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.

Visual and motor neglect: Clinical and neurocognitive aspects

Attention allows us to prioritize the processing of external information according to our goals, but also to cope with sudden, unforeseen events. Attention processes rely on the coordinated activity of large-scale brain networks. At the cortical level, these systems are mainly organized in fronto-parietal networks, with functional and anatomical asymmetries in favor of the right hemisphere. Dysfunction of these right-lateralized networks often produce severe deficit of spatial attention, such as visual neglect. Other brain-damaged patients avoid moving the limbs contralateral to their brain lesion, even in the absence of sensorimotor deficits (motor neglect). This paper first summarizes past and current evidence on brain networks of attention; then, it presents clinical and experimental findings on visual and motor neglect, and on the possible mechanisms of clinical recovery.

DTI-MR tractography of white matter damage in stroke patients with neglect

Left visual neglect is a dramatic neurological condition that impairs awareness of left-sided events. Neglect has been classically reported after strokes in the territory of the right middle cerebral artery. However, the precise lesional correlates of neglect within this territory remain discussed. Recent evidence strongly suggests an implication of dysfunction of large-scale perisylvian networks in chronic neglect, but the quantitative relationships between neglect signs and damage to white matter (WM) tracts have never been explored. In this prospective study, we used diffusion tensor imaging (DTI) tractography in twelve patients with a vascular stroke in the right hemisphere. Six of these patients showed signs of neglect. Nonparametric voxel-based comparisons between neglect and controls on fractional anisotropy maps revealed clusters in the perisylvian WM and in the external capsule. Individual DTI tractography identified specific disconnections of the fronto-parietal and fronto-occipital pathways in the neglect group. Voxel-based correlation statistics highlighted correlations between patients' performance on two visual search tasks and damage to WM clusters. These clusters were located in the anterior limb of the internal capsule and in the WM underlying the inferior frontal gyrus, along the trajectory of the anterior segment of the arcuate fasciculus (asAF). These results indicate that chronic visual neglect can result from, and correlate with, damage to fronto-parietal connections in the right hemisphere, within large-scale cortical networks important for orienting of spatial attention, arousal and spatial working memory.

Representation and disconnection in imaginal neglect

Patients with neglect failure to detect, orient, or respond to stimuli from a spatially confined region, usually on their left side. Often, the presence of perceptual input increases left omissions, while sensory deprivation decreases them, possibly by removing attention-catching right-sided stimuli (Bartolomeo, 2007). However, such an influence of visual deprivation on representational neglect was not observed in patients while they were imagining a map of France (Rode et al., 2007). Therefore, these patients with imaginal neglect either failed to generate the left side of mental images (Bisiach & Luzzatti, 1978), or suffered from a co-occurrence of deficits in automatic (bottom-up) and voluntary (top-down) orienting of attention. However, in Rode et al.'s experiment visual input was not directly relevant to the task; moreover, distraction from visual input might primarily manifest itself when representation guides somatomotor actions, beyond those involved in the generation and mental exploration of an internal map (Thomas, 1999). To explore these possibilities, we asked a patient with right hemisphere damage, R.D., to explore visual and imagined versions of a map of France in three conditions: (1) 'imagine the map in your mind' (imaginal); (2) 'describe a real map' (visual); and (3) 'list the names of French towns' (propositional). For the imaginal and visual conditions, verbal and manual pointing responses were collected; the task was also given before and after mental rotation of the map by 180 degrees . R.D. mentioned more towns on the right side of the map in the imaginal and visual conditions, but showed no representational deficit in the propositional condition. The rightward inner exploration bias in the imaginal and visual conditions was similar in magnitude and was not influenced by mental rotation or response type (verbal responses or manual pointing to locations on a map), thus suggesting that the representational deficit was robust and independent of perceptual input in R.D. Structural and diffusion MRI demonstrated damage to several white matter tracts in the right hemisphere and to the splenium of corpus callosum. A second right-brain damaged patient (P.P.), who showed signs of visual but not imaginal neglect, had damage to the same intra-hemispheric tracts, but the callosal connections were spared. Imaginal neglect in R.D. may result from fronto-parietal dysfunction impairing orientation towards left-sided items and posterior callosal disconnection preventing the symmetrical processing of spatial information from long-term memory.

[Presentation of an assessment battery for visual mental imagery and visual perception]

INTRODUCTION

The relationship between visual perception and visual mental imagery are at the center of a lively theoretical debate between those postulating common neurocognitive processes between perception and imagery and those who emphasize the differences between these two entities. Neuropsychology can make an important contribution to this debate, by assessing associations and dissociations between perceptual and imaginal deficits in patients with brain damage. However, currently there is no standardized test battery available for such assessments.

MATERIAL AND METHODS

Here we present a battery of paper-and-pencil tests assessing different domains of visual mental imagery and visual perception abilities: object form and color, animals, orthographic material, numbers, faces, and space. We also explored the effects of age, educational level and gender on performance on a group of 103 participants free of neurological damage.

RESULTS

The battery includes two parts: one composed of 14 tests assessing mental imagery and the second part composed of eight tests assessing the abilities of visual perception. We calculated the correlations between the tests, and found that, with the exception of orthographic material, there were generally poor correlations between imagery and perceptual tests.

CONCLUSION

This result seems inconsistent with hypotheses postulating a strict correspondence between perceptual and imagery abilities.

Brain networks of spatial awareness: evidence from diffusion tensor imaging tractography

Left unilateral neglect, a dramatic condition which impairs awareness of left-sided events, has been classically reported after right hemisphere cortical lesions involving the inferior parietal region. More recently, the involvement of long range white matter tracts has been highlighted, consistent with the idea that awareness of events occurring in space depends on the coordinated activity of anatomically distributed brain regions. Damage to the superior longitudinal fasciculus (SLF), linking parietal to frontal cortical regions, or to the inferior longitudinal fasciculus (ILF), connecting occipital and temporal lobes, has been described in neglect patients. In this study, four right-handed patients with right hemisphere strokes underwent a high definition anatomical MRI with diffusion tensor imaging (DTI) sequences and a pencil and paper neglect battery of tests. We used DTI tractography to visualise the SLF, ILF and the inferior fronto-occipital fasciculus (IFOF), a pathway running the depth of the temporal lobe, not hitherto associated with neglect. Two patients with cortical involvement of the inferior parietal and superior temporal regions, but intact and symmetrical fasciculi, showed no signs of neglect. The other two patients with signs of left neglect had superficial damage to the inferior parietal cortex and white matter damage involving the IFOF. These findings suggest that superficial damage to the inferior parietal cortex per se may not be sufficient to produce visual neglect. In some cases, a lesion to the direct connections between ventral occipital and frontal regions (ie, IFOF) may contribute to the manifestation of neglect by impairing the top down modulation of visual areas from the frontal cortex.

Négligence spatiale unilatérale : une conséquence dramatique mais souvent négligée des lésions de l’hémisphère droit

INTRODUCTION

Unilateral Spatial Neglect (USN) is a common consequence of right brain damage. In the most severe cases, behavioral signs of USN can last several years and compromise patients' autonomy and social rehabilitation. These clinical facts stress the need for reliable procedures of diagnosis and rehabilitation.

STATE OF THE ART

The last 3 decades have witnessed an explosion of studies on USN, which raises issues related to complex cognitive activities such as mental representation, spatial attention and consciousness. USN is probably a heterogeneous syndrome, but some of its underlying mechanisms might be understood as an association of disorders of spatial attention. A bias of automatic orienting towards right-sided objects seems typical of left USN. Afterwards, patients find it difficult to disengage their attention in order to explore the rest of the visual scene. Neglected objects are sometimes processed in an "implicit" way.

PERSPECTIVES

The development of behavioural paradigms and of neuroimaging techniques and their application to the study of USN has advanced our understanding of the functional mechanisms of attention and spatial awareness, as well as of their neural bases. A number of new procedures for rehabilitation have recently been proposed.

CONCLUSION

The present review describes the clinical presentation of USN, its anatomical basis and some of possible accounts of different aspects of neglect behavior. Results of computer simulations and of rehabilitation techniques are also presented with implications for the functioning of normal neurocognitive systems.

Looking while imagining: the influence of visual input on representational neglect

BACKGROUND

Subjects with hemispatial neglect often exhibit representational neglect: a failure to report details from the left side of mentally visualized images. This failure could reflect impaired ability to generate the left side of the mental image, or it could reflect failure to explore the left side of a normally generated mental image. When subjects with hemispatial neglect look at pictures or drawings, their attention tends to be drawn to objects on the right side, thereby aggravating their failure to explore the left side. If representational neglect represents a failure to explore the left side of a normally generated mental visual image, then it should be improved by blindfolding, which removes the attention-catching right-sided stimuli. However, if representational neglect represents a failure to generate the left side of the mental visual image, then blindfolding should have little impact on reporting of details of the image.

METHODS

To determine which of these explanations is correct, we asked eight normal participants and eight brain-damaged patients with left representational neglect to imagine the map of France and to name as many towns as possible in 2 minutes. In different sessions, participants performed the task with eyes open or while blindfolded.

RESULTS

Normal participants mentioned more towns while blindfolded than with vision, thus suggesting a distracting effect of visual details on mental imagery. Patients with neglect, however, showed no appreciable effect of blindfolding on reporting of details from either side of mental images.

CONCLUSION

Representational neglect may represent a failure to generate the left side of mental images.

Right spatial neglect after left hemisphere stroke: qualitative and quantitative study

OBJECTIVES

Comparatively little research has been conducted on right neglect after left brain damage. The authors sought to assess contralateral neglect in subacute left hemisphere stroke patients using a comprehensive test battery validated in a large control group after right hemisphere stroke.

METHODS

Seventy-eight left hemisphere stroke patients were assessed. The test battery included a preliminary assessment of anosognosia and visual extinction, a clinical assessment of gaze orientation and personal neglect, and paper-and-pencil tests of spatial neglect in the peripersonal space. Only nonverbal tests were used.

RESULTS

Drawing and cancellation tasks revealed neglect in 10 to 13% of patients. The combined battery was more sensitive than any single test alone. A total of 43.5% of patients showed some degree of neglect on at least one measure. Anatomic analyses showed that neglect was more common and severe when the posterior association cortex was damaged.

CONCLUSIONS

The frequency of occurrence of right neglect was, as expected, much lower than that reported in a study using the same assessment battery in right brain damage stroke patients. Nevertheless, neglect was found in a substantial proportion of patients at a subacute stage, suggesting that it should be considered in the rehabilitation planning of left brain damage stroke patients.

The influence of limb crossing on left tactile extinction

BACKGROUND

Previous research on patients with left tactile extinction has shown that crossing of hands, so that each hand is on the opposite side of the body midline relative to the other, improves detection of stimuli given to the left hand.

OBJECTIVES

To study the influence of the spatial position of limbs on left tactile extinction, and its relations with left visual neglect.

METHODS

Normal participants and patients with right cerebral hemisphere damage and left tactile extinction were asked to detect single or double light touch stimuli applied to their cheeks, hands, or knees with their arm and legs either in anatomical or in crossed position, increasing the attentional load of the task.

RESULTS

In patients with left extinction, limb crossing caused a deterioration in performance for stimuli applied to right body parts, with only a tendency to an improvement in detection for left body parts (only two of 24 patients showed substantial (>20%) improvement in left extinction after limb crossing). After crossing, left limb detections of double stimuli decreased with increasing degrees of visual neglect.

CONCLUSIONS

In conditions of high attentional load, limb crossing may impair tactile detection in most patients with left extinction, and particularly in those showing signs of left visual neglect. These results underline the importance of general attentional capacity in determining tactile extinction. Attentional and somatotopic mechanisms of extinction may assume different weights in different patients.

Sensitivity of clinical and behavioural tests of spatial neglect after right hemisphere stroke

OBJECTIVES

The lack of agreement regarding assessment methods is responsible for the variability in the reported rate of occurrence of spatial neglect after stroke. The aim of this study was to assess the sensitivity of different tests of neglect after right hemisphere stroke.

METHODS

Two hundred and six subacute right hemisphere stroke patients were given a test battery including a preliminary assessment of anosognosia and of visual extinction, a clinical assessment of gaze orientation and of personal neglect, and paper and pencil tests of spatial neglect in the peripersonal space. Patients were compared with a previously reported control group. A subgroup of patients (n=69) received a behavioural assessment of neglect in daily life situations.

RESULTS

The most sensitive paper and pencil measure was the starting point in the cancellation task. The whole battery was more sensitive than any single test alone. About 85% of patients presented some degree of neglect on at least one measure. An important finding was that behavioural assessment of neglect in daily life was more sensitive than any other single measure of neglect. Behavioural neglect was considered as moderate to severe in 36% of cases. A factorial analysis revealed that paper and pencil tests were related to two underlying factors. Dissociations were found between extrapersonal neglect, personal neglect, anosognosia, and extinction. Anatomical analyses showed that neglect was more common and severe when the posterior association cortex was damaged.

CONCLUSIONS

The automatic rightward orientation bias is the most sensitive clinical measure of neglect. Behavioural assessment is more sensitive than any single paper and pencil test. The results also support the assumption that neglect is a heterogeneous disorder.

[Presenting a battery for assessing spatial neglect. Norms and effects of age, educational level, sex, hand and laterality]

The aim of this study was to build up a battery for assessing spatial neglect, then to analyse the norms and potential effects of age, education level, sex, hand used, and laterality. It was also to contribute evaluating the pseudoneglect phenomenon described by Heilman, which consists in a tendency of normal subjects to neglect the right peripersonal space. Tasks selected were presented to important groups of normal subjects, most often larger than 450. The battery comprised of a bell cancellation test, scene copy, clock drawing, two line bisection tasks, identification of overlapping figures, text reading, writing task, and the representational task of the France map. For each of them, different variables were selected, especially investigating the difference between performance in the right and the left hemispaces. This study allowed defining the threshold values (percentiles 5 and 95) for deciding of the pathological character of a patient performance. It also showed that the pseudoneglect phenomenon is more obvious in some tasks such as line bisection, and probably also in the representational task of the France map and writing. His importance and at times his side were influenced by the factors we studied, with between tasks differences, but also by the nature of the task to be performed, and especially his verbal component.

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.

Modulating the attentional bias in unilateral neglect: the effects of the strategic set

Left unilateral neglect is a neurological condition characterized by an impairment in orienting and responding to events occurring on the left side. To gain insight into the brain mechanisms of space processing and to provide theoretical foundations for patient rehabilitation, it is important to explore the attentional bias shown by neglect patients in the light of existing models of normal attentional orienting. Three experiments tested the hypothesis that attentional bias in neglect involves primarily exogenous, or stimulus-based, orienting of attention, with relatively preserved endogenous, or voluntary, orienting. Six patients with right hemisphere damage and left unilateral neglect and 18 age-matched participants without brain damage performed a cued reaction time (RT) task to targets which could appear in one of two lateral boxes. Cues consisted of a brief brightening of the contour of one of the boxes. The target followed the cue at 150, 550, or 1000 ms stimulus-onset asynchrony (SOA). In experiment 1, the cues were not informative about the future location of the target, and thus elicited a purely exogenous orienting of attention. Controls showed slowed RTs to the cued locations at SOAs > 150 ms, consistent with the notion of inhibition of return (IOR). Neglect patients had no evidence of IOR for right targets; they showed a disproportionate cost for left targets preceded by right (invalid) cues; this cost was maximal at the shortest SOA, consistent with the idea of a biased exogenous orienting in neglect. In experiment 2, 80% of the cues were valid (i.e., they correctly predicted the location of the impending target), thus inducing an initially exogenous, and later endogenous, attentional shift toward the cued box. Neglect patients showed again a cost for left invalidly cued targets, which this time persisted at SOAs > 150 ms, as if patients' attention had been cued to the right side not only exogenously, but also endogenously, thus rendering more difficult an endogenous reorienting toward the left. In experiment 3, only 20% of the cues were valid, so that the best response strategy was to endogenously orient attention toward the box opposite to the cued one. Controls were able to take advantage of invalid cues to rapidly respond to targets. In this condition, neglect patients were able to nullify their spatial bias; they achieved their fastest RTs to left targets, which were in the range of their RTs to right targets. However, for neglect patients fast responses to left targets occurred only at 1000 ms SOA, while controls were able to redirect their attention to the uncued box already at 550 ms SOA. Altogether, these results suggest that endogenous orienting is relatively spared, if slowed, in unilateral neglect.

Unilateral neglect: the effect of competing stimuli on estimated line length

Normal subjects and patients with right hemisphere lesions with or without signs of left unilateral neglect judged the length of a horizontal line presented on the left or on the right side of space. In half of the trials, the line was presented with a centrally located square or diamond, and subjects had to identify the central stimulus before performing the judgment of length. The presence of the central stimulus improved accuracy of performance in controls and in patients without neglect; neglect patients, however, produced more overestimations of left-sided lines when these was presented with a central stimulus than when the lines occurred in isolation. This finding underlines the importance of attentional factors in length estimates performed by neglect patients in their neglected space.

Retest effects and cognitive decline in longitudinal follow-up of patients with early HD

OBJECTIVE

To assess the natural progression of cognitive impairment in Huntington's disease (HD) and to reveal factors that may mask this progression.

BACKGROUND

Although numerous cross-sectional studies reported cognitive deterioration at different stages of the disease, progressive cognitive deterioration has been, up to now, difficult to demonstrate in neuropsychological longitudinal studies.

METHODS

The authors assessed 22 patients in early stages of HD at yearly intervals for 2 to 4 years (average, 31.2 +/- 10 months), using a comprehensive neuropsychological battery based on the Core Assessment Program for Intracerebral Transplantation in Huntington's Disease (CAPIT-HD).

RESULTS

The authors observed a significant decline in different cognitive functions over time: these involved primarily attention and executive functions but also involved language comprehension, and visuospatial immediate memory. Episodic memory impairment that was already present at the time of enrollment did not show significant decline. The authors found a significant retest effect at the second assessment in many tasks.

CONCLUSION

Many attention and executive tasks adequately assess the progression of the disease at an early stage. For other functions, the overlapping of retest effects and disease progression may confuse the results. High interindividual and intraindividual variability seem to be hallmarks of the disease.

Variability of response times as a marker of diverted attention

Anderson et al. (Variability not ability: another basis for performance decrements in neglect. Neuropsychologia 2000;38:785-796) have recently reported that variability of response times (RTs) progressively increases from the right to the left side in left neglect patients. Anderson et al. propose that this lack of consistency is an important determinant of patients' behaviour, and may result from a deficit independent of other mechanisms causing neglect. Here we suggest that an increase of variability, and not only of RTs, is to be expected when attention is exogenously biased away from the probed location. Consequently, space-based variability can be interpreted in the framework of existing models of unilateral neglect. According to one such model, a basic impairment in left neglect is a bias toward rightward exogenous orienting of attention. As a result, left targets often fail to rapidly capture patients' attention, thus yielding slow RTs. However, since the probability for a left target attracting attention is low but not null, relatively fast RTs can occur on those rare occasions in which a left target does capture patients' attention. The coexistence of these relatively fast with slow RTs could be at the basis of space-based variability in neglect. Empirical support for our hypothesis comes from the results of a re-analysis for variability of cued RTs obtained in 18 normal individuals and six left neglect patients. Cues were peripheral and non-informative, thus eliciting an exogenous attentional shift. For normal individuals, invalid trials yielded less consistent response times than valid trials at short (150 ms) cue-target interval; for neglect patients, a similar phenomenon occurred for left invalidly-cued targets, thus paralleling the disproportionate cost in RTs typically evoked by this condition in unilateral neglect. We conclude by discussing some possible determinants of gradient-shaped effects and by outlining the implications of space-based variability for current models of unilateral neglect.

Motor and cognitive improvements in patients with Huntington's disease after neural transplantation

BACKGROUND

Huntington's disease is a neurodegenerative disease of genetic origin that mainly affects the striatum. It has severe motor and cognitive consequences and, up to now, no treatment. Motor and cognitive functions can be restored in experimental animal models by means of intrastriatal transplantation of fetal striatal neuroblasts. We explored whether grafts of human fetal striatal tissue could survive and have detectable effects in five patients with mild to moderate Huntington's disease.

METHODS

After 2 years of preoperative assessment, patients were grafted with human fetal neuroblasts into the right striatum then, after a year, the left striatum. Final results were assessed 1 year later on the basis of neurological, neuropsychological, neurophysiological, and psychiatric tests. The results obtained were compared with those of a cohort of 22 untreated patients at similar stages of the disease who were followed up in parallel. Repeated magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning with fluorine-18-labelled fluorodeoxyglucose was also done to assess metabolic activity.

FINDINGS

The final PET-scan assessment showed increased metabolic activity in various subnuclei of the striatum in three of five patients, contrasting with the progressive decline recorded in the two other patients in the series, as seen in patients with untreated Huntington's disease. Small areas of even higher metabolic activity, coregistering with spherical hyposignals on MRI were also present in the same three patients, suggesting that grafts were functional. Accordingly, motor and cognitive functions were improved or maintained within the normal range, and functional benefits were seen in daily-life activities in these three patients, but not in the other two.

INTERPRETATION

Fetal neural allografts could be associated with functional, motor, and cognitive improvements in patients with Huntington's disease.

Lack of impairments on leftward and rightward line extension tasks in neglect patients

We asked 16 right-brain damaged patients with left unilateral neglect, 9 right-brain damaged patients without neglect and 11 healthy control subjects to bisect horizontal lines or to extend them rightward or leftward. Although in the line bisection task patients with neglect showed the typical rightward deviation of the subjective line midpoint, they did not show any significant difference when compared to the other two experimental groups in both rightward and leftward line extension tasks. These results suggest that neglect for the left side of space is usually observed in tasks requiring an automatic lateral orienting of attention, but not in tasks in which this lateral orienting is submitted to a continuous intentional control.

Correlation between the position of the egocentric reference and right neglect signs in left-brain-damaged patients

Fourteen control subjects and thirty left-brain-damaged (LBD) patients with or without neglect performed a straight-ahead pointing task with their left hand while blindfolded. Results showed a significant correlation between the position of the egocentric reference and the presence of right neglect signs. We discuss here the egocentric hypotheses of spatial bias.

[Right parietal lesions, spatial neglect and egocentric reference]

Using a proprioceptive "straight-ahead" pointing task, we determined the position of the subjective sagittal middle in thirty unselected patients with unilateral vascular lesions in the right hemisphere and twenty-two normal controls. Patients with extensive right parietal damage (n = 16) showed an ipsilesional (rightward) deviation of their egocentric reference, whereas patients with lesions that substantially spared the right parietal lobe (n = 14) showed a contralesional (leftward) deviation. No significant correlation emerged between the position of the egocentric reference and the performance on a neglect battery. These results can help explain some dissociations between left neglect signs and ipsilesional deviation of the egocentric reference, and raise some questions about the links among lesion location, neglect signs and egocentric frame of reference.

Safety and tolerability assessment of intrastriatal neural allografts in five patients with Huntington's disease

This study describes issues related to the safety and tolerability of fetal striatal neural allografts as assessed in five patients with Huntington's disease. Huntington's disease (HD) is characterized by motor, cognitive, and behavioral disturbances. The latter include psychological disturbances and, as a consequence, we took particular care to analyze behavioral changes, in addition to the usual "safety" follow-up. We conducted multidisciplinary follow-up at least 2 years before and 1 year after grafting. Psychological care extended to close relatives. The grafting procedure itself was altogether safe and uneventful, and there were no apparent clinical deleterious effects for 1 year. The immunosuppressive treatment, however, was complicated by various problems (irregular compliance, errors of handling, side effects). Direct psychological consequences of the transplantation procedure were rare and not worrisome, although mood alteration requiring treatment was observed in one patient. Indirectly, however, the procedure required patients and relatives to accept constraints that tended to complicate familial situations already marred by aggressivity and depression. All patients and close relatives expressed major expectations, in spite of our strong and repeated cautioning. It is clearly important to be aware of these particular conditions since they may eventually translate into psychological difficulties in coping with the long-term clinical outcome of the procedure, if not beneficial. Despite an overall good tolerance, therefore, this follow-up calls for caution regarding the involvement of HD patients in experimental surgical protocols.

The heparin management test: a new device for monitoring anticoagulation during coronary intervention

Whole blood coagulation analysers are widely used during percutaneous coronary interventions. The precise degree of anticoagulation in patients is important in this setting. The aim of this investigation was to compare the results obtained with ACT (Hemochron) and HMT, the Heparin Management Test (TAS) in patients undergoing percutaneous coronary interventions. Patients (n = 100) were enrolled prospectively. Each patient received 10,000 units of heparin. At the end of the procedure, the mean ACT was 284+/-31 seconds and the mean HMT was 292+/-33 seconds. The correlation between the two methods was highly significant (r = 0.64, p<0.001). The HMT correlates well with ACT values in patients undergoing percutaneous coronary interventions. Its use in the management of these patients should be considered.

Left unilateral neglect or right hyperattention?

BACKGROUND

Contradictory interpretations of left unilateral neglect suggest that it reflects either decreased attention toward the left or increased attention toward the right. According to the right-hyperattention postulate, increasing severity of neglect should result from an increasingly stronger bias toward the right. Thus, response times to right-sided targets should become progressively faster as neglect increases in severity across patients. The left-hypoattention postulate predicts that as neglect increases, progressively less-attentional resources are deployed in both hemispaces. Thus, response times to right targets should progressively increase with increasing neglect.

METHODS

We analyzed the distribution of manual response times to left- and right-sided targets in 24 patients with right hemisphere lesions and varying degrees of left neglect.

RESULTS

Not only the responses to left targets but also those to right targets became progressively slower as neglect increased, consistent with the hypoattention account. However, the two regression lines were not parallel. With increasing neglect, responses to left targets increased more steeply than those to right targets did.

CONCLUSIONS

A rightward attentional bias is present in patients with left neglect, together with left hypoattention. However, this rightward bias is one of defective, and not enhanced, attention.

Facilitation instead of inhibition for repeated right-sided events in left neglect

When two visual events appear consecutively in the same spatial location, our response to the second event is slower than that to the first. This inhibition for repeated events may reflect a bias toward sampling novel locations, a bias useful for exploring the visual space. Patients with right hemisphere damage and left neglect explore asymmetrically a visual scene. They are initially attracted by right-sided items and become stuck to them, being unable to reorient their attention toward the left. Here we show that neglect patients show facilitation instead of inhibition for repeated events on the right, non-neglected side. Patients without neglect showed normal inhibition. Our observation may explain why neglect patients' exploration of space cannot extend beyond a few right-sided objects.

Egocentric frame of reference: its role in spatial bias after right hemisphere lesions

The reference shift hypothesis of unilateral neglect holds that spatial bias in left neglect stems from a rightward deviation of patients' egocentric frame of reference (ER). Twenty five unselected right brain-damaged patients participated in a straight-ahead pointing task to assess the position of their ER (Experiment 1). A rightward ER shift emerged only in the subgroup of patients with extensive parietal lesions. In Experiment 2, we found that the position of the ER did not predict the outcome of various visuospatial neglect tests (r = 0.07 to 0.27). In Experiment 3, no significant positive correlation emerged between the ER position and visual (r = 0.26) or tactile (r = -0.48) extinction. Two further experiments examined the relationships between the ER position and patients' performance on a reaction time test of directional motor bias (Experiment 4), and on a test of response times to lateralised visual stimuli (Experiment 5). Results showed that the ER position did not predict the distribution of accuracy scores or response times in either task (Experiment 3: accuracy: r = 0.06; response times: r = 0.16; Experiment 4: accuracy: r = 0.09; response times: r = 0.04). We concluded that the position of the ER plays no crucial role in the behavioural consequences of spatial bias induced by right hemisphere lesions.

Scanning direction and line bisection: a study of normal subjects and unilateral neglect patients with opposite reading habits

Sixty normal dextrals (30 left-to-right and 30 right-to-left readers) and two left unilateral neglect patient with opposite reading habits performed a passive line bisection task. In order to study the effect of scanning direction on performance, subjects had to stop a mark moving on the to-be-bisected line either from the left to the right or in the opposite direction. Results showed that the position of the subjective middle was dependent upon the scanning direction of the line for all the subjects. A leftward deviation appeared for left to right scanning, whereas a rightward shift occurred when the mark moved from the right to the left. These results emphasize the role of scanning direction in space organization and are discussed with respect to the explanatory hypotheses of unilateral neglect.

Right-side neglect in Alzheimer's disease

Unilateral neglect--the inability to pay attention to events occurring on one side of space--usually occurs for left-side events after focal right-hemisphere damage. We report a 73-year-old woman with probable AD and no evidence of focal brain lesions who showed signs of right-side neglect and extinction. Neglect was more severe after 1 year. Neuroimaging techniques demonstrated an asymmetry of cortical involvement, with cortical atrophy and hypoperfusion predominant in the left posterior regions. Unilateral neglect should be assessed systematically in AD.