Dopaminergic stimulation in unilateral neglect

A scoping review and critique of the Input-Output subtyping dimension of spatial neglect

Spatial neglect is a common and debilitating disorder after stroke whereby individuals have difficulty reporting, orienting, and/or responding to the contralesional side of space. Given the heterogeneity of neglect symptom presentation, various neglect subtypes have been proposed to better characterize the disorder. This review focuses on the distinction between Input neglect (i.e., difficulty perceiving and/or attending to contralesional stimuli) and Output neglect (i.e., difficulty planning and/or executing movements toward contralesional stimuli). Conceptualizations of Input and Output neglect have varied considerably. We provide a novel summary of the terminology, measurement approaches, and neural correlates of these subtypes. A protocol detailing our systematic scoping review strategy is registered on the Open Science Framework (https://osf.io/bvtxf/). For feasibility and greater comparability across studies, we limited our inclusion criteria to tasks focused on visual stimuli and upper-limb movements. A total of 110 articles were included in the review. Subtyping tasks were categorized based on whether they mainly manipulated aspects of the input (i.e., congruence of visual input with motor output, presence of visual input) or the output (i.e., modality, goal, or direction of output) to produce an Input-Output subtype dissociation. We used our review results to identify four main critiques of this literature: 1) lack of consistency/clarity in conceptual models; 2) methodological issues of dissociating Input and Output subtypes; 3) a need for updated neural theories; and 4) barriers to clinical application. We discuss the lessons learned from this subtyping dimension that can be applied to future research on neglect subtype assessment and treatment.

Recent advances in treatment of spatial neglect: networks and neuropsychology

INTRODUCTION

Spatial neglect remains an underdiagnosed and undertreated consequence of stroke that imposes significant disability. A growing appreciation of brain networks involved in spatial cognition is helping us to develop a mechanistic understanding of different therapies under development.

AREAS COVERED

This review focuses on neuromodulation of brain networks for the treatment of spatial neglect after stroke, using evidence-based approaches including 1) Cognitive strategies that are more likely to impact frontal lobe executive function networks; 2) Visuomotor adaptation, which may depend on the integrity of parietal and parieto- and subcortical-frontal connections and the presence of a particular subtype of neglect labeled Aiming neglect; 3) Non-invasive brain stimulation that may modulate relative levels of activity of the two hemispheres and depend on corpus callosum connectivity; and 4) Pharmacological modulation that may exert its effect primarily via right-lateralized networks more closely involved in arousal.

EXPERT OPINION

Despite promising results from individual studies, significant methodological heterogeneity between trials weakened conclusions drawn from meta-analyses. Improved classification of spatial neglect subtypes will benefit research and clinical care. Understanding the brain network mechanisms of different treatments and different types of spatial neglect will make possible a precision medicine treatment approach.

Right-deviating prismatic adaptation reduces obsessions in a community sample

Background and aims

Patients with obsessive-compulsive (OC) disorder are impaired in disengaging attention from negative valence stimuli and show an attentional bias toward the right space. This pattern in OC disorder is similar to the impaired disengagement of attention from stimuli in the ipsilesional space as a consequence of a right-hemispheric cerebral lesion in patients with neglect, suggesting a right hemispheric dysfunction in patients with OC disorder. The attentional impairment in patients with neglect is reduced by a visuomotor procedure, such as prismatic adaptation (PA) with right-deviating lenses. Thus, here, we explored whether right-deviating PA is also effective in reducing OC psychological symptoms.

Methods

Participants with a high rate of OC symptoms completed self-report measures of such symptoms before and after right- or left-deviating PA.

Results

Right-deviating PA, and not left-deviating PA, reduced OC symptoms more prominently on obsessions than compulsions.

Conclusion

Results support the idea that right-deviating PA might be considered an effective technique to modulate OC symptoms. This has implications for theories about the underlying mechanisms of OC symptoms and the consideration of PA as a complementary procedure to psychological treatments.

Spatial neglect treatment: The brain's spatial-motor Aiming systems

Animal and human literature supports spatial-motor "Aiming" bias, a frontal-subcortical syndrome, as a core deficit in spatial neglect. However, spatial neglect treatment studies rarely assess Aiming errors. Two knowledge gaps result: spatial neglect rehabilitation studies fail to capture the impact on motor-exploratory aspects of functional disability. Also, across spatial neglect treatment studies, discrepant treatment effects may also result from sampling different proportions of patients with Aiming bias. We review behavioural evidence for Aiming spatial neglect, and demonstrate the importance of measuring and targeting Aiming bias for treatment, by reviewing literature on Aiming spatial neglect and prism adaptation treatment, and presenting new preliminary data on bromocriptine treatment. Finally, we review neuroanatomical and network disruption that may give rise to Aiming spatial neglect. Because Aiming spatial neglect predicts prism adaptation treatment response, assessment may broaden the ability of rehabilitation research to capture functionally-relevant disability. Frontal brain lesions predict both the presence of Aiming spatial neglect, and a robust response to some spatial neglect interventions. Research is needed that co-stratifies spatial neglect patients by lesion location and Aiming spatial neglect, to personalize spatial neglect rehabilitation and perhaps even open a path to spatial retraining as a means of promoting better mobility after stroke.

Exploring the use of dopaminergic medication to treat hemispatial inattention during in-patient post-stroke neurorehabilitation

Hemispatial inattention (HSI), a lateralised impairment of spatial processing, is a common consequence of stroke. It is a poor prognostic indicator for functional recovery and interferes with the progress during in-patient neurorehabilitation. Dopaminergic medication has shown promise in improving HSI in the chronic post-stroke period but is untested in more acute settings, e.g. during in-patient neurorehabilitation. We audited the use of dopaminergic medication in ten sequential patients with post-stroke HSI, on an open-label exploratory basis. Patients' response to medication was assessed individually, using a three-week Off-On-Off protocol. We employed a mixture of bedside and functional measures, and made a multidisciplinary judgement of efficacy in individual patients. In six out of 10 patients, there was a convincing improvement of HSI while on medication, which reversed when it was paused. There was a mean 57% relative increase in target detection in the star cancellation test on the most affected side (on vs. off medication). In the six responders, medication was therefore continued throughout their admission without adverse effects. The star cancellation test was sensitive to HSI in most patients but in two cases failed to detect changes that were picked up by a functional assessment (Kessler Functional Neglect Assessment Protocol). We found this multidisciplinary approach to be feasible in an in-patient neurorehabilitation setting. We suggest further research to explore the efficacy of dopaminergic medication in improving neurorehabilitation outcomes for patients with post-stroke HSI. We suggest that more detailed N-of-1 assessments of treatment response, with internal blinding, may be a productive approach.

Methylphenidate reduces orienting bias in healthy individuals

BACKGROUND

Healthy individuals show subtle orienting bias, a phenomenon known as pseudoneglect, reflected in a tendency to direct greater attention toward one hemispace. Accumulating evidence indicates that this bias is an individual trait, and attention is preferentially directed contralaterally to the hemisphere with higher dopamine signaling. Administration of methylphenidate (MPH), a dopamine transporter inhibitor, was shown to normalize aberrant spatial attention bias in psychiatric and neurological patients, suggesting that the reduced orienting bias following administration of MPH reflects an asymmetric effect of the drug, increasing extracellular dopamine in the hemisphere with lower dopamine signaling.

AIM

We predicted that, similarly to its effect on patients with brain pathology, MPH will reduce the orienting bias in healthy subjects.

METHODS

To test this hypothesis, we examined the behavioral effects of a single dose (20 mg) of MPH on orienting bias in 36 healthy subjects (18 females) in a randomized, double-blind placebo-controlled, within-subject design, using the greyscales task, which has been shown to detect subtle attentional biases in both patients and healthy individuals.

RESULTS/OUTCOMES

Results demonstrate that healthy individuals vary in both direction and magnitude of spatial orienting bias and show reduced magnitude of orienting bias following MPH administration, regardless of the initial direction of asymmetry.

CONCLUSIONS/INTERPRETATIONS

Our findings reveal, for the first time in healthy subjects, that MPH decreases spatial orienting bias in an asymmetric manner. Given the well-documented association between orienting bias and asymmetric dopamine signaling, these findings also suggest that MPH might exert a possible asymmetric neural effect in the healthy brain.

Preliminary effects of prefrontal tDCS on dopamine-mediated behavior and psychophysiology

The ability to manipulate dopamine in vivo through non-invasive, reversible mechanisms has the potential to impact clinical, translational, and basic research. Recent PET studies have demonstrated increased dopamine release in the striatum after bifrontal transcranial direct current stimulation (tDCS). We sought to extend this work by examining whether bifrontal tDCS could demonstrate an effect on behavioral and physiological correlates of subcortical dopamine activity. We conducted a preliminary between-subjects study (n = 30) with active and sham tDCS and used spontaneous eye blink rate (EBR), facial attractiveness ratings, and greyscales orienting bias as indirect proxies for dopamine functioning. The initial design and analyses were pre-registered (https://osf.io/gmnpc). Stimulation did not significantly affect any of the three measures, though effect sizes were often moderately large and were all in the predicted directions. Additional exploratory analyses suggested that stimulation's effect on EBR might depend on pre-stimulation dopamine levels. Our results suggest that larger samples than those that are standard in tDCS literature should be used to assess the effect of tDCS on dopamine using indirect measures. Further, exploratory results add to a growing body of work demonstrating the importance of accounting for individual differences in tDCS response.

Reward sensitivity predicts dopaminergic response in spatial neglect

It has recently been revealed that spatial neglect can be modulated by motivational factors including anticipated monetary reward. A number of dopaminergic agents have been evaluated as treatments for neglect, but the results have been mixed, with no clear anatomical or cognitive predictors of dopaminergic responsiveness. Given that the effects of incentive motivation are mediated by dopaminergic pathways that are variably damaged in stroke, we tested the hypothesis that the modulatory influences of reward and dopaminergic drugs on neglect are themselves related. We employed a single-dose, double-blind, crossover design to compare the effects of Co-careldopa and placebo on a modified visual cancellation task in patients with neglect secondary to right hemisphere stroke. Whilst confirming that reward improved visual search in this group, we showed that dopaminergic stimulation only enhances visual search in the absence of reward. When patients were divided into REWARD-RESPONDERs and REWARD-NON-RESPONDERs, we found an interaction, such that only REWARD-NON-RESPONDERs showed a positive response to reward after receiving Co-careldopa, whereas REWARD-RESPONDERs were not influenced by drug. At a neuroanatomical level, responsiveness to incentive motivation was most associated with intact dorsal striatum. These findings suggest that dopaminergic modulation of neglect follows an 'inverted U' function, is dependent on integrity of the reward system, and can be measured as a behavioural response to anticipated reward.

Left-shifting prism adaptation boosts reward-based learning

Visuospatial cognition has an inherent lateralized bias. Individual differences in the direction and magnitude of this bias are associated with asymmetrical D2/3 dopamine binding and dopamine system genotypes. Dopamine level affects feedback-based learning and dopamine signaling asymmetry is related to differential learning from reward and punishment. High D2 binding in the left hemisphere is associated with preference for reward. Prism adaptation (PA) is a simple sensorimotor technique, which modulates visuospatial bias according to the direction of the deviation. Left-deviating prism adaptation (LPA) induces rightward bias in healthy subjects. It is therefore possible that the right side of space increases in saliency along with left hemisphere dopaminergic activity. Right-deviating prism adaptation (RPA) has been used mainly as a control condition because it does not modulate behavior in healthy individuals. Since LPA induces a rightward visuospatial bias as a result of left hemisphere modulation, and higher dopaminergic activity in the left hemisphere is associated with preference for rewarding events we hypothesized that LPA would increase the preference for learning with reward. Healthy volunteers performed a computer-based probabilistic classification task before and after LPA or RPA. Consistent with our predictions, PA altered the preference for rewarded versus punished learning, with the LPA group exhibiting increased learning from reward. These results suggest that PA modulates dopaminergic activity in a lateralized fashion.

Pharmacological interventions for unilateral spatial neglect after stroke

BACKGROUND

Unilateral spatial neglect (USN) is characterized by the inability to report or respond to people or objects presented on the side contralateral to the lesioned side of the brain and has been associated with poor functional outcomes and long stays in hospitals and rehabilitation centers. Pharmacological interventions (medical interventions only, use of drugs to improve the health condition), such as dopamine and noradrenergic agonists or pro-cholinergic treatment, have been used in people affected by USN after stroke, and effects of these treatments could provide new insights for health professionals and policy makers.

OBJECTIVES

To evaluate the effectiveness and safety of pharmacological interventions for USN after stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (April 2015), the Cochrane Central Register of Controlled Trials (April 2015), MEDLINE (1946 to April 2015), the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to April 2015), EMBASE (1980 to April 2015), PsycINFO (1806 to April 2015) and Latin American Caribbean Health Sciences Literature (LILACS) (1982 to April 2015). We also searched trials and research registers, screened reference lists, and contacted study authors and pharmaceutical companies (April 2015).

SELECTION CRITERIA

We included randomized controlled trials (RCTs) and quasi-randomized controlled trials (quasi-RCTs) of pharmacological interventions for USN after stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed risk of bias in the included studies and extracted data.

MAIN RESULTS

We included in the review two studies with a total of 30 randomly assigned participants. We rated the quality of the evidence as very low as the result of study limitations, small numbers of events, and small sample sizes, with imprecision in the confidence interval (CI). We were not able to perform meta-analysis because of heterogeneity related to the different interventions evaluated between included studies. Very low-quality evidence from one trial (20 participants) comparing effects of rivastigmine plus rehabilitation versus rehabilitation on overall USN at discharge showed the following: Barrage (mean difference (MD) 0.30, 95% confidence interval (CI) -0.18 to 0.78); Letter Cancellation (MD 10.60, 95% CI 2.07 to 19.13); Sentence Reading (MD 0.20, 95% CI -0.69 to 1.09), and the Wundt-Jastrow Area Illusion Test (MD -4.40, 95% CI -8.28 to -0.52); no statistical significance was observed for the same outcomes at 30 days' follow-up. In another trial (10 participants), study authors showed statistically significant reduction in omissions in the three cancellation tasks under transdermal nicotine treatment (mean number of omissions 2.93 ± 0.5) compared with both baseline (4.95 ± 0.8) and placebo (5.14 ± 0.9) (main effect of treatment condition: F (2.23) = 11.06; P value < 0.0001). One major adverse event occurred in the transdermal nicotine treatment group, and treatment was discontinued in the affected participant. None of the included trials reported data on several of the prespecified outcomes (falls, balance, depression or anxiety, poststroke fatigue, and quality of life).

AUTHORS' CONCLUSIONS

The quality of the evidence from available RCTs was very low. The effectiveness and safety of pharmacological interventions for USN after stroke are therefore uncertain. Additional large RCTs are needed to evaluate these treatments.

Treatment of Visual Perceptual Disorders Post Stroke

Visual perceptual disorders are a common clinical consequence of stroke. They include unilateral neglect, which has a major impact on rehabilitation outcome. The nature of the behavioral deficits associated with neglect has suggested that behavioral modification strategies may improve performance. This article presents a critical review and synthesis of published research evidence for the effectiveness of treatments for visual perceptual disorders after stroke. The strongest evidence for rehabilitation effectiveness was for the following: (a) specific treatment for perceptual disorders; and (b) specific training for neglect (including visual scanning). Findings also suggest that more research is needed into how the assessment of specific features of visual perceptual disorders might lead to improved methods for rehabilitation, including the use of assistive devices for mobility and activities of daily living.

Large-scale changes in network interactions as a physiological signature of spatial neglect

The relationship between spontaneous brain activity and behaviour following focal injury is not well understood. Here, we report a large-scale study of resting state functional connectivity MRI and spatial neglect following stroke in a large (n=84) heterogeneous sample of first-ever stroke patients (within 1-2 weeks). Spatial neglect, which is typically more severe after right than left hemisphere injury, includes deficits of spatial attention and motor actions contralateral to the lesion, and low general attention due to impaired vigilance/arousal. Patients underwent structural and resting state functional MRI scans, and spatial neglect was measured using the Posner spatial cueing task, and Mesulam and Behavioural Inattention Test cancellation tests. A principal component analysis of the behavioural tests revealed a main factor accounting for 34% of variance that captured three correlated behavioural deficits: visual neglect of the contralesional visual field, visuomotor neglect of the contralesional field, and low overall performance. In an independent sample (21 healthy subjects), we defined 10 resting state networks consisting of 169 brain regions: visual-fovea and visual-periphery, sensory-motor, auditory, dorsal attention, ventral attention, language, fronto-parietal control, cingulo-opercular control, and default mode. We correlated the neglect factor score with the strength of resting state functional connectivity within and across the 10 resting state networks. All damaged brain voxels were removed from the functional connectivity:behaviour correlational analysis. We found that the correlated behavioural deficits summarized by the factor score were associated with correlated multi-network patterns of abnormal functional connectivity involving large swaths of cortex. Specifically, dorsal attention and sensory-motor networks showed: (i) reduced interhemispheric functional connectivity; (ii) reduced anti-correlation with fronto-parietal and default mode networks in the right hemisphere; and (iii) increased intrahemispheric connectivity with the basal ganglia. These patterns of functional connectivity:behaviour correlations were stronger in patients with right- as compared to left-hemisphere damage and were independent of lesion volume. Our findings identify large-scale changes in resting state network interactions that are a physiological signature of spatial neglect and may relate to its right hemisphere lateralization.

Cingulate neglect in humans: disruption of contralesional reward learning in right brain damage

Motivational valence plays a key role in orienting spatial attention. Nonetheless, clinical documentation and understanding of motivationally based deficits of spatial orienting in the human is limited. Here in a series of one group-study and two single-case studies, we have examined right brain damaged patients (RBD) with and without left spatial neglect in a spatial reward-learning task, in which the motivational valence of the left contralesional and the right ipsilesional space was contrasted. In each trial two visual boxes were presented, one to the left and one to the right of central fixation. In one session monetary rewards were released more frequently in the box on the left side (75% of trials) whereas in another session they were released more frequently on the right side. In each trial patients were required to: 1) point to each one of the two boxes; 2) choose one of the boxes for obtaining monetary reward; 3) report explicitly the position of reward and whether this position matched or not the original choice. Despite defective spontaneous allocation of attention toward the contralesional space, RBD patients with left spatial neglect showed preserved contralesional reward learning, i.e., comparable to ipsilesional learning and to reward learning displayed by patients without neglect. A notable exception in the group of neglect patients was L.R., who showed no sign of contralesional reward learning in a series of 120 consecutive trials despite being able of reaching learning criterion in only 20 trials in the ipsilesional space. L.R. suffered a cortical-subcortical brain damage affecting the anterior components of the parietal-frontal attentional network and, compared with all other neglect and non-neglect patients, had additional lesion involvement of the medial anterior cingulate cortex (ACC) and of the adjacent sectors of the corpus callosum. In contrast to his lateralized motivational learning deficit, L.R. had no lateral bias in the early phases of attentional processing as he suffered no contralesional visual or auditory extinction on double simultaneous tachistoscopic and dichotic stimulation and detected, with no exception, single contralesional visual and auditory stimuli. In a separate study, we were able to compare L.R. with another RBD patient, G.P., who had a selective lesion in the right ACC, in the adjacent callosal connections and the medial-basal prefrontal cortex. G.P. had no contralesional neglect and displayed normal reward learning both in the left and right side of space. These findings show that contralesional reward learning is generally preserved in RBD patients with left spatial neglect and that this can be exploited in rehabilitation protocols. Contralesional reward learning is severely disrupted in neglect patients when an additional lesion of the ACC is present: however, as demonstrated by the comparison between L.R. and G.P. cases, selective unilateral lesion of the right ACC does not produce motivational neglect for the contralesional space.

Dopamine system genes are associated with orienting bias among healthy individuals

Healthy individuals display subtle orienting bias, manifested as a tendency to direct greater attention toward one hemispace, and evidence suggests that this bias reflects an individual trait, which may be modulated by asymmetric dopamine signaling in striatal and frontal regions. The current study examined the hypothesis that functional genetic variants within dopaminergic genes (DAT1 3' VNTR, dopamine D2 receptor Taq1A (rs1800497) and COMT Val158Met (rs4680)) contribute to individual differences in orienting bias, as measured by the greyscales paradigm, in a sample of 197 young healthy Israeli Jewish participants. For the Taq1A variant, homozygous carriers of the A2 allele displayed significantly increased leftward orienting bias compared to the carriers of the A1 allele. Additionally, and as previously reported by others, we found that bias towards leftward orienting of attention was significantly greater among carriers of the 9-repeat allele of the DAT1 3' VNTR as compared to the individuals who were homozygous for the 10-repeat allele. No significant effect of the COMT Val158Met on orienting bias was found. Taken together, our findings support the potential influence of genetic variants on inter-individual differences in orienting bias, a phenotype relevant to both normal and impaired cognitive processes.

Brain plasticity-based therapeutics

The primary objective of this review article is to summarize how the neuroscience of brain plasticity, exploiting new findings in fundamental, integrative and cognitive neuroscience, is changing the therapeutic landscape for professional communities addressing brain-based disorders and disease. After considering the neurological bases of training-driven neuroplasticity, we shall describe how this neuroscience-guided perspective distinguishes this new approach from (a) the more-behavioral, traditional clinical strategies of professional therapy practitioners, and (b) an even more widely applied pharmaceutical treatment model for neurological and psychiatric treatment domains. With that background, we shall argue that neuroplasticity-based treatments will be an important part of future best-treatment practices in neurological and psychiatric medicine.

Don't neglect 'neglect'- an update on post stroke neglect

OBJECTIVES

Post-stroke neglect is common and an independent predictor of functional outcome. Assessment of neglect is very demanding, the treatment extremely difficult and the literature vast; we performed a literature search for all aspects of this difficult subject.

METHODS

We searched the PubMed, EMBASE databases and historical manuals for authoritative studies on post stroke neglect between 1951 and 2011.

FINDINGS

There is a great dearth of randomised controlled data on neglect because standardised assessment does not occur frequently. Eighty-eight manuscripts were identified in the literature, which were quite heterogeneous in their content and addressing diverse aspects of this clinical entity.

INTERPRETATION AND IMPLICATIONS

The most important historical papers were selected along with the most widely accepted and proven strategies for assessment and treatment. Standardised assessment of neglect does not always occur, but several useful strategies are available and are described in the following sections.

Reward modulates spatial neglect

BACKGROUND

Reward has been shown to affect attention in healthy individuals, but there have been no studies addressing whether reward influences attentional impairments in patients with focal brain damage.

METHODS

Using two novel variants of a widely-used clinical cancellation task, we assessed whether reward modulated impaired attention in 10 individuals with left neglect secondary to right hemisphere stroke.

RESULTS

Reward exposure significantly reduced neglect, as measured by total targets found, left-sided targets found and centre of cancellation, across the patient group. Lesion analysis showed that lack of response to reward was associated with damage to the ipsilateral striatum.

CONCLUSIONS

This is the first experimental evidence that reward can modulate attentional impairments following brain damage. These results have significant implications for the development of behavioural and pharmacological therapies for patients with attentional disorders.

Rehabilitation of spatial neglect

Spatial neglect is a frequent cause of disability associated with high costs and duration of hospital stay, increased family burden, and requirements for skilled chronic care. This condition is disproportionately more frequent with right than left hemispheric injury and it is characterized by perceptual, representational, and behavioral deficits involving or directed towards the left hemispace or the left hemibody. Spatial dysfunction is conceptualized into two major components: the perceptual/representational "where" component that results mainly from injury to posterior brain regions and the premotor/intentional "aiming" component that results mostly from damage to anterior brain regions. Additionally, deficits in arousal, vigilance, affective symptoms, and disorders of emotional communication may compound the clinical manifestations of spatial neglect. Evidence-based sources that evaluate the effectiveness of rehabilitation treatments for neglect are, unfortunately, unable to provide a unified consensus for the efficacy of a given treatment approach. The reasons for this failure are related to internal inconsistencies defining appropriate criteria for treatment success and lack of characterization of neglect mechanisms and considerations of patient characteristics related to treatment failure. In this chapter we advocate the use of visual scanning, limb activation therapy, and "general treatment" because we believe that they are appropriately supported by different sources and they may be useful for experimental trials and standardized clinical care. We advocate an integrative approach that takes advantage of the same rehabilitation strategy or task to treat different perceptual, representational, and premotor components of neglect. A variety of therapies that may be familiar to the rehabilitation team may be useful as long as they are applied in a systematized program and are based on good clinical judgment. Information regarding adjuvant pharmacological therapy is sparse but different agents with aminergic and cholinergic activity may be useful. Medication with sedative, antidopaminergic or anticholinergic properties may interfere with the rehabilitation process and should be avoided.

The nonspatial side of spatial neglect and related approaches to treatment

In addition to deficits in spatial attention, individuals with persistent spatial neglect almost universally exhibit nonspatially lateralized deficits in sustained and selective attention, and working memory. However, nonspatially lateralized deficits in neglect have received considerably less attention in the literature than deficits in spatial attention. This is in spite of the fact that nonspatially lateralized deficits better predict the chronicity and functional disability associated with neglect than spatially lateralized deficits. Furthermore, only a few treatment studies have specifically targeted nonspatially lateralized deficits as a means to improve spatial neglect. In this chapter, we will briefly review several models of spatial attention bias in neglect before focusing on nonspatial deficits and the mechanisms of nonspatial-spatial interactions and implications for treatment. Treatment approaches that more completely address nonspatial deficits and better account for their interactions with spatial attention will likely produce better outcomes.

Neuroplasticity and functional recovery in multiple sclerosis

The development of therapeutic strategies that promote functional recovery is a major goal of multiple sclerosis (MS) research. Neuroscientific and methodological advances have improved our understanding of the brain's recovery from damage, generating novel hypotheses about potential targets and modes of intervention, and laying the foundation for development of scientifically informed recovery-promoting strategies in interventional studies. This Review aims to encourage the transition from characterization of recovery mechanisms to development of strategies that promote recovery in MS. We discuss current evidence for functional reorganization that underlies recovery and its implications for development of new recovery-oriented strategies in MS. Promotion of functional recovery requires an improved understanding of recovery mechanisms that can be modulated by interventions and the development of robust measurements of therapeutic effects. As imaging methods can be used to measure functional and structural alterations associated with recovery, this Review discusses their use to obtain reliable markers of the effects of interventions.

Dopamine asymmetries predict orienting bias in healthy individuals

Pseudoneglect is traditionally viewed as reflecting right hemisphere specialization for processing spatial information, resulting in orienting toward the contralateral, left, hemispace. Recent evidence suggests that healthy individuals differ from each other in both direction and magnitude of orienting bias, and moreover, the bias displayed by a person is consistent across time, suggesting that it may represent a trait of the individual. Animal studies reveal consistent orienting bias within an individual, which reflects asymmetry in dopaminergic brain systems. We measured basal D2-like receptor binding using positron emission tomography and the high-affinity ligand [F-18]fallypride, to test the hypothesis that asymmetry in dopaminergic neurotransmission in healthy humans modulates the orienting bias in humans. As predicted, we found that individual differences in the direction and magnitude of the orienting bias were strongly associated with the pattern of asymmetric binding of dopamine (DA) D2 receptors in the striatum, as well as clusters in the frontal and temporal cortex. These findings show for the first time that orienting bias reflects individual differences in the lateralization of DA systems in the healthy human brain.

Dopamine transporter genotype predicts attentional asymmetry in healthy adults

A number of recent studies suggest that DNA variation in the dopamine transporter gene (DAT1) influences spatial attention asymmetry in clinical populations such as ADHD, but confirmation in non-clinical samples is required. Since non-spatial factors such as attentional load have been shown to influence spatial biases in clinical conditions, here we sought to determine whether any association between DAT1 genotype and spatial bias might be moderated by non-spatial attentional load. Healthy adults were asked to react to sudden onset peripheral targets while demand on non-spatial attention was manipulated via a central task. Participants were genotyped for a DAT1 variable number of tandem repeat (VNTR) polymorphism. The 10-repeat allele of this variant is a replicated susceptibility allele for ADHD and has been shown to associate with spatial bias. As expected, an overall leftward asymmetry/pseudoneglect was observed when the data were averaged across the entire sample. When data were stratified by DAT1 genotype, individuals lacking homozygosity for the 10-repeat DAT1 allele (non-10/10) showed a pronounced leftward bias that was significantly different from zero. In line with past reports from children with ADHD, this leftward bias was attenuated in individuals who were homozygous for the DAT1 10-repeat allele (10/10), suggestive of relatively weaker right hemisphere dominance for spatial attention. This effect of DAT1 genotype on spatial bias was not modulated by non-spatial attention load. These data confirm in healthy adult participants both the existence and the direction of the relationship previously reported between DAT1 genotype and spatial bias in children with ADHD. These data add to a growing body of evidence showing that spatial attentional asymmetry is a stable quantitative trait, with individual differences in this trait significantly predicted by common DNA variation in the DAT1 gene.

The effects of the dopamine agonist rotigotine on hemispatial neglect following stroke

Hemispatial neglect following right-hemisphere stroke is a common and disabling disorder, for which there is currently no effective pharmacological treatment. Dopamine agonists have been shown to play a role in selective attention and working memory, two core cognitive components of neglect. Here, we investigated whether the dopamine agonist rotigotine would have a beneficial effect on hemispatial neglect in stroke patients. A double-blind, randomized, placebo-controlled ABA design was used, in which each patient was assessed for 20 testing sessions, in three phases: pretreatment (Phase A1), on transdermal rotigotine for 7-11 days (Phase B) and post-treatment (Phase A2), with the exact duration of each phase randomized within limits. Outcome measures included performance on cancellation (visual search), line bisection, visual working memory, selective attention and sustained attention tasks, as well as measures of motor control. Sixteen right-hemisphere stroke patients were recruited, all of whom completed the trial. Performance on the Mesulam shape cancellation task improved significantly while on rotigotine, with the number of targets found on the left side increasing by 12.8% (P = 0.012) on treatment and spatial bias reducing by 8.1% (P = 0.016). This improvement in visual search was associated with an enhancement in selective attention but not on our measures of working memory or sustained attention. The positive effect of rotigotine on visual search was not associated with the degree of preservation of prefrontal cortex and occurred even in patients with significant prefrontal involvement. Rotigotine was not associated with any significant improvement in motor performance. This proof-of-concept study suggests a beneficial role of dopaminergic modulation on visual search and selective attention in patients with hemispatial neglect following stroke.

Age-related changes in visual pseudoneglect

Pseudoneglect is a slight but consistent leftward attentional bias commonly observed in healthy young populations, purportedly explained by right hemispheric dominance. It has been suggested that normal aging might be associated with a decline of the right hemisphere. According to this hypothesis, a few studies have shown that elderly tend to exhibit a rightward attentional bias in line bisection. In the present study, we tested this hypothesis in young and older participants using a perceptual landmark task. Results yield evidence for an age-related shift, from a strong attentional leftward bias in young adults toward a suppressed or even a reversed bias in the elderly. Right hemisphere impairment coupled to a left hemispheric compensation might explain the perceptual shift observed in older adults. However, a decline in corpus callosum function cannot be excluded. Alternatively, these results may be in agreement with the hypothesis of an age-related specific inhibition of return dysfunction, an overt attentional orienting mechanism, and/or a decrease of dopamine.

Rehabilitation in practice: Hemispatial neglect: approaches to rehabilitation

This series of articles for rehabilitation in practice aims to cover a knowledge element of the rehabilitation medicine curriculum. Nevertheless they are intended to be of interest to a multidisciplinary audience. The competency addressed in this article is 'The trainee consistently demonstrates a knowledge of the pathophysiology of various specific impairments including cognitive dysfunction including perception' and 'management approaches for specific impairments including cognitive dysfunction including perception'. The article focuses on hemispatial neglect as a common and difficult to manage problem in clinical practice.

The effect of nicotine on visuospatial attention in chronic spatial neglect depends upon lesion location

The deficit to reorient attention from ipsilesional to contralesional space is one key feature of the spatial neglect syndrome. As previous studies suggest that reorienting of visuospatial attention is modulated by cholinergic neurotransmission, we investigated whether cholinergic stimulation with nicotine (Nicorette 2 mg, Pharmacia/Pfizer, Helsingborg, Sweden) facilitates attentional reorienting in spatial neglect patients. Nine nonsmoking patients with stable neglect symptoms were investigated in a within-subject cross-over design. We used a location-cueing paradigm and analysed reaction time (RT) differences between validly and invalidly cued, as well as between neutrally cued and uncued targets as a function of hemifield and drug. Moreover, since the nicotine effect is mediated by parietal brain areas in healthy subjects, we tested whether lesion location influences the pharmacological effect. Nicotine speeded RTs in valid and invalid trials nonspecifically, without modulating the validity effect in the location-cueing task in the whole group of patients. Lesion-symptom mapping revealed a relationship between lesion site and the pharmacological effect on reorienting to contralesional space in right parietal and temporal brain regions. We conclude that in patients with chronic spatial neglect the performance in the location-cueing paradigm can be modulated by a cholinergic stimulant provided that the lesion spares right parietal and temporal cortex.

Rehabilitation approaches to hemineglect

BACKGROUND

Hemineglect is a difficult neurologic condition to rehabilitate. It arises predominantly from right brain injury, and manifests heterogeneously in clinical deficits such as poor visual exploration to the left, inaccurate assessment of the midpoint of a line, left limb hypokinesis, and anosognosia. Most of the cognitive dysfunction produced by hemineglect is because of an asymmetric distribution of attention, either with respect to extrapersonal space or to an object being viewed. Many treatments draw on hemineglect theory to attempt to mediate the basic asymmetry of attention.

REVIEW SUMMARY

Treatment approaches can be divided into 2 main categories. Extrinsic or "top-down" approaches require active participation of the patient under the guidance of a therapist. The most common approach of this type is visual scanning therapy in which the patient is continually instructed to move the gaze leftward into the neglected space. Intrinsic or "bottom-up" approaches manipulate stimulus characteristics, sensory input, or the brain directly in an attempt to alter the interhemispheral attentional imbalance. Examples of this approach include vestibular stimulation of the left side, sensory activation of the left limb, and transcranial magnetic stimulation of the overactive left hemisphere. Combined approaches such as prism adaptation have also shown good results.

CONCLUSIONS

Hemineglect is a complicated disorder that poses challenges to treatment. A paucity of clinical trial evidence limits our ability to extrapolate experimental mediation of hemineglect to globally improved functioning. Nonetheless, many treatment approaches appear promising. Underlying neuroscience may help guide future treatment approaches.

Effects of psychostimulants on alertness and spatial bias in healthy participants

Converging evidence from neuropsychological and neuroimaging studies suggests that the ability to maintain an alert, ready-to-respond state is mediated by a network of right-hemisphere frontal and parietal cortical areas. This right lateralization may help to explain why visuospatial hemineglect, a cluster of deficits in detecting and responding to contralesional stimuli, is more common and persistent after right-hemisphere lesions. Indeed, it has been hypothesized that this asymmetry reflects a direct, functional link between alertness and spatial attention. In the present study, we investigated whether a pharmacologically induced increase in alertness would influence lateral bias in healthy people. Eighteen healthy participants were each given placebo or the psychostimulant drugs methylphenidate 40 mg or modafinil 400 mg on separate days and completed an hour-long version of the spatially sensitive landmark task. For those participants who demonstrated the expected alerting effect of modafinil, there was a significant Condition by Time interaction, consistent with the effects of the drug resisting time-on-task rightward drifts in spatial bias in the placebo condition. In contrast, no effect of methylphenidate on spatial bias was observed. These results suggest that spatial bias may be modulated by a psychostimulant-induced increase in alertness, supporting the hypothesis of a direct, functional link between right-hemisphere systems controlling alertness and visuospatial attention.

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

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

Translation Research for the Rehabilitation of Left Spatial Neglect and Associated Disorders of Attention in Stroke Patients

The syndrome of unilateral neglect, typified by a lateralized attention bias and neglect of contralateral space, is an important cause of morbidity and disability after a stroke. In this review, we discuss the challenges that face researchers attempting to elucidate the mechanisms and effectiveness of rehabilitation treatments. The neglect syndrome is a heterogeneous disorder, and it is not clear which of its symptoms cause ongoing disability. We review current methods of neglect assessment and propose logical approaches to selecting treatments, while acknowledging that further study is still needed before some of these approaches can be translated into routine clinical use. We conclude with systems-level suggestions for hypothesis development that would hopefully form a sound theoretical basis for future approaches to the assessment and treatment of neglect.

Schizotypy and pseudoneglect: a critical update on theories of hemispheric asymmetries

INTRODUCTION

Positive schizotypy has been associated with a leftward spatial bias (pseudoneglect) in different tasks and populations. We tested whether this relationship (1) can be observed for two different hemispatial tasks in the same participants, and (2) is specific to positive schizotypy.

METHODS

Forty right-handed men performed a conventional line bisection task and a whole-body movement task. In the latter task, participants were presented with illuminated target locations on the floor, and had to visit the remembered locations (equal number in right and left hemispace) after a short time interval. We assessed side preferences in both tasks. Positive schizotypy, negative schizotypy, and cognitive disorganisation were assessed with a validated self-report questionnaire.

RESULTS

Irrespective of schizotypy, pseudoneglect was observed in both tasks. We found a rightward bisection and walking bias as a function of positive schizotypy, and also as a function of cognitive disorganisation for walking initiation.

DISCUSSION

This unexpected finding resulted in a review of hemispheric asymmetry for function in schizotypy, and in the discussion of potential variables that might account for the present discrepancy. We suggest that different schizotypy questionnaires and their presentation mode might be a potential contributor to the opposite findings in the literature.

Amantadine treatment of hemispatial neglect: a double-blind, placebo-controlled study

OBJECTIVE

The resemblance of some aspects of the hemispatial neglect syndrome (hypokinesia, decreased arousal) to aspects of Parkinsonian syndromes, and the success of amantadine in treating disorders of attention, prompted a placebo-controlled, double-blind trial of amantadine, an inhibitor of the N-methyl D-aspartate (NMDA) glutamate receptor that modulates dopamine transmission, in four patients with chronic hemispatial neglect.

DESIGN

Patients received placebo or 100 mg of amantadine twice a day in an ABA design. Dependent measures of drug effect included an extensive battery of tests assessing arousal, hemiinattention, hemihypokinesia, personal neglect, disability, anosognosia, family burden, and naturalistic action.

RESULTS

There was no evidence of increased adverse effects with the treatment drug compared with placebo. Of the 17 measures used to assess treatment response in the four patients (68 measures total), linear regressions revealed significant positive treatment effects on very few (four) measures (uncorrected for multiple comparisons), and scattered negative responses to treatment were evident on three measures. The vast majority of measures showed no change in response to treatment.

CONCLUSIONS

Possible reasons for failure of treatment effects in the present study are discussed. Additional study will be required to determine whether there are neglect patients who may benefit from amantadine.

Anatomical correlates of directional hypokinesia in patients with hemispatial neglect

Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prevent patients from attending and responding to the side of space and of the body opposite a damaged hemisphere (contralesional side). Neglect also involves motor deficits: patients may be slower to initiate a motor response to targets appearing in the left hemispace, even when using their unaffected arm (directional hypokinesia). Although this impairment is well known, its anatomical correlate has not been established. We tested 52 patients with neglect after right hemisphere stroke, and conducted an anatomical analysis on 29 of them to find the anatomical correlate of directional hypokinesia. We found that patients with directional hypokinesia had a lesion involving the ventral lateral putamen, the claustrum, and the white matter underneath the frontal lobe. Most importantly, none of the patients without directional hypokinesia had a lesion in the same region. The localization of neglect's motor deficits to the basal ganglia establishes interesting homologies with animal data; it also suggests that a relative depletion of dopamine in the nigrostriatal pathway on the same side of the lesion may be an important pathophysiological mechanism potentially amenable to intervention.

Cognitive Rehabilitation Interventions for Neglect and Related Disorders: Moving from Bench to Bedside in Stroke Patients

The spatial neglect syndrome, defined by asymmetric attention and action not attributed to primary motor or sensory dysfunction and accompanied by functional disability, is a major cause of post-stroke morbidity. In this review, we consider the challenges and obstacles facing scientific researches wishing to evaluate the mechanisms and effectiveness of rehabilitation interventions. Spatial neglect is a heterogeneous disorder, for which consensus research definitions are not currently available, and it is unclear which of the deficits associated with the syndrome causes subsequent disability. We review current opinion about methods of assessment, suggest a rational approach to selecting therapies which requires further study, and make systems-level and theoretical recommendations for building theory. We lastly review some creative questions for consideration in future research.

Therapeutic effects of caloric stimulation and optokinetic stimulation on hemispatial neglect

Hemispatial neglect refers to a cognitive disorder in which patients with unilateral brain injury cannot recognize or respond to stimuli located in the contralesional hemispace. Hemispatial neglect in stroke patients is an important predictor for poor functional outcome. Therefore, there is a need for effective treatment for this condition. A number of interventions for hemispatial neglect have been proposed, although an approach resulting in persistent improvement is not available. Of these interventions, our review is focused on caloric stimulation and optokinetic stimulation. These lateralized or direction-specific stimulations of peripheral sensory systems can temporarily improve hemispatial neglect. According to recent functional MRI and PET studies, this improvement might result from the partial (re)activation of a distributed, multisensory vestibular network in the lesioned hemisphere, which is a part of a system that codes ego-centered space. However, much remain unknown regarding exact signal timing and directional selectivity of the network.

Rebalancing parietal activation underlies resolution of hemispatial neglect after right frontal stroke

This study sought to identify changes in neural activation, revealed by functional magnetic resonance imaging (fMRI), associated with the recovery of left hemispatial neglect after a right frontal stroke. The investigators studied 11 subjects who had left neglect after strokes that included damage to the right frontal cortex (in many cases also involving the right parietal and/or temporal cortex) using traditional behavioral tests for hemispatial neglect and spatial attention tasks during fMRI in the acute and chronic stages of recovery. They found that patients showed abnormally increased left dorsal parietal activation and abnormally decreased right dorsal parietal activation in the acute stage, and that activation normalized (decreased on the left and increased on the right) when left neglect improved. Activation in the visual cortex was also acutely higher in the left than right ventral and dorsal occipital cortex, but became more balanced with recovery. Activation in the right superior temporal gyrus depended on the accuracy in reorienting to unexpected targets in the right or left visual field, and was influenced by the stage of recovery. The results were interpreted as providing additional support for a new model of the neuroanatomical basis of hemispatial neglect. This model leads to specific predictions regarding interventions that may be useful for reducing persistent hemispatial neglect after stroke. For example, suppressing hyperactivity in the left dorsal parietal cortex using transcranial magnetic stimulation may to help restore the balance of activation during spatial attention and improve directed attention to the left.

Auditory Neglect: What and Where in Auditory Space

A sound that we hear in a natural setting allows us to identify the sound source and to localise it in space. Several lines of evidence indicate that the two aspects are processed in anatomically distinct cortical networks. Auditory areas that are part of the What or Where processing streams have been identified recently in man and in non-human primates. Comparison between anatomical and activation studies suggests that processing within either stream can be modulated by specific attentional factors. Attending to auditory events can be affected in neglect. Bisiach et al. (1984) described systematic directional errors to the ipsilesional space, which was considered a manifestation of hemispatial neglect and interpreted as a disruption of the neural network providing the internal representation of egocentric space. The other manifestation of auditory neglect is contralesional extinction in dichotic listening condition (Heilman and Valenstein, 1972). Recently two types of auditory neglect have been described, one corresponding to a primarily attentional deficit associated with basal ganglia lesions and the other to distortions of auditory space representations associated with parieto-prefrontal lesions (Bellmann et al., 2001). Based on studies of sound detection and sound recognition following hemispheric lesions we argue that the two types of neglect correspond to disturbed processing in either the What or the Where stream.

Hemispatial neglect

The syndrome of hemispatial neglect is characterised by reduced awareness of stimuli on one side of space, even though there may be no sensory loss. Although it is extremely common, it has proven to be a challenging condition to understand, and to treat. New insights from detailed behavioural and anatomical studies in patients, as well as functional imaging in healthy individuals, have begun to reveal some of the component deficits underlying the disorder. This review focuses on important clinical issues in neglect, including bedside diagnostic tests and emerging therapeutic and rehabilitation methods, involving both behavioural and drug treatments.

Infusion of apomorphine into the dorsocentral striatum produces acute drug-induced recovery from neglect produced by unilateral medial agranular cortex lesions in rats

Previous studies have shown that systemic administration of apomorphine is effective in producing acute drug-induced recovery from neglect induced by unilateral medial agranular cortex (AGm) lesions. More recent studies have demonstrated that recovery from neglect may be due to plastic changes occurring in the dorsal central striatum (DCS). Further, lesions of the DCS produce neglect that does not respond to systemic administration of apomorphine, suggesting that this area may be crucial for the therapeutic effects of apomorphine. In the present study, the behavioral effects of apomorphine infused into the DCS of animals with AGm lesion-induced neglect were examined to determine whether the DCS is a site of drug action. An infusion of 0.375 micro g of apomorphine into the DCS, but not a lateral striatal control area, was effective in producing acute recovery from neglect. The results of this study support the crucial role of the DCS in recovery from neglect induced by unilateral AGm lesions and suggest that the DCS may be an important site of action for the therapeutic effects of apomorphine. Because dopamine agonist therapy has been shown to be effective in humans with neglect, the results of the current study may represent an important step in the development of future pharmacotherapies.