edited by Mark D'Esposito Neurological Foundations of Cognitive Neuroscience
Contents Preface ix 1 Neglect:A Disorder of Spatial Attention 1 Anjan Chatterjee Balint's Syndrome:A Disorder of Visual Cognition Robert Rafal 3 Amnesia:A Disorder of Episodic Michael S.Mega 4 Semantic Dementia:A Disorder of Semantic Memory 67 John R.Hodges Topographical Disorientation: A Disorder of Way-Finding Ability 89 Geoffrey K.Aguirre 6 Acquired Dyslexia:A Disorder of Reading 109 H.Branch Coslett 7 Acalculia:A Disorder of Numerical Cognition 129 Darren R.Gitelmar guage Production 165 Michael P.Alexander 9 Wernicke Aphasia:A Disorder of Central L anguage Processing 175 Jeffrey R.Binder Apraxia:A Disorder of Motor Control 239 Scott Grafton 11 Lateral Prefrontal Syndrome: A Disorder of Executive Control 259 Robert T.Knight and Mark D'Esposito Contributors 281 Index 283
Preface ix 1 Neglect: A Disorder of Spatial Attention 1 Anjan Chatterjee 2 Bálint’s Syndrome: A Disorder of Visual Cognition 27 Robert Rafal 3 Amnesia: A Disorder of Episodic Memory 41 Michael S. Mega 4 Semantic Dementia: A Disorder of Semantic Memory 67 John R. Hodges 5 Topographical Disorientation: A Disorder of Way-Finding Ability 89 Geoffrey K. Aguirre 6 Acquired Dyslexia: A Disorder of Reading 109 H. Branch Coslett 7 Acalculia: A Disorder of Numerical Cognition 129 Darren R. Gitelman 8 Transcortical Motor Aphasia: A Disorder of Language Production 165 Michael P. Alexander 9 Wernicke Aphasia: A Disorder of Central Language Processing 175 Jeffrey R. Binder 10 Apraxia: A Disorder of Motor Control 239 Scott Grafton 11 Lateral Prefrontal Syndrome: A Disorder of Executive Control 259 Robert T. Knight and Mark D’Esposito Contributors 281 Index 283 Contents
Preface It is an exciting time for the discipline of cogni- and functional neuroimaging studies of both normal tive neuroscience.In the past 10 years we have individuals and neurological patients-aimed at witnessed an explosion in the development and understanding the neural mechanisms underlying advancement of methods that allow us to precisely the cognitive functions affected in each particular examine the neural mechanisms underlving cog clinical syndrome.In many chapters,there are con- nitive processes.functional magnetic resonance flicting data derived from different methodologies ing.for example,has provided markedly im- and the authors have tried to reconcile these differ- proved spatial and temporal resolution of brain ences.Often these attempts at understandine how structure and function.which has led to answers to these data may be converg ent,rather than diverg new questions,and the reexamination of old ques has shed new light on the cognitive mechanisms tions Howe ver.in my inion.the explosive im that functional neur oimaging has had on goal of preparing this book was not to simply may in s clin obehavioral 6 with brain da rom our the study of Such descriptions can be found in excellent window into the al and Thus. Nor was the oal to creating neuro The ouldhiehiehy ook is to con the st nts of the clin nical udy of on in s my hope that reac chapter the varie vill of cognitive neu Anjan Ch aptly at understan chapter on neglect synd ne: ction can be cause for al m if the udying the abnormal bra n.The neglect research was to es abl a unifi from patients with neurological and psy mprenen ve theory of clinic syndrom chiatric disorders provided the foundation for the However.when neglect is used to understand the discipline of cognitive neuroscience and should organization of spatial attention and representatior continue to be an important methodological tool then the behavioral heterogeneity is actually critical in future studies. to its use as an investigative tool.These words Each chapter in this book was written by a neu capture perfectly my intent for this book rologist who also practices cognitive neuroscience. Many neurologists in training and in practice Each chapter begins with a description of a case lack exposure to cognitive neuroscience.Similarly. report.often a patient seen by the author.and many newly trained cognitive neuroscientists describes the symptoms seen in this patient,laying lack exposure to the rich history of investigations the foundation for the cognitive processes to be of brain-behavior relationships in neurological explored.After the clinical description.the authors patients.I am optimistic that this book will serve have provided a historical background about what both groups well.It is a privilege to have assembled we have learned about these particular neurobe an outstanding group of neurologists and cognitive havioral syndromes through clinical observation neuroscientists to present their unique perspective and neuropsychological investigation.Each chapter on the physical basis of the human mind. then explores investigations using a variety of methods-single-unit electrophysiological record- ing in awake-behaving monkeys,behavioral studies of normal healthy subjects.event-related potential
It is an exciting time for the discipline of cognitive neuroscience. In the past 10 years we have witnessed an explosion in the development and advancement of methods that allow us to precisely examine the neural mechanisms underlying cognitive processes. Functional magnetic resonance imaging, for example, has provided markedly improved spatial and temporal resolution of brain structure and function, which has led to answers to new questions, and the reexamination of old questions. However, in my opinion, the explosive impact that functional neuroimaging has had on cognitive neuroscience may in some ways be responsible for moving us away from our roots—the study of patients with brain damage as a window into the functioning of the normal brain. Thus, my motivation for creating this book was to provide a collection of chapters that would highlight the interface between the study of patients with cognitive deficits and the study of cognition in normal individuals. It is my hope that reading these chapters will remind us as students of cognitive neuroscience that research aimed at understanding the function of the normal brain can be guided by studying the abnormal brain. The incredible insight derived from patients with neurological and psychiatric disorders provided the foundation for the discipline of cognitive neuroscience and should continue to be an important methodological tool in future studies. Each chapter in this book was written by a neurologist who also practices cognitive neuroscience. Each chapter begins with a description of a case report, often a patient seen by the author, and describes the symptoms seen in this patient, laying the foundation for the cognitive processes to be explored. After the clinical description, the authors have provided a historical background about what we have learned about these particular neurobehavioral syndromes through clinical observation and neuropsychological investigation. Each chapter then explores investigations using a variety of methods—single-unit electrophysiological recording in awake-behaving monkeys, behavioral studies of normal healthy subjects, event-related potential and functional neuroimaging studies of both normal individuals and neurological patients—aimed at understanding the neural mechanisms underlying the cognitive functions affected in each particular clinical syndrome. In many chapters, there are con- flicting data derived from different methodologies, and the authors have tried to reconcile these differences. Often these attempts at understanding how these data may be convergent, rather than divergent, has shed new light on the cognitive mechanisms being explored. The goal of preparing this book was not to simply describe clinical neurobehavioral syndromes. Such descriptions can be found in many excellent textbooks of behavioral and cognitive neurology. Nor was the goal to provide a primer in cognitive neuroscience. The goal of this book is to consider normal cognitive processes in the context of patients with cognitive deficits. Each of the clinical syndromes in this book is markedly heterogeneous and the range of symptoms varies widely across patients. As Anjan Chatterjee aptly states in his chapter on the neglect syndrome: “This heterogeneity would be cause for alarm if the goal of neglect research was to establish a unified and comprehensive theory of the clinical syndrome. However, when neglect is used to understand the organization of spatial attention and representation, then the behavioral heterogeneity is actually critical to its use as an investigative tool.” These words capture perfectly my intent for this book. Many neurologists in training and in practice lack exposure to cognitive neuroscience. Similarly, many newly trained cognitive neuroscientists lack exposure to the rich history of investigations of brain–behavior relationships in neurological patients. I am optimistic that this book will serve both groups well. It is a privilege to have assembled an outstanding group of neurologists and cognitive neuroscientists to present their unique perspective on the physical basis of the human mind. Preface
Neglect:A Disorder of Spatial Attention Anjan Chatterjee produce subtle differences in deficits of these ptentmay meglect pants oftheiro bod are of A fferences themselve: tion and represen tions through the syndrome of parts of their environment,and even parts of scenes neglect is possible precisely because neglect is in their imagination.This clinical syndrome is pro- heterogeneous (Chatterjee,1998). duced by a lateralized disruption of spatial attention and representation and raises several questions of interest to cognitive neuroscientsts.How do humans Case Report represent space?How do humans direct spatial attention?How is attention related to perception? Neglect is How is attention related to action? with left brain d Spatial attention and representation can also be neglect following right brain damage.although similar studied in humans with functional neuroimaging deficits are seen sometimes following left brain damage. and with animal lesion and single-cell neurophysi- A 65-year-old woman presented to the hospital becaus She w ethargic Ior ological studies.Despite the unique methods and weakne approaches of these different disciplines,there is considerable convergence in our understanding of ber left hand was held in front of ber eves.she sug how the brain organizes and represents space.In that the limb belonged to the examiner.As her level of this chapter.I begin by describing the clinical syn- arousal improved.she continued to orient to her right.even drome of neglect.Following this description.I when approached and spoke outline the major theoretical approaches and bio- the foo ie of h logical correlates of the clinical phenomena.I then turn to prominent issues in recent neglect research Her speech was mildly dysarthric.She answered and to relevant data from human functional neuro questions correctly.but in a flat tone.Although her imaging and animal studies.Finally,I conclude with conversation was superficially appropriate.she seemed several issues that in my view warrant further unconcered about her condition or even about being in the hosp en why sh consideration As a prelude.it should be clear that neglect is When rofe to he .she neous disorder.Its manifestations vary would look at and lift her right arm.Over several days considerably across patients (Chatteriee.1998 after hearing from her physicians that she had had a stroke Halligan Marshall.1992.1998).This hete m if the s oal of PIst【o move er ler ged h arch v to establish nsive the clinical noted that she was pleasant and enga ng for short periods r when d de d the but not particularly motivated during therapy sessionsand e fatigued easily. oral heterogeneity y is actually critica nths after her ns use as eft-sike e.obvious signs attention, on,and sensation on the left.but after about 6 months she also damage to parts of these networks can experienced uncomfortable sensations both on the skin and"inside"her left arm.The patient continued to fatigue
Anjan Chatterjee Unilateral spatial neglect is a fascinating clinical syndrome in which patients are unaware of entire sectors of space on the side opposite to their lesion. These patients may neglect parts of their own body, parts of their environment, and even parts of scenes in their imagination. This clinical syndrome is produced by a lateralized disruption of spatial attention and representation and raises several questions of interest to cognitive neuroscientsts. How do humans represent space? How do humans direct spatial attention? How is attention related to perception? How is attention related to action? Spatial attention and representation can also be studied in humans with functional neuroimaging and with animal lesion and single-cell neurophysiological studies. Despite the unique methods and approaches of these different disciplines, there is considerable convergence in our understanding of how the brain organizes and represents space. In this chapter, I begin by describing the clinical syndrome of neglect. Following this description, I outline the major theoretical approaches and biological correlates of the clinical phenomena. I then turn to prominent issues in recent neglect research and to relevant data from human functional neuroimaging and animal studies. Finally, I conclude with several issues that in my view warrant further consideration. As a prelude, it should be clear that neglect is a heterogeneous disorder. Its manifestations vary considerably across patients (Chatterjee, 1998; Halligan & Marshall, 1992, 1998). This heterogeneity would be cause for alarm if the goal of neglect research were to establish a unified and comprehensive theory of the clinical syndrome. However, when neglect is used to understand the organization of spatial attention and representation, then the behavioral heterogeneity is actually critical to its use as an investigative tool. Distributed neuronal networks clearly mediate spatial attention, representation, and movement. Focal damage to parts of these networks can 1 Neglect: A Disorder of Spatial Attention produce subtle differences in deficits of these complex functions. These differences themselves are of interest. A careful study of spatial attention and representations through the syndrome of neglect is possible precisely because neglect is heterogeneous (Chatterjee, 1998). Case Report Neglect is more common and more severe with right than with left brain damage. I will refer mostly to left-sided neglect following right brain damage, although similar deficits are seen sometimes following left brain damage. A 65-year-old woman presented to the hospital because of left-sided weakness. She was lethargic for 2 days after admission. She tended to lie in bed at an angle, oriented to her right, and ignored the left side of her body. When her left hand was held in front of her eyes, she suggested that the limb belonged to the examiner. As her level of arousal improved, she continued to orient to her right, even when approached and spoken to from her left. She ate only the food on the right side of her hospital tray. Food sometimes collected in the left side of her mouth. Her speech was mildly dysarthric. She answered questions correctly, but in a flat tone. Although her conversation was superficially appropriate, she seemed unconcerned about her condition or even about being in the hospital. When asked why she was hospitalized, she reported feeling weak generally, but denied any specific problems. When referring to her general weakness, she would look at and lift her right arm. Over several days, after hearing from her physicians that she had had a stroke and having repeatedly been asked by her physical therapist to move her left side, she acknowledged her left-sided weakness. However, her insight into the practical restrictions imposed by her weakness was limited. Her therapists noted that she was pleasant and engaging for short periods, but not particularly motivated during therapy sessions and fatigued easily. Three months after her initial stroke, obvious signs of left neglect abated. Her left-sided weakness also improved. She had slightly diminished somatosensory sensation on the left, but after about 6 months she also experienced uncomfortable sensations both on the skin and “inside” her left arm. The patient continued to fatigue
Anjan Chatterjee 2 eshowing esion in the posterior division of the right middle erera artery involving the inferior parietal lobule and the posterior superior temporal gyrus. easily and remained at hon much of the time.Her mg ership lim artery (figure 1.1).Her lesion involved the posterio inferior parietal lobule,Brodmann areas (BA)39 and 40 h over and touch their left sid poerir pat of the uerior a for hemipl gia can also be thought of as a disorder of personal awareness. In this condition.patients are aware Clinical Examination of Neglect of their contralesional limb,but are not aware of its paralysis (Bisiach,1993).Anosognosia for Bedside tests for neglect are designed to asses hemiplegia is not an all-or-none phenomenon,and atients' awareness of the contralesional parts of patients may have partial awareness of their con- their own body (personal ntralesiona tralesional weakness (Chatterjee Mennemeier sectors of space eglect)and cor 1996).Misoplegia is a rare disorder in which tralesional s simulta patients are aware of their own limb,but develop an with competing ipsilesional stimuli(extinction) intense dislike for it (Critchley.1974). Personal Neglect Extrapersonal Neglect Personal neglect refers to neglect of contralesiona Extrapersonal neglect can be assessed using bedside parts wn tasks such as line bisection.cancellation,drawing dy. ents groor ally pro and reading.Line bisection tasks assess a patient's ability to estimate the center of a simple stimulus Patients wh perso left sideo their body migh Patients are asked to place a mark at the midpoint of lines (usually horizontal).The task is generally e a c or m eup,or might not shave the left side of their face(Beschin Robertson, 99 administered without restricting head or eye move- To assess personal neglect,patients are asked about ments and without time limitations.Patients with their left arm after this limb is brought into their left-sided neglect typically place their mark to the
easily and remained at home much of the time. Her magnetic resonance imaging (MRI) scan showed an ischemic stroke in the posterior division of the right middle cerebral artery (figure 1.1). Her lesion involved the posterior inferior parietal lobule, Brodmann areas (BA) 39 and 40 and the posterior part of the superior temporal gyrus, BA 22. Clinical Examination of Neglect Bedside tests for neglect are designed to assess patients’ awareness of the contralesional parts of their own body (personal neglect), contralesional sectors of space (extrapersonal neglect), and contralesional stimuli when presented simultaneously with competing ipsilesional stimuli (extinction). Personal Neglect Personal neglect refers to neglect of contralesional parts of one’s own body. Observing whether patients groom themselves contralesionally provides a rough indication of personal neglect. Patients who ignore the left side of their body might not use a comb or makeup, or might not shave the left side of their face (Beschin & Robertson, 1997). To assess personal neglect, patients are asked about their left arm after this limb is brought into their view. Patients with left personal neglect do not acknowledge ownership of the limb. When asked to touch their left arm with their right hand, these patients fail to reach over and touch their left side (Bisiach, Perani, Vallar, & Berti, 1986). A phenomenon called anosognosia for hemiplegia can also be thought of as a disorder of personal awareness. In this condition, patients are aware of their contralesional limb, but are not aware of its paralysis (Bisiach, 1993). Anosognosia for hemiplegia is not an all-or-none phenomenon, and patients may have partial awareness of their contralesional weakness (Chatterjee & Mennemeier, 1996). Misoplegia is a rare disorder in which patients are aware of their own limb, but develop an intense dislike for it (Critchley, 1974). Extrapersonal Neglect Extrapersonal neglect can be assessed using bedside tasks such as line bisection, cancellation, drawing, and reading. Line bisection tasks assess a patient’s ability to estimate the center of a simple stimulus. Patients are asked to place a mark at the midpoint of lines (usually horizontal). The task is generally administered without restricting head or eye movements and without time limitations. Patients with left-sided neglect typically place their mark to the Anjan Chatterjee 2 Figure 1.1 Contrast-enhanced magnetic resonance image showing lesion in the posterior division of the right middle cerebral artery, involving the inferior parietal lobule and the posterior superior temporal gyrus
Neglect 3 right of the true midposition (Schenkenberg. of arrays in which targets are difficult to discrimi- Bradford,Ajax,1980).Patients make larger nate from distracter stimuli (Rapcsak,Verfaellie. errors with longer lines (Chatterjee.Dajani.& Fleet,Heilman.1989)may increase the sensitiv- Gage 1994a)If stimuli are placed in space con ity of cancellation tasks.Thus,using arrays with a tralateral to their lesion.patients frequently make large number of stimuli (generally more than fifty) larger errors (Heilman Valenstein.1979).Thus and with distracters that are difficult to discrimina using long lines (generally greater than 20cm) from the targets increases the sensitivity of cancel placed to the left of the patic s trunk increases the onal neglect. sensitivity of detecting extrapersonal neglect using In drawing tasks.pa line bisection tasks Cancellation tasks assess how well a patient me ory (fi s 1.3 and 1.4).Wher explores the contralesional side of extrar asked to with multiple objects. e (figure 1.2).Patients are gets which they nted with a ts with cts in the parts, tasks are adm inis ithou left side of individual whe ns and the in the art at the 6 y,pate in a ve left sided 992a. may ven misplace neglect 1973)and ofte ody,s quadra at a target in th 1992 owe to be ading ta asks can be given by having patie nt Ricci 1999 nan, 1997. patient cancel negiect may sided targets repeatedly. Inc sing the number of D inging their gaze to the left margi ne page targets may uncover neglect that is not evident on ng t may arrays with fewer targets(Chatterjee,Mennemeier. lines starting in the middle of the page and prod Heilman.1992b:Chatterjee et al..1999).The use sequences of words or sentences that do not make sense.When reading single words,they may eithe omit left-sided letters or substitute confabulated letters (Chatterjee,1995).Thus the word "walnut might be read as either "nut"or "peanut."This reading disorder is called "neglect dyslexia" (Kinsboure Warrington.1962). Extinction to Double Simultaneous Stimulation Patients who are aware of single left-sided stimuli may neglect or "extinguish"these stimuli when left-sided stimuli are presented simultaneously with right-sided stimuli(Bender Furlow,1945) Figure 1.2 Extinction may occur for visual,auditory,or tactile ample of a cancellation task showing left neglect.Tha stimuli (Heilman.Pandya.Geschwind,1970). Visual extinction can be assessed by asking patients SK Is given wit ut me constraints and without restrict ng eye or hea moven to count fingers or to report finger movements
right of the true midposition (Schenkenberg, Bradford, & Ajax, 1980). Patients make larger errors with longer lines (Chatterjee, Dajani, & Gage, 1994a). If stimuli are placed in space contralateral to their lesion, patients frequently make larger errors (Heilman & Valenstein, 1979). Thus, using long lines (generally greater than 20cm) placed to the left of the patient’s trunk increases the sensitivity of detecting extrapersonal neglect using line bisection tasks. Cancellation tasks assess how well a patient explores the contralesional side of extrapersonal space (figure 1.2). Patients are presented with arrays of targets which they are asked to “cancel.” Cancellation tasks are also administered without restricting head or eye movements and without time limitations. Patients typically start at the top right of the display and often search in a vertical pattern (Chatterjee, Mennemeier, & Heilman, 1992a). They neglect left-sided targets (Albert, 1973) and often targets close to their body, so that a target in the left lower quadrant is most likely to be ignored (Chatterjee, Thompson, & Ricci, 1999; Mark & Heilman, 1997). Sometimes patients cancel rightsided targets repeatedly. Increasing the number of targets may uncover neglect that is not evident on arrays with fewer targets (Chatterjee, Mennemeier, & Heilman, 1992b; Chatterjee et al., 1999). The use of arrays in which targets are difficult to discriminate from distracter stimuli (Rapcsak, Verfaellie, Fleet, & Heilman, 1989) may increase the sensitivity of cancellation tasks. Thus, using arrays with a large number of stimuli (generally more than fifty) and with distracters that are difficult to discriminate from the targets increases the sensitivity of cancellation tasks in detecting extrapersonal neglect. In drawing tasks, patients are asked to either copy drawings presented to them or to draw objects and scenes from memory (figures 1.3 and 1.4). When asked to copy drawings with multiple objects, or complex objects with multiple parts, patients may omit left-sided objects in the array and/or omit the left side of individual objects, regardless of where they appear in the array (Marshall & Halligan, 1993; Seki & Ishiai, 1996). Occasionally, patients may draw left-sided features of target items with less detail or even misplace left-sided details to the right side of their drawings (Halligan, Marshall, & Wade, 1992). Reading tasks can be given by having patients read text or by having them read single words. Patients with left-sided neglect may have trouble bringing their gaze to the left margin of the page when reading text. As a consequence, they may read lines starting in the middle of the page and produce sequences of words or sentences that do not make sense. When reading single words, they may either omit left-sided letters or substitute confabulated letters (Chatterjee, 1995). Thus the word “walnut” might be read as either “nut” or “peanut.” This reading disorder is called “neglect dyslexia” (Kinsbourne & Warrington, 1962). Extinction to Double Simultaneous Stimulation Patients who are aware of single left-sided stimuli may neglect or “extinguish” these stimuli when left-sided stimuli are presented simultaneously with right-sided stimuli (Bender & Furlow, 1945). Extinction may occur for visual, auditory, or tactile stimuli (Heilman, Pandya, & Geschwind, 1970). Visual extinction can be assessed by asking patients to count fingers or to report finger movements Neglect 3 Figure 1.2 Example of a cancellation task showing left neglect. That task is given without time constraints and without restricting eye or head movements
Anjan Chatterjee Figure 1.4 Example of a drawing copied by a patient with left neglect. tion of gaze can modulate extinction (Vaishnavi. Calhoun.Chatteriee.1999). be licldb Extinction may h Thompso s placed in their ha 1998 Figure 1.3 of a spontaneous drawing by a patient with left tion may neglect. ple sional Stacy.1990 presented to both visual fields compared with single visual fields.Auditory extinction can be assessed by asking them to report which ear hears a noise made General Theories of Neglect by snapped fingers or two coins rubbed together at one or both ears.Tactile extinction can be assessed General theories emphasize behaviors common by lightly touching patients either unilaterally or bilaterally and asking them to report where they oduces the were touched.Patients'eyes should be closed when These theories include attentional and tactile extinction is being assessed since their direc- tional theories
presented to both visual fields compared with single visual fields. Auditory extinction can be assessed by asking them to report which ear hears a noise made by snapped fingers or two coins rubbed together at one or both ears. Tactile extinction can be assessed by lightly touching patients either unilaterally or bilaterally and asking them to report where they were touched. Patients’ eyes should be closed when tactile extinction is being assessed since their direction of gaze can modulate extinction (Vaishnavi, Calhoun, & Chatterjee, 1999). Extinction may even be elicited by having patients judge relative weights placed in their hands simultaneously (Chatterjee & Thompson, 1998). Patients with extinction may dramatically underestimate left-sided weights when a weight is also placed on their right hand. Finally, extinction may also be observed with multiple stimuli in ipsilesional space (Feinberg, Haber, & Stacy, 1990; Rapcsak, Watson, & Heilman, 1987). General Theories of Neglect General theories emphasize behaviors common to patients with neglect and try to isolate the core deficit, which produces the clinical syndrome. These theories include attentional and representational theories. Anjan Chatterjee 4 Figure 1.3 Example of a spontaneous drawing by a patient with left neglect. Figure 1.4 Example of a drawing copied by a patient with left neglect
Neglect 5 Attentional Theories weak vector.Therefore,after right brain damage the left hemisphere's unfettered vector of attention Attentional theories are based on the idea that is powerfully oriented to the right.Since the right neglect is a disorder of spatial attention.Spatial hemisphere's intrinsic vector of attention is only attention is the process by which objects in certain weakly directed after left brain damage,there is not a similar orientation bias to the left.Thus,right sided neglect is less common than left-sided volve selection for perception or for actions.The idea that objects in spatial locations are selected for Heilman and co-workers,in contrast to action has ven rise to the notion of"intentional neglect,"in which patients are disinclined to act in tial attention (Heilman or toward contralesional space.(Intentional eg 1979:Heilman Van Den Abell.1980).Patients is discussed more fully later in this cha Attention is gen rally phic slowing than with left br ope Normally. the They also demonst rate nished sses ed with Visual subjects left her visual scene eiagaceod e righ to be cap The oth often oper spa while the acros ent spatial locati afte h nage can produc left.Thus. isphere is i fter Vecera the right and no often have relatively preserved preattentive vision. occur with the same severity as after right brair as evidenced by their ability to separate figure from damage.Mesulam (1981.1990).emphasizing the ground and their susceptibility to visual illusions distributed nature of neural networks dedicated (Driver,Baylis,Rafal,1992:Mattingley,Davis. to spatial attention.also proposed a similar hemi Driver,199/:Ricci,Calhoun, spheric organization for spatial attention 2000:Vallar.Daini.Antonucci.2000) Posner and colleagues proposed an influential In neglect.attention is directed ipsilesionally model of spatial attention composed of elementary and therefore patients are aware of stimuli only in operations.such as engaging.disengaging.and this sector of space.A major concern of general shifting (Posner,Walker,Friedrich,Rafal,1984: attentional theories is to understand why neglect Posner Dehaene.1994).They reported that is more common and severe after right than after patients with right superior parietal damage are left brain damage.Kinsbourne postulates that each selectively impaired in disengaging attention from hemisphere generates a vector of spatial attention right-sided stimuli before they shift and engage directed toward contralateral space,and these left-sided stimuli.This disengage deficit is likely to attentional vectors are inhibited by the opposite account for some symptoms of visual extinction. hemisphere (Kinsbourne,1970.1987).The left In more recent versions of this theory.Posner and hemisphere's vector of spatial attention is strongly colleagues proposed a posterior and an anterion biased,while the right hemisphere produces only a attentional network,which bears considerable
Attentional Theories Attentional theories are based on the idea that neglect is a disorder of spatial attention. Spatial attention is the process by which objects in certain spatial locations are selected for processing over objects in other locations. The processing may involve selection for perception or for actions. The idea that objects in spatial locations are selected for action has given rise to the notion of “intentional neglect,” in which patients are disinclined to act in or toward contralesional space. (Intentional neglect is discussed more fully later in this chapter.) Attention is generally considered effortful and usually operates serially. Normally, the nervous system processes visual information in stages. Visual elements, such as color, movement, and form, are extracted initially from the visual scene. These elements are segregated or grouped together “preattentively,” to parse the visual scene before attention is engaged. Preattentive processing is generally considered automatic and often operates in parallel across different spatial locations. Brain damage can produce selective deficits at this preattentive level with relatively normal spatial attention (Ricci, Vaishnavi, & Chatterjee, 1999; Vecera & Behrmann, 1997). By contrast, patients with neglect often have relatively preserved preattentive vision, as evidenced by their ability to separate figure from ground and their susceptibility to visual illusions (Driver, Baylis, & Rafal, 1992; Mattingley, Davis, & Driver, 1997; Ricci, Calhoun, & Chatterjee, 2000; Vallar, Daini, & Antonucci, 2000). In neglect, attention is directed ipsilesionally, and therefore patients are aware of stimuli only in this sector of space. A major concern of general attentional theories is to understand why neglect is more common and severe after right than after left brain damage. Kinsbourne postulates that each hemisphere generates a vector of spatial attention directed toward contralateral space, and these attentional vectors are inhibited by the opposite hemisphere (Kinsbourne, 1970, 1987). The left hemisphere’s vector of spatial attention is strongly biased, while the right hemisphere produces only a weak vector. Therefore, after right brain damage, the left hemisphere’s unfettered vector of attention is powerfully oriented to the right. Since the right hemisphere’s intrinsic vector of attention is only weakly directed after left brain damage, there is not a similar orientation bias to the left. Thus, rightsided neglect is less common than left-sided neglect. Heilman and co-workers, in contrast to Kinsbourne, propose that the right hemisphere is dominant for arousal and spatial attention (Heilman, 1979; Heilman & Van Den Abell, 1980). Patients with right brain damage have greater electroencephalographic slowing than those with left brain damage. They also demonstrate diminished galvanic skin responses compared with normal control subjects or patients with left hemisphere damage (Heilman, Schwartz, & Watson, 1978). This diminished arousal interacts with hemispheric biases in directing attention. The right hemisphere is thought to be capable of directing attention into both hemispaces, while the left hemisphere directs attention only into contralateral space. Thus, after right brain damage, the left hemisphere is ill equipped to direct attention into left hemispace. However, after left brain damage, the right is capable of directing attention into both hemispaces and neglect does not occur with the same severity as after right brain damage. Mesulam (1981, 1990), emphasizing the distributed nature of neural networks dedicated to spatial attention, also proposed a similar hemispheric organization for spatial attention. Posner and colleagues proposed an influential model of spatial attention composed of elementary operations, such as engaging, disengaging, and shifting (Posner, Walker, Friedrich, & Rafal, 1984; Posner & Dehaene, 1994). They reported that patients with right superior parietal damage are selectively impaired in disengaging attention from right-sided stimuli before they shift and engage left-sided stimuli. This disengage deficit is likely to account for some symptoms of visual extinction. In more recent versions of this theory, Posner and colleagues proposed a posterior and an anterior attentional network, which bears considerable Neglect 5
Anjan Chatterjee 6 resemblance to Heilman's and Mesulam's ideas of neglect of stimuli in extra onal space (Anderso distributed networks.Som parts of this network are ntralateral n entation and others to with neglect also be impaired in entatio (Bisiac ani,1979). Representational Theories iglia,Paolucci,&Pizz Representational theories propose that the inabilit raising the inriguir g possib form adequa mental representa patients'dreams are spatially restricted 19931. ph in the Par 0978ak bs Attentional versus Representational Theories representational theories are often con wo perspe s:looking into the square t ward th trasted with attentional th it is not clear tha attentional and representational theories of neglect square (figure really in conflict (see e the contributions in only reported landmarks to the nght of their imag Halligan Marshall,1994.for related discussions) ined position in the piazza.Neglect for images Sensory-attentional and representational theories evoked from memory may be dissociated from seem to be describing different aspects of the same phenomena.Awareness of external stimuli occurs by mentally reconstructing objects in the world. It is therefore not clear that describing attention directed in exteral space avoids the need to consider mental representations.Similarly,mental representations.even when internally evoked.are selectively generated and maintained.It is not clear how describing spatially selective representation avoids the need to consider spatial attention.Atten- tional theories refer to the process and dynamics that support mental representations.Representa- tional theories refer to the structural features of the disordered system.Each theoretical approach seems inextricably linked to the other. Biological Correlates of Neglect Neglect is seen with a variety of lesions involving different cortical and subcortical structures.It is also associated with dysregulation of specific neuro- transmitter systems. Figure 1.5 Two views of the Piazza del Duomo in Milan.Italy
resemblance to Heilman’s and Mesulam’s ideas of distributed networks. Some parts of this network are preferentially dedicated to selecting stimuli in space for perception and others to selecting stimuli in space on which to act. Representational Theories Representational theories propose that the inability to form adequate contralateral mental representations of space underlies the clinical phenomenology in neglect (Bisiach, 1993). In a classic observation, Bisiach and Luzzatti (1978) asked two patients to imagine the Piazza del Duomo in Milan, Italy, from two perspectives: looking into the square toward the cathedral and looking from the cathedral into the square (figure 1.5). In each condition, the patients only reported landmarks to the right of their imagined position in the piazza. Neglect for images evoked from memory may be dissociated from neglect of stimuli in extrapersonal space (Anderson, 1993; Coslett, 1997). In addition to difficulty in evoking contralateral representations from memory, patients with neglect may also be impaired in forming new contralateral representations (Bisiach, Luzzatti, & Perani, 1979). Rapid eye movements in sleeping neglect patients are restricted ipsilaterally (Doricchi, Guariglia, Paolucci, & Pizzamiglio, 1993), raising the intriguing possibility that these patients’ dreams are spatially restricted. Attentional versus Representational Theories Although representational theories are often contrasted with attentional theories, it is not clear that attentional and representational theories of neglect are really in conflict (see the contributions in Halligan & Marshall, 1994, for related discussions). Sensory-attentional and representational theories seem to be describing different aspects of the same phenomena. Awareness of external stimuli occurs by mentally reconstructing objects in the world. It is therefore not clear that describing attention directed in external space avoids the need to consider mental representations. Similarly, mental representations, even when internally evoked, are selectively generated and maintained. It is not clear how describing spatially selective representation avoids the need to consider spatial attention. Attentional theories refer to the process and dynamics that support mental representations. Representational theories refer to the structural features of the disordered system. Each theoretical approach seems inextricably linked to the other. Biological Correlates of Neglect Neglect is seen with a variety of lesions involving different cortical and subcortical structures. It is also associated with dysregulation of specific neurotransmitter systems. Anjan Chatterjee 6 Figure 1.5 Two views of the Piazza del Duomo in Milan, Italy
Neglect 7 Cortical Lesions of sensory information from the thalamus to the cortex.In turn,descending projections from the Neglect is more common and more severe in cases polymodal association cortices inhibit the nucleus of right than left hemisphere damage (Gainotti. reticularis.Therefore damage to these systems may Messerli Tissot 1972)The characteristic lesion result in a release of the inhibitory action of the involves the right inferior parietal lobe brodmann nucleus reticularis on thalamic relay nuclei. areas 39 and 40 (Heilman.Watson.Valenstein producing impairment of contralesional sensory bint.a lg nuds loat Valenstein.Heilman.1981 Ferber&Himmelbach.2001)have suggested that are asse orily in the thalamus.which has recipr ciated most co in the absence of visual field defects.Neglect also be olateral efr (Heilman Valenstein,197:HusainKe ices neglect (Hier,Davis 1996:Maeshima Funahashi.Ogu Itak Komai.1994)and cin s (Wa Heilman.Caut en.King.1973).Se Distributed Neural Networks The ion that lesions to disparate areas 1998) and and 0 The area ated with neg distribut med spa nPoknmodal I area into wh ic n,1979 Watson et al ons to th the idea that n anato 08 for poo a spatial d not one i in ontralesional loca ons (Watson et al ory proc sing (such as visual feld defect 1973)or poor motivation (Mesulam.1990)in The polymodal nature of the deficit means that neglect patients neglect may be evident in different sensory and Mesulam (1981.1990).emphasizing the mono- motor systems,without necessarily being restricted synaptic interconnectivity of the different brain to one modality. regions associated with neglect,also proposed a similar model suggesting that different regions Subcortical Lesions within a large-scale network control different aspects of an individual's interaction with the Subcortical lesions in the thalamus,basal ganglia spatial environment.He suggested that dorsolateral and midbrain may also produce neglect.Neglect prefrontal damage produces abnormalities of con- in humans is associated with decreased arousa tralesional exploratory behavior and that posterion (Heilman et al..1978).Interruptions of ascending parietal damage produces the perceptual disorder monoaminergic or cholinergic proiections mav in seen in neglect. part mediate this clinical manifestation (Watson. The appealingly straightforward idea that lesions Heilman,Miller,King.1974). in different locations within this distributed network The extension of the reticular system into the are associated with different behavioral manifesta thalamus is a thin shell of neurons encasing much tions of neglect is not entirely supported by the of the thalamus and is called the"nucleus reticu- evidence (Chatterjee,1998).The most commonly laris."The nucleus reticularis neurons inhibit relays cited association is that parietal lesions produce the
Cortical Lesions Neglect is more common and more severe in cases of right than left hemisphere damage (Gainotti, Messerli, & Tissot, 1972). The characteristic lesion involves the right inferior parietal lobe, Brodmann areas 39 and 40 (Heilman, Watson, & Valenstein, 1994). Recently, Karnath and colleagues (Karnath, Ferber & Himmelbach, 2001) have suggested that lesions to the right superior temporal gyrus are associated most commonly with extrapersonal neglect in the absence of visual field defects. Neglect may also be observed after dorsolateral prefrontal (Heilman & Valenstein, 1972; Husain & Kennard, 1996; Maeshima, Funahashi, Ogura, Itakura, & Komai, 1994) and cingulate gyrus lesions (Watson, Heilman, Cauthen, & King, 1973). Severe neglect is more likely if the posterior-superior longitudinal fasciculus and the inferior-frontal fasciculus are damaged in addition to these cortical areas (Leibovitch et al., 1998). The cortical areas associated with neglect are supramodal or polymodal areas into which unimodal association cortices project (Mesulam, 1981). This observation underscores the idea that neglect is a spatial disorder, not one of primary sensory processing (such as a visual field defect). The polymodal nature of the deficit means that neglect may be evident in different sensory and motor systems, without necessarily being restricted to one modality. Subcortical Lesions Subcortical lesions in the thalamus, basal ganglia, and midbrain may also produce neglect. Neglect in humans is associated with decreased arousal (Heilman et al., 1978). Interruptions of ascending monoaminergic or cholinergic projections may in part mediate this clinical manifestation (Watson, Heilman, Miller, & King, 1974). The extension of the reticular system into the thalamus is a thin shell of neurons encasing much of the thalamus and is called the “nucleus reticularis.” The nucleus reticularis neurons inhibit relays of sensory information from the thalamus to the cortex. In turn, descending projections from the polymodal association cortices inhibit the nucleus reticularis. Therefore damage to these systems may result in a release of the inhibitory action of the nucleus reticularis on thalamic relay nuclei, producing impairment of contralesional sensory processing (Watson, Valenstein, & Heilman, 1981). Damage to the pulvinar, a large nucleus located posteriorily in the thalamus, which has reciprocal connections with the posterior parietal lobule, may result in neglect. Lesions of the basal ganglia, which are tightly linked to prefrontal and cingulate cortices, may also produce neglect (Hier, Davis, Richardson, & Mohr, 1977). Distributed Neural Networks The clinical observation that lesions to disparate cortical and subcortical structures produce neglect led Heilman and co-workers to propose that a distributed network mediates spatially directed attention (Heilman, 1979; Watson et al., 1981). The limbic connections to the anterior cingulate may provide an anatomical basis for poor alertness for stimuli in contralesional locations (Watson et al., 1973) or poor motivation (Mesulam, 1990) in neglect patients. Mesulam (1981, 1990), emphasizing the monosynaptic interconnectivity of the different brain regions associated with neglect, also proposed a similar model suggesting that different regions within a large-scale network control different aspects of an individual’s interaction with the spatial environment. He suggested that dorsolateral prefrontal damage produces abnormalities of contralesional exploratory behavior and that posterior parietal damage produces the perceptual disorder seen in neglect. The appealingly straightforward idea that lesions in different locations within this distributed network are associated with different behavioral manifestations of neglect is not entirely supported by the evidence (Chatterjee, 1998). The most commonly cited association is that parietal lesions produce the Neglect 7
