Visual neglect for far and near extra-personal space in humans

Spatial Neglect Subtypes, Definitions and Assessment Tools: A Scoping Review

Objective: The objective of this scoping review was to capture the reported definitions for the subtypes of neglect post stroke and map the range of assessment tools employed for each neglect subtype.

Methods: EMBASE, Emcare, Medline, and psychINFO were searched from database inception. Searching included all allied terms and mesh headings for stroke, spatial neglect, measurement, screening tools, psychometric properties. Two reviewers independently screened studies for inclusion. Primary studies with documented protocols of a spatial neglect tool for adults post stroke, with some aspect of validity or reliability were included. Two reviewers independently reviewed the documented protocols of each tool to determine the underlying subtypes and disagreements were resolved through discussion.

Results: There were 371 articles included with 292 tools used for the screening or diagnosis of neglect. The majority of studies (67%) included a tool that did not specify the neglect subtype being assessed, therefore an analysis of the underlying subtypes for each tool is presented.

Conclusions: There is no consistency with the terms used to refer to the syndrome of spatial neglect with over 200 different terms used within the included studies to refer to the syndrome as a whole or one of its subtypes. It is essential to unify the terminology and definition for each neglect subtype. There are hundreds of neglect tools available, however many are not able to differentiate presenting subtypes. It is important for clinicians and researchers to critically evaluate the neglect tools being used for the screening and diagnosis of neglect.

Attention upturned: Bias toward and away from the affected side of the body and near space in a case of complex regional pain syndrome

People with Complex Regional Pain Syndrome (CRPS) following limb injury can show neuropsychological symptoms in the absence of observable brain pathologies. These can include sensory changes, distorted body representation, and inattention to their affected limb and its surrounding space, resembling post-stroke hemispatial neglect. The precise nature and mechanisms of these neuropsychological symptoms are unclear, however insights could be gained by testing for dissociations and associations that have been observed in stroke patients. Drawing from clinical and experimental methods for investigating spatial attention bias and related symptoms in stroke patients, we conducted a detailed investigation of neuropsychological symptoms in a woman with CRPS of her left arm who initially presented to us with pronounced inattention to her affected side. The patient showed visual and tactile neglect and extinction on her affected side on confrontation tests, but no attention deficits on "bedside" tests of neglect. On sensitive computer-based measures, attention biases were found in the patient's body and near space (in Temporal Order Judgements), but not far or imagined space (on the Greyscales task and Mental Number Line Bisection). Unique to the current literature, the patient showed a reversal in her Temporal Order Judgement bias across time, from inattention (first and second session) to hyperattention (third session) to her affected side. In contrast, pain and self-reported body representation distortion were similar across the three sessions. The patient had reduced central and peripheral visual acuity, however these deficits were near symmetrical and therefore could not explain her performance on the visual attention tasks. Given that spatial attention bias has been linked to imbalance in relative activation of the two cerebral hemispheres, we administered a Global-Local processing task to test for hemispheric asymmetry. This revealed no difference in global compared to local interference refuting any hemispheric imbalance. Instead, the patient showed impaired performance (compared to controls) on incongruent trials regardless of trial type, consistent with executive impairment. We conclude that spatial attention bias in CRPS can generalize across different sensory modalities and extend beyond the affected limb to the external space around it, independent of any low-level sensory disturbances. This bias is not necessarily directed away from the affected side or stable over time. People with CRPS can also demonstrate more generalized neuropsychological changes in sensory and executive functions. Our observations refute several existing theories about the mechanisms of attention bias in CRPS, and their relationship to pain, and have potential implications for treatment.

The downsized hand in personal neglect

Introduction: Personal neglect (PN) refers to a form of hemi-inattention toward the contralesional body space and it usually occurs following a right brain lesion. Recent studies suggest that PN indicates a disorder of body representation. Specifically, patients with PN show difficulties in identifying differences between left and right hands and have an altered visuospatial body map, which is associated with disrupted mental body representations. However, the metric representation of the body, and in particular the hands, has not been systematically addressed in patients showing this form of neglect. Method: In the present study, we have investigated this representation by testing the perceived hands' width of 11 hemiplegic patients with right hemisphere cerebral lesions (5 with PN) and 12 healthy controls on a judgment of passability task. Patients and controls were asked to imagine inserting their hand (left and right) through a series of vertical apertures of different sizes and to judge whether their hand could fit through. Due to the heterogeneity of the data, both parametric and non-parametric approaches were used. Furthermore, additional single-case analyses were conducted. Results: Study findings showed that patients with PN showed a significant underestimation of the left hand compared with their right hand. In contrast, whilst the right hand was equally distorted in both patients' groups, the hemiplegic patients with no evidence of PN tended to perceive the affected hand as larger than their ipsilesional one. Conclusions: In line with the literature, our findings confirm an underlying distorted body representation following right brain damage. However, for the first time, we report both a quantitative and qualitative difference in impact of hemiplegia and PN on body representation of the contralesional body space.

The 'Neglected' Personal Neglect

A review of patients with brain injury showing personal neglect is presented. The aim is to shed light on this aspect of neglect often unresearched or only indirectly investigated, and to discuss recent findings concerning the methods used to assess personal neglect, its neural correlates and its association with the more often explored aspect of extrapersonal neglect. The review was performed using PubMed and PsychInfo databases to search for papers published in the last 123 years (until January 2018). We reviewed 81 papers describing either single or group studies for a total of 2247 patients. The results of this review showed that various aspects of personal neglect are still controversial and outcomes potentially contradictory. Despite the data reported in the present review suggest that personal neglect is more frequently associated with lesions of the right hemisphere, the left hemisphere may also play an important role. Not surprisingly, personal neglect and extrapersonal neglect seem to co-occur. However double dissociations of these two forms of neglect have been reported, and they seem to dissociate both from a functional and an anatomical perspective. More recent interpretations of personal neglect suggest that it may result from a disrupted body representation. The development of reliable psychometric tools with shared diagnostic criteria is essential to identify different degrees of personal neglect for different body parts and to better refine personal neglect in comparison to extrapersonal neglect and disorders related to distortions of personal domain.

Assessment of Unilateral Spatial Neglect Using a Free Mobile Application for Italian Clinicians

Background: Unilateral Spatial Neglect (USN) is traditionally assessed with paper-and-pencil tests or computer-based tests. Thanks to the wide-spreading of mobile devices, and the extensive capabilities that they have in dealing complex elements, it is possible to provide clinicians with tools for cognitive assessment. Contemporary 3D engine is, in general generally, able to deploy complex 3D environments for iOS, Android and Windows mobile, i.e., most of the mobile phone and tablet operative systems. Results: This brand-new scenario and pressing requests from professionals, pushed us to build an application for the assessment of USN. Our first attempt was to replicate the classic cognitive tests, traditionally used at this purpose. Ecological assessment is difficult in real scenarios so we implemented virtual environments to assess patients' abilities in realistic situations. At the moment, the application is available only for iPad and iPhone for free, from the Apple Store, under the name of "Neglect App." The App contains traditional tests (e.g., barrage with and without distractors) and ecological tests (e.g., to distribute the tea in a table to close people). Scoring of each test is available to the clinicians through a database with the executed ecological tasks, that are stored locally. Conclusion: In conclusion, Neglect App is an advanced mobile platform for the assessment of Neglect.

Further to the right: Viewing distance modulates attentional asymmetries ('pseudoneglect') during visual exploration

Previous studies showed that the small leftward bias found in healthy humans' spatial judgments of lines ("pseudoneglect") shifts to the right with increasing distance between stimuli and observer. In this study, we investigated whether such a modulation of attentional asymmetry can also be observed in free visual exploration. Participants freely explored photographs of naturalistic scenes for 7 s in near (60 cm) and far (140 cm) space. After an initial leftward bias, followed by a compensatory rightward bias, gaze positions were significantly more leftward in near compared to far space (around 4 s from scene onset). Our results show that the modulation of attentional asymmetries by viewing distance previously reported for spatial judgments generalizes to free visual exploration, and we revealed the temporal dynamics of these asymmetries by fine-grained eye movement analysis. In contrast, an effect of viewing distance was reduced or absent when eye movements are under strong top-down control, as in systematic serial visual search (Sensitive Negelct Test). Finally, there was no effect of viewing distance in the landmark task (as also reported in a minority of other studies), suggesting that this effect may depend on specific, yet unidentified task characteristics.

Dissociating the neural mechanisms of distance and spatial reference frames

This study investigated if the neural mechanisms involved in processing distance (near and far) and frame of reference (egocentric and allocentric) can be dissociated. 36 participants completed a conjunction visual search task using either an egocentric (deciding if the target was to their left or right) or an allocentric (deciding if the target was to the left or right of a reference object) frame. Both tasks were performed in near (57 cm) and far (171 cm) space conditions. Participants were separated into three groups, and each received transcranial magnetic stimulation (TMS) to a different site; right posterior parietal cortex (rPPC), right ventral occipital cortex (rVO), or right frontal eye field (rFEF) in addition to sham TMS. The results show that rFEF is critical in the processing of each search at each distance whereas, contrary to previous detection results, TMS over rVO did not affect performance for any condition. TMS over rPPC revealed that specialised egocentric processing in the parietal cortex does not generalise to far space, providing evidence of a separation of the reference frame/distance conflation in the literature.

To the Other Side of the Neglected Brain

The human brain is characterized by the lateralization of cognitive functions. Multiple lines of evidence suggest the deployment of visuospatial attention is controlled by a frontoparietal network, with a right hemisphere dominance. Among cortical areas included in the network, the right posterior parietal cortex (PPC) has been proposed to be a crucial node and has also been implicated on clinical grounds. Here, the authors provide an overview of the existent literature giving evidence to a functional asymmetry of the parietal cortices in directing visuospatial attention, focusing on those studies seeking to characterize the causal role of PPC, applying transcranial magnetic stimulation and its combination with imaging techniques, such as electroencephalography and fMRI. First, the role of PPC and how this region exerts its control over remote areas of both hemispheres is discussed. The second part discusses studies involving neglect patients shedding light on the complex interplay between left and right PPC, strongly supporting the hemispheric rivalry theory. Finally, studies demonstrating changes of neglect disorders following the manipulation of the unaffected hemisphere activation will be discussed.

Near and far space: Understanding the neural mechanisms of spatial attention

Visuospatial neglect is a multicomponent syndrome, and one dissociation reported is between neglect for near (peripersonal) and far (extrapersonal) space. Owing to patient heterogeneity and extensive lesions, it is difficult to determine the precise neural mechanisms underlying this dissociation using clinical methodology. In this study, transcranial magnetic stimulation was used to examine the involvement of three areas in the undamaged brain, while participants completed a conjunction search task in near and far space. The brain areas investigated were right posterior parietal cortex (rPPC), right frontal eye field (rFEF), and right ventral occipital cortex (rVO), each of which has been implicated in visuospatial processing. The results revealed a double dissociation, whereby rPPC was involved for search in near space only, whilst rVO only became necessary when the task was completed in far space. These data provide clear evidence for a dorsal and ventral dissociation between the processing of near and far space, which is compatible with the functional roles previously attributed to the two streams. For example, the involvement of the dorsal stream in near space reflects its role in vision for action, because it is within this spatial location that actions can be performed. The results also revealed that rFEF is involved in the processing of visual search in both near and far space and may contribute to visuospatial attention and/or the control of eye-movements irrespective of spatial frame. We discuss our results with respect to their clear ramifications for clinical diagnosis and neurorehabilitation.

Mirror writing resulting from an egocentric representation disorder: a case report

Buchwald (1878 ) used the term 'mirror writing' to indicate writing in the reverse direction to what is normal in a particular language and in which the individual letters are also reversed. Cases of healthy individuals (i.e., Leonardo da Vinci and Lewis Carroll) as well as brain-damaged patients have been described in the literature. Here, we report the case of PM, a 70-year-old right-handed woman who showed right hemiplegia and mirror writing following a stroke in the left lenticular nucleus and internal capsulae. PM underwent a complete neuropsychological evaluation, which included copying, dictation and spontaneous writing in both hemispaces with both hands. She was also tested for topographical disorientation, visuo-spatial disorders and body schema deficits. We observed isolated mirror writing only when PM wrote with the left hand, without differences between hemispaces. She also showed a left-right disorientation, a body topological map disorder and an egocentric misrepresentation. The presence of mirror writing not confined to one hemispace and the co-presence of executive function disorders, as well as anosognosia, suggests damage to our patient's sub-cortical frontal network. As no previous interpretation fits with PM's symptoms, we hypothesize that mirror writing resulted from damage to her egocentric frame of reference. This hypothesis allows us to interpret the patient's array of disorders, including mirror writing, body topological map disorder, left-right confusion and egocentric representation.

Spatial neglect: clinical and neuroscience review: a wealth of information on the poverty of spatial attention

Hemispatial neglect (HSN) is a frequent, conspicuous neurobehavioral accompaniment of brain injury. Patients with HSN share several superficial similarities, leading earlier clinical neuroscientists to view neglect as a unitary condition associated with brain structures that mediate relatively discrete spatial cognitive mechanisms. Over the last two decades, research largely deconstructed the neglect syndrome, revealing a remarkable heterogeneity of behaviors and providing insight into multiple component processes, both spatial and nonspatial, that contribute to hemispatial neglect. This review surveys visual HSN, presenting first the means for detection and diagnosis in its manifold variations. We summarize cognitive operations relevant to spatial attention and evidence for their role in neglect behaviors and then briefly consider neural systems that may subserve the component processes. Finally, we propose several methods for rehabilitating HSN, including the challenges facing remediation of such a heterogeneous cognitive disorder.

Pure representational neglect and navigational deficits in a case with preserved visuo-spatial working memory

We describe a patient who, after right hemisphere damage, showed severe, persistent, pure representational neglect but no evidence of perceptual neglect and no deficits in spatial working memory when evaluated with a traditional clinical test (Corsi Block Tapping test). This finding provides evidence against a full explanation of representational neglect within the context of visuo-spatial working memory. Indeed, this patient showed a peculiar deficit in navigational tasks requiring re-orientation in a novel environment by means of his mental representation of the environment. Since no representational neglect was observed in tests requiring mental representation of single or multiple objects (i.e., o'clock test) we suggest that in our patient representational neglect is caused by damage to the cognitive system involved in coding and storing environmental information to be used during navigation.

Crossing the pillars of Hercules: the role of spatial frames of reference in error making

This paper introduces a perspective accounting for errors that may occur as a result of the human interaction with the three-dimensional (3D) space. Particularly, we are interested in errors that are caused by cognitively crossing the boundary between peripersonal and extrapersonal space. Several behavioural, neurophysiological, and neuropsychological perspectives are reviewed in order to develop the theoretical framework on which our ideas are founded. We argue that cognitively crossing the boundary implies switching from one frame of reference to another, which, as a consequence, implies specific costs. The results of five experiments (overall involving 76 participants) support our hypothesis, suggesting the existence of different action-oriented spatial frames of reference.

Visuospatial neglect in near and far space: dissociation between line bisection and letter cancellation

The differential performance on a line bisection and a cancellation task in near and far space was studied. A group of 10 patients with severe left-sided visuospatial neglect and a group of 10 right-brain damaged patients without neglect were examined. The stimuli were presented at a distance of 60 cm (near space) and 160 cm (far space), respectively, and corrected for visual angle. In the line bisection task, patients were asked to point to the estimated line centre with a pencil (near space) or a stick (far space). In the cancellation task, patients pointed to all target stimuli they could detect using either a pencil (near space) or a stick (far space). Most patients with left hemineglect showed a more prominent neglect in far space as compared to near space for the line bisection task, whereas no difference of performance between near and far space was found in the control patients. In contrast, no group showed a distance effect in the cancellation task. The observation that only line bisection is influenced by the distance of the stimulus suggests that line bisection and cancellation are processed differentially. It is proposed that line bisection requires an allocentric reference system focusing attention on objects, whereas cancellation tasks are based on an egocentric reference system responsible for visuospatial attention. Our results indicate that distance changes perception within the allocentric but not within the egocentric system.

Gradients of detection in neglect: comparison of peripersonal and extrapersonal space

Previous studies of target-cancellation performance in visuospatial neglect patients have reported lateral (left-right) and radial (near-far) gradients of attentional ability. The purpose of the present study was to replicate the reported attentional gradients in peripersonal space (within arms reach) and to examine whether lateral gradients of detection also appear in extrapersonal space (beyond arms reach), using equivalent tasks with no manual requirement. The relationship between radial gradients in peripersonal space and neglect severity (degree of lateral gradient) in extrapersonal space was also of interest. Right-hemisphere stroke subjects, with and without neglect, and healthy control subjects named visual targets on scanning sheets placed in peripersonal and extrapersonal space. The neglect group showed lateral gradients of increasing target detection from left to right in both peripersonal and extrapersonal space, which were not evident in the performance of either of the control groups. Double dissociations of neglect severity in peripersonal and extrapersonal space were also found in analyses of individual performance. Lesion analyses showed that peripersonal neglect was related to dorsal stream damage and extrapersonal neglect was related to ventral stream damage. Group analyses showed no significant radial gradients in peripersonal space in the three groups. In addition, while analyses of some individuals found significant near-far and far-near radial gradients, there was no correlation between radial gradients in peripersonal space and neglect severity in extrapersonal space. These results are discussed in terms of theorised hemispheric mechanisms of spatial attention and the relationship of neglect in the two co-ordinate spaces to the extent and location of damaged neurons in the right hemisphere.

Are action and perception in near and far space additive or interactive factors?

Functional imaging has revealed differential neural mechanisms underlying action directed toward near or far space. Because some neuropsychological studies of patients with visuospatial neglect failed to show near/far dissociations with perceptual tasks, we investigated whether action and perception elicit distinct cerebral representations in near and far space. We measured regional cerebral blood flow with positron emission tomography in normal volunteers who performed manual line bisection (action) and made line bisection judgments (perception). Stimuli were presented in near space or far space. Far space presentation enhanced activations in occipital cortex extending into the medial occipitotemporal cortex bilaterally, while near space presentation enhanced left occipital-parietal, parietal, and premotor cortex activity. Manual bisection activated the extrastriate, superior parietal, and premotor cortex bilaterally, while bisection judgments activated the right inferior parietal cortex, anterior cingulate, right dorsolateral prefrontal cortex, and extrastriate and superior temporal cortex bilaterally. The neural mechanisms responsible for the two tasks (perceptual/motor) were not differentially modulated by space of presentation.

Spatial cognition: evidence from visual neglect

Recent work on human attention and representational systems has benefited from a growing interplay between research on normal attention and neuropsychological disorders such as visual neglect. Research over the past 30 years has convincingly shown that, far from being a unitary condition, neglect is a protean disorder whose symptoms can selectively affect different sensory modalities, cognitive processes, spatial domains and coordinate systems. These clinical findings, together with those of functional neuroimaging, have increased knowledge about the anatomical and functional architecture of normal subsystems involved in spatial cognition. We provide a selective overview of how recent investigations of visual neglect are beginning to elucidate the underlying structure of spatial processes and mental representations.

So near yet so far: neglect in far or near space depends on tool use

The study of unilateral spatial neglect has shown that space can be dissociated on a peripersonal versus extrapersonal basis. We report a novel type of dissociation based on tool use in a patient suffering from left neglect. Line bisection was carried out in near and far space, using a stick and a laser pointer. A rightward bias was always found for the former, but not for the latter. Neglect thus appears to be contingent not only on distance, but also on the motor action required by the task.

Coding of Far and Near Space in Neglect Patients

Far (extrapersonal) and near (peripersonal) spaces are behaviorally defined as the space outside arm-reaching distance and the space within arm-reaching distance. Animal and human studies have shown that this behavioral distinction corresponds in the brain to a composite neural architecture for space representation. In this paper we discuss how the activation of the neural correlates of far and near space can be modulated by the use of tools that change the effective spatial relationship between the agent's body and the target object. When subjects reach for a far object with a tool, it is possible to show that far space is remapped as near. We shall also argue that space remapping may not occur when far space is reached by walking instead of using a tool.

Perceptual awareness and its loss in unilateral neglect and extinction

We review recent evidence from studies of patients with unilateral neglect and/or extinction, who suffer from a loss of awareness for stimuli towards the affected side of space. We contrast their deficit with the effects of damage to primary sensory areas, noting that such areas can remain structurally intact in neglect, with lesions typically centred on the right inferior parietal lobe. In keeping with preservation of initial sensory pathways, many recent studies have shown that considerable residual processing can still take place for neglected or extinguished stimuli, yet without reaching the patient's awareness. This ranges from preserved visual grouping processes through to activation of identity, semantics and emotional significance. Similarly to 'preattentive' processing in normals, such residual processing can modulate what will enter the patient's awareness. Recent studies have used measures such as ERPs and fMRI to determine the neural correlates of conscious versus unconscious perception in the patients, which in turn can be related to the anatomy of their lesions. We relate the patient findings to neurophysiological data from areas in the monkey parietal lobe, which indicate that these serve as cross-modal and sensorimotor interfaces highlighting currently relevant locations as targets for intentional action. We speculate on the special role such brain regions may play in perceptual awareness, seeking to explain how damage to a system which appears primarily to code space could eliminate awareness even for non-spatial stimulus properties at affected locations. This may relate to the extreme nature of 'winner-takes-all' functions within the parietal lobe, and their correspondingly strong influence on other brain areas.

Spatial hemineglect in humans

The paper reviews the main findings of studies of hemispatial neglect after acquired brain lesions in people. The behavioral consequences of experimentally induced lesions in animals and electrophysiological studies, which shed light on the nature of the disorder, are briefly considered. Neglect is behaviorally defined as a deficit in processing or responding to sensory stimuli in the contralateral hemispace, a part of the own body, the part of an imagined scene, or may include the failure to act with the contralesional limbs despite intact motor functions. Neglect in humans is frequently encountered after right parieto-temporal lesions and leads to a multicomponent syndrome of sensory, motor and representational deficits. Relevant findings relating to neglect, extinction and unawareness are reviewed and include the following topics: etiological and anatomical basis, recovery; allocentric, egocentric, object-centered and representational neglect; motor neglect and directional hypokinesia; elementary sensorimotor and associated disorders; subdivisions of space and frames of reference; extinction versus neglect; covert processing of information; unawareness of deficits; human and animal models; effects of sensory stimulation and rehabilitation techniques.

Asymmetries of visuospatial attention are modulated by viewing distance and visual field elevation: pseudoneglect in peripersonal and extrapersonal space

Many factors influence the degree of leftward error (pseudoneglect) that typifies the line bisection performance of normal subjects. We find that viewing distance also exerts a modulating influence on spatial attention in normal subjects, as it appears to do in neglect syndrome. Using forced-choice tachistoscopic line bisection, 38 right-handed subjects (15 male, 23 female) bisected horizontal lines (13.7 degrees w x 0.24 degrees h) presented in the midsagittal plane as a function of line elevation (- 3.6 degrees, 0 degrees, and 3.6 degrees relative to horizontal midline) and viewing distance (45 and 90 cm). We find a significant main effect of viewing distance, F (1, 37) = 10.04, p = .003, where pseudoneglect is larger in peripersonal (45 cm) than in extrapersonal (90 cm) space. We replicate an effect of line elevation, F (2, 74) = 4.40, p = .016, where pseudoneglect is greatest in the superior visual field (McCourt and Jewell, 1999). The interaction was not significant, p > .05. Thus, we find evidence for independent spatiotopic (viewing distance) and retinotopic (line elevation) effects on line bisection performance in normal observers, suggesting that the allocation of visuospatial attention is modulated within multiple frameworks.

Space and attention in parietal cortex

The space around us is represented not once but many times in parietal cortex. These multiple representations encode locations and objects of interest in several egocentric reference frames. Stimulus representations are transformed from the coordinates of receptor surfaces, such as the retina or the cochlea, into the coordinates of effectors, such as the eye, head, or hand. The transformation is accomplished by dynamic updating of spatial representations in conjunction with voluntary movements. This direct sensory-to-motor coordinate transformation obviates the need for a single representation of space in environmental coordinates. In addition to representing object locations in motoric coordinates, parietal neurons exhibit strong modulation by attention. Both top-down and bottom-up mechanisms of attention contribute to the enhancement of visual responses. The saliance of a stimulus is the primary factor in determining the neural response to it. Although parietal neurons represent objects in motor coordinates, visual responses are independent of the intention to perform specific motor acts.

Near and far visual space in unilateral neglect

A 24-year-old right-handed woman with a right temporal hematoma showed marked left visual neglect for far but not near space in a variety of tasks systematically given in near and far distance conditions. This case thus provides the dissociation opposite to Halligan and Marshall's patient, who had neglect for near but not far space after a right parietal stroke. Furthermore, although she made rightward errors in bisecting far-distant lines, our patient made smaller opposite leftward errors for near-distant lines. The evidence that unilateral neglect of far and near visual space may exist independently supports a division in the neural systems subserving attention to different compartments of the extrapersonal space in humans.

Right personal neglect following a left hemisphere stroke. A case report

Neglect phenomena may occur in both extrapersonal and personal space. Whereas extrapersonal neglect has been found associated with both right- and left-sided brain lesions, no case of right personal neglect following a left-sided lesion has been so far reported. We describe a right-handed female patient who, after two left-hemisphere strokes, exhibited a florid personal neglect, but no extrapersonal neglect, anosognosia or somatoparaphrenia. The symptom persisted for a few weeks and then gradually disappeared. At least in the early phase of disease, a personal neglect can also be observed in patients with left brain damage.

Domain-specific forms of neglect

In this paper, it is assumed that domain specificity is one of the crucial criteria of modularity. It is also assumed that hemispatial neglect is basically a spatial attention deficit. Then, the literature that has shown, on the basis of either single or double dissociations, that neglect can be confined to very specific representational domains is reviewed. In particular, two recent studies are summarized that reported dissociations between perceptual and motor neglect and between visual and tactile neglect. It is suggested that disorders of spatial attention can affect just one spatial representational domain. This satisfies the domain specificity criterion of modularity and suggests that spatial attention mechanisms may be modular.

Impairments of movement execution in unilateral neglect: a kinematic analysis of directional bradykinesia

A kinematic analysis was performed on goal-directed movements made by 14 patients with right hemisphere damage and left unilateral neglect (seven mild, seven severe), and 14 healthy controls. Leftward and rightward pen strokes of varying extents were made to targets of varying size on a centrally located digitising tablet. While mild unilateral neglect patients performed like controls, patients with severe unilateral neglect were slower to initiate leftward than rightward strokes and were slow and inefficient in movement execution. Leftward strokes made by severe unilateral neglect patients were characterised by prolonged movement time, lower peak velocity and departed from optimal bell-shaped velocity profiles. Their leftward strokes also showed prolonged accelerative phases, implying difficulties in force production, while the high proportion of their total movement time spent in decelerating with rightward strokes suggested an abnormal emphasis on terminal visual guidance. Leftward strokes made by these patients also contained more submovements than rightward strokes, suggesting poor force control. An impaired internal representation of the location of left-sided targets and desired movement trajectories in severe unilateral neglect causes breakdown in the temporal control of goal-directed movements.

Left visuo-spatial neglect can be worse in far than in near space

We tested five patients with marked left-sided visuo-spatial neglect and two control subjects on a test of line bisection. A series of horizontal lines was presented to each subject, who had to indicate the centre with a projection light-pen. All five patients misplaced the centre to the right, in accordance with their left-sided neglect. However, in all five the angular displacement was greater for lines well beyond reach, than for lines of identical angular size within reaching distance. This result, precisely because it is opposite to that of a previous report, supports the conclusion that there are separate dissociated neural systems concerned with the perception of, and response to, stimuli in near and far space.

Comparisons of hemi-inattention produced by unilateral lesions of the posterior parietal cortex or medial agranular prefrontal cortex in rats: neglect, extinction, and the role of stimulus distance

Neglect in human and non-human primates has been demonstrated following unilateral lesions of both posterior parietal and prefrontal areas. While it has now been well established that a unilateral lesion of the rodent analog of dorsolateral prefrontal cortex, medial agranular cortex (AGm), results in neglect, the effects of unilateral damage restricted to rodent posterior parietal cortex (PPC) have not been examined in detail. The current study assessed rats with unilateral lesions of PPC or AGm on their ability to orient to unilateral and bilateral stimulation. Since it has been proposed in both the primate and rodent literatures that frontal areas may be responsible for the perception of near space while parietal areas may be responsible for far space, stimuli were presented at two different distances. Lesions of PPC and AGm resulted in severe neglect relative to control operates, with both PPC and AGm operates manifesting severe hemi-inattention and allesthesia relative to control operates. After behavioral recovery from neglect there was no evidence of extinction to bilateral simultaneous stimulation. While neglect to visual stimuli predominated in unilateral PPC operates, unilateral AGm operates had severe neglect in all modalities. In addition, while both left and right PPC operates showed contralesional neglect, AGm operates demonstrated the lateralized differences in neglect reported in previous studies. All groups demonstrated an approximately equivalent level of neglect to stimuli presented at the two different distances, and thus failed to support the suggestion of a peripersonal-extrapersonal dichotomy between frontal and parietal areas in rodents.

Personal and extrapersonal space: a case of neglect dissociation

Dissociation between personal and extrapersonal neglect has rarely been observed in man. In this study we present a case of severe personal neglect in the absence of a deficit for extrapersonal space. An extensive neuropsychological assessment demonstrates the absence of cognitive impairments in visuo-spatial processing and confirms the selective presence of a severe representational deficit of the left side of the body.

Directional hypokinesia in spatial hemineglect: a case study

A patient with an ischaemic lesion involving the right frontal lobe and basal ganglia showed left spatial hemineglect in visuomotor exploratory tasks, requiring the use of the right unaffected hand. Her performance was, however, entirely preserved, with no evidence of neglect, when she was required to identify targets among distractors in both the left and right halves of space, and in the Wundt-Jastrow illusion test. The latter tasks do not require any arm movement in extrapersonal space. In this patient spatial hemineglect may be explained in terms of defective organisation of movements towards the left half-space (directional hypokinesia). The frontal lesion of the patient may be the neural correlate of this selective disorder. This pattern of impairment may be contrasted with the typical deficit found in patients with right brain damage with perceptual neglect. One case had a defective performance both in visuomotor and in purely perceptual tasks.

Good recovery in visual scanning in a patient with persistent anosognosia

A patient with hemineglect disturbance (N.G.) due to a right hemispheric lesion was admitted to rehabilitative training which featured the use of procedures devised in a previous study (Pizzamiglio et al., 1990) both in a standard way and with the addition of optokinetic stimulation. This latter paradigm produces an automatic reaction which favors the spatial orienting of the patient toward his (left) neglected side. N.G. showed good recovery in visual scanning and, by the end of training, reached a level of recovery similar to other neglect patients. However, his recovery was particularly slow and no change was observed in his attitude toward the visual disturbance. The conclusion is reached that recovery in visual scanning also can be obtained in patients with persistent anosognosic disturbances. Stimulations such as the optokinetic condition which influence patients' behavior at an automatic level may play an important role in this recovery. CBF studies obtained before and after training showed a CBF improvement mainly in the right temporoparietal regions, behind the lesion, and in the left frontal cortex. The implications of these findings on various theoretical interpretations of the hemineglect disturbance are briefly discussed.

The influence of stimulus properties on visual neglect

Twenty five patients with right cerebral hemisphere damage and neglect participated in a series of bisection experiments. As expected, long lines were bisected to the right of true midpoint. By contrast, large circles and long white paper strips were bisected accurately, or with leftward errors. Small objects were less sensitive to stimulus properties: short lines and paper strips, and small circles, were bisected to the left of true midpoint, and these leftward errors were equally common as rightward errors with long lines. When asked to draw a perpendicular line of the same length as the presented horizontal line, patients overestimated the length of short lines but underestimated that of long lines. Presenting lines in near and far extrapersonal space selectively affected bisection of short lines. The results suggest that two opposing, independent mechanisms determine bisection performance in left neglect.

Left neglect for near but not far space in man

It has been suggested that, among the many visual areas of the human brain, there might be one set of spatial maps specialized for 'near' (peripersonal) and another for 'far' (extrapersonal) space. A distinction between 'grasping distance' and 'walking distance', or between a 'reaching field' and a pointing or throwing field has commonly been made. Evidence for such a division has been found in monkeys. Unilateral ablation of the frontal eye field (area 8) produces a more prominent inattention (or 'neglect') for objects in contralesional far space than in near space; by contrast, unilateral ablation of frontal area 6, which receives direct projections from area 7b (the rostral part of the inferior parietal lobules) results in inattention to visual stimuli limited to contralesional near space. Despite predictions that comparable dissociations should be found in man, there has been no convincing evidence. We report here such evidence in a patient with a unilateral right hemisphere stroke. Within peripersonal space, he showed severe left visuo-spatial neglect on conventional tests, including the highly sensitive task of line bisection. When line bisection was performed in extrapersonal space, neglect was abolished or attenuated.