patient Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 13 described in Chapter 8 has bilateral medial occipital lobe lesions; although he can see and describe the form of objects, he is unable to recognize what it is he is seeing. This condition is called visual agnosia. Again, there is some functional division be- tween the occipital lobes of the left and right hemispheres, with the left occipital lobe being more concerned with visual language functions such as reading, and the right occipital lobe being more concerned with visually judging the orientation of lines or objects in space. The frontal lobes, which are anterior to the central sulcus, are concerned with motor functions and executive functions such as forming abstract concepts and plan- ning and executing actions based on the information received from the posterior cor- tex. Motor functions are mediated by the primary and premotor frontal cortex, and the left frontal lobe includes the speech area Broca’s area. The executive functions are mediated by the prefrontal lobes and are integrated with emotional and motiva- tional states via part of the limbic system (the cingulate cortex), which forms the medial parts of the frontal lobes. The functional verbal–nonverbal division between the left and right prefrontal lobes is less marked than in the posterior lobes, but it nevertheless can be demonstrated with some neuropsychological tasks. For example, patients with left frontal lesions are frequently less able to produce words beginning with a specific letter under time pressure than those with right frontal lesions; conversely, patients with right frontal lesions are sometimes less able to create different designs than patients with left frontal damage. Other deficits resulting from frontal-lobe damage include recent memory deficits (frontal amnesia), wherein the patient is unable to use memory strategies (e.g., logi- cally structuring the material he wishes to memorize) and as a result has difficulty learning and recalling new information. The other main area of disturbance found after frontal-lobe lesions is related to the close anatomic and functional connections between the limbic structures and the frontal lobes and is often described as a personality Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. change (see Chapter 9). This can be the onset of an apathetic, aspontaneous, or even mute state or an increase in aggression or the display of inappropriate behaviors. Functional Systems Simple motor and sensory functions, and even some more complex perceptual func- tions, are mediated by a particular group of neurons; therefore, damage to these neu- rons results in an unambiguous deficit. For example, damage to the area of motor cortex that mediates hand movements results in a paralysis of the hand on the opposite side of the body. Many of our higher cognitive functions, such as reading or memory, are, however, the result of quite complex functional systems, composed of a number of different brain areas working together to produce a behavior. The concept of a functional system was proposed by Luria (1973), who further proposed that in terms of double dissociation, damage to area A will result in the impairment of a factor or subcomponent a, and all functional systems that include this factor will suffer. Like- Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  14 FRACTURED MINDS wise, when area B is damaged, all functional systems that include subcomponent b will suffer. As an example, damage to the right parietal lobe may impair the ability to con- ceptualize spatial relationships. In turn, this impairment may disrupt many functional systems and result in a wide range of behavioral deficits. The patient may no longer be able to do jigsaw puzzles, may become easily lost in an unfamiliar environment, may have difficulty learning and remembering new tasks that have a spatial compo- nent, and may no longer be able to perform calculations on paper or mentally that involve carrying figures from one column to another (a spatial task). The concept of functional systems suggests one possible way of overcoming an impairment. If the patient can find a new way to reach the same endpoint while avoiding the necessity to include the impaired subcomponent, then recovery of func- tion is possible. For example, he may be able to overcome his calculation difficulty by using a calculator that does not require a spatial ability but that simply requires pressing the right numbers and mathematical symbols in the correct order. In some cases of spontaneous recovery of function, the impaired functional system may re- structure itself, perhaps by bypassing the damaged neurons. Nearby undamaged neu- rons can sprout new dendrites that “fill the gap” left by the dead or damaged neurons and connect with the dendritic trees of undamaged neurons in other cortical areas. The new cortical area could either “learn” the cognitive subcomponent that was pre- viously mediated by the now-damaged neurons or could supply a different cognitive subcomponent that allows the functional system to remain viable, albeit using a slightly different process. This restructuring would, of course, take place outside the awareness of the patient, although he may unknowingly assist the process by contin- uing to practice the impaired behavior. Disconnection Syndrome Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. A number of disorders are thought to result from an anatomic disconnection between two cortical areas (Geschwind 1965). One example is provided by a type of apraxia (ideomotor apraxia; see Chapter 6), wherein the patient is unable to perform skilled movements to verbal command but can perform them spontaneously. Several mech- anisms have been put forward to explain this condition, but one disconnection expla- nation is that it is caused by damage to the fiber connection (the arcuate fasciculus) between the language comprehension area in the posterior left temporal lobe and the motor association cortex in the left frontal lobe. The disconnection can be within one cerebral hemisphere as in the above example, or it can be between hemispheres, as in the case where the corpus callosum connecting the hemispheres is damaged. For example, damage to the anterior section of the corpus callosum can result in a disconnection between the verbal comprehension area in the left hemisphere and the motor strip in the right hemisphere. As a consequence, the patient may not be able to comb his hair on verbal command with his left hand Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 15 (innervated by the right motor strip) but can do so with his right hand, as the left motor strip is still connected to the left verbal comprehension area. Experiments with split-brain subjects who have had the corpus callosum cut as a treatment for epilepsy have produced many examples of a “pure” disconnection syn- drome (see Chapter 18). For example, an object flashed in the right visual field (and therefore projected to the left hemisphere) can be described or named by the split brain subject because the speech faculty is also in the left hemisphere. An object flashed in the left visual field (and therefore projected to the right hemisphere) cannot be described in speech or writing, but the isolated right hemisphere, via the left hand, can respond nonverbally to the object it sees by pointing to a matching stimulus or to the name on a list (Sperry et al. 1969). The finding that the right hemisphere can point to a name on a list demonstrates that it does have the ability to comprehend simple language, although it cannot express itself in words. Neuropsychological Terminology In the company of most medical and scientific disciplines, neurology and neuropsy- chology are well endowed with their own jargon. Although jargon should be avoided wherever possible, to understand the vast neurological and neuropsychological liter- ature it is necessary to have a grasp of the most common of these terms. For example, deficit, dysfunction, symptom, impairment, and disorder are used synonymously and can refer to any motor, sensory, perceptual, behavioral, psychological, emotional, or cognitive abnormality. A syndrome refers to a group of symptoms that characteristi- cally occur together after brain damage (see Chapter 6). In many cases, jargon terms can provide shorthand descriptions for complex disorders. Fortunately, a few simple rules can simplify their interpretation for the beginner; indeed, it can even be fun trying to work out what deficits a patient should have by breaking down the diagnostic label into its component parts. Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. Any label containing phasia refers to a speech disorder; graphia refers to writing, and lexia to reading. Praxia means to work or perform purposeful actions, and gnosia means to know. If the base word is prefixed by an a, strictly speaking it means that that function is completely absent (e.g., agnosia means not to know); prefixed by dys, it means partial impairment (e.g., dyslexia means to have a marked reading difficulty). However, these conventions are often not adhered to, and a patient labeled as having expressive aphasia may not be totally mute but more accurately may be dysphasic. Sometimes the main label is preceded by a common English word that signifies the specific type of disorder. Therefore, visual agnosia means not to know what one is seeing, and tactile agnosia means not to know what one is touching. A patient with dressing apraxia has difficulty with the actions related to dressing and may try to put his left leg into the right sleeve and his right leg into the left leg of the garment, thus getting into an impossible tangle. In addition, many terms can be partially, if not fully, understood if the base of the word is known. For example, prosopagnosia denotes an Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  16 FRACTURED MINDS inability to recognize or know faces, and anosognosia is to deny knowledge, as in the case of a patient who denies she has paralyzed limbs. Some patients who suffer from cortical blindness deny that they are blind; this disorder is termed visual anosognosia. Many of these terms appear in the following case studies and are defined when they first arise. Other terms commonly used to describe brain–behavior relations include unilateral and bilateral, which refer to damage in one hemisphere or both hemispheres, respec- tively, and contralesional and contralateral, which refer to impairments (or body parts) and lesions that are opposite each other. For example, a paralyzed right arm is caused by a lesion in the contralateral (left) motor strip; alternatively, a lesion in the arm section of the left motor strip causes paralysis of the contralesional (right) arm. In another example, a patient may ignore or neglect stimuli in the contralesional hem- ispace (the side of space opposite the brain lesion). Assumptions that Underlie Clinical Neuropsychology The study of brain-damaged patients to understand the workings of the normal brain and mind relies on two important assumptions. The first is that the brain of the patient was normal before the brain damage, an assumption that is often challenged when patients with long-term neurological conditions are used as experimental subjects in an attempt to understand normal brain functioning. For example, patients with long- standing epilepsy who later in life undergo neurosurgery in an attempt to cure their epilepsy often participate in experiments to discover what impairments result from removing the temporal lobe (see Chapters 3 and 4). The argument that their brains may have been organized differently from normal as the result of their epilepsy can to a large extent be dismissed as we assess more patients without epilepsy who dem- onstrate the same sort of impairments after traumatic temporal lobe injury. Experiments with patients who have undergone a surgical splitting of the cerebral Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. commissures (the large band of fibers connecting the two cerebral hemispheres), again in an attempt to control severe, long-term epileptic seizures, face similar criticisms (see Chapter 18). Fortunately, the results of experiments on normal people, in which stimuli are briefly flashed to one hemisphere or the other, generally support the find- ings of the split-brain studies, suggesting that their brains do not differ greatly from normal. The second assumption underlying both cognitive and clinical neuropsychology experiments is that we can generalize about brain–behavior relations from one “nor- mal” human to another. The main criticism of this assumption is the evidence that not all patients with a lesion to a specific area of the brain suffer the same impairments. For example, most but not all adult patients who sustain damage to the inferior, posterior left frontal gyrus (Broca’s area) suffer impairment of language. Nevertheless, as the result of numerous studies of the impairments of brain-damaged people, it is generally accepted that it is valid to make broad generalizations about brain–behavior Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  INTRODUCTION TO CLINICAL NEUROPSYCHOLOGY 17 relationships from one human to another. The most obvious of these generalizations is that the left cerebral hemisphere is dominant for speech in most people. Making generalizations in the case of children is more difficult, as the brain de- velops functions at different rates as the child grows older. Thus, the practice of child clinical neuropsychology and experiments with brain-damaged children, although having much in common with adult neuropsychology, require different tests with age- appropriate normative data and different clinical methods and skills. A number of good books have been written about this subject area for readers with a particular interest in the neuropsychological problems of children (Anderson et al. 2001; Sattler 1992; Spreen, Risser, and Edgell 1995). Focal Lesions and Diffuse Brain Damage A focal lesion, as its name suggests, is damage restricted to a circumscribed area of the brain. Lesion is a general term used to describe any type of focal brain damage. Infarct or infarction refers to any area of dead brain. The most common cause of a focal lesion is a stroke, caused by a blockage or spasm of a cerebral artery and a loss of blood and oxygen to the part of the brain that artery supplies (see Chapter 5). Focal lesions can also be caused by a circumscribed area of bleeding that forms a blood clot within the brain substance (an intracerebral hematoma; see Chapter 5). In an open head injury the skull is fractured, and an object may penetrate the skull and underlying brain (e.g., bone fragments, bullets, or metal from an automobile ac- cident), damaging the brain tissue through which it passes. The neurosurgeon usually cleans the wound, removing the object and any damaged tissue and debris, and leaving a clean focal lesion that does not affect the rest of the brain. Studies of the impairments demonstrated by patients with lesions from penetrating objects or focal strokes have contributed a great deal to our understanding of the functional organization of the brain (e.g., Luria 1970; Newcombe 1969). Neurosurgical operations to remove or Copyright © 2005. Oxford University Press, Incorporated. All rights reserved. resect tumors or to remove parts of the brain that cause epilepsy (as in the case of temporal lobectomies) also result in focal lesions (see Chapters 3 and 4). Some viruses attack specific areas of the brain, causing focal damage, often bi- laterally. For example, the herpes simplex encephalitis virus usually targets the medial temporal lobes and sometimes attacks the inferior temporal and frontal areas as well, resulting in severe memory deficits and, in some cases, executive deficits (Utley, Og- den, Gibb, McGrath, and Anderson 1997). Brain tumors and brain abscesses are also focal lesions in the sense that they cause neural death by destroying neurons directly or via pressure effects. However, malignant tumors, while appearing to have a circum- scribed boundary on a CT brain scan, may be widespread with no clear division between diseased and healthy brain. It is therefore important to be cautious when proposing associations between a tumor lesion in a specific area of the brain and the impairments that the patient demonstrates (see Chapters 6 and 7). Diffuse brain damage refers to damage that affects many areas of the brain, as in Ogden, Jenni A.. Fractured Minds : A Case-Study Approach to Clinical Neuropsychology, Oxford University Press, Incorporated, 2005. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/rug/detail.action?docID=271491. Created from rug on 2025-02-17 15:22:07.  18 FRACTURED MINDS Alzheimer’s disease and other dementias (see Chapter 17). The damage can often be visualized on a CT or MRI scan or at postmortem as atrophy, which is shriveled or shrunken cortex and white matter, signifying neuronal death, and usually affecting large areas of the cortex. Brain atrophy decreases the brain mass and allows the fluid- filled ventricles in the middle of the brain and the subarachnoid space around the brain to expand. Other disease processes such as meningitis and encephalitis can also result in widespread brain damage that is sometimes transient and sometimes permanent. Progressive diseases other than AD, such as Huntington’s disease (HD), Parkin- son’s disease (PD), and multiple sclerosis (MS), cause increasing impairment of motor and cognitive functions as time goes on. HD (see Chapter 16) is a progressive degen- erative genetic disorder, and 50% of the children of a parent with HD will develop the disease (Mendelian autosomal dominant inheritance) and inevitably will become demented. The caudate nucleus, putamen, and globus pallidus become severely atro- phied, but as the disease advances, brain atrophy is widespread and thus diffuse. PD (see Chapter 15) is a disease of unknown cause that usually becomes apparent in the sixth decade and involves neurotransmitter deficits (dopamine) as a result of loss of dopamine-producing neurons in the substantia nigra of the basal ganglia. Al- though the majority of PD patients suffer from severe motor disorders and a number of mild to moderate cognitive impairments, only a small percentage become demented.