Visuospatial Neglect - a Theory-Informed Overview of Current and Emerging Strategies and a Systematic Review on the Therapeutic Use of Non-invasive Brain Stimulation

A bibliometric review of unilateral neglect: Trends, frontiers, and frameworks

BACKGROUND

Owing to the adverse effects of unilateral neglect (UN) on rehabilitation outcomes, fall risk, and activities of daily living, this field has gradually got considerable interest. Notwithstanding, there is presently an absence of efficient portrayals of the entire research field; hence, the motivation behind this study was to dissect and evaluate the literature published in the field of UN following stroke and other nonprogressive brain injuries to identify hotspots and trends for future research.

MATERIALS AND METHODS

Original articles and reviews related to UN from 1970 to 2022 were retrieved from the Science Citation Index Expanded of the Web of Science Core Collection. CiteSpace, VOSviewer, and Bibliometrix software were used to observe publication fields, countries, and authors.

RESULTS

A total of 1,202 publications were incorporated, consisting of 92% of original articles, with an overall fluctuating upward trend in the number of publications. Italy, the United Kingdom, and the United States made critical contributions, with Neuropsychologia being the most persuasive academic journal, and Bartolomeo P. ranked first in both the quantity of publications and co-citations. Keywords were divided into four clusters, and burst keyword detection demonstrated that networks and virtual reality might additionally emerge as frontiers of future development and warrant additional attention.

CONCLUSIONS

UN is an emerging field, and this study presents the first bibliometric analysis to provide a comprehensive overview of research in the field. The insights and guidance garnered from our research on frontiers, trends, and popular topics could prove highly valuable in facilitating the rapid development of this field while informing future research directions.

Targeted non-invasive brain stimulation boosts attention and modulates contralesional brain networks following right hemisphere stroke

Right hemisphere stroke patients frequently present with a combination of lateralised and non-lateralised attentional deficits characteristic of the neglect syndrome. Attentional deficits are associated with poor functional outcome and are challenging to treat, with non-lateralised deficits often persisting into the chronic stage and representing a common complaint among patients and families. In this study, we investigated the effects of non-invasive brain stimulation on non-lateralised attentional deficits in right-hemispheric stroke. In a randomised double-blind sham-controlled crossover study, twenty-two patients received real and sham transcranial Direct Current Stimulation (tDCS) whilst performing a non-lateralised attentional task. A high definition tDCS montage guided by stimulation modelling was employed to maximise current delivery over the right dorsolateral prefrontal cortex, a key node in the vigilance network. In a parallel study, we examined brain network response to this tDCS montage by carrying out concurrent fMRI during stimulation in healthy participants and patients. At the group level, stimulation improved target detection in patients, reducing overall error rate when compared with sham stimulation. TDCS boosted performance throughout the duration of the task, with its effects briefly outlasting stimulation cessation. Exploratory lesion analysis indicated that response to stimulation was related to lesion location rather than volume. In particular, reduced stimulation response was associated with damage to the thalamus and postcentral gyrus. Concurrent stimulation-fMRI revealed that tDCS did not affect local connectivity but influenced functional connectivity within large-scale networks in the contralesional hemisphere. This combined behavioural and functional imaging approach shows that brain stimulation targeted to surviving tissue in the ipsilesional hemisphere improves non-lateralised attentional deficits following stroke. This effect may be exerted via contralesional network effects.

Assessment and treatment of visuospatial neglect using active learning with Gaussian processes regression

Visuospatial neglect is a disorder characterised by impaired awareness for visual stimuli located in regions of space and frames of reference. It is often associated with stroke. Patients can struggle with all aspects of daily living and community participation. Assessment methods are limited and show several shortcomings, considering they are mainly performed on paper and do not implement the complexity of daily life. Similarly, treatment options are sparse and often show only small improvements. We present an artificial intelligence solution designed to accurately assess a patient's visuospatial neglect in a three-dimensional setting. We implement an active learning method based on Gaussian process regression to reduce the effort it takes a patient to undergo an assessment. Furthermore, we describe how this model can be utilised in patient oriented treatment and how this opens the way to gamification, tele-rehabilitation and personalised healthcare, providing a promising avenue for improving patient engagement and rehabilitation outcomes. To validate our assessment module, we conducted clinical trials involving patients in a real-world setting. We compared the results obtained using our AI-based assessment with the widely used conventional visuospatial neglect tests currently employed in clinical practice. The validation process serves to establish the accuracy and reliability of our model, confirming its potential as a valuable tool for diagnosing and monitoring visuospatial neglect. Our VR application proves to be more sensitive, while intra-rater reliability remains high.

Virtual reality tasks with eye tracking for mild spatial neglect assessment: a pilot study with acute stroke patients

Objective

Increasing evidence shows that traditional neuropsychological tests are insensitive for detecting mild unilateral spatial neglect (USN), lack ecological validity, and are unable to clarify USN in all different spatial domains. Here we present a new, fully immersive virtual reality (VR) task battery with integrated eye tracking for mild visual USN and extinction assessment in the acute state of stroke to overthrow these limitations.

Methods

We included 11 right-sided stroke patients and 10 healthy controls aged 18-75 years. Three VR tasks named the Extinction, the Storage and the Shoot the target tasks were developed to assess USN. Furthermore, neuropsychological assessment examining various parts of cognitive functioning was conducted to measure general abilities. We compared VR and neuropsychological task performance in stroke patients - those with (USN+, n = 5) and without USN (USN-, n = 6) - to healthy controls (n = 10) and tentatively reported the usability of VR system in the acute state of stroke.

Results

Patients had mostly mild neurological and USN symptoms. Nonetheless, we found several differences between the USN+ and healthy control groups in VR task performance. Compared to controls, USN+ patients showed visual extinction and asymmetry in gaze behavior and detection times in distinct spatial locations. Extinction was most evident in the extrapersonal space and delayed detection times on the extreme left and on the left upper parts. Also, USN+ patients needed more time to complete TMT A compared with USN- patients and TMT B compared with controls. VR system usability and acceptance were rated high; no relevant adverse effects occurred.

Conclusion

New VR technology with eye tracking enables ecologically valid and objective assessment methods with various exact measures for mild USN and thus could potentially improve future clinical assessments.

Rethinking Remapping: Circuit Mechanisms of Recovery after Stroke

Stroke is one of the most common causes of disability, and there are few treatments that can improve recovery after stroke. Therapeutic development has been hindered because of a lack of understanding of precisely how neural circuits are affected by stroke, and how these circuits change to mediate recovery. Indeed, some of the hypotheses for how the CNS changes to mediate recovery, including remapping, redundancy, and diaschisis, date to more than a century ago. Recent technological advances have enabled the interrogation of neural circuits with ever greater temporal and spatial resolution. These techniques are increasingly being applied across animal models of stroke and to human stroke survivors, and are shedding light on the molecular, structural, and functional changes that neural circuits undergo after stroke. Here we review these studies and highlight important mechanisms that underlie impairment and recovery after stroke. We begin by summarizing knowledge about changes in neural activity that occur in the peri-infarct cortex, specifically considering evidence for the functional remapping hypothesis of recovery. Next, we describe the importance of neural population dynamics, disruptions in these dynamics after stroke, and how allocation of neurons into spared circuits can restore functionality. On a more global scale, we then discuss how effects on long-range pathways, including interhemispheric interactions and corticospinal tract transmission, contribute to post-stroke impairments. Finally, we look forward and consider how a deeper understanding of neural circuit mechanisms of recovery may lead to novel treatments to reduce disability and improve recovery after stroke.

Music-based interventions for unilateral spatial neglect: A systematic review

This study aimed to evaluate the effects of music-based interventions on unilateral spatial neglect. Five databases were retrieved prior to May 5, 2022. A range of study designs were considered, including randomized controlled trials, controlled clinical trials, cohorts, and case series/reports. Types of music-based interventions were not limited. Methodological quality of randomized trials were evaluated using the RoB 2 tool, and the RoBiNT scale was utilized to assess the quality of case studies. Two authors independently summarized main results for assessments. Search strategies identified 186 potentially relevant articles, and 10 articles were collected for in-depth analysis. Preliminary results showed that USN patients performed better in cancellation tests than bisection tests after music-based intervention. In summary, pleasant music listening may have a beneficial effect on the visual attention of USN patients, and it can be hypothesized that this is related to the positive mood and emotions of patients induced by music. Music with a dynamic auditory stimulus as a new music listening programme in USN rehabilitation is worthy of further investigation. Instrument playing intervention can be considered as a multisensory stimulation to ameliorate neglect performance via multiple mechanisms. However, current results only support the short-term positive effects of music-based interventions on USN.

A frontal transcallosal inhibition loop mediates interhemispheric balance in visuospatial processing

Interhemispheric communication through the corpus callosum is required for both sensory and cognitive processes. Impaired transcallosal inhibition causing interhemispheric imbalance is believed to underlie visuospatial bias after frontoparietal cortical damage, but the synaptic circuits involved remain largely unknown. Here, we show that lesions in the mouse anterior cingulate area (ACA) cause severe visuospatial bias mediated by a transcallosal inhibition loop. In a visual-change-detection task, ACA callosal-projection neurons (CPNs) were more active with contralateral visual field changes than with ipsilateral changes. Unilateral CPN inactivation impaired contralateral change detection but improved ipsilateral detection by altering interhemispheric interaction through callosal projections. CPNs strongly activated contralateral parvalbumin-positive (PV+) neurons, and callosal-input-driven PV+ neurons preferentially inhibited ipsilateral CPNs, thus mediating transcallosal inhibition. Unilateral PV+ neuron activation caused a similar behavioral bias to contralateral CPN activation and ipsilateral CPN inactivation, and bilateral PV+ neuron activation eliminated this bias. Notably, restoring interhemispheric balance by activating contralesional PV+ neurons significantly improved contralesional detection in ACA-lesioned animals. Thus, a frontal transcallosal inhibition loop comprising CPNs and callosal-input-driven PV+ neurons mediates interhemispheric balance in visuospatial processing, and enhancing contralesional transcallosal inhibition restores interhemispheric balance while also reversing lesion-induced bias.

Digital Therapeutics for the Egocentric and Allocentric Neglects in Patients with Brain Injury: A Mini Review

Various therapeutic approaches have been developed for neglect. Many studies have demonstrated the effect of digital therapeutics (DTx) on neglect. However, few studies have reported the effects of DTx on egocentric and allocentric neglect. The differentiation of types of neglect and separate interventions is crucial in the rehabilitation process. In this article, seven studies on DTx on egocentric and allocentric neglect were reviewed. DTx, which was employed in these studies, could be classified as follows: (1) software adaptation in traditional treatment, (2) VR game using the head-mount display as treatment, and (3) the development of a new digital program like ReMoVES. In addition, more studies and more effective results were reported for egocentric neglect than for allocentric neglect. In future studies, each effect on egocentric and allocentric neglect should be identified in detail with the appropriate use of differential evaluation and long-term application of independent DTx.

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.

Effects of Twins Therapy on Egocentric and Allocentric Neglect in Stroke Patients: A Feasibility Study

(1) Background: Existing treatment methods for neglect are concentrated on egocentric neglect and may lead to various problems such as cost/space constraints and portability. Therefore, this study seeks to determine how a new treatment (also known as twins therapy, TT) for stroke patients can improve an existing problem associated with neglect. (2) Method: A pre/post-test control group research design was used and both groups continued to receive existing rehabilitation treatment, whilst TT intervention was only added to the experimental group. TT intervention was conducted for a total of 20 sessions (1 session for 30 min/day, 5 days/week, for 4 weeks). (3) Result: There was no significant difference in the manual function test (MFT) and the Korean version of the Modified Barthel Index (K-MBI) items (p > 0.05) before and after the TT intervention. However, the score and execution time of the apple cancellation test showed a significant reduction only in the experimental group (p < 0.05). (4) Conclusion: TT not only improved egocentric neglect, but also allocentric neglect symptoms in stroke patients.

Short- and Long-Term Effects of Repetitive Transcranial Magnetic Stimulation on Poststroke Visuospatial Neglect: A Systematic Review and Meta-analysis of Randomized Controlled Trials

OBJECTIVE

This systematic review and meta-analysis aimed to assess the effects of repetitive transcranial magnetic stimulation and select a suitable protocol for poststroke visuospatial neglect.

DESIGN

PubMed, Cochrane Library, and Embase databases were searched for relevant studies from the inception date to October 31, 2021. The inclusion criteria were (1) randomized controlled trials, (2) people with visuospatial neglect, (3) treatment with different repetitive transcranial magnetic stimulation protocols, (4) comparison with sham or blank control, and (5) reports of performance measurements.

RESULTS

Data were obtained from 11 randomized controlled trials. The effects of immediate and 1-mo postintervention were measured using line bisection test, cancellation test, and Catherine Bergego Scale. Results showed statistically significant improvement when applying low-frequency (0.5-1 Hz) repetitive transcranial magnetic stimulation or continuous theta burst stimulation to the left hemisphere on short- and long-term line bisection test (standardized mean difference = -1.10, 95% confidence interval = -1.84 to -0.37; standardized mean difference = -1.25, 95% confidence interval = -2.11 to -0.39) and cancellation test (standardized mean difference = 1.08, 95% confidence interval = 0.45 to 1.71; standardized mean difference = 1.45, 95% confidence interval = 0.42, 2.47).

CONCLUSIONS

Repetitive transcranial magnetic stimulation may be considered a treatment option for poststroke visuospatial neglect. This review proves that a decrease in neuronal excitation in the left hemisphere, which restores the interhemispheric balance, benefits poststroke visuospatial neglect.

Computer-based assessment of unilateral spatial neglect: A systematic review

Background

To date, no gold standard exists for the assessment of unilateral spatial neglect (USN), a common post-stroke cognitive impairment, with limited sensitivity provided by currently used clinical assessments. Extensive research has shown that computer-based (CB) assessment can be more sensitive, but these have not been adopted by stroke services yet.

Objective

We conducted a systematic review providing an overview of existing CB tests for USN to identify knowledge gaps and positive/negative aspects of different methods. This review also investigated the benefits and barriers of introducing CB assessment tasks to clinical settings and explored practical implications for optimizing future designs.

Methodology

We included studies that investigated the efficacy of CB neglect assessment tasks compared to conventional methods in detecting USN for adults with brain damage. Study identification was conducted through electronic database searches (e.g., Scopus), using keywords and standardized terms combinations, without date limitation (last search: 08/06/2022). Literature review and study selection were based on prespecified inclusion criteria. The quality of studies was assessed with the quality assessment of diagnostic accuracy studies tool (Quadas-2). Data synthesis included a narrative synthesis, a table summarizing the evidence, and vote counting analysis based on a direction of effect plot.

Results

A total of 28 studies met the eligibility criteria and were included in the review. According to our results, 13/28 studies explored CB versions of conventional tasks, 11/28 involved visual search tasks, and 5/28 other types of tasks. The vote counting analysis revealed that 17/28 studies found CB tasks had either equal or higher sensitivity than conventional methods and positive correlation with conventional methods (15/28 studies). Finally, 20/28 studies showed CB tasks effectively detected patients with USN within different patient groups and control groups (17/28).

Conclusions

The findings of this review provide practical implications for the implementation of CB assessment in the future, offering important information to enhance a variety of methodological issues. The study adds to our understanding of using CB tasks for USN assessment, exploring their efficacy and benefits compared to conventional methods, and considers their adoption in clinical environments.

Brain stimulation can reduce unilateral spatial neglect after stroke: ELETRON trial

BACKGROUND

Rehabilitation top-down techniques based on brain stimulation present variable outcomes in unilateral spatial neglect (USN) after stroke. This study aimed to examine the effects of physical therapy after anodal and cathodal direct current stimulation (A-tDCS and C-tDCS, respectively) to improve visuospatial and functional impairments in individuals with USN after stroke.

METHODS

This double-blinded, pilot randomized clinical trial enrolled patients with USN after ischemic stroke. Randomization was stratified according to Behavior Inattention Test Conventional (BIT-C) and Catherine Bergego Scale (CBS). Outpatient physical therapy was conducted for 7.5 weeks after 20 min of tDCS. The primary outcome was the USN degree evaluated by the BIT-C. Secondary outcomes were the difference in CBS score, stroke severity [National Institutes of Health Stroke Scale (NIHSS)], disability [modified Rankin Scale (mRS)], autonomy [Barthel Index (BI), functional independence measure (FIM)], and quality of life (EQ-5D). Outcomes were analyzed using ANCOVA model corrected by age, baseline NIHSS and baseline BIT-C. Pairwise posthoc comparisons were performed using Bonferroni correction.

RESULTS

In the primary outcomes, A-tDCS led to greater improvement in BIT-C after intervention (MD: 18.4; 95%CI: 3.9-32.8; p=0.008) compared to sham. However, no significant differences were observed between A-tDCS and C-tDCS (MD: 13.9; 95%CI: -0.3-28.1; p=0.057), or C-tDCS and sham (MD: 4.5; 95%CI: -9.7-18.8; p=0.99). There were no significant differences between groups in terms of secondary outcomes.

CONCLUSIONS

A-tDCS associated with physical therapy can decrease the severity of USN after stroke. However, these preliminary findings must be confirmed by collecting additional evidence in a larger phase III trial.

REGISTRATION

URL: https://ensaiosclinicos.gov.br/; Unique Identifier RBR-78jvzx This article is protected by copyright. All rights reserved.

Using non-invasive transcranial direct current stimulation for neglect and associated attentional deficits following stroke

Neglect is a disabling neuropsychological syndrome that is frequently observed following right-hemispheric stroke. Affected individuals often present with multiple attentional deficits, ranging from reduced orienting towards contralesional space to a generalized impairment in maintaining attention over time. Although a degree of spontaneous recovery occurs in most patients, in some individuals this condition can be treatment-resistant with prominent ongoing non-spatial deficits. Further, there is a large inter-individual variability in response to different therapeutic approaches. Given its potential to alter neuronal excitability and affect neuroplasticity, non-invasive brain stimulation is a promising tool that could potentially be utilized to facilitate recovery. However, there are many outstanding questions regarding its implementation in this heterogeneous patient group. Here we provide a critical overview of the available evidence on the use of non-invasive electrical brain stimulation, focussing on transcranial direct current stimulation (tDCS), to improve neglect and associated attentional deficits after right-hemispheric stroke. At present, there is insufficient robust evidence supporting the clinical use of tDCS to alleviate symptoms of neglect. Future research would benefit from careful study design, enhanced precision of electrical montages, multi-modal approaches exploring predictors of response, tailored dose-control applications and increased efforts to evaluate standalone tDCS versus its incorporation into combination therapy.

Efficacy of Unilateral and Bilateral Parietal Transcranial Direct Current Stimulation on Right Hemispheric Stroke Patients With Neglect Symptoms: A Proof-of-Principle Study

Different transcranial direct current stimulation (tDCS) protocols have been tested to improve visuospatial neglect (VSN). So far, methodological heterogenity limits reliable conclusions about optimal stimualtion set-up. With this proof-of-principle study behavioral effects of two promising (uni- vs. bilateral) stimulation protocols were directly compared to gain more data for an appropriate tDCS protocol in subacute neglect patients. Notably, each tDCS set-up was combined with an identical sham condition to improve comparability. In a double-blind sham-controlled cross-over study 11 subacute post-stroke neglect patients received 20 minutes or 30 seconds (sham) tDCS (2 mA, 0.8 A/m²) parallel to neglect therapy randomized in unilateral (anode-reference: P4-Fp2 10-20 electroencephalography [EEG] system) and bilateral manner (anode-cathode: P4-P3) and 48h wash-out in-between. Before and immediately after stimulation performance were measured in cancellation task (bell test), and line bisection (deviation error). Significant difference between active and assigned sham condition was found in line bisection but not cancellation task. Particularly, deviation error was reduced after bilateral tDCS (hedges g^* = 0.6) compared to bilateral sham, no such advantage were obtained for unilateral stimulation (hedges g^* = 0.2). Using a direct comparison approach findings add further evidence that stimulating both hemispheres (bilateral) is superior in alleviating VSN symptoms than unilateral stimulation in subacute neglect.

Spatial Neglect and Anosognosia After Right Brain Stroke

PURPOSE OF REVIEW

Up to 80% of survivors of right brain stroke leave acute care without being diagnosed with a major invisible disability. Studies indicate that a generic cognitive neurologic evaluation does not reliably detect spatial neglect, nor does it identify unawareness of deficit after right brain stroke; this article reviews the symptoms, clinical presentation, and management of these two cognitive disorders occurring after right brain stroke.

RECENT FINDINGS

Stroke and occupational therapy practice guidelines stress a quality standard for spatial neglect assessment and treatment to reduce adverse outcomes for patients, their families, and society. Neurologists may attribute poor outcomes associated with spatial neglect to stroke severity. However, people with spatial neglect are half as likely to return to home and community, have one-third the community mobility, and require 3 times as much caregiver supervision compared with similar stroke survivors. Multiple randomized trials support a feasible first-line rehabilitation approach for spatial neglect: prism adaptation therapy; more than 20 studies reported that this treatment improves daily life independence. Evidence-based treatment of anosognosia is not as developed; however, treatment for this problem is also available.

SUMMARY

This article guides neurologists' assessment of right brain cognitive disorders and describes how to efficiently assemble and direct a treatment team to address spatial neglect and unawareness of deficit.

Improved visuospatial neglect after tDCS and computer-assisted cognitive training in Posterior Cortical Atrophy: a single-case study

Visuospatial neglect (VN) frequently occurs in Posterior Cortical Atrophy (PCA) and requires specific rehabilitation. In this single-case study, we investigated the efficacy of a computer-assisted cognitive training (CCT) alone or coupled with multiple sessions of anodal transcranial direct-current stimulation (A-tDCS) over the right posterior parietal cortex in improving left VN symptoms in a patient with PCA. The digital ReMoVES platform was used for both VN assessment and training. We found a significant improvement after CCT combined with A-tDCS within the limits of a single-case, our results suggest, for the first time, the usefulness of this combined approach in a neurodegenerative disorder.

Blinding in electric current stimulation in subacute neglect patients with current densities of 0.8 A/m2: a cross-over pilot study

Objective

Neglect after stroke is a disabling disorder and its rehabilitation is a major challenge. Transcranial direct current stimulation (tDCS) seems to be a promising adjuvant technique to improve standard care neglect therapy. Since electric fields are influenced by age-related factors, higher current densities are probably needed for effective treatment in aged stroke patients. Validation of treatment efficacy requires sham-controlled experiments, but increased current densities might comprise blinding. Therefore, a pilot study was conducted to test sham adequacy when using current density of 0.8 A/m². Whether especially neglect patients who mainly suffer from perceptual and attentional deficits are able to differentiate beyond chance active from sham tDCS was investigated in a randomized cross-over design (active/sham stimulation) in 12 early subacute patients with left-sided hemineglect. Stimulation (0.8 A/m²) was performed simultaneous to standard care neglect therapy.

Results

Odds ratio of correct guessing an atDCS condition compared to wrongly judge an atDCS condition as sham was 10.00 (95%CI 0.65–154.40, p = 0.099). However, given the small sample size and high OR, although likely somewhat overestimated, results require careful interpretation and blinding success in neglect studies with current densities of 0.8 A/m² should be further confirmed.