Contraversive pushing in non-stroke patients

Abstract Background Pusher syndrome is a disorder of postural control observed in patients with right or left brain damage associated with hemiparesis. Those patients show a peculiar behavior of actively pushing away from the nonhemiparetic side and resisting against passive correction, with a tendency to fall toward the paralyzed side. Thus far this phenomenon has been exclusively associated with stroke patients. Objective We investigate the occurrence, imaging features and clinical evolution of pusher behavior in patients with acute encephalic lesions at a tertiary emergency hospital. Methods Pusher patients were identified from 530 inpatients during a 1 year period. Patients were evaluated using a standardized Scale for Contraversive Pushing (SCP), neurological examination, assessment of neuropsychological symptoms, activities of daily living function and neuroimaging studies. Results We found eight patients (1.5%) with severe contraversive pushing, three female and five male. Age at symptoms onset ranged from 48 to 80 years (mean 65.4). All patients had scores equal or above 1.5 in each tested parameter of the SCP. Six patients (75 %) had right-hemisphere brain damage. A stroke etiology was found in four patients. The other four patients had non-stroke etiology (three traumatic, one metastatic tumor). Stroke patients showed complete recovery of pusher behavior at a mean duration of 15.3 weeks. In patients with brain trauma, pushing behavior was completely resolved in a mean time of 5 weeks. Conclusions The results demonstrate that contraversive pushing may also occur in patients with non-stroke neurological lesions and suggest that resolution of symptoms may vary according to the underlying etiology.     

The pusher syndrome reverses the orienting bias caused by spatial neglect

Spatial neglect can be accompanied by a pusher syndrome (PS) which is characterized by a postural deviation towards the contralesional side. In this study, the representation of the body orientation in the horizontal plane was evaluated in neglect patients with and without PS. The participants had to align a luminous rod with the straight ahead direction, a method allowing the measure of both horizontal components of subjective straight ahead, i.e. lateral shift and yaw rotation. Eighteen patients with a lesion of the right hemisphere were compared with ten healthy participants. Patients had neglect and PS (P + N+; n = 3), neglect only (P − N+; n = 10), or neither neglect nor PS (P − N−; n = 5). P + N+ patients showed a significant leftward shift contrasting with the rightward shift of P − N+. No shift occurred in patients without neglect and controls. No significant yaw error was recorded in any groups. The original result of this study was an inversion of the sign of the bias in neglect patients with PS. This could be related to the postural disorders characterizing this syndrome, and which are opposite to those usually observed in spatial neglect. Thus, these data suggest a link between disorders of spatial representations and disorders of posture.     

The visual vertical in the pusher syndrome

The subjective visual vertical (SVV) was investigated in right brain–damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3°; n = 6) and mild in the nonneglect non–pusher patients (–1.8°; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2°; n = 4), but anticlockwise in the non–pusher neglect patients (–6.6°; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2°; sitting: +9.2°). Intra–individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.     

Visual spatial neglect in multiple sclerosis

Neuropsychological dysfunction in multiple sclerosis (MS) patients is now a well-established clinical finding. We examined the entity of visual spatial neglect in demyelinating disease and its correlation to the functional and neuroradiological parameters. The phenomenon of visual spatial neglect was examined in 20 (5 male and 15 female) MS patients. Two different examination methods were used – the line bisection test and the random shape cancellation test. The results were compared with 20 aged matched control individuals. The correlation of the visual spatial neglects to neurological deficits and handicaps, using Kurtzke's Expanded Disability Status Scale (EDSS), as well as with the MRI's neuroradiological findings, was analyzed. A highly significant different result on the line bisection test for three various line lengths (p = .006, p < .0001, p < .001) with displacement towards the right side was found. In all the cancellation subtests, a significant difference in error rate was found in comparing patients to controls toward a higher one on the left side of the MS patients (p = .005, p < .002, p < .0001 and p = .02 in the left side subtest, and p = n.s. in the right side subtest). There was no significant correlation between the cancellation tests and bisection results and the EDSS scale data, as well as with the neuroradiological findings. The present results demonstrate the presence of visual spatial neglect among MS patients, even without the demonstration of a characteristic neuroanatomical lesion. The hypotheses for this finding are discussed with a stress on the possibility of disruption of multiple intrahemispheric connections, especially under the condition of asymmetry of dominance regarding spatial attention.     

The origin of contraversive pushing: evidence for a second graviceptive system in humans

BACKGROUND: Stroke patients may exhibit the peculiar behavior of actively pushing away from the nonhemiparetic side, leading to lateral postural imbalance and a tendency to fall toward the paralyzed side. This phenomenon has been called the "pusher syndrome." OBJECTIVE: The current study analyzes the mechanism leading to contraversive pushing. METHODS: The subjective postural vertical (SPV) and subjective visual vertical (SVV) were determined in five consecutively admitted patients with severe contraversive pushing and in controls. Whereas adjustment of the SPV reflects the perceived upright orientation of the body, the SVV provides a sensitive and direction-specific measurement of peripheral and central vestibular dysfunction. RESULTS: The deficit leading to contraversive pushing is an altered perception of the body's orientation in relation to gravity. Pusher patients experience their body as oriented "upright" when it is tilted 18 degrees to the nonhemiparetic, ipsilesional side. In contrast, perception of the SVV was undisturbed. CONCLUSIONS: A separate pathway seems to be present in humans for sensing the orientation of gravity apart from the one for orientation perception of the visual world. This second graviceptive system decisively contributes to humans' control of upright body posture. Contraversive pushing occurring after stroke lesions may represent the behavioral correlate of a disturbed neural representation of this system.     

Perception of the vertical in patients with right hemispheric lesion: effect of galvanic vestibular stimulation

Patients with right-brain injury present, more frequently in the acute phase, with a deviation of the subjective vertical (SV) contralateral to the lesion. The aim of this study was to investigate the influence of galvanic vestibular stimulation (GVS) on this disorder. Twelve patients presenting with a right hemispheric lesion, seven with neglect (N+) and five without (N-) were compared to eight control subjects. They had to orient vertically a luminous rod in darkness, in three galvanic stimulation (1.5 mA) conditions: cathode left, cathode right and no stimulation (baseline). Without stimulation, the patients' SV, and especially that of N+, showed an anticlockwise deviation. In comparison with baseline values, GVS induced a deviation toward the side opposite to the cathode in the three groups. In the patients, the deviation was of larger amplitude and appeared greater for left than for right cathodic stimulation. In conclusion, we showed an influence of vestibular stimulation on the SV of right brain-injured patients, especially when spatial neglect was present. As left cathodic stimulation can reduce the SV deviation associated with spatial neglect, such a tool could be introduced in rehabilitation.     

Neglect dyslexia and the early stages of visual word recognition

Abstract

Neglect dyslexia is an acquired reading disorder in which one side of words or letter strings is misidentified. Caramazza and Hillis (Cognitive Neuropsychology 1990; 7: 391-445) proposed that the disorder reflects an impairment in the early stages of visual word recognition. Three levels of representation are involved, each with corresponding spatial coordinates. These levels reflect a progression away from the physical stimulus toward a more abstract representation of a word. The errors made by a patient with a level one deficit are relative to the location of a word in the visual field. The errors made by a patient with a level two deficit are relative to the spatial position of a letter(s) within the stimulus. The errors made by a patient with a level three deficit are relative to the ordinal position of a letter(s) within a word. We describe how this model may be used to interpret the differing patterns of performance found in neglect dyslexia and evaluate the model according to 19 published single case studies of neglect dyslexia. It is concluded that the model is well supported by these data and may therefore be viewed as a model of the early stages of reading in intact readers.     

Evaluating Unilateral Spatial Neglect Post Stroke: Working Your Way Through the Maze of Assessment Choices

Abstract

This study identified, using a comprehensive review of the literature, 62 standardized and nonstandardized assessment tools that exist to evaluate unilateral spatial neglect (USN). Each standardized tool was critically appraised according to its purpose (hemispace assessed), psychometric properties, and client appropriateness. The findings on the 28 standardized tools were compiled into a USN Assessment Summary Guide to facilitate clinical decision-making regarding the standardized USN assessments that are appropriate for specific clients at different phases of their recovery post stroke.     

Assessing chronic stroke survivors with aphasia sheds light on prevalence of spatial neglect

Background: Stroke is a chronic disease. Standardized assessment is essential in order to determine areas for treatment. Individuals with aphasia are often excluded from research, because it is believed that their language impairments may impact their ability to provide informed consent. Thus, right spatial neglect could be under-diagnosed.

Objective: This study was developed to (1) determine the frequency of spatial neglect in chronic left-brain stroke survivors with aphasia, (2) determine the clinical utility of an aphasia-friendly consent form, and (3) determine any differences between neglect and no-neglect groups regarding activities of daily living (ADL) performance and community independence.

Methods: Forty-six people were consented at community center. Three were screen failures secondary to the exclusion criteria. A novel, aphasia-friendly consent form was developed to facilitate participation of individuals with aphasia. This enabled 93% or 40 out of the 43 recruited participants to be included in this study. The Behavioral Inattention Test-conventional and the Catherine Bergego Scale via Kessler Foundation Neglect Assessment Process (CBS via KF-NAP) were utilized to determine neglect. The Life Space Questionnaire was used to determine community mobility and independence. The Barthel Index (BI) was used for objective clarification of performance in ADL.

Results: Successful use of the consent form resulted in determination that five out of 40 (12.5%) met criteria for spatial neglect; (on the CBS via KF-NAP). The neglect group had lower scores on the Life Space, suggesting less community mobility and independence, however, it was not statistically significant (p = 0.16). Differences in BI scores were also not significant (p = .013) but the neglect group did have reduced independence.

Conclusions: This study demonstrates the need to administer functional neglect assessments in left-brain stroke and to include individuals with aphasia in research.     

How do patients with neglect see a horizontal line?

Abstract. Twelve patients with left unilateral spatial neglect were examined with a newly devised coloured line bisection task. They were presented with a horizontal line printed in blue on one side and in red on the other side; the proportions of the blue and red segments were varied. Immediately after placement of the subjective midpoint, the line was concealed and the patients were asked to name the colours of the right and left ends. Five patients who identified the left-end colour almost correctly had no visual field defect, while the other seven whose colour naming was impaired on the left side had left visual field defect. The rightward bisection errors were similarly distributed in the fair and poor colour-naming patients except for two patients from the latter group. The lesions of the fair colour-naming patients spared the lingual and fusiform gyri, which are known to be engaged in colour processing. Patients with neglect whose visual field is preserved may neglect the leftward extension of a line but not the colour in the neglected space. The poor colournaming patients frequently failed to name the left-end colour that appeared to the left of their subjective midpoint, which indicates that they hardly searched leftward beyond that point. In such trials, they reported that the left end had the same colour as the right end. The results suggest that in patients with neglect and left visual field defect, both the leftward extent and the colour of a line may be represented on the basis of the information from the attended right segment.     

Precision of perceived direction of gravity in partial bilateral vestibulopathy correlates with residual utricular function

Objective

Gait imbalance in patients with bilateral-vestibular-deficiency (BVD) was linked to increased variability in perceived direction of gravity while upright. We hypothesized this to be true also when roll-tilted. Moreover, as utricular input is essential for spatial orientation, we predicted the variability of perceived vertical to correlate inversely with utricular function.

Recovery from cortical blindness mediated by destruction of nontectotectal fibers in the commissure of the superior colliculus in the cat

Transection of the commissure of the superior colliculus restores visual orientation behavior to a cat previously rendered hemianopic by a unilateral visual cortical lesion (the Sprague effect). Using two methods, we asked whether this recovery resulted from the severing of the tectotectal component of the commissure or whether the destruction of some other connection was responsible. First, we transected either the rostral or the caudal one-half of the tectal commissure in hemianopic cats. If destruction of tectotectal fibers is responsible for the Sprague effect, then only rostral transections should produce the recovery since nearly all tectotectal connections lie in the rostral one-half of the commissure. However, rostral cuts failed to produce a recovery, whereas caudal commisurotomies did. Second, ibotenic acid was used to destroy the cells in the superior colliculus contralateral to the cortical lesion. This lesion eliminated the contralateral tectotectal pathway from the contralateral colliculus but left other fibers (originating elsewhere but coursing through the commissure) largely intact. These ibotenic acid lesions failed to produce the recovery; but when the caudal portion of the tectal commissure was subsequently transected in the same animals, the recovery was observed. The results of both experiments support the conclusion that the transection of a nontectotectal component of the commissure of the superior colliculus is responsible for the recovery of visual orientation behavior in a cortically blind cat.     

Prism adaptation and spatial attention: a study of visual search in normals and patients with unilateral neglect

Visuomotor adaptation to a prism-induced lateral displacement of the visual field induces mild perceptual biases in healthy individuals and improves symptoms of unilateral neglect. The present study employed a speeded visual search task to test the hypothesis that prism adaptation induces an adaptive redistribution of selective spatial attention. In Experiment 1, 32 neurologically healthy, right-handed participants were adapted to a 15° prism–induced lateral (left or right) displacement of the visual field. Spatial attention was measured by search time and error-rate in unique-feature (“preattentive”) and feature-absent (“serial”) visual search tasks, before and after prism adaptation. The single target appeared at different locations within arrays of 12, 24 or 48 items. Contrary to the attentional hypothesis, the pattern of search performance across the display remained unchanged following prism adaptation. In Experiment 2, we tested four patients with unilateral right hemisphere damage on the visual search tasks, before and after adaptation to 15° rightward-displacing prisms. All four patients showed a pathological gradient of spatial attention toward the ipsilesional side prior to adaptation. Consistent with the results from Experiment 1, the gradient in search performance shown by the patients did not change following prism adaptation. Taken together, these findings suggest that the perceptual aftereffects in normals and amelioration of unilateral neglect following prism adaptation are not mediated by an adaptive redistribution of spatial attention.     

Posterior pusher syndrome: A report of two cases

“Pusher syndrome” is classically described as a disorder of body orientation in the coronal plane. Although it mainly occurs in stroke patients, non-stroke causes have been described. Pusher behaviour is characterized by a tilt towards the contralesional paretic side and a resistance to external attempts to rectify. It may occur with or without hemispatial neglect, which in itself may be the cause of a usually ipsilesional shift of attention and body orientation in the axial plane.     

Judging the angles formed by visible and imaginary clock hands: a study of hemispatial effects in healthy volunteers

Healthy, right-handed volunteers (six male, six female) either saw or imagined the hands of a clock set a particular time. In both conditions, they then judged whether the angle between the clock hands was greater than or less than 90 degrees. Subjects pressed one of two response keys to indicate their decision, and hand of response (left/right) was counterbalanced within and between subjects. The subjects had significantly longer reaction times and made significantly more errors when the imaginary angles formed by the clock hands were located in left hemispace (e.g. 8:30) than right hemispace (e.g. 4:30). With visible hands, there was no reaction time difference between visual hemifields, although significantly more errors were made when the angle formed by the hands fell within the left visual field. In the perceptual task (visible hands), reaction times and error rates increased monotonically as the distance between the hands approximated more closely to 90 degrees. This psychophysical relationship was not found in the representational task (imaginary hands). Rather, there was a significant positive correlation between reaction times/error rates and the magnitude of the number indicative of the position of the minute hand. The latter finding is consistent with the hypothesis that the lateral asymmetry in the representational task (reaction times and error rates are higher in left hemispace) is due to the time taken to mentally rotate the imaginary minute hand in a clockwise direction. No such operation is required in the perceptual condition where the hands are clearly visible.     

The relationship between visual perception and visual mental imagery: a reappraisal of the neuropsychological evidence

Visual perception and visual mental imagery, the faculty whereby we can revisualise a visual item from memory, have often been regarded as cognitive functions subserved by common mechanisms. Thus, the leading cognitive model of visual mental imagery holds that visual perception and visual imagery share a number of mental operations, and rely upon common neural structures, including early visual cortices. In particular, a single visual buffer would be used "bottom-up" to display visual percepts and "top-down" to display internally generated images. The proposed neural substrate for this buffer consists of some cortical visual areas organised retinotopically, that is, the striate and extrastriate occipital areas. Empirical support for this model came from the report of brain-damaged patients showing an imagery deficit which parallels a perceptual impairment in the same cognitive domain. However, recent reports of patients showing double dissociations between perception and imagery abilities challenged the perception-imagery equivalence hypothesis from the functional point of view. From the anatomical point of view, the available evidence suggests that occipital damage is neither necessary nor sufficient to produce imagery deficits. On the other hand, extensive left temporal damage often accompanies imagery deficits for object form or colour. Thus, visual mental imagery abilities might require the integrity of brain areas related to vision, but at an higher level of integration than previously proposed.     

Validation of a low-cost virtual reality system for training street-crossing. A comparative study in healthy,neglected and non-neglected stroke individuals

Unilateral spatial neglect is a common consequence of stroke that directly affects the performance of activities of daily living. This impairment is traditionally assessed with paper-and-pencil tests that can lack correspondence to real life and are easily compensated. Virtual reality can immerse patients in more ecological scenarios, thus providing therapists with new tools to assess and train the effects of this impairment in simulated real tasks. This paper presents the clinical validation and convergent validity of a low-cost virtual reality system for training street-crossing in stroke patients with and without neglect. The performance of neglect patients was significantly worse than the performance of non-neglect and healthy participants. In addition, several correlations between the scores in the system and in the traditional scales were detected.     

Geographic information has to be spatialized to be neglected: a representational neglect case

A patient with unilateral neglect had to evoke mentally the map of France in two different conditions. In the first condition, he was asked to build an iconic representation of the map of France and to list all the towns that he could 'see' on this mental image within two minutes. In the second condition, he had to remember and name as many French towns as possible within two minutes, without being instructed to form a mental image. Left representational neglect was observed in the first condition only, i.e., when an iconic representation was required. These findings, which were replicated four months later, suggest a dual mode of coding, retrieval, or both, of geographic information and show that, although topographic, geographic data has to be spatialized to be neglected.     

The prediction of functional dependency by lateralized and non‐lateralized neglect in a large prospective stroke sample

Background and purpose: Lateralized and non‐lateralized impairments in visual attention have been identified as important components in patients with visuospatial neglect. This study investigated the course of these two phenomena across time in relation to neurological symptoms and functional outcome in a large consecutive and prospective stroke sample. Methods: A total of 375 consecutive stroke patients were divided into three groups (lateralized, non‐lateralized or no visual inattention) acutely and 3 months post‐stroke using the star cancellation test. Neurological impairments, localization of brain damage, asymmetry in clinical symptoms and functional outcome were assessed. Possible group differences were analysed, and stepwise logistic regressions were performed to examine the relative importance of predictors of functional dependency. Results: Participants with acute lateralized inattention differed (P ≤ 0.05) from the other two groups by more often exhibiting severe neurological symptoms, functional dependency and persisting visual inattention. The regression analyses selected acute lateralized inattention as an important and independent predictor of functional dependency following right hemisphere damage, but not following left hemisphere damage. Conclusions: The results emphasize the prognostic value of lateralized inattention and the importance of separating lateralized and non‐lateralized symptoms of visual inattention at the commencement of rehabilitation.