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