Visual neglect after left-hemispheric lesions: a voxel-based lesion–symptom mapping study in 121 acute stroke patients

Recovery of Visuospatial Neglect With Standard Treatment: A Systematic Review and Meta-Analysis

BACKGROUND

Visuospatial neglect is a common consequence of stroke and is characterized by impaired attention to contralesional space. Currently, the extent and time course of recovery from neglect are not clearly established. This systematic review and meta-analysis aimed to determine the recovery trajectory of poststroke neglect with standard treatment.

METHODS

PsycInfo, Embase, and MEDLINE were searched for articles reporting recovery rates of neglect after stroke. Time since stroke was categorized into early (0-3 months), mid (3-6 months), and late (>6 months) recovery phases. Random-effects models for pooled prevalence were generated for each phase, and potential sources of heterogeneity were explored with metaregressions. Methodological quality of each study was assessed using the Joanna Briggs Institute checklist, with low-quality studies excluded in sensitivity analyses.

RESULTS

The search captured 4130 articles including duplicates, and 111 full-text reviews were undertaken. A total of 27 studies reporting data from 839 stroke survivors with neglect were included for review. Meta-analyses indicated a recovery rate of 42% in the early phase, which increased to 53% in the mid-recovery phase. Additional recovery in the late phase was minimal, with an estimated 56% recovery rate. Heterogeneity of studies was high (I2>75%) in all 3 phases of recovery. Estimates were robust to sensitivity analyses. Metaregressions showed significantly greater recovery in studies that included patients with left-hemisphere lesions (β=0.275, P<0.05, I2=84%).

CONCLUSIONS

Most recovery from neglect occurs in the first 3 months, although additional gains can be expected up to 6 months poststroke. While a large proportion of patients recover from neglect, over 40% show persistent symptoms. Further research is needed on effective rehabilitation interventions, particularly focusing on patients most at risk of chronic visuospatial neglect.

REGISTRATION

URL: https://www.crd.york.ac.uk/PROSPERO/; Unique identifier: CRD42023388763.

Comprehensive voxel-wise, tract-based, and network lesion mapping reveals unique architectures of right and left visuospatial neglect

Visuospatial neglect is a common, post-stroke cognitive impairment which is widely considered to be a disconnection syndrome. However, the patterns of disconnectivity associated with visuospatial neglect remain unclear. Here, we had 480 acute stroke survivors [age = 72.8 (SD = 13.3), 44.3% female, 7.5 days post-stroke (SD = 11.3)] undertake routine clinical imaging and standardised visuospatial neglect testing. The data were used to conduct voxel-wise, tract-level, and network-level lesion-mapping analyses aimed at localising the neural correlates of left and right egocentric (body-centred) and allocentric (object-centred) visuospatial neglect. Only minimal anatomical homogeneity was present between the correlates of right and left egocentric neglect across all analysis types. This finding challenges previous work suggesting that right and left visuospatial neglect are anatomically homologous, and instead suggests that egocentric neglect may involve damage to a shared, but hemispherically asymmetric attention network. By contrast, egocentric and allocentric neglect was associated with disconnectivity in a distinct but overlapping set of network edges, with both deficits related to damage across the dorsal and ventral attention networks. Critically, this finding suggests that the distinction between egocentric and allocentric neglect is unlikely to reflect a simple dichotomy between dorsal versus ventral networks dysfunction, as is commonly asserted. Taken together, the current findings provide a fresh perspective on the neural circuitry involved in regulating visuospatial attention, and provide important clues to understanding the cognitive and perceptual processes involved in this common and debilitating neuropsychological syndrome.

Identifying large vessel occlusion at first glance in telemedicine

BACKGROUND

Telemedicine has rapidly emerged as an important tool in emergency neurology. In particular, reliable biomarkers of large vessel occlusions (LVOs) are critically necessary in order to identify the need for in-hospital mechanical thrombectomy (MT). Based on pathophysiological factors, we propose that the presence of head and/or gaze deviation alone signifies cortical hypoperfusion and is therefore a highly sensitive marker for the presence of LVO.

METHODS

We retrospectively analyzed a cohort of 160 patients, examined via telemedicine and suspected to have had an acute stroke; this included patients with ischemic or hemorrhagic stroke, transient ischemic attack, and stroke mimics. An assessment of head and gaze deviation and NIHSS score evaluation was performed. In a second analysis, patients who only had ischemia in the anterior circulation (n = 110) were evaluated.

RESULTS

Head and/or gaze deviation alone was found to be a reliable marker of LVO (sensitivity: 0.66/specificity: 0.92), as well as a sound indicator for MT (0.82/0.91), in patients with suspected ischemic stroke. The performance of this indicator further improved when patients with ischemia in the anterior circulation only were assessed (LVO: 0.70/0.93; MT: 0.86/0.90). In both analyses, head and/or gaze deviation served as a better indicator for LVO or MT compared to the prevalence of motor deficits or aphasia. Of note, in patients who had ischemia in the anterior circulation, head and/or gaze deviation performed better than the NIHSS score as an indicator for MT.

CONCLUSION

These findings confirm that the presence of head and/or gaze deviation serves as a reliable biomarker in stroke-based telemedicine for the diagnosis of LVO, as well as a strong indicator for MT. Furthermore, this marker is just as reliable as the NIHSS score but easier to assess. We therefore suggest that any stroke patient who displays head and/or gaze deviation should immediately be scheduled for vessel imaging and subsequently transported to a MT-competent center.

Prism Adaptation Treatment for Right-Sided and Left-Sided Spatial Neglect: A Retrospective Case-Matched Study

Objective

To compare the effectiveness of prism adaptation treatment (PAT) between patients with right- and left-sided spatial neglect (SN).

Design

Retrospective case-matched design.

Setting

Inpatient rehabilitation hospitals and facilities.

Participants

A total of 118 participants were selected from a clinical dataset of 4256 patients from multiple facilities across the United States. Patients with right-sided SN (median age: 71.0 [63.5-78.5] years; 47.5% female; 84.8% stroke, 10.1% traumatic/nontraumatic brain injury) were matched 1:1 with patients with left-sided SN (median age: 70.0 [63.0-78.0] years; 49.2% female; 86.4% stroke, 11.8% traumatic/nontraumatic brain injury) based on age, neglect severity, overall functional ability at admission, and number of PAT sessions completed during their hospital stay.

Intervention

Prism adaptation treatment.

Main Outcome Measures

Primary outcomes were pre-post change on the Kessler Foundation Neglect Assessment Process (KF-NAP) and the Functional Independence Measure (FIM). Secondary outcomes were whether the minimal clinically important difference was achieved for pre-post change on the FIM.

Results

We found greater KF-NAP gain for patients with right-sided SN than those with left-sided SN (Z = 2.38, P=.018). We found no differences between patients with right-sided and left-sided SN for Total FIM gain (Z=-0.204, P=.838), Motor FIM gain (Z=-0.331, P=.741), or Cognitive FIM gain (Z=-0.191, P=.849).

Conclusions

Our findings suggest PAT is a viable treatment for patients with right-sided SN just as it is for patients with left-sided SN. Therefore, we suggest prioritizing PAT within the inpatient rehabilitation setting as a treatment to improve SN symptoms regardless of brain lesion side.

The neuroanatomy of visuospatial neglect: A systematic review and analysis of lesion-mapping methodology

While visuospatial neglect is commonly associated with damage to the right posterior parietal cortex, neglect is an anatomically heterogenous syndrome. This project presents a systematic review of 34 lesion-mapping studies reporting on the anatomical correlates of neglect. Specifically, the reported correlates of egocentric versus allocentric, acute versus chronic, personal versus extra-personal, and left versus right hemisphere neglect are summarised. The quality of each included lesion-mapping analysis was then evaluated to identify methodological factors which may help account for the reported variance in correlates of neglect. Overall, the existing literature strongly suggests that egocentric and allocentric neglect represent anatomically dissociable conditions and that the anatomy of these conditions may not be entirely homologous across hemispheres. Studies which have compared the anatomy of acute versus chronic neglect have found that these conditions are associated with distinct lesion loci, while studies comparing the correlates of peripersonal/extrapersonal neglect are split as to whether these neglect subtypes are anatomically dissociable. The included studies employed a wide range of lesion-mapping analysis techniques, each producing results of varying quality and generalisability. This review concludes that the reported underlying anatomical correlates of heterogeneous visuospatial neglect vary considerably. Future, high quality studies are needed to investigate patterns of disconnection associated with clearly defined forms of visuospatial neglect in large and representative samples.

Increased scene complexity during free visual exploration reveals residual unilateral neglect in recovered stroke patients

Unilateral neglect is a common cognitive syndrome after stroke, which is defined as a spatially specific unawareness of the contralesional space. The syndrome is caused by disruptions of attentional networks in the brain, which impair the patients' ability to direct attention towards the contralesional space. During recovery, patients often learn to compensate by voluntarily directing their attention to the neglected side at the expense of cognitive resources. In this study, we examined the impact of the complexity of visual input on free visual exploration behavior of unilateral neglect and apparently recovered patients. We asked whether increasing scene complexity would allow the detection of residual unilateral neglect in recovered patients by increasing the amount of cognitive resources needed for visual processing and limiting capacities for compensation. Using virtual reality, we analyzed the spatial distribution of gaze of unilateral neglect patients, patients who had, according to conventional diagnostics, recovered from the syndrome, stroke patients with no history of unilateral neglect, and age-matched healthy controls. We manipulated the complexity of an immersive virtual scene presented on head mounted displays. We identified the orientation bias towards the ipsilesional side as a sensitive and specific marker of unilateral neglect, which was present in unilateral neglect and recovered patients but absent in stroke patients with no history of unilateral neglect and controls. Increasing scene complexity exacerbated the orientation shift in unilateral neglect patients and revealed that three out of nine (33%) recovered patients had a high probability of suffering from residual unilateral neglect as estimated by a generalized linear model using the median horizontal gaze position as a predictor.

Right Unilateral Spatial Neglect Improves with Intrinsic Motivation

Background. In the acute phase of stroke, it is well known that the incidence and severity of unilateral spatial neglect (USN) are more significant in the right hemisphere injuries. Still, the detection of USN in left hemisphere injuries has been increasing in recent years. This trend is because behavioral assessments have prevented the exclusion of patients who are difficult to assess for USN or apathy using conventional paper-and-pencil tests (e.g., aphasia). Right USN and post-stroke apathy share many common lesions. Therefore, clinical symptoms may overlap, but little validation considers this. Case Study. A man (62 years old) determined to have the right USN and apathy was treated for six weeks in 3 terms. In the first term (weeks 1 to 2), the patient was treated for the right USN by conventional therapy. In the second term (3–4 weeks), treatment for right USN and apathy by goal-directed therapy based on affinity behavior was implemented. In the third term (5–6 weeks), goal-directed therapy based on affinity behavior was discontinued, and treatment was returned to conventional therapy only. In the second term (goal-directed therapy based on affinity behavior), the improvement in patients' apathy (clinical assessment for spontaneity) was more significant than the effect size in the third term (conventional therapy). There were no significant differences in USN (catherine bergego scale) and intrinsic motivation (pittsburgh rehabilitation participation scale). However, the effect size in the second term tended to be larger than in the third term (conventional therapy). Clinical Rehabilitation Impact. This report aims to demonstrate the limitations of current treatment for cases determined to have both right USN and apathy. Second, to assess the extent to which this new intervention can complement the limitations of current treatment.

Right-side spatial neglect and white matter disconnection after left-hemisphere strokes

Spatial neglect usually concerns left-sided events after right-hemisphere damage. Its anatomical correlates are debated, with evidence suggesting an important role for fronto-parietal white matter disconnections in the right hemisphere. Here, we describe the less frequent occurrence of neglect for right-sided events, observed in three right-handed patients after a focal stroke in the left hemisphere. Patients were tested 1 month and 3 months after stroke. They performed a standardized paper-and-pencil neglect battery and underwent brain MRI with both structural and diffusion tensor (DT) sequences, in order to assess both grey matter and white matter tracts metrics. Lesions were manually reconstructed for each patient. Patients presented signs of mild right-sided neglect during visual search and line bisection. One patient also showed pathological performance in everyday life. Structural MRI demonstrated left parietal strokes in two patients, in the region extending from the postcentral gyrus to the temporo-parietal junction. One of these two patients also had had a previous occipital stroke. The remaining patient had a left frontal stroke, affecting the precentral, the postcentral gyri and the basal ganglia. DT MRI tractography showed disconnections in the fronto-parietal regions, concerning principally the superior longitudinal fasciculus (SLF). These results suggest an important role for left SLF disconnection in right-side neglect, which complements analogous evidence for right SLF disconnection in left-side neglect.

Lesion symptom mapping of domain-specific cognitive impairments using routine imaging in stroke

INTRODUCTION

This large-scale lesion-symptom mapping study investigates the necessary neuro-anatomical substrates of 5 cognitive domains frequently affected post stroke: Language, Attention, Praxis, Number, and Memory. This study aims to demonstrate the validity of using routine clinical brain imaging and standard bedside cognitive screening data from a large, real-world patient cohort for lesion-symptom mapping.

PATIENTS AND METHODS

Behavioural cognitive screening data from the Oxford Cognitive Screen and routine clinical neuroimaging from 573 acute patients was used in voxel-based lesion-symptom mapping analyses. Patients were classed as impaired or not on each of the subtests within 5 cognitive domains.

RESULTS

Distinct patterns of lesion damage were associated with different domains. Language functions were associated with damage to left hemisphere fronto-temporal areas. Visuo-spatial functions were associated with damage to posterior occipital areas (Visual Field) and the right temporo-parietal region (Visual Neglect). Different memory impairments were linked to distinct voxel clusters within the left insular and opercular cortices. Deficits which were not associated with localised voxels (e.g. executive function, praxis) represent distributed, bilateral functions.

DISCUSSION

The standardised, brief Oxford Cognitive Screen was able to reliably differentiate distinct neural correlates critically involved in supporting domain-specific cognitive abilities.

CONCLUSION

By demonstrating and replicating known brain anatomy correlates within real-life clinical cohorts using routinely collected scans and standard bedside screens, we open up VLSM techniques to a wealth of clinically relevant studies which can capitalise on using existing clinical data.

Simultaneous modeling of reaction times and brain dynamics in a spatial cueing task

Understanding how brain activity translates into behavior is a grand challenge in neuroscientific research. Simultaneous computational modeling of both measures offers to address this question. The extension of the dynamic causal modeling (DCM) framework for blood oxygenation level‐dependent (BOLD) responses to behavior (bDCM) constitutes such a modeling approach. However, only very few studies have employed and evaluated bDCM, and its application has been restricted to binary behavioral responses, limiting more general statements about its validity. This study used bDCM to model reaction times in a spatial attention task, which involved two separate runs with either horizontal or vertical stimulus configurations. We recorded fMRI data and reaction times (n= 26) and compared bDCM with classical DCM and a behavioral Rescorla–Wagner model using Bayesian model selection and goodness of fit statistics. Results indicate that bDCM performed equally well as classical DCM when modeling BOLD responses and as good as the Rescorla–Wagner model when modeling reaction times. Although our data revealed practical limitations of the current bDCM approach that warrant further investigation, we conclude that bDCM constitutes a promising method for investigating the link between brain activity and behavior.

Lesion-symptom mapping with NIHSS sub-scores in ischemic stroke patients

Background

Lesion-symptom mapping (LSM) is a statistical technique to investigate the population-specific relationship between structural integrity and post-stroke clinical outcome. In clinical practice, patients are commonly evaluated using the National Institutes of Health Stroke Scale (NIHSS), an 11-domain clinical score to quantitate neurological deficits due to stroke. So far, LSM studies have mostly used the total NIHSS score for analysis, which might not uncover subtle structure–function relationships associated with the specific sub-domains of the NIHSS evaluation. Thus, the aim of this work was to investigate the feasibility to perform LSM analyses with sub-score information to reveal category-specific structure–function relationships that a total score may not reveal.

Methods

Employing a multivariate technique, LSM analyses were conducted using a sample of 180 patients with NIHSS assessment at 48-hour post-stroke from the ESCAPE trial. The NIHSS domains were grouped into six categories using two schemes. LSM was conducted for each category of the two groupings and the total NIHSS score.

Results

Sub-score LSMs not only identify most of the brain regions that are identified as critical by the total NIHSS score but also reveal additional brain regions critical to each function category of the NIHSS assessment without requiring extensive, specialised assessments.

Conclusion

These findings show that widely available sub-scores of clinical outcome assessments can be used to investigate more specific structure–function relationships, which may improve predictive modelling of stroke outcomes in the context of modern clinical stroke assessments and neuroimaging.

Trial registration number

NCT01778335.

Right and left neglect are not anatomically homologous: A voxel-lesion symptom mapping study

Visuospatial neglect is a heterogenous syndrome which can occur following damage to either right or left hemisphere areas. This study employs voxel-lesion symptom mapping to identify the neural correlates of left and right egocentric and allocentric neglect in a large acute stroke cohort. A cohort of 446 acute stroke survivors (age = 26-95, 44% female) completed neuropsychological neglect assessment and routine clinical imaging. Similar to previous investigations, left egocentric and left allocentric neglect were associated with damage to distinct clusters of voxels within the posterior parietal and temporo-parietal junction areas. Unlike previous investigations, right egocentric neglect was found to most strongly associated with damage to more posterior voxels within left occipital cortical areas. Right allocentric neglect was found to be most strongly associated with damage to the anterior limb of the left internal capsule. Interestingly, the right hemisphere homologues of the areas implicated in right-lateralised neglect were not overlapping with those associated with left neglect impairment. This dissociation was present across both egocentric and allocentric neglect impairment. The results of this investigation suggest that right egocentric/allocentric neglect should not be characterised as a consequence of damage to left-hemisphere homologues of the right hemisphere attentional systems. These findings support the characterisation of visuospatial neglect as a heterogenous cluster of impairments rather than a unitary syndrome and provide novel insight into the neural correlates of spatial attention.

Speech apraxia and oral apraxia: association or dissociation? A multivariate lesion-symptom mapping study in acute stroke patients

The anatomical relationship between speech apraxia (SA) and oral apraxia (OA) is still unclear. To shed light on this matter we studied 137 patients with acute ischaemic left-hemisphere stroke and performed support vector regression-based, multivariate lesion–symptom mapping. Thirty-three patients presented with either SA or OA. These two symptoms mostly co-occurred (n = 28), except for few patients with isolated SA (n = 2) or OA (n = 3). All patient with either SA or OA presented with aphasia (p < 0.001) and these symptoms were highly associated with apraxia (p < 0.001). Co-occurring SA and OA were predominantly associated with insular lesions, while the insula was completely spared in the five patients with isolated SA or OA. Isolated SA occurred in case of frontal lesions (prefrontal gyrus and superior longitudinal fasciculus), while isolated OA occurred in case of either temporoparietal or striatocapsular lesions. Our study supports the notion of a predominant, but not exclusive, role of the insula in verbal and non-verbal oral praxis, and indicates that frontal regions may contribute exclusively to verbal oral praxis, while temporoparietal and striatocapsular regions contribute to non-verbal oral praxis. However, since tests for SA and OA so far intrinsically also investigate aphasia and apraxia, refined tests are warranted.

Video-Oculography During Free Visual Exploration to Detect Right Spatial Neglect in Left-Hemispheric Stroke Patients With Aphasia: A Feasibility Study

Spatial neglect has been shown to occur in 17–65% of patients after acute left-hemispheric stroke. One reason for this varying incidence values might be that left-hemispheric stroke is often accompanied by aphasia, which raises difficulties in assessing attention deficits with conventional neuropsychological tests entailing verbal instructions. Video-oculography during free visual exploration (FVE) requires only little understanding of simple non-verbal instruction and has been shown to be a sensitive and reliable tool to detect spatial neglect in patients with right-hemispheric stroke. In the present study, we aimed to investigate the feasibility of FVE to detect neglect in 10 left-hemispheric stroke patients with mild to severe aphasia as assessed by means of the Token Test, Boston Naming Test and Aachener Aphasie Test. The patient’s individual deviation between eye movement calibration and validation was recorded and compared to 20 age-matched healthy controls. Furthermore, typical FVE parameters such as the landing point of the first fixation, the mean gaze position (in ° of visual angle), the number and duration of visual fixations and the mean visual exploration area were compared between groups. In addition, to evaluate for neglect, the Bells cancellation test was performed and neglect severity in daily living was measured by means of the Catherine Bergego Scale (CBS). Our results showed that the deviation between calibration and validation did not differ between aphasia patients and healthy controls highlighting its feasibility. Furthermore, FVE revealed the typical neglect pattern with a significant leftward shift in visual exploration bahaviour, which highly correlated with neglect severity as assessed with CBS. The present study provides evidence that FVE has the potential to be used as a neglect screening tool in left-hemispheric stroke patients with aphasia in which compliance with verbal test instructions may be compromised by language deficits.

The extreme capsule and aphasia: proof-of-concept of a new way relating structure to neurological symptoms

We present anatomy-based symptom-lesion mapping to assess the association between lesions of tracts in the extreme capsule and aphasia. The study cohort consisted of 123 patients with acute left-hemispheric stroke without a lesion of language-related cortical areas of the Stanford atlas of functional regions of interest. On templates generated through global fibre tractography, lesions of the extreme capsule and of the arcuate fascicle were quantified and correlated with the occurrence of aphasia (n = 18) as defined by the Token Test. More than 15% damage of the slice plane through the extreme capsule was a strong independent predictor of aphasia in stroke patients, odds ratio 16.37, 95% confidence interval: 3.11–86.16, P < 0.01. In contrast, stroke lesions of >15% in the arcuate fascicle were not associated with aphasia. Our results support the relevance of a ventral pathway in the language network running through the extreme capsule.

Interaction between cognitive reserve and age moderates effect of lesion load on stroke outcome

The concepts of brain reserve and cognitive reserve were recently suggested as valuable predictors of stroke outcome. To test this hypothesis, we used age, years of education and lesion size as clinically feasible coarse proxies of brain reserve, cognitive reserve, and the extent of stroke pathology correspondingly. Linear and logistic regression models were used to predict cognitive outcome (Montreal Cognitive Assessment) and stroke-induced impairment and disability (NIH Stroke Scale; modified Rankin Score) in a sample of 104 chronic stroke patients carefully controlled for potential confounds. Results revealed 46% of explained variance for cognitive outcome (p < 0.001) and yielded a significant three-way interaction: Larger lesions did not lead to cognitive impairment in younger patients with higher education, but did so in younger patients with lower education. Conversely, even small lesions led to poor cognitive outcome in older patients with lower education, but didn’t in older patients with higher education. We observed comparable three-way interactions for clinical scores of stroke-induced impairment and disability both in the acute and chronic stroke phase. In line with the hypothesis, years of education conjointly with age moderated effects of lesion on stroke outcome. This non-additive effect of cognitive reserve suggests its post-stroke protective impact on stroke outcome.

Functional dissociation of multiple-object tracking mechanisms based on hemispheric asymmetries

BACKGROUND

A number of theoretical accounts have been put forward to explain the ability to simultaneously track multiple visually indistinguishable objects over a period of time. Serial processing models of visual tracking focus on the maintenance of the spatial locations of every single item over time. A more recent mechanism describes multiple object tracking as the ability to maintain a higher order representation of an abstract spatial configuration built by the illusory connection of the tracked items through their transition.

OBJECTIVE

The current study investigates the correspondence between these serial and parallel tracking accounts and the right hemispheric specialization for the space-based vs. left hemispheric for object-based attentional processing.

METHODS

Electrophysiological brain responses were recorded in two groups of patients with right- and left hemispheric lesions while performing in a multiple object tracking task.

RESULTS

The results suggest a failure to distinguish single item information for the right hemispheric patients accompanied by the absence of a known electrophysiological marker associated with single item tracking. Importantly, left hemispheric patients showed a graded behavioral and electrophysiological response to probe stimuli as a function of the congruence of the probe with the relevant target stimuli.

CONCLUSIONS

The current data suggest that the differential contribution of serial and parallel tracking mechanisms during object tracking can partly be explained by the different functional contributions of the right and left brain hemispheres.

Lateralization, functional specialization, and dysfunction of attentional networks

The present review covers the latest findings on the lateralization of the dorsal and ventral attention systems, their functional specialization, and their clinical relevance for stroke-induced attentional dysfunction. First, the original assumption of a bilateral dorsal system for top-down attention and a right-lateralized ventral system for stimulus-driven attention is critically reviewed. The evidence for the involvement of the left parietal cortex in attentional functions is discussed and findings on putative pathways linking the dorsal and ventral network are presented. In the second part of the review, we focus on the different attentional subsystems and their lateralization, discussing the differences between spatial, feature- and object-based attention, and motor attention. We also review studies based on predictive coding frameworks of attentional functions. Finally, in the third section, we provide an overview of the consequences of specific disruption within the attention networks after stroke. The role of the interhemispheric (im)balance is discussed, and the results of new promising therapeutic approaches employing brain stimulation techniques such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) are presented.

Midlevel visual deficits after strokes involving area human V4

We present the results of 51 stroke patients with free central visual fields of which about half suffer from clear deficits of midlevel vision undetected by standard clinical tests. These patients yield significantly elevated thresholds for detection and/or discrimination between forms defined by motion, colour, or line orientation ('texture'). As demonstrated by voxel-based lesion-symptom mapping (VLSM) the underlying lesions involve mainly area human V4 (hV4) located in the posterior third of the fusiform gyrus and extending into the lingual gyrus. Patient's detection thresholds correlate only very weakly between the submodalities tested, indicating partly separate neural networks on mid-level vision for colour, motion, and texture detection. Correlations are far stronger for form discrimination tasks, indicating partly shared mechanisms for even simple form discrimination of distinct visual submodalities. We conclude that deficits of visual perception are far more common after strokes in visual brain areas than is apparent in clinical practice. Our results further clarify the functional organization of midlevel visual cortical areas.

Attentional reorientation along the meridians of the visual field: Are there different neural mechanisms at play?

Hemispatial neglect, after unilateral lesions to parietal brain areas, is characterized by an inability to respond to unexpected stimuli in contralesional space. As the visual field's horizontal meridian is most severely affected, the brain networks controlling visuospatial processes might be tuned explicitly to this axis. We investigated such a potential directional tuning in the dorsal and ventral frontoparietal attention networks, with a particular focus on attentional reorientation. We used an orientation‐discrimination task where a spatial precue indicated the target position with 80% validity. Healthy participants (n = 29) performed this task in two runs and were required to (re‐)orient attention either only along the horizontal or the vertical meridian, while fMRI and behavioral measures were recorded. By using a general linear model for behavioral and fMRI data, dynamic causal modeling for effective connectivity, and other predictive approaches, we found strong statistical evidence for a reorientation effect for horizontal and vertical runs. However, neither neural nor behavioral measures differed between vertical and horizontal reorienting. Moreover, models from one run successfully predicted the cueing condition in the respective other run. Our results suggest that activations in the dorsal and ventral attention networks represent higher‐order cognitive processes related to spatial attentional (re‐)orientating that are independent of directional tuning and that unilateral attention deficits after brain damage are based on disrupted interactions between higher‐level attention networks and sensory areas.

Dissociation of visual extinction and neglect in the left hemisphere

Visual neglect and extinction are two distinct visuospatial attention deficits that frequently occur after right hemisphere cerebral stroke. However, their different lesion profiles remain a matter of debate. In the left hemisphere, a domain-general dual-loop model with distinct computational abilities onto which several cognitive functions may project, has been proposed: a dorsal stream for sensori-motor mapping in time and space and a ventral stream for comprehension and representation of concepts. We wondered whether such a distinction may apply to visual extinction and neglect in left hemisphere lesions. Of 165 prospectively studied patients with acute left hemispheric ischemic stroke with a single lesion on MRI, 122 had no visuospatial attention deficit, 10 had extinction, 31 neglect and 2 had both, visual extinction and neglect. Voxel-based-lesion-symptom mapping (VLSM, FDR<.05) showed a clear anatomical dissociation. Extinction occurred after damage to the parietal cortex (anterior bank of the intraparietal sulcus, inferior parietal lobe, and supramarginal gyrus), while visual neglect occurred after damage mainly to the temporal lobe (superior and middle temporal lobe, anterior temporal pole), inferior ventral premotor cortex, frontal operculum, angular gyrus, and insula. Direct comparison of both conditions linked extinction to intraparietal sulcus and supramarginal gyrus (FDR<.05). Thus, in the left hemisphere extinction seems to be related to dorsal stream lesions, whereas neglect maps more on the ventral stream. These data cannot be generalized to the right hemisphere. However, a domain-general point-of-view may stimulate discussion on visuospatial attention processing also in the right hemisphere.

Structural integrity of white matter tracts as a predictor of acute ischemic stroke outcome

BACKGROUND AND PURPOSE

Clinical assessment scores in acute ischemic stroke are only moderately correlated with lesion volume since lesion location is an important confounding factor. Many studies have investigated gray matter indicators of stroke severity, but the understanding of white matter tract involvement is limited in the early phase after stroke. This study aimed to measure and model the involvement of white matter tracts with respect to 24-h post-stroke National Institutes of Health Stroke Scale (NIHSS).

MATERIAL AND METHODS

A total of 96 patients (50 females, mean age 66.4 ± 14.0 years, median NIHSS 5, interquartile range: 2-9.5) with follow-up fluid-attenuated inversion recovery magnetic resonance imaging data sets acquired one to seven days after acute ischemic stroke onset due to proximal anterior circulation occlusion were included. Lesions were semi-automatically segmented and non-linearly registered to a common reference atlas. The lesion overlap and tract integrity were determined for each white matter tract in the AALCAT atlas and used to model NIHSS outcomes using a supervised linear-kernel support vector regression method, which was evaluated using leave-one-patient-out cross validation.

RESULTS

The support vector regression model using the tract integrity and tract lesion overlap measurements predicted the 24-h NIHSS score with a high correlation value of r = 0.7. Using the tract overlap and tract integrity feature improved the modeling accuracy of NIHSS significantly by 6% (p < 0.05) compared to using overlap measures only.

CONCLUSION

White matter tract integrity and lesion load are important predictors for clinical outcome after an acute ischemic stroke as measured by the NIHSS and should be integrated for predictive modeling.

Setting the midpoint of sentences: The role of the left hemisphere

The human brain has a remarkable capacity to focus processing resources based on the features and the relevance of the task at hand. The two cerebral hemispheres contribute differentially to this capacity, with the left hemisphere linguistic and right hemisphere visuo-spatial abilities each offering unique contributions. For example, previous research has established that healthy participants set the subjective mid-point of written sentences more leftwards of center, compared to unpronounceable letter strings or simple lines. Remarkably, patients with right hemisphere damage exhibiting unilateral spatial neglect also show this pattern, even though, as well known in the literature, they tend toward a rightward- bias for non-linguistic stimuli. This evidence suggests that the leftward bias for sentential material is due to linguistic, mainly left-hemisphere mediated processes, which are largely unimpaired in right brain-damaged patients, and intact in heathy participants. To test this hypothesis, we compared sentence bisection performance to that of letter strings and simple lines in left brain-damaged patients (with and without aphasia). If the larger leftward bias in the bisection of sentential material is based on linguistic processes, then the left brain-damaged patients should show a reduction or absence of a leftward bias in sentence bisection. We tested twenty-four left brain-damaged patients (12 with aphasia and 12 without aphasia), and 24 age-matched elderly participants (patients and controls were all right-handed). Participants were asked to bisect 240 stimuli, comprising: (i) affirmative and interrogative clauses, (ii) sentences with lexical and syntactic violations, (iii) letter strings and (iv) simple lines. As predicted, neurologically intact participants showed larger leftward biases in bisecting written readable sentences compared to strings of letters. In contrast, the left hemispheredamaged patients (both with and without aphasia) showed no differences in bisecting sentences and letter strings or lines. These findings indicate that the larger leftward bias exhibited by healthy participants in the bisection of sentences is likely due to ortho-phonological coding taking place implicitly during the bisection task. This ortho-phonological coding is impaired with left brain damage - also in absence of apparent aphasia - leading to the left hemispheredamaged patients showing a reduced leftward bias in sentence bisection. These findings support the hypothesis that the leftward bias in the bisection of written sentences is the result of ortho-phonological influences rather than visual-spatial biases.

Visual-spatial neglect after right-hemisphere stroke: behavioral and electrophysiological evidence

Background:

Visual-spatial neglect (VSN) is a neuropsychological syndrome, and right-hemisphere stroke is the most common cause. The pathogenetic mechanism of VSN remains unclear. This study aimed to investigate the behavioral and event-related potential (ERP) changes in patients with or without VSN after right-hemisphere stroke.

Methods:

Eleven patients with VSN with right-hemisphere stroke (VSN group) and 11 patients with non-VSN with right-hemisphere stroke (non-VSN group) were recruited along with one control group of 11 age- and gender-matched healthy participants. The visual-spatial function was evaluated using behavioral tests, and ERP examinations were performed.

Results:

The response times in the VSN and non-VSN groups were both prolonged compared with those of normal controls (P < 0.001). In response to either valid or invalid cues in the left side, the accuracy in the VSN group was lower than that in the non-VSN group (P < 0.001), and the accuracy in the non-VSN group was lower than that in controls (P < 0.05). The P1 latency in the VSN group was significantly longer than that in the control group (F[2, 30] = 5.494, P = 0.009), and the N1 amplitude in the VSN group was significantly lower than that in the control group (F[2, 30] = 4.343, P = 0.022). When responding to right targets, the left-hemisphere P300 amplitude in the VSN group was significantly lower than that in the control group (F[2, 30] = 4.255, P = 0.025). With either left or right stimuli, the bilateral-hemisphere P300 latencies in the VSN and non-VSN groups were both significantly prolonged (all P < 0.05), while the P300 latency did not differ significantly between the VSN and non-VSN groups (all P > 0.05).

Conclusions:

Visual-spatial attention function is impaired after right-hemisphere stroke, and clinicians should be aware of the subclinical VSN. Our findings provide neuroelectrophysiological evidence for the lateralization of VSN.

Cognitive reserve impacts on disability and cognitive deficits in acute stroke

OBJECTIVE

Although post-stroke cognitive deficit can significantly limit patient independence and social re-integration, clinical routine predictors for this condition are lacking. 'Cognitive reserve' limits the detrimental effects of slowly developing neurodegeneration. We aimed to determine whether comparable effects also exist in acute stroke. Using 'years of education' as a proxy, we investigated whether cognitive reserve beneficially influences cognitive performance and disability after stroke, whilst controlling for age and lesion size as measure of stroke pathology.

METHODS

Within the first week of ischemic right hemisphere stroke, 36 patients were assessed for alertness, working memory, executive functions, spatial neglect, global cognition and motor deficit at 4.9 ± 2.1 days post-stroke, in addition to routine clinical tests (NIH Stroke Scale, modified Rankin Scale on admission < 24 h post-stroke and at discharge 9.5 ± 4.7 days post-stroke). The impact of education was assessed using partial correlation analysis adjusted for lesion size, age, and the time interval between stroke and assessment. To validate our results, we compared groups with similar age and lesion load, but different education levels.

RESULTS

In the acute stroke phase, years of education predicted both severity of education independent (alertness) and education dependent (working memory, executive functions, global cognition) cognitive deficits and disability (modified Rankin Scale). Spatial neglect seemed to be independent.

INTERPRETATION

Proxies of cognitive reserve should be considered in stroke research as early as in the acute stroke phase. Cognitive reserve contributes to inter-individual variability in the initial severity of cognitive deficits and disability in acute stroke, and may suggest individualised rehabilitation strategies.

Dissociating frontal and temporal correlates of phonological and semantic fluency in a large sample of left hemisphere stroke patients

Previous lesion studies suggest that semantic and phonological fluency are differentially subserved by distinct brain regions in the left temporal and the left frontal cortex, respectively. However, as of yet, this often implied double dissociation has not been explicitly investigated due to mainly two reasons: (i) the lack of sufficiently large samples of brain-lesioned patients that underwent assessment of the two fluency variants and (ii) the lack of tools to assess interactions in factorial analyses of non-normally distributed behavioral data. In addition, previous studies did not control for task resource artifacts potentially introduced by the generally higher task difficulty of phonological compared to semantic fluency.

We addressed these issues by task-difficulty adjusted assessment of semantic and phonological fluency in 85 chronic patients with ischemic stroke of the left middle cerebral artery. For classical region-based lesion-behavior mapping patients were grouped with respect to their primary lesion location. Building on the extension of the non-parametric Brunner-Munzel rank-order test to multi-factorial designs, ANOVA-type analyses revealed a significant two-way interaction for cue type (semantic vs. phonological) by lesion location (left temporal vs. left frontal vs. other as stroke control group). Subsequent contrast analyses further confirmed the proposed double dissociation by demonstrating that (i) compared to stroke controls, left temporal lesions led to significant impairments in semantic but not in phonological fluency, whereas left frontal lesions led to significant impairments in phonological but not in semantic fluency, and that (ii) patients with frontal lesions showed significantly poorer performance in phonological than in semantic fluency, whereas patients with temporal lesions showed significantly poorer performance in semantic than in phonological fluency.

The anatomical specificity of these findings was further assessed in voxel-based lesion-behavior mapping analyses using the multi-factorial extension of the Brunner-Munzel test. Voxel-wise ANOVA-type analyses identified circumscribed parts of left inferior frontal gyrus and left superior and middle temporal gyrus that significantly double-dissociated with respect to their differential contribution to phonological and semantic fluency, respectively. Furthermore, a main effect of lesion with significant impairments in both fluency types was found in left inferior frontal regions adjacent to but not overlapping with those showing the differential effect for phonological fluency.

The present study hence not only provides first explicit evidence for the anatomical double dissociation in verbal fluency at the group level but also clearly underlines that its formulation constitutes an oversimplification as parts of left frontal cortex appear to contribute to both semantic and phonological fluency.

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Lesion study on neural correlates of phonological and semantic fluency

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Evidence for dissociable and for overlapping contributions

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Left superior and middle temporal gyri specifically crucial for semantic fluency

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Left IFG pars opercularis specifically crucial for phonological fluency

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Left IFG pars triangularis critical for both semantic and phonological fluency

Large Vessel Occlusion in Acute Stroke

Background and Purpose—

To date, no clinical score has become widely accepted as an eligible prehospital marker for large vessel occlusion (LVO) and the need of mechanical thrombectomy (MT) in ischemic stroke. On the basis of pathophysiological considerations, we propose that cortical symptoms such as aphasia and neglect are more sensitive indicators for LVO and MT than motor deficits.

Methods—

We, thus, retrospectively evaluated a consecutive cohort of 543 acute stroke patients including patients with ischemia in the posterior circulation, hemorrhagic stroke, transient ischemic attack, and stroke mimics to best represent the prehospital setting.

Results—

Cortical symptoms alone showed to be a reliable indicator for LVO (sensitivity: 0.91; specificity: 0.70) and MT (sensitivity: 0.90; specificity: 0.60) in acute stroke patients, whereas motor deficits showed a sensitivity of 0.85 for LVO (specificity: 0.53) and 0.87 for MT (specificity: 0.48).

Conclusions—

We propose that in the prehospital setting, the presence of cortical symptoms is a reliable indicator for LVO and its presence justifies transportation to an MT-capable center.

[Networks involved in motor cognition : Physiology and pathophysiology of apraxia]

Apraxia is an umbrella term for different disorders of higher motor abilities that are not explained by elementary sensorimotor deficits (e. g. paresis or ataxia). Characteristic features of apraxia that are easy to recognize in clinical practice are difficulties in pantomimed or actual use of tools as well as in imitation of meaningless gestures. Apraxia is bilateral, explaining the cognitive motor disorders and occurs frequently (but not exclusively) after left hemispheric lesions, as well as in neurodegenerative diseases, such as corticobasal syndrome and Alzheimer's disease. Apraxic deficits can seriously impair activities of daily living, which is why the appropriate diagnosis is of great relevance. At the functional anatomical level, different cognitive motor skills rely on at least partly different brain networks, namely, a ventral processing pathway for semantic components, such as tool-action associations, a ventro-dorsal pathway for sensorimotor representations of learnt motor acts, as well as a dorso-dorsal pathway for on-line motor control and, probably, imitation of meaningless gestures. While these networks partially overlap with language-relevant regions, more clear cut dissociations are found between apraxia deficits and disorders of spatial attention. In addition to behavioral interventions, noninvasive neuromodulation approaches, as well as human-computer interface assistance systems are a growing focus of interest for the treatment of apraxia.