Laterally directed arm movements and right unilateral neglect after left hemisphere damage.

Signs of unilateral neglect for events occurring in one hemispace most often result from right hemisphere lesions. Right unilateral neglect after left hemisphere damage is much rarer, and has received less attention. The present study explores the relationships between right unilateral neglect and asymmetries in producing laterally directed arm movements in the horizontal plane in left brain-damaged (LBD) patients. Participants produced right- or left-directed arm movements with their left arm in response to centrally located visual stimuli. Results showed that LBD patients with signs of right unilateral neglect were consistently slowed when producing arm movements toward the right (neglected) side, as compared to left-directed movements. Taking into account patients with and without signs of neglect, this directional asymmetry positively correlated with a reaction-time measure of perceptual spatial bias. These findings stand in contrast with previous results obtained with the same experimental paradigm in right brain-damaged patients, in whom a consistent slowing of leftward-directed movements was rare and apparently unrelated to the presence and severity of left neglect. These conflicting results are discussed with respect to the hypothesis that different mechanisms may underlie left and right unilateral neglect.     

Unilateral spatial neglect in Alzheimer's disease A line bisection study

Neuropsychological studies on Alzheimer's disease (AD) have rarely mentioned about unilateral spatial neglect in spite of widespread use of visuospatial tasks. We reported a 62-year-old woman with probable AD who showed moderate dementia with left unilateral spatial neglect and relatively preserved language function. An extensive line bisection study with either hand confirmed her having left unilateral spatial neglect. Single photon emission computed tomography revealed relative hypoperfusion in the right temporal and parietal regions. AD patients with disproportionate right hemisphere dysfunction may exhibit left unilateral spatial neglect if tested adequately in the stage of mild to moderate dementia. We consider that application of the line bisection test to AD patients contributes to estimation of their right hemisphere function.     

Conflict and integration of spatial attention between disconnected hemispheres

OBJECTIVES: To clarify how the disconnected hemispheres perceive a line and bisect it with successful or unsuccessful integration of spatial attention. METHODS: Eye movements were recorded when a patient with an extensive callosa infarction bisected horizontal lines. The lesion extended into the left cingulate gyrus. RESULTS: When the patient bisected lines with the right hand, the gaze was initially directed rightward and shifted further to the right side with the execution of manual response, which resulted in rightward errors. Shortly after bisection, rapid ocular searches occurred to the left side, whereas the rightward errors did not decrease throughout the trials. When using the left hand, there was no deviation of the gaze before presentation of lines. In the first few trials, the patient bisected the line with a leftward error and then searched rapidly to the right side. The subsequent bisections were almost accurate, as the subjective midpoint was placed near the point of the initial fixation that fell around the true centre. Ocular searching was mostly absent during and after line bisection. CONCLUSIONS: In callosa disconnection, left unilateral spatial neglect may appear when use of the right hand induces a rightward bias in the attentional control of the left hemisphere and damage to its cingulate gyrus inhibits interhemispheric integration of attention. Resultant rightward errors of line bisection often cause interhemispheric conflict of attention, as the right hemisphere perceives the longer extent on the left side. By contrast, the disconnected but intact right hemisphere may bisect a line accurately by integrating attention to the extents perceived in the left and right visual fields.     

Unilateral spatial neglect in AD: significance of line bisection performance

BACKGROUND: Unilateral spatial neglect has been rarely reported in patients with AD, although they often have right and left asymmetry of temporoparietal dysfunction. OBJECTIVE: To investigate if patients with AD would show unilateral spatial neglect in the line bisection test, and to reveal the relationship between their neglect and the area of cerebral dysfunction. Method: Thirty-two patients with mild to moderate AD and 32 age-matched healthy control subjects underwent an extensive line bisection test. SPECT was also obtained for the patients. RESULTS: Rightward bisection errors exceeded the normal range in 25% of patients with AD. They exhibited greater rightward errors for the longer lines in the left hemispace than in the right hemispace, and with the right hand than with the left hand; this corresponds to the characteristics of neglect seen after right hemisphere lesions. All patients who bisected 200 mm lines with errors over 10 mm showed disproportionate lowering of performance IQ and asymmetric right hemisphere hypoperfusion, especially in the temporoparietal region. Seventy-five percent of the patients performed normally in the center presentation but erred slightly toward the body midline in the right and left hemispaces. CONCLUSION: Left unilateral spatial neglect in mild to moderate AD may be rather common if tested with the line bisection test. Rightward errors over 10 mm suggest right temporoparietal dysfunction. In AD, three or more bisections of 200 mm lines in the center presentation are recommended for detection of neglect. Patients with AD but without neglect may have difficulty in shifting attention into the peripheral sector of the egocentric space.     

A cortical network for directed attention and unilateral neglect

Unilateral neglect reflects a disturbance in the spatial distribution of directed attention. A review of unilateral neglect syndromes in monkeys and humans suggests that four cerebral regions provide an integrated network for the modulation of directed attention within extrapersonal space. Each component region has a unique functional role that reflects its profile of anatomical connectivity, and each gives rise to a different clinical type of unilateral neglect when damaged. A posterior parietal component provides an internal sensory map and perhaps also a mechanism for modifying the extent of synaptic space devoted to specific portions of the external world; a limbic component in the cingulate gyrus regulates the spatial distribution of motivational valence; a frontal component coordinates the motor programs for exploration, scanning, reaching, and fixating; and a reticular component provides the underlying level of arousal and vigilance. This hypothetical network requires at least three complementary and interacting representations of extrapersonal space: a sensory representation in posterior parietal cortex, a schema for distributing exploratory movements in frontal cortex, and a motivational map in the cingulate cortex. Lesions in only one component of this network yield partial unilateral neglect syndromes, while those that encompass all the components result in profound deficits that transcend the mass effect of the larger lesion. This network approach to the localization of complex functions offers an alternative to more extreme approaches, some of which stress an exclusive concentration of function within individual centers in the brain and others which advocate a more uniform (equipotential or holistic) distribution. In human beings, unilateral neglect syndromes are more frequent and severe after lesions in the right hemisphere. Also, right hemisphere mechanisms appear more effective in the execution of attentional tasks. Furthermore, the attentional functions of the right hemisphere span both hemispaces, while the left hemisphere seems to contain the neural apparatus mostly for contralateral attention. This evidence indicates that the right hemisphere of dextrals has a functional specialization for the distribution of directed attention within extrapersonal space.     

Neuropsychological approach to visual attention]

Visual experience depends critically on visual attention, which selects a particular aspect of a visual display. Recent clinical, neuroimaging, and animal studies revealed that visual attention was divided into active and passive or top-down and bottom-up attention. Although these dichotomies are clear-cut in definition, visual attention could be modulated by many factors. Detailed observation of brain-injured patients provides with evidence for dynamic and fine control of visual attention. We observed patients with dorsal simultanagnosia and that with callosal disconnection syndrome. Patients with dorsal simultanagnosia demonstrated that extent of visual attention was dynamically changed depending on the level of visual processing. Despite the ability to read a kanji character and to describe its components correctly, a patient could not notice a component that he had just written and could not assemble individual components to make up a correct kanji character. He could point to an overlapping area of two figures. But once he started to color the overlapping area, he missed the margin of the area and colored much larger area. Another patient with dorsal simultanagnosia missed borderlines between columns of a newspaper and read letters continuously across columns. In contrast, he could point to lines between figures or meaningless patterns easily. These findings indicated that visual attention was directed automatically to meaningful characters. A patients with callosal disconnection syndrome demonstrated left unilateral spatial neglect only when he used his right hand to draw figures. Right hand movement, controlled by the left hemisphere, elicited visual attention to the right hemispace, resulting in the left unilateral spatial neglect. Thus visual attention is not simply top-down or bottom up, but is implicitly affected by the visual recognition as well as motor component of the task.     

Left hemispatial neglect with a splenial lesion

ABSTRACT

With injury of the anterior two-thirds of the corpus callosum, each hemisphere’s attentional bias to contralateral hemispace becomes manifest with each hand deviating ipsilaterally during line bisection tasks. Patients with infarctions in the right posterior cerebral artery distribution with occipital and splenial damage can also exhibit spatial neglect. The goal of this report is to learn the role of the splenium of the corpus callosum in mediating visuospatial attention. A right-handed woman with Marchiafava-Bignami disease and damage to the splenium of her corpus callosum without evidence of a mesial frontal, parietal, or occipital injury was assessed for spatial neglect with line bisections. When bisecting lines in her left hemispace with her right hand, she deviated to the right, but revealed no major deviations when the line was place in the midline, in right hemispace, or when bisecting lines with her left hand. This patient provides evidence that damage to the splenium can induce a special form of asymmetrical spatial neglect. This asymmetry might be related to the disconnected right hemisphere’s ability to allocate attention to both right and left hemispaces with the disconnected left hemisphere’s ability to allocate attention to the right but not left hemispace.     

Visual attentional disturbance with unilateral lesions in the basal ganglia and deep white matter.

To elucidate the role of the basal ganglia and deep white matter in the visual attention mechanism, a new visual attention task was carried out by 15 patients, 9 with left-side and 6 with right-side basal ganglia and/or deep white matter damage without visual field defects, and by 12 normal subjects. Their reaction times were recorded in response to a random visual stimulation by pushing a button with the hand ipsilateral to the side of the lesion. All the patients with damage to the right side of the brain had a longer reaction time in the left space than in the right or middle space. With conventional test, only one of them showed left unilateral spatial neglect. Seven of the 9 patients with a left lesion had a significantly longer reaction time in the right space than in the left. None had unilateral spatial neglect. Both the right and left brain-damaged groups showed longer reaction times in both spaces, compared to the normal groups. There was no significant difference in reaction time among the control subjects. These findings suggest that the basal ganglia and deep white matter in each hemisphere play some role in directing visual attentional factors into both spaces. Visual attentional disturbance was highly evident even with left-side brain damage, and this kind of disturbance is not usually revealed with the current tasks used for testing unilateral spatial neglect.     

The nature of unilateral neglect in the olfactory sensory system

This study investigated two major theories of unilateral neglect utilizing the ipsilaterally innervated olfactory sense. The sensory theory states that unilateral neglect is due to a diminished or attenuated sensory input. The representational theory states that unilateral neglect is due to a disordered internal representation, which is not dependent on sensory input. Results of the study revealed that right hemisphere lesion patients with left unilateral neglect failed to respond to their left contralateral nostril on olfactory double simultaneous stimulation, consistent with the representational theory because the left nostril has no direct sensory input to the right hemisphere.     

Reading direction and spatial neglect

Many American and European investigators have reported that hemispatial neglect is more frequent and more severe after right than left hemisphere lesions. This hemispheric asymmetry may be due to biological asymmetries, learned behavior, or both. Readers of European languages, unlike readers of Semitic languages, scan from left to right. Learned rightward scanning may increase the unilateral neglect associated with right hemisphere lesions and reduce the severity of neglect associated with left hemisphere lesions. To learn if hemispheric asymmetries of neglect are influenced by learned scanning behavior, we used line bisection and cancellation tasks to study patients with unilateral stroke who read only a Semitic or European language before the age of fifteen. We found that independent of reading direction, unilateral neglect was more commonly associated with right than left hemisphere lesions. After right hemisphere damage right to left readers bisected lines closer to center than left to right readers, but on the cancellation test readers of European languages did not perform differently than readers of Semitic languages. These findings suggest that whereas learned scan direction may influence the severity of neglect when measured by line bisection, these learned directional scans cannot fully account for the observed hemisphere asymmetries of neglect. They also suggest that the line bisection test is more influenced by the direction of scanning than is the cancellation test.     

Dissociated neglect behavior following sequential strokes in the right hemisphere

A 42-year-old woman suffered two focal right hemisphere strokes, sequentially damaging different components of a proposed cerebral network for the spatial distribution of attention. Her first stroke was centered in the right frontal lobe and resulted in left hemi-spatial neglect but only for tasks that emphasize exploratory-motor components of directed attention. A second stroke occurred 20 days later in the parietal lobe and led to the emergence of perceptual-sensory aspects of neglect. This case strongly supports the existence of a distributed anatomic-functional network subserving directed attention.     

Horizontal visual motion modulates focal attention in left unilateral spatial neglect.

Patients with unilateral spatial neglect are impaired in directing focal attention toward the contralesional side of space. Provision of static spatial cues on the neglected side has previously been shown to help overcome this deficit. Common movement of visual stimuli may also guide the allocation of spatial attention, although such effects have not been examined in patients with unilateral spatial neglect. Eleven patients with right hemisphere damage and clinical evidence of left unilateral spatial neglect, and 11 matched, healthy controls were tested on a task of horizontal line bisection. Lines were presented on a computer display, with a neutral, static, or slowly drifting, random dot background. Under conditions of motion, background stimuli drifted either leftward or rightward, across the full width of the display, at speeds that did not elicit optokinetic nystagmus or perceptual aftereffects. Controls were accurate in all conditions, and showed minimal effects of background conditions. By contrast, patients with left unilateral spatial neglect were sensitive to leftward background motion, showing a significant leftward shift in bisection error, relative to neutral, static, and rightward moving backgrounds. There was no significant effect of rightward motion in comparison with the neutral and static conditions. The extent to which patients were susceptible to the effects of background motion was not related to severity of unilateral spatial neglect, as measured by clinical tests. The benefits of leftward motion may reflect activity of preserved motion processing mechanisms, which provide input to an otherwise dysfunctional attentional network. The use of visual motion to assist in contralesionally guiding focal attention may be useful in the rehabilitation of unilateral spatial neglect.     

Callosal neglect

BACKGROUND: According to the interhemispheric inhibition model of neglect, the uninjured hemisphere inhibits (via the corpus callosum) the injured hemisphere but the injured hemisphere can no longer inhibit the opposite hemisphere, which becomes hyperactive and produces an ipsilesional attentional bias. Alternatively, according to the compensation hypothesis, the uninjured hemisphere helps compensate for the damaged hemisphere, which is impaired in directing attention to contralateral stimuli. If the inhibition model of neglect is correct, callosal disconnection should reduce neglect. If the compensation model is correct, however, it may increase or induce neglect. PATIENT: A 32-year-old woman, at age 14 years, developed a right frontal astrocytoma and was treated with surgery and radiation but had a cardiopulmonary arrest secondary to aspiration. Subsequent imaging studies revealed damage to the frontal, parietal, and occipital regions of the right hemisphere and damage to the temporal region of the left hemisphere. After discharge, she was able to return to school and drive a car, without any evidence of neglect. About 10 years later, she developed complex partial and atonic seizures that were multifocal and medically intractable. She underwent a complete section of her corpus callosum at age 31 years. RESULTS: One year after the callosal section, she demonstrated (1) diminished spontaneous saccades to the left, hypometric leftward saccades, and left gaze impersistence; (2) left arm hemispatial limb akinesia; (3) unilateral spatial neglect; and (4) motor and cognitive impersistence. CONCLUSION: In patients with right hemisphere injury, callosal section may induce or enhance motor-intentional deficits and hemispatial neglect.     

Crossover is not a consequence of neglect: a test of the orientation/estimation hypothesis.

Most patients with neglect demonstrate a crossover effect on line bisection. Crossover refers to a pattern of performance in which long lines (>10 cm) are bisected ipsilateral to brain injury and short lines (<2 cm) are bisected contralateral to brain injury. Crossover bisections on short lines are of interest because they are not predicted by contemporary theories concerning neglect. However, we propose that the effect depends on two independent factors that normally influence bisection performance but are merely exaggerated in neglect--a tendency to overestimate the length of short lines and underestimate long lines and a tendency to orient attention preferentially in one spatial direction. We predicted that both patients with unilateral left and right hemisphere injury would demonstrate crossover on line bisection and that they would overestimate short lines and underestimate long lines upon direct visual inspection. Further, the 2 groups were predicted to demonstrate crossover in opposite directions owing to different lesion-induced biases in attentional orientation. Testing 5 patients with right hemisphere injury and 7 patients with left hemisphere injury confirmed each prediction. Additionally, errors in length estimation were exaggerated among patients with right hemisphere injury, most of whom had neglect. It is concluded that while crossover is accentuated in cases of neglect, it is not a consequence of neglect per se. As such, crossover bisections are not at odds with contemporary neglect theory.     

Neglect severity after left and right brain damage

While unilateral spatial neglect after left brain damage is undoubtedly less common than spatial neglect after a right hemisphere lesion, it is also assumed to be less severe. Here we directly test this latter hypothesis using a continuous measure of neglect severity: the so-called Center of Cancellation (CoC). Rorden and Karnath (2010) recently validated this index for right brain damaged neglect patients. A first aim of the present study was to evaluate this new measure for spatial neglect after left brain damage. In a group of 48 left-sided stroke patients with and without neglect, a score greater than -0.086 on the Bells Test and greater than -0.024 on the Letter Cancellation Task turned out to indicate neglect behavior for acute left brain damaged patients. A second aim was to directly compare the severity of spatial neglect after left versus right brain injury by using the new CoC measure. While neglect is less frequent following left than right hemisphere injury, we found that when this symptom occurs it is of similar severity in acute left brain injury as in patients after acute right brain injury.     

From competition to cooperation: Visual neglect across the hemispheres

Visuospatial neglect is a frequent and disabling consequence of injuries to the right hemisphere. Patients with neglect show signs of impaired attention for left-sided events, which depends on dysfunction of fronto-parietal networks. After unilateral injury, such as stroke, these networks and their contralateral homologs can reorganize following multiple potential trajectories, which can be either adaptive or maladaptive. This article presents possible factors influencing the profile of evolution of neglect towards recovery or chronicity, and highlights potential mechanisms that may constrain these processes in time and space. The integrity of white matter pathways within and between the hemisphere appears to pose crucial connectivity constraints for compensatory brain plasticity from remote brain regions. Specifically, the availability of a sufficient degree of inter-hemispheric connectivity might be critical to shift the role of the undamaged left hemisphere in spatial neglect, from exerting maladaptive effects, to promoting compensatory activity.     

Clock Drawing in Children With Perinatal Stroke

BackgroundChildren with perinatal stroke may show evidence of contralateral spatial neglect. The goal of this study was to determine whether the Clock Drawing Test commonly used in adults to identify neglect would be effective in detecting neglect in children with perinatal stroke.MethodsThirty-eight individuals (age range 6-21 years) with left hemisphere or right hemisphere perinatal onset unilateral lesions and 179 age-matched controls were given a free-drawn Clock Drawing Test in a cross-sectional design. An adapted scoring system that evaluated right- and left-sided errors separately was developed as part of the investigation.ResultsChildren with right hemisphere lesions made a greater number of errors on both the right and left sides of the clock drawings in all age subgroups (6-8 years, 9-14 years, and 15-21 years) compared with controls. Children with right hemisphere lesions showed greater left and right errors in the younger groups compared with controls, with significantly poorer performance on the left at 6-8 years, suggestive of contralateral neglect. However, by ages 15-21 years, the right hemisphere lesion subjects no longer differed from controls.ConclusionsClock drawing can identify spatial neglect in children with early hemispheric damage. However, brain development is a dynamic process, and as children age, spatial neglect may no longer be evident. These findings demonstrate the limitations of predicting long-term outcome after perinatal stroke from early neurocognitive data. Children with perinatal stroke may require different neural pathways to accomplish specific skills or to overcome deficits, but ultimately they may have “typical” outcomes.     

Auditory sustained attention is a marker of unilateral spatial neglect

The relationships between performance on a non-spatially-lateralized measure of sustained attention and spatial bias on tests sensitive to unilateral neglect were considered in a group of 44 patients with right hemisphere lesions following stroke. As predicted from earlier studies showing a strong association between unilateral spatial neglect and sustained attention, performance on a brief and monotonous tone-counting measure formed a significant predictor of spatial bias across a variety of measures of unilateral visual neglect. This study provides further evidence for a very close link between two attentional systems hitherto regarded as being quite separate, namely a spatial attention system implicated in unilateral neglect and a sustained attention system. A close connection between these two systems was predicted by Posner, who argued that the right hemisphere-dominant sustained attention system provides a strong modulatory influence on the functioning of the lateralized posterior attention system.     

Topography of somatosensory processing: cerebral lateralization and focused attention.

Healthy dextrals underwent fMRI during a task of graphesthesia requiring detection of any number written consecutively from an otherwise random number sequence. Test conditions included (1) focus on unilateral right hand stimuli, (2) focus on unilateral left hand stimuli, (3) focus on right hand only during bilateral hand stimulation, (4) focus on left hand only during bilateral hand stimulation, and (5) rest. Attention to unilateral hand stimulation produced bihemispheric activation with minimal or no activation of ipsilateral primary sensorimotor region. Attention to unilateral left hand stimuli resulted in more activation than attention to unilateral right hand stimuli. Stimulation of the nonattended hand activated the contralateral somatosensory area, but to a lesser spatial extent than attended stimuli. Comparing focused attention to the left versus right side during identical sensory inputs (i.e., bilateral hand stimulation), focused attention to the right hand increased activation in the left somatosensory region, but focused attention to the left hand increased activation in both cerebral hemispheres. Thus, focused attention to unilateral somatosensory stimuli produces bilateral cerebral activation, but the increase in blood flow is greater in the contralateral hemisphere. Unattended stimuli activate the contralateral primary somatosensory area. Left/right asymmetries were demonstrated consistent with cerebral lateralization.     

Right hemispatial ipsilesional neglect with chronic right hemisphere strokes

Background: Patients who present with spatial neglect after stroke often perform normally on tests for neglect after a few weeks. Whereas tests for neglect are often performed directly in front of a patient, in their actual environments many important stimuli may be present within their left or right hemispace. The presence and severity of neglect often depends on the hemisphere injured. It is possible, in chronic stroke, for spatial judgments to be influenced by an interaction of stroke laterality and the spatial location of stimuli. The objective of this study was to learn if unilateral hemispheric chronic strokes contribute to a spatial bias with laterally presented stimuli.

Method: There were 70 participants, 62 with unilateral chronic strokes (>6 months post onset) including 35 with left hemisphere damage (LHD), 27 with right hemisphere damage (RHD), and 8 demographically similar people without history of stroke. Participants were asked to bisect 300 lines presented with distractors on the left, right, or both sides of the line, or no distractor, on a touch-screen monitor in right, center or left hemispace.

Results: There was a significant interaction between the side of the hemispheric lesion and the side of the body where these lines were presented. Specifically, in right space, patients with RHD deviated leftward in comparison to the other groups. Furthermore, there was an interaction between group and distractor induced bias. All three groups approached the left distractor, and the patients with LHD also approached the right distractor.

Conclusions: Although spatial neglect is more severe in contralesional than ipsilesional hemispace in the period immediately following a stroke, over time patients with RHD may develop ipsilesional neglect that is more severe in ipsilesional than contralesional space. The mechanism underlying this bias is not known and may be related to attempted compensation or the development of a contralateral attentional/intentional grasp.