Anatomical and neurological correlates of acute and chronic visuospatial neglect following right hemisphere stroke

The Association of Personal Neglect with Motor, Activities of Daily Living, and Participation Outcomes after Stroke: A Systematic Review

Despite its potential clinical impact, the association of personal neglect (PN) with motor, activities of daily living (ADL), and participation outcomes after stroke is not well-understood. This first-ever systematic review on the topic therefore evaluates this association, taking into account suggested subtypes of PN, including body representation neglect, somatosensory neglect, motor neglect, and premotor neglect. A systematic literature search was conducted on February 17, 2023 in PubMed, Web of Science, Scopus, PubPsych, and PsycArticles databases. The study adheres to the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses, and its protocol was registered on PROSPERO (CRD42020187460). Eleven observational studies were included, gathering 1,400 individuals after stroke (429 showed PN). Results show that individuals with body representation neglect after stroke have significantly decreased movement control and motor strength, lower functional mobility, and ADL independency compared with those without body representation neglect after stroke. Individuals with motor neglect after stroke showed worse motor function and spasticity than to those without motor neglect after stroke. Nonspecified PN (i.e., PN evaluated with an outcome measure that does not allow subcategorization) was related to worse lateropulsion with pushing, longer length of stay and greater odds of being discharged to somewhere other than home. No study evaluated somatosensory and premotor neglect. This review highlights the limited research in this area and emphasizes the need for a more comprehensive PN assessment. However, currently available assessment tools show limited ability to accurately diagnose PN subtypes and future research should prioritize the development of comprehensive diagnostic test batteries.

Brain Substrates for Distinct Spatial Processing Components Contributing to Hemineglect in Humans

Several cortical and sub-cortical regions in the right hemisphere, particularly in parietal and frontal lobe, but also in temporal lobe and thalamus, are part of neural networks critically implicated in spatial and attentional functions. Damage to different sites within these networks can cause hemispatial neglect. The aim of this study was to identify the neural substrates of different spatial processing components that are known to contribute to neglect symptoms. First, three different spatial tasks (visual search, bisection, and visual memory) were tested in 27 patients with focal right brain-damage. Voxel-based lesion-symptom mapping was used to determine the relationships between specific sites of damage and severity of deficits in these three spatial tasks. Secondly, fMRI was used in 26 healthy controls who performed the same tasks. In the healthy group, fMRI results showed a differential activation of regions within the parietal and frontal lobes during bisection and visual search, respectively. In the patients, we confirmed a critical role of right lateral parietal cortex in bisection, but lesions in frontal and temporal lobe were more critical for visual search. These data support the existence of distinct components in spatial attentional processes that might be damaged to different degrees in neglect patients.

Exploratory examination of lexical and neuroanatomic correlates of neglect dyslexia

OBJECTIVE

This study examined lexical and neuroanatomic correlates of reading errors in individuals with spatial neglect, defined as a failure to respond to stimuli in the side of space opposite a brain lesion, causing functional disability.

METHOD

One-hundred and ten participants with left spatial neglect after right-hemisphere stroke read aloud a list of 36 words. Reading errors were scored as "contralesional" (error in the left half of the word) or as "other." The influence of lexical processing on neglect dyslexia was studied with a stepwise regression using word frequency, orthographic neighborhood (number of same length neighbors that differ by 1 letter), bigram and trigram counts (number of words with the same 2- and 3-letter combinations), length, concreteness, and imageability as predictors. MRI/CT images of 92 patients were studied in a voxelwise lesion-symptom analysis (VLSM).

RESULTS

Longer length and more trigram neighbors increased, while higher concreteness reduced, the rate of contralesional errors. VLSM revealed lesions in the inferior temporal sulcus, middle temporal and angular gyri, precuneus, temporal pole, and temporo-parietal white matter associated with the rate of contralesional errors.

CONCLUSIONS

Orthographic competitors may decrease word salience, while semantic concreteness may help constrain the selection of available word options when it is based on degraded information from the left side of the word. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Disruption of the ascending arousal system and cortical attention networks in post-stroke delirium and spatial neglect

Delirium is an acute attention and cognitive dysfunction, adversely affecting functional outcomes and mortality. As many as half of hospitalized right brain stroke survivors may develop delirium. Further, about 50% of right stroke patients experience spatial neglect, impairing safety and recovery. In this review we explore the brain mechanisms, which may explain the high incidence of delirium and spatial neglect after right-brain stroke. We suggest that brain networks for spatial attention and arousal, composed of ascending projections from the midbrain nuclei and integrating dorsal and ventral cortical and limbic components, may underlie impairments in delirium and spatial neglect. We propose that lateralized deficits in spatial neglect may arise because cortical and limbic components of these functional networks are disproportionally impaired by right-brain strokes, and that spatial neglect may lower the threshold for developing delirium. An improved understanding of the brain basis of delirium and spatial neglect could provide a critical biomarker for initiating preventive care in stroke patients at high risk of hospital morbidity and loss of independence.

Differential white matter involvement associated with distinct visuospatial deficits after right hemisphere stroke

Visuospatial attention depends on the integration of multiple processes, and people with right hemisphere lesions after a stroke may exhibit severe or no visuospatial deficits. The anatomy of core components of visuospatial attention is an area of intense interest. Here we examine the relationship between the disruption of core components of attention and lesion distribution in a heterogeneous group (N = 70) of patients with right hemisphere strokes regardless of the presence of clinical neglect. Deficits of lateralized spatial orienting, measured as the difference in reaction times for responding to visual targets in the contralesional or ipsilesional visual field, and deficits in re-orienting attention, as measured by the difference in reaction times for invalidly versus validly cued targets, were measured using a computerized spatial orienting task. Both measures were related through logistic regression and a novel ridge regression method to anatomical damage measured with magnetic resonance imaging. While many regions were common to both deficit maps, a deficit in lateralized spatial orienting was more associated with lesions in the white matter underlying the posterior parietal cortex, and middle and inferior frontal gyri. A deficit in re-orienting of attention toward unattended locations was associated with lesions in the white matter of the posterior parietal cortex, insular cortex and less so with white matter involvement of the anterior frontal lobe. An hodological analysis also supports this partial dissociation between the white matter tracts that are damaged in lateralized spatial biases versus impaired re-orienting. Our results underscore that the integrity of fronto-parietal white matter tracts is crucial for visuospatial attention and that different attention components are mediated by partially distinct neuronal substrates.

Acute Ischemic Lesions Associated with Impairments in Expression and Recognition of Affective Prosody

PURPOSE

We aimed to: (a) review existing data on the neural basis of affective prosody;(b) test the hypothesis that there are double dissociations in impairments of expression and recognition of affective prosody; and (c) identify areas of infarct associated with impaired expression and/or recognition of affective prosody after acute right hemisphere (RH) ischemic stroke.

METHODS

Participants were tested on recognition of emotional prosody in content-neutral sentences. Expression was evaluated by measuring variability in fundamental frequency. Voxel-based symptom mapping was used to identify areas associated with severity of expressive deficits.

RESULTS

We found that 9/23 patients had expressive prosody impairments; 5/9 of these patients also had impaired recognition of affective prosody; 2/9 had selective deficits in expressive prosody; recognition was not tested in 2/9. Another 6/23 patients had selective impairment in recognition of affective prosody. Severity of expressive deficits was associated with lesions in right temporal pole; patients with temporal pole lesions had deficits in expression and recognition.

CONCLUSIONS

Expression and recognition of prosody can be selectively impaired. Damage to right anterior temporal pole is associated with impairment of both, indicating a role of this structure in a mechanism shared by expression and production of affective prosody.

Effects of pro-cholinergic treatment in patients suffering from spatial neglect

Spatial neglect is a neurological condition characterized by a breakdown of spatial cognition contralateral to hemispheric damage. Deficits in spatial attention toward the contralesional side are considered to be central to this syndrome. Brain lesions typically involve right fronto-parietal cortices mediating attentional functions and subcortical connections in underlying white matter. Convergent findings from neuroimaging and behavioral studies in both animals and humans suggest that the cholinergic system might also be critically implicated in selective attention by modulating cortical function via widespread projections from the basal forebrain. Here we asked whether deficits in spatial attention associated with neglect could partly result from a cholinergic deafferentation of cortical areas subserving attentional functions, and whether such disturbances could be alleviated by pro-cholinergic therapy. We examined the effect of a single-dose transdermal nicotine treatment on spatial neglect in 10 stroke patients in a double-blind placebo-controlled protocol, using a standardized battery of neglect tests. Nicotine-induced systematic improvement on cancellation tasks and facilitated orienting to single visual targets, but had no significant effect on other tests. These results support a global effect of nicotine on attention and arousal, but no effect on other spatial mechanisms impaired in neglect.

Long-lasting amelioration of walking trajectory in neglect after prismatic adaptation

In the present study we explored the effect of prismatic adaptation (PA) applied to the upper right limb on the walking trajectory of a neglect patient with more severe neglect in far than in near space. The patient was asked to bisect a line fixed to the floor by walking across it before and after four sessions of PA distributed over a time frame of 67 days. Gait path was analyzed by means of an optoelectronic motion analysis system. The walking trajectory improved following PA and the result was maintained at follow-up, 15 months after treatment. The improvement was greater for the predicted bisection error (estimated on the basis of the trajectory extrapolated from the first walking step) than for the observed bisection error (measured at line bisection). These results show that PA may act on high level spatial representation of gait trajectory rather than on lower level sensory-motor gait components and suggest that PA may have a long-lasting rehabilitative effect on neglect patients showing a deviated walking trajectory.

Mapping the functional neuroanatomy of spatial neglect and human parietal lobe functions: progress and challenges

Spatial neglect is generally defined by various deficits in processing information from one (e.g., left) side of space contralateral to focal (e.g., right) hemisphere damage. Although classically associated with parietal lobe functions, there is now compelling evidence that neglect can follow lesions in many different cortical and subcortical sites, suggesting a dysfunction in distributed brain networks. In addition, neglect is likely to result from a combination of distinct deficits that co-occur due to concomitant damage affecting juxtaposed brain areas and their connections, but the exact nature of core deficits and their neural substrates still remains unclear. The present review describes recent progress in identifying functional components of the neglect syndrome and relating them to distinct subregions of parietal cortex. A comprehensive understanding of spatial neglect will require a more precise definition of cognitive processes implicated in different behavioral manifestations, as well as meticulous mapping of these processes onto specific brain circuits, while taking into account functional changes in activity that may arise in structurally intact areas subsequent to damage in distant portions of the relevant networks.

Time course of visuospatial neglect early after stroke: a longitudinal cohort study

The aim of the current study was to investigate recovery of visuospatial neglect during the first year after stroke. Visuospatial neglect was measured using two frequently and widely used tests: the letter cancellation test (LCT) and the line bisection test (LBT). This was a prospective cohort study of 101 stroke patients. Of these 101 patients, 51 patients showed visuospatial neglect. All time-dependent measures were taken weekly, starting from within 14 days after stroke onset. From week 10-20 biweekly measurements were obtained. Follow-up measurements were performed at weeks 26, 38, and finally 52. For the present study, number of misses in the LCT, split on contralesional versus ipsilesional side, as well as the deviation from the actual midpoint in mm in the LBT were used. The longitudinal relationship of (bi)weekly time on improvement in LBT and LCT were investigated using random coefficient analysis and joinpoint analyses. Results indicated that progress of time is an independent covariate that reflects neurological recovery of visuospatial neglect. Additionally, trend changes were obtained in between 12 and 14 weeks post-stroke with respect to the neglected side. This is the first prospective cohort study in which the time course of neglect is investigated by using intensive serial measurements in the early months post-stroke.

The prognosis of allocentric and egocentric neglect: evidence from clinical scans

We contrasted the neuroanatomical substrates of sub-acute and chronic visuospatial deficits associated with different aspects of unilateral neglect using computed tomography scans acquired as part of routine clinical diagnosis. Voxel-wise statistical analyses were conducted on a group of 160 stroke patients scanned at a sub-acute stage. Lesion-deficit relationships were assessed across the whole brain, separately for grey and white matter. We assessed lesions that were associated with behavioural performance (i) at a sub-acute stage (within 3 months of the stroke) and (ii) at a chronic stage (after 9 months post stroke). Allocentric and egocentric neglect symptoms at the sub-acute stage were associated with lesions to dissociated regions within the frontal lobe, amongst other regions. However the frontal lesions were not associated with neglect at the chronic stage. On the other hand, lesions in the angular gyrus were associated with persistent allocentric neglect. In contrast, lesions within the superior temporal gyrus extending into the supramarginal gyrus, as well as lesions within the basal ganglia and insula, were associated with persistent egocentric neglect. Damage within the temporo-parietal junction was associated with both types of neglect at the sub-acute stage and 9 months later. Furthermore, white matter disconnections resulting from damage along the superior longitudinal fasciculus were associated with both types of neglect and critically related to both sub-acute and chronic deficits. Finally, there was a significant difference in the lesion volume between patients who recovered from neglect and patients with chronic deficits. The findings presented provide evidence that (i) the lesion location and lesion size can be used to successfully predict the outcome of neglect based on clinical CT scans, (ii) lesion location alone can serve as a critical predictor for persistent neglect symptoms, (iii) wide spread lesions are associated with neglect symptoms at the sub-acute stage but only some of these are critical for predicting whether neglect will become a chronic disorder and (iv) the severity of behavioural symptoms can be a useful predictor of recovery in the absence of neuroimaging findings on clinical scans. We discuss the implications for understanding the symptoms of the neglect syndrome, the recovery of function and the use of clinical scans to predict outcome.

Left-deviating prism adaptation in left neglect patient: reflexions on a negative result

Adaptation to right-deviating prisms is a promising intervention for the rehabilitation of patients with left spatial neglect. In order to test the lateral specificity of prism adaptation on left neglect, the present study evaluated the effect of left-deviating prism on straight-ahead pointing movements and on several classical neuropsychological tests in a group of five right brain-damaged patients with left spatial neglect. A group of healthy subjects was also included for comparison purposes. After a single session of exposing simple manual pointing to left-deviating prisms, contrary to healthy controls, none of the patients showed a reliable change of the straight-ahead pointing movement in the dark. No significant modification of attentional paper-and-pencil tasks was either observed immediately or 2 hours after prism adaptation. These results suggest that the therapeutic effect of prism adaptation on left spatial neglect relies on a specific lateralized mechanism. Evidence for a directional effect for prism adaptation both in terms of the side of the visuomanual adaptation and therefore possibly in terms of the side of brain affected by the stimulation is discussed.

Daisy, Daisy, Give Me Your Answer Do! Case Studies of Left Visual Neglect in Patients with Acute Cerebral Lesions

Patients with acute brain lesions often demonstrate dramatic forms of visual neglect; however their unstable medical conditions and rapidly changing neglect make it impossible to carry out rigorous experimentation to test theories of neglect. Careful assessment of their disorders can, however, inform rehabilitation strategies, and stimulate tentative neglect hypotheses that can later be tested more rigourously on the much rarer patients who have persisting neglect. The neglect behaviours of two patients with acute lesions are described in terms of environment-centred and object-based frames of reference. TT, with a right parietal glioma, has difficulty describing unexpected details on the left sides of pictures, in contrast to SM, with a right frontal abscess, who describes pictures accurately. Both patients, however, show left-sided neglect when copying pictures. When asked to copy daisy pictures, including half daisies, TT copied half daisy heads, including half of the half daisies, but SM missed only whole daisy heads to the left of other daisies. Their different responses to these daisy pictures is tentatively explained in terms of their ability to perceive whether or not half daisies appear “ridiculous”. SM also embellished the right sides of her drawings, suggesting an interaction between this dysexecutive behaviour and neglect.

Exploring the neural correlates of visual creativity

Although creativity has been called the most important of all human resources, its neural basis is still unclear. In the current study, we used fMRI to measure neural activity in participants solving a visuospatial creativity problem that involves divergent thinking and has been considered a canonical right hemisphere task. As hypothesized, both the visual creativity task and the control task as compared to rest activated a variety of areas including the posterior parietal cortex bilaterally and motor regions, which are known to be involved in visuospatial rotation of objects. However, directly comparing the two tasks indicated that the creative task more strongly activated left hemisphere regions including the posterior parietal cortex, the premotor cortex, dorsolateral prefrontal cortex (DLPFC) and the medial PFC. These results demonstrate that even in a task that is specialized to the right hemisphere, robust parallel activity in the left hemisphere supports creative processing. Furthermore, the results support the notion that higher motor planning may be a general component of creative improvisation and that such goal-directed planning of novel solutions may be organized top-down by the left DLPFC and by working memory processing in the medial prefrontal cortex.

Spatial attention deficits in humans: the critical role of superior compared to inferior parietal lesions

According to a longstanding view, inferior as opposed to superior parietal cortex critically contributes to the spatial attentional deficits encountered following unilateral parietal ischemic lesions. We review the evidence on which this view is based and contrast it with more recent structural lesion evidence concerning the critical role of the intraparietal sulcus in spatial attention deficits. In a classical spatial cueing paradigm, focal lesions of the posterior and of the middle segment of the intraparietal sulcus give rise to a pathological invalidity effect that is indistinguishable from that seen after classical inferior parietal lesions. When a competing distracter is added to a target stimulus, the deleterious consequences of focal IPS lesions are again very similar to those classically observed following inferior parietal lesions. The deficit could not be accounted for by functional effects at a distance affecting inferior parietal cortex. These single-case lesion data establish the critical role of the posterior and the middle IPS segment in spatially selective attention and are in line with a vast amount of functional imaging evidence in the intact brain pointing to the prominent role of the intraparietal sulcus in spatial attention, along with inferior parietal cortex under specific circumstances. Functional imaging has also provided hints about the differences in functional contribution between inferior and superior parietal cortex. These hypotheses await further confirmation based on lesion evidence.

The anatomy of spatial neglect

Spatial neglect is often perceived as a "heterogeneous collection of symptoms" with controversial anatomical correlates. However, a clear framework for core and satellite symptoms exists. Here we review the literature when viewed from the perspective of these different syndromes, and find clear pattern of anatomical injury. Specifically, the combined symptoms of biased gaze direction and search - with no awareness of these symptoms-is seen following structural damage to (particularly right hemisphere) perisylvian regions. Object centered deficits such as biased line bisection are due to more posterior (and possibly inferior) injury. Finally, extinction is associated with damage to the temporo-parietal junction. Further, we describe key choices that must be made to parse the spatial and attentional syndromes that result from right hemisphere injury, including the investigation of both acute and chronic injury as well as the use of functional and structural modalities.

The anatomy underlying acute versus chronic spatial neglect: a longitudinal study

Our aim was to examine how brain imaging in the initial phase of a stroke could predict both acute/subacute as well as chronic spatial neglect. We present the first voxel-wise longitudinal lesion-behaviour mapping study, examining acute/subacute as well as chronic performance in the same individuals. Acute brain imaging (acquired on average 6.2 days post-injury) was used to evaluate neglect symptoms at the initial (mean 12.4 days post-stroke) and the chronic (mean 491 days) phase of the stroke. Chronic neglect was found in about one-third of the patients with acute neglect. Analysis suggests that lesion of the superior and middle temporal gyri predict both acute/subacute as well as chronic neglect. At the subcortical level, the basal ganglia as well as the inferior occipitofrontal fasciculus/extreme capsule appear to play a significant role for both acute/subacute as well as chronic neglect. Beyond, the uncinate fasciculus was critically related to the emergence of chronic spatial neglect. We infer that individuals who experience spatial neglect in the initial phase of the stroke yet do not have injury to these cortical and subcortical structures are likely to recover, and thus have a favourable prognosis.

Reperfusion of specific cortical areas is associated with improvement in distinct forms of hemispatial neglect

OBJECTIVE

To test the hypothesis that restoring blood flow to specific right cortical regions in acute stroke results in improvement in distinct forms of hemispatial neglect distinguished by reference frame: viewer-centered versus stimulus-centered neglect.

METHODS

Twenty five patients with acute right stroke were evaluated at Day 1 and Day 3-5 with a battery of neglect tests and Diffusion- and Perfusion-Weighted MR Imaging. Multivariate linear regression analysis revealed Brodmann areas (BAs) where reperfusion predicted degree of improvement in scores on each type of neglect, independently of reperfusion of other areas, total change in the volume of infarct or hypoperfusion, and age.

RESULTS

Reperfusion of dorsal frontoparietal cortex (including BAs 40, 46, and 4) independently predicted improvement in viewer-centered neglect, such as detecting stimuli on left in line cancellation and scene copying (r=.951; p<.0001). Reperfusion of a more ventral temporo-occipital cortex, including right BAs 37, 38, 21 and 18, independently contributed to improvement in stimulus-centered neglect, such as detecting left gaps in circles (r=.926; p<.0001). Reperfusion of right midfusiform gyrus (temporal occipital cortex), change in total volume of ischemia, change in volume of hypoperfusion and age predicted degree of improvement in reading (reduction in "neglect dyslexic" errors; r=.915; p<.0001). Results demonstrate that reperfusing specific cortical regions yields improvement in different types of neglect.

Structural connectivity for visuospatial attention: significance of ventral pathways

In the present study, we identified the most probable trajectories of point-to-point segregated connections between functional attentional centers using a combination of functional magnetic resonance imaging and a novel diffusion tensor imaging-based algorithm for pathway extraction. Cortical regions activated by a visuospatial attention task were subsequently used as seeds for probabilistic fiber tracking in 26 healthy subjects. Combining probability maps of frontal and temporoparietal regions yielded a network that consisted of dorsal and ventral connections. The dorsal connections linked temporoparietal cortex with the frontal eye field and area 44 of the inferior frontal gyrus (IFG). Traveling along superior longitudinal and arcuate fascicles, these fibers are well described in relation to spatial attention. However, the ventral connections, which traveled in the white matter between insula (INS) cortex and putamen parallel to the sylvian fissure, were not previously described for visuospatial attention. Linking temporoparietal cortex with anterior INS and area 45 of IFG, these connections may provide an anatomical substrate for crossmodal cortical integration needed for stimulus perception and response in relation to current intention. The newly anatomically described integral network for visuospatial attention might improve the understanding of spatial attention deficits after white matter lesions.

Repetitive long-term prism adaptation permanently improves the detection of contralesional visual stimuli in a patient with chronic neglect

The aim of the current study was to investigate long-term effects in spatial awareness after daily exposure to prism adaptation during three months in a patient with hemispatial neglect. Results showed improvement in the detection of stimuli in the contralesional visual field, as measured with perimetry, in the contralesional visual field up to 24 months after ending prism adaptation. These perimetrical results suggest that compensatory eye movements are an unlikely candidate for an underlying mechanism.

Neuroanatomy of hemispatial neglect and its functional components: a study using voxel-based lesion-symptom mapping

Spatial neglect is a perplexing neuropsychological syndrome, in which patients fail to detect (and/or respond to) stimuli located contralaterally to their (most often right) hemispheric lesion. Neglect is characterized by a wide heterogeneity, and a role for multiple components has been suggested, but the exact nature of the critical components remains unclear. Moreover, many different lesion sites have been reported, leading to enduring controversies about the relative contribution of different cortical and/or subcortical brain regions. Here we report a systematic anatomo-functional study of 80 patients with a focal right hemisphere stroke, who were examined by a series of neuropsychological tests assessing different clinical manifestations of neglect. We first performed a statistical factorial analysis of their behavioural performance across all tests, in order to break down neglect symptoms into coherent profiles of co-varying deficits. We then examined the neural correlates of these distinct neglect profiles using a statistical voxel-based lesion-symptom mapping method that correlated the anatomical extent of brain damage with the relative severity of deficits along the different profiles in each patient. Our factorial analysis revealed three main factors explaining 82% of the total variance across all neglect tests, which suggested distinct components related to perceptive/visuo-spatial, exploratory/visuo-motor, and allocentric/object-centred aspects of spatial neglect. Our anatomical voxel-based lesion-symptom mapping analysis pointed to specific neural correlates for each of these components, including the right inferior parietal lobule for the perceptive/visuo-spatial component, the right dorsolateral prefrontal cortex for the exploratory/visuo-motor component, and deep temporal lobe regions for the allocentric/object-centred component. By contrast, standard anatomical overlap analysis indicated that subcortical damage to paraventricular white matter tracts was associated with severe neglect encompassing several tests. Taken together, our results provide new support to the view that the clinical manifestations of hemispatial neglect might reflect a combination of distinct components affecting different domains of spatial cognition, and that intra-hemispheric disconnection due to white matter lesions might produce severe neglect by impacting on more than one functional domain.

Neural substrates of visuospatial processing in distinct reference frames: evidence from unilateral spatial neglect

There is evidence for different levels of visuospatial processing with their own frames of reference: viewer-centered, stimulus-centered, and object-centered. The neural locus of these levels can be explored by examining lesion location in subjects with unilateral spatial neglect (USN) manifest in these reference frames. Most studies regarding the neural locus of USN have treated it as a homogenous syndrome, resulting in conflicting results. In order to further explore the neural locus of visuospatial processes differentiated by frame of reference, we presented a battery of tests to 171 subjects within 48 hr after right supratentorial ischemic stroke before possible structural and/or functional reorganization. The battery included MR perfusion weighted imaging (which shows hypoperfused regions that may be dysfunctional), diffusion weighted imaging (which reveals areas of infarct or dense ischemia shortly after stroke onset), and tests designed to disambiguate between various types of neglect. Results were consistent with a dorsal/ventral stream distinction in egocentric/allocentric processing. We provide evidence that portions of the dorsal stream of visual processing, including the right supramarginal gyrus, are involved in spatial encoding in egocentric coordinates, whereas parts of the ventral stream (including the posterior inferior temporal gyrus) are involved in allocentric encoding.

Perfusion imaging of the right perisylvian neural network in acute spatial neglect

Recent studies have suggested a tightly connected perisylvian neural network associated with spatial neglect. Here we investigated whether structural damage in one part of the network typically is accompanied with functional damage in other, structurally intact areas of this network. By combining normalized fluid-attenuated inversion-recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI) we asked whether or not lesions centering on fronto-temporal regions co-occur with abnormal perfusion in structurally intact parietal cortex. With thresholds applied to delineate behaviourally relevant malperfusion of brain tissue, the analysis of normalized time-to-peak (TTP) and maximal signal reduction (MSR) perfusion maps did not reveal significant changes outside the area of structural damage. In particular, we found no abnormal perfusion in the structurally intact inferior parietal lobule (IPL) and/or the temporo-parietal junction (TPJ). The present results obtained in three consecutively admitted neglect patients with fronto-temporal lesions indicate that structural damage in one part of the right perisylvian network associated with spatial neglect does not necessarily require dysfunction by malperfusion in other, structurally intact parts of the network to provoke spatial neglect. The neural tissue in the fronto-temporal cortex appears to have an original role in processes of spatial orienting and exploration.

Effectiveness of prism adaptation in neglect rehabilitation: a controlled trial study

BACKGROUND AND PURPOSE

This study was conducted to investigate the effectiveness on neglect recovery of a 2-week treatment based on prism adaptation (PA) in comparison to an analogous visuomotor training performed without prisms, ie, neutral pointing (NP).

METHODS

Twenty neglect patients were divided into 2 matched groups, one was submitted to PA (PA group) and the other to NP (NP group) for 10 daily sessions over a period of 2 weeks. After the end of NP treatment, the patients in the NP group were also submitted to PA treatment. Neglect was assessed before and after each treatment and 1 month after the end of the PA treatment.

RESULTS

Visuospatial abilities improved after both PA and NP treatment; however, the improvement was significantly higher in the patients in the PA group than in the patients in the NP group. Moreover, when the patients in the NP group were submitted to PA, they further improved up to the level reached by patients in the PA group, ie, to nonpathological scores. Long-lasting beneficial effects of PA were confirmed 1 month from the end of treatment.

CONCLUSIONS

The leftward recalibration of sensorimotor reference frames induced by PA is effective to obtain proper neglect recovery, although visuomotor training based on pointing might partially improve neglect symptoms.

Subcortical neglect is not always a transient phenomenon: evidence from a 1-year follow-up study

Compared to cortical lesions, spatial neglect following subcortical stroke is most frequently seen as a mild and transient phenomenon. Since this assumption is based on only few observations, we reexamined the prognosis and severity of spatial neglect in patients with circumscribed right-sided basal ganglia or thalamic lesions in the acute and in the chronic phase of the stroke. On average, 1.15 years after stroke, spatial neglect had persisted in about 40% of the patients with subcortical lesions. The severity was reduced to about one third. The results argue against the view that spatial neglect following subcortical lesions typically has a favorable prognosis.

Cortical and subcortical anatomy of chronic spatial neglect following vascular damage

Background

The role of the inferior parietal lobule (IPL) and superior temporal gyrus (STG) or subcortical pathways as possible anatomical correlates of spatial neglect is currently intensely discussed. Some of the conflicting results might have arisen because patients were examined in the acute stage of disease.

Methods

We examined the anatomical basis of spatial neglect in a sample of patients examined in the post-acute stage following right-hemispheric vascular brain damage. Lesions of 28 patients with chronic spatial neglect were contrasted to lesions of 22 control patients without neglect using lesion subtraction techniques and voxel-wise comparisons.

Results

The comparisons identified the temporo-parietal junction (TPJ) with underlying white matter, the supramarginal gyrus, the posterior STG, and the insula as brain regions damaged significantly more often in neglect compared to non-neglect patients. In a subgroup of neglect patients showing particularly large cancellation bias together with small errors on line bisection damage was prevalent deep in the frontal lobe while damage of patients with the reverse pattern was located in the white matter of the TPJ.

Conclusion

Considering our results and the findings of previous studies, spatial neglect appears to be associated with a network of regions involving the TPJ, inferior IPL, posterior STG, the insular cortex, and posterior-frontal projections. Frontal structures or projections may be of particular relevance for spatial exploration, while the IPL may be important for object-based attention as required for line bisection.

Impaired perceptual memory of locations across gaze-shifts in patients with unilateral spatial neglect

Right hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such as left hemispatial neglect. Neglect involves not only pathological biases in attention and exploration but also deficits in internal representations of space and spatial working memory. Here we designed a new paradigm to test whether one potential component may involve a failure to maintain an updated representation of visual locations across delays when a gaze-shift intervenes. Right hemisphere patients with varying severity of left spatial neglect had to encode a single target location and retain it across an interval of 2 or 3 sec, during which the target was transiently removed, before a subsequent probe appeared for a same/different location judgment. During the delay, gaze could have to shift to either side of the remembered location, or no gaze-shift was required. Patients showed a dramatic loss of memory for target location after shifting gaze to its right (toward their "intact" ipsilesional side), but not after leftward gaze-shifts. Such impairment arose even when the target initially appeared in the right visual field, before being updated leftward due to right gaze, and even when gaze returned to the screen center before the memory probe was presented. These findings indicate that location information may be permanently degraded when the target has to be remapped leftward in gaze-centric representations. Across patients, the location-memory deficit induced by rightward gaze-shifts correlated with left neglect severity on several clinical tests. This paradoxical memory deficit, with worse performance following gaze-shifts to the "intact" side of space, may reflect losses in gaze-centric representations of space that normally remap a remembered location dynamically relative to current gaze. Right gaze-shifts may remap remembered locations leftward, into damaged representations, whereas left gaze-shifts will require remapping rightward, into intact representations. Our findings accord with physiological data on normal remapping mechanisms in the primate brain but demonstrate for the first time their impact on perceptual spatial memory when damaged, while providing new insights into possible components that may contribute to the neglect syndrome.

Visual attention capacity after right hemisphere lesions

Recently there has been a growing interest in visual short-term memory (VSTM) including the neural basis of the function. Processing speed, another main aspect of visual attention capacity, has received less investigation. For both cognitive functions human lesion studies are sparse. We used a whole report experiment for estimation of these two parameters in 22 patients with right side stroke. Psychophysical performance was analyzed using Bundesen's [Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523-547] Theory of Visual Attention (TVA) and compared statistically to lesion location and size measured by MRI. Visual processing speed was impaired in the contralesional hemifield for most patients, but typically preserved ipsilesionally, even after large cortico-subcortical lesions. When bilateral deficits in processing speed occurred, they were related to damage in the right middle frontal gyrus or leukoaraiosis. The storage capacity of VSTM was also normal for most patients, but deficits were found after severe leukoaraiosis or large strokes extending deep into white matter. Thus, the study demonstrated the importance of white-matter connectivity for both VSTM capacity and ipsilesional processing speed. The study also showed that lesions in a large region of the right hemisphere, including the putamen, insula, and inferior frontal cortex, do not lead to general deficits in the capacity of visual attention.

Awareness and knowing: Implications for rehabilitation

It has been known for well over a century that brain-damaged patients are often unaware of the very deficits that impair performance in everyday life. Pathologies of awareness have been described for many neurological, psychiatric and neuropsychological deficits and the construct of "awareness" or "insight" understandably now receives attention from many researchers within the clinical and cognitive neurosciences. This paper does not attempt to explain the nature of consciousness or its impairment but rather considers four aspects of consciousness/awareness that health care professionals interested in understanding, measuring and improving deficits of awareness should consider.

Persisting asymmetries of vision after right side lesions

Visual neglect and extinction are well-known effects of lesions in the right hemisphere. This study shows that even with minor or no clinical signs of these deficits, and in the stable phase of recovery, asymmetric visual perception is common after right side lesions. Whole, partial and colour report experiments were used to estimate psychophysical parameters related to visual capacity and attentional weighting in 26 patients with stroke in the right side of the brain. The results were analyzed using Bundesen's Theory of Visual Attention (TVA [Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523-547]) including bootstrap estimation of the measurement error related to each test result [Habekost, T., & Bundesen, C. (2003). Patient assessment based on a theory of visual attention (TVA): Subtle deficits after a right frontal-subcortical lesion. Neuropsychologia, 41, 1171-1188]. Lesions were examined by MR scanning and analyzed statistically. Two main types of deficit were found. The first type was related to perception of unilateral displays, where most patients showed left side reductions of visual processing speed. This visual asymmetry correlated with injury to the putamen and surrounding white matter. The second deficit type occurred with bilateral displays, which increased the visual asymmetry (extinction effect) for most patients with large cortico-subcortical lesions, but rarely for patients with focal lesions. However, in a single case with pulvinar damage, visual asymmetry occurred selectively with bilateral stimulation. Overall, the study provided an overview of the cognitive structure and lesion anatomy of subtle visual asymmetries after right side stroke.

Asymmetric deterioration of spatial awareness with diminishing levels of alertness in normal children and children with ADHD

BACKGROUND

There is growing literature suggesting that some children diagnosed with attention deficit hyperactivity disorder (ADHD) can show a significant bias in attention away from left space. Here we examine mechanisms that may underpin these effects in both clinical and non-clinical child populations. Unilateral spatial inattention (unilateral neglect) is a commonly reported consequence of stroke in adults. Although for most patients the problem is relatively transient, persistent forms of neglect are almost exclusively associated with right hemisphere lesions. It has been suggested that this chronicity may result from co-existing disruption to right hemisphere dominant systems that mediate alertness. Here we present two studies examining the relationship between sustained attention and left spatial awareness in childhood.

METHOD

In the first, normal children without the ADHD diagnosis were administered a non-spatial test of sustained attention/alertness. Children who performed poorly at this task, relative to their more attentive peers, showed a modest but reliable delay in awareness of left-sided visual information. Furthermore, attention towards the left declined for both groups as a function of time-on-task, suggesting a significant within-subject modulatory effect of alertness on spatial awareness. The second study examines this relationship in children referred to clinical services for attention problems. Irrespective of their final diagnosis, children were divided into two groups according to their performance in sustained attention/alertness tasks.

RESULTS

The results suggest that, regardless of the children's clinical diagnosis, diminished sustained attention/alertness levels formed the strongest predictor of relatively delayed awareness of information presented within left visual space. Two children within this group exhibited signs of hitherto undetected spatial neglect as severe as that observed in some brain-injured adults.

CONCLUSIONS

Clinical and theoretical implications are discussed.

Normalized perfusion MRI to identify common areas of dysfunction: patients with basal ganglia neglect

Perfusion-weighted imaging (PWI) is used to identify brain regions that are receiving enough blood supply to remain structurally intact, but not enough to function normally. Previous observations suggest that spatial neglect due to subcortical stroke can be explained by dysfunction of cortical areas rather than through the neuronal loss in the subcortical structures itself. The present study aimed to identify the dysfunctional cortical regions induced by basal ganglia stroke in patients with spatial neglect. In a patient group with stroke lesions centring on the basal ganglia, we examined the common area(s) of structurally intact but dysfunctional cortical tissue by using spatial normalization of PWI maps as well as symmetric voxel-wise inter-hemispheric comparisons. These new techniques allow comparison of the structurally intact but abnormally perfused areas of different individuals in the same stereotaxic space, and at the same time avoid problems due to regional perfusion differences and to possible observer-dependent biases. We found that strokes centring on the right basal ganglia which provoke spatial neglect induce abnormal perfusion in a circumscribed area of intact cortex that typically involves those three regions that have previously been described to provoke spatial neglect when damaged directly by cortical infarction: the superior temporal gyrus, the inferior parietal lobule and the inferior frontal gyrus. The data suggest that spatial neglect following a right basal ganglia lesion typically is caused by the dysfunction of (part of) these specific cortical areas.

Visual neglect in the first weeks after a stroke in the right hemisphere

The aim of the study was to characterize symptoms of visual neglect among patients who recently survived a stroke in the right hemisphere (RH), and to contribute to the understanding of change in symptoms during the first months after a RH stroke. Thirteen patients with a RH stroke and twenty controls were assessed by using standard neglect tests. Five patients were followed up by repetitive test sessions during the next four months. To assess more subtle symptoms, reaction-time (RT) measures derived from an experimental cue-target paradigm were included in the final test session. A high frequency of neglect symptoms was documented at the first test session. The changes in performance during the first weeks were characterized by a high inter-individual as well as a high intra-individual variability. Although the remission rate on standard tests was high in the follow-up study, the RT measures indicated sustained symptoms of visual extinction in all patients. The long-term implication of the changes of neglect symptoms during the first weeks after a stroke and signs of sustained symptoms of visual extinction calls for further longitudinal studies including a larger group of patients.

Attentional functions of parietal and frontal cortex

A model of normal attentional function, based on the concept of competitive parallel processing, is used to compare attentional deficits following parietal and frontal lobe lesions. Measurements are obtained for visual processing speed, capacity of visual short-term memory (VSTM), spatial bias (bias to left or right hemifield) and top-down control (selective attention based on task relevance). The results show important differences, but also surprising similarities, in parietal and frontal lobe patients. For processing speed and VSTM, deficits are selectively associated with parietal lesions, in particular lesions of the temporoparietal junction. We discuss explanations based on either grey matter or white matter lesions. In striking contrast, measures of attentional weighting (spatial bias and top-down control) are predicted by simple lesion volume. We suggest that attentional weights reflect competition between broadly distributed object representations. Parietal and frontal mechanisms work together, both in weighting by location and weighting by task context.

Functional MRI changes before and after onset of reported emotions

The social nature of emotion is evident in the importance of facial and vocal displays in emotion-related behavior. This is the first brain-imaging study to use simulated face-to-face social interactions to evoke emotional responses and to compare valence-related activations before and after subjective onset of emotional response. Videotapes were prepared with actresses who described happy or unhappy experiences. Functional magnetic resonance imaging (fMRI) at 1.5 T was used to acquire BOLD images in 21 healthy young adults before, after, and during viewing of the happy and sad tapes. Subjects pushed buttons to indicate the onset of subjective emotional responses. Group data were analyzed by a bootstrap randomization method after anatomical normalization. Significant activation was detected in frontal and sensory regions prior to the reported onset of emotional response, and this activity showed a marked decrease after the report of conscious emotional experience. Significant differences between happy and sad conditions were evident in multiple brain regions both before and after the reported onset of emotional response, including the middle and superior temporal gyri, the middle frontal gyrus, the caudate, and the hippocampus. Socially relevant emotional stimulation is feasible and evokes robust responses. The neural correlates of the evoked emotion are multiple, widely distributed, and inclusive of areas important in many cognitive tasks. Positive and negative emotional responses include activation of common and distinctive brain regions.

A biased competition based neurodynamical model of visual neglect

On the computational basis of a neurodynamical cortical model, we investigate a specific top-down visual cognitive impairment in brain-damaged patients known as visual spatial neglect. The computational cortical model accounts the neurodynamics underlying selective visual attention, is based on the "biased competition hypothesis" and structured in several network modules which can be related with the different areas of the dorsal and ventral path of the visual cortex. Spatial and object attention are accomplished by a multiplicative gain control that emerges dynamically through intercortical mutual biased coupling. By damaging the model in different ways, a variety of dysfunctions associated with visual neglect can be simulated and explained as disruption of specific subsystems. Essentially, the damage destabilizes the underlying intra- and intermodular mutually biased neurodynamical competition that macroscopically yields the functional deficits observed in visual neglect patients. In particular, we are able to explain the asymmetrical effect of spatial cueing on neglect, and the phenomenon of extinction in the framework of visual search.