Mechanisms of neglect: Implications for rehabilitation

Dual tasking negatively impacts obstacle avoidance abilities in post-stroke individuals with visuospatial neglect: Task complexity matters!

BACKGROUND

Persons with perceptual-attentional deficits due to visuospatial neglect (VSN) after a stroke are at a risk of collisions while walking in the presence of moving obstacles. The attentional burden of performing a dual-task may further compromise their obstacle avoidance performance, putting them at a greater risk of collisions.

OBJECTIVE

The objective of this study was to compare the ability of persons with (VSN+) and without VSN (VSN-) to dual task while negotiating moving obstacles.

METHODS

Twenty-six stroke survivors (13 VSN+, 13 VSN-) were assessed on their ability to (a) negotiate moving obstacles while walking (locomotor single task); (b) perform a pitch-discrimination task (cognitive single task) and (c) simultaneously perform the walking and cognitive tasks (dual task). We compared the groups on locomotor (collision rates, minimum distance from obstacle and onset of strategies) and cognitive (error rates) outcomes.

RESULTS

For both single and dual task walking, VSN+ individuals showed higher collision rates compared to VSN- individuals. Dual tasking caused deterioration of locomotor (more collisions, delayed onset and smaller minimum distances) and cognitive performances (higher error rate) in VSN+ individuals. Contrastingly, VSN- individuals maintained collision rates, increased minimum distance, but showed more cognitive errors, prioritizing their locomotor performance.

CONCLUSION

Individuals with VSN demonstrate cognitive-locomotor interference under dual task conditions, which could severely compromise safety when ambulating in community environments and may explain the poor recovery of independent community ambulation in these individuals.

Adding transcutaneous electrical nerve stimulation to visual scanning training does not enhance treatment effect on hemispatial neglect: a randomized, controlled, double-blind study

BACKGROUND

Left-sided transcutaneous electrical nerve stimulation (TENS) increases right hemispheric activity, which may improve the rehabilitative outcome of hemispatial neglect.

OBJECTIVE

To examine the behavioral effect of electrical stimulation of the nerve afferents of the left hand during early neuropsychological rehabilitation of post-stroke patients with hemispatial neglect.

METHODS

This randomized, controlled, double-blind study included 29 patients (enrolled in the experimental or control group) with left hemispatial neglect after right hemispheric stroke. For 3 weeks, patients received 15 therapeutic sessions involving TENS (active or sham) with a mesh glove applied on the entire left hand during the first 30 minutes of a 45-minute conventional visual scanning training (VST). Signs of hemispatial neglect were assessed using a psychometric test before and after treatment.

RESULTS

Univariate analysis of covariance revealed that differences between the control and experimental groups were not significant after treatment (F(1, 22) = 0.294, P = 0.593) when adjusted for pre-treatment scores and time since stroke onset. This suggested that electrical stimulation failed to mitigate the severity of hemispatial neglect symptoms.

CONCLUSION

Our study did not provide evidence of the effectiveness of TENS when added to VST during early rehabilitation for patients with post-stroke hemispatial neglect. Other techniques (applied alone or together) should be sought to improve recovery in this population.

Spatial distribution of attention and inter-hemispheric competition

Considerable evidence has demonstrated functional asymmetry in spatial attention between the left and right hemispheres. In the present study, we aimed to examine the theoretical models of spatial attention by considering distribution and inter-hemispheric competition in neurologically healthy participants. Participants searched for a green circle target among green diamond non-targets in the presence or absence of a red singleton. Assuming that the salient singleton would increase the activation of the corresponding hemisphere, we manipulated the sides of the singleton visual fields and target visual fields. When the salient singleton was presented to the right visual field, target detection was faster for left visual field targets than for right visual field targets. In contrast, when the salient singleton was presented to the left visual field, target detection time was equivalent for left and right visual field targets. These results suggest that when the perceptually salient singleton acts as an activator, distribution of attention differs depending on the activated hemisphere induced by inter-hemispheric competition. These findings are in line with Kinsbourne's opponent processor theory.

The implications of state-dependent tDCS effects in aging: Behavioural response is determined by baseline performance

Young adults typically display a processing advantage towards the left side of space ("pseudoneglect"), possibly as a result of right parietal dominance for spatial attention. This bias is ameliorated with age, with older adults displaying either no strongly lateralised bias, or a slight bias towards the right. This may represent an age-related reduction of right hemispheric dominance and/or increased left hemispheric involvement. Here, we applied anodal transcranial direct current stimulation (atDCS) to the right posterior parietal cortex (PPC; R-atDCS), the left PPC (L-atDCS) and a Sham protocol in young and older adults during a titrated lateralised visual detection task. We aimed to facilitate visual detection sensitivity in the contralateral visual field with both R-atDCS and L-atDCS relative to Sham. We found no differences in the effects of stimulation between young and older adults. Instead the effects of atDCS were state-dependent (i.e. related to task performance at baseline). Relative to Sham, poor task performers were impaired in both visual fields by anodal stimulation of the left posterior parietal cortex (PPC). Conversely, good performers maintained sensitivity in both visual fields in response to R-atDCS, although this effect was small. We highlight the importance of considering baseline task ability when designing tDCS experiments, particularly in older adults.

Long-term effects of continuous theta-burst stimulation in visuospatial neglect

Objective

To investigate whether the efficacy of continuous theta-burst stimulation (cTBS) for improving visuospatial neglect can be enhanced by providing more days of stimulation and more stimulation trains per day.

Methods

In a prospective study, right-handed patients with right hemisphere stroke and visuospatial neglect were randomized to cTBS or sham cTBS treatment for 2 weeks and were followed up for 4 weeks. The cTBS group received active cTBS over the posterior parietal cortex of the unaffected hemisphere, combined with conventional rehabilitation therapy. Changes in scores for two paper–pencil tests for visuospatial neglect (star cancellation and line bisection) were evaluated.

Results

In each group, 10 patients completed follow up. Compared with the sham group, star cancellation test scores in the cTBS group were improved by 37.03% at the end of treatment and by 47.21% after 4 weeks’ follow up, and the line bisection score improved by 21.37% at the end of treatment and by 35.99% after 4 weeks’ follow up.

Conclusions

These results suggest that the efficacy of cTBS in visuospatial neglect can be enhanced and prolonged by increasing the days of stimulation and the number of stimulation trains per day over the left posterior parietal cortex.

Frontoparietal regions may become hypoactive after intermittent theta burst stimulation over the contralateral homologous cortex in humans

Brain injury to the dorsal frontoparietal networks, including the posterior parietal cortex (PPC) and dorsolateral prefrontal cortex (DLPFC), commonly cause spatial neglect. However, the interaction of these different regions in spatial attention is unclear. The aim of the present study was to investigate whether hyperexcitable neural networks can cause an abnormal interhemispheric inhibition. The Attention Network Test was used to test subjects following intermittent theta burst stimulation (iTBS) to the left or right frontoparietal networks. During the Attention Network Test task, all subjects tolerated each conditioning iTBS without any obvious iTBS-related side effects. Subjects receiving real-right-PPC iTBS showed significant enhancement in both alerting and orienting efficiency compared with those receiving either sham-right-PPC iTBS or real-left-PPC iTBS. Moreover, subjects exposed to the real-right-DLPFC iTBS exhibited significant improvement in both alerting and executive control efficiency, compared with those exposed to either the sham-right-DLPFC or real-left-DLPFC conditioning. Interestingly, compared with subjects exposed to the sham-left-PPC stimuli, subjects exposed to the real-left-PPC iTBS had a significant deficit in the orienting index. The present study indicates that iTBS over the contralateral homologous cortex may induce the hypoactivity of the right PPC through interhemispheric competition in spatial orienting attention.

Caloric vestibular stimulation and postural control in patients with spatial neglect following stroke

The impact of spatial neglect remains a substantial challenge to patients undergoing rehabilitation following stroke. Beyond the relatively well-described implications for visuospatial function, neglect is increasingly shown to have a negative impact on the wider aspects of sensori-motor performance with corresponding implications for activities including gait and balance. Caloric vestibular stimulation (CVS) administered to the contralesional ear has previously been shown to improve performance in patients with spatial neglect. Here, in Experiment One, we investigated the effect of CVS on clinical measures of spatial neglect and postural control in three groups of patients following stroke; left brain damaged patients (LBD, n = 6), right brain damaged patients without neglect (RBD-, n = 6), and right brain damaged patients with neglect (RBD+ , n = 6). While post-stimulation scores demonstrated an improvement for participants with spatial neglect, further analysis of postural scores indicated that improvement was selective for asymmetrical activities, with symmetrical activities remaining unchanged. We interpret these results with reference to the related problem of extinction which predicts that activities demanding synchronous bilateral activity (symmetrical activities) would cause greater difficulties for patients with neglect. In Experiment Two, we tested a further six RBD+ patients on the same measures following CVS to the ipsilesional (right) ear. There was no significant improvement in perceptual or postural scores. Our findings are supportive of previous studies that demonstrate improvement in perception and movement for patients with spatial neglect following contralesional CVS and suggest that these improvements may have clinical benefits.

A general neuropsychological model of delusion

INTRODUCTION

Neurocognitive accounts of delusion have traditionally highlighted perceptual misrepresentation, as the primary trigger in addition to other cognitive deficits that maintain the delusion. Here, a general neurocognitive model of delusional disorder (DSM-IV) is proposed, not so much based on perceptual or cognitive deficits after right hemisphere damage as on cognitive propensities, specifically excessive inferencing (especially jumping to conclusions) and excessive reference to the self, due to left hemisphere overactivity.

METHOD

The functional imaging, topographic EEG, and experimental imaging literatures on delusional disorder are reviewed, and 37 previously published cases of postunilateral lesion delusion (DSM-IV type, grandeur, persecution, jealousy, erotomania, or somatic), are reviewed and analysed multivariately.

RESULTS

Functional imaging and EEG topography data were slightly more indicative of left hemisphere overactivity in delusional disorder. In addition, 73% of the postunilateral lesion cases (χ(2)=7.8, p=.005) of delusional disorder (DSM-IV type) had a right hemisphere lesion, whereas only 27% had a left hemisphere lesion.

CONCLUSION

Left hemisphere release appears to be a more primary cause of delusional disorder than right hemisphere impairment, the latter merely entailing loss of inhibition of delusional beliefs. We propose that most patients with DSM-IV diagnoses of delusional disorder could be afflicted by excessive left hemisphere activity, but further research is necessary.

Rehabilitation approaches to hemineglect

BACKGROUND

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

REVIEW SUMMARY

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

CONCLUSIONS

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

Motor neglect: Implications for movement and rehabilitation following stroke

PURPOSE

The syndrome of unilateral neglect following stroke is associated with poor outcome and presents significant challenges to those providing therapy for affected individuals. In contrast to a number of reviews which have recently appeared in therapy and rehabilitation journals relating to sensory aspects of neglect, this review focuses on 'motor neglect'.

SEARCH STRATEGY

We searched the clinical and scientific literature for papers concerning motor neglect. The search included the databases Web of Science, Pubmed and Cinahl, primarily using the term 'motor neglect'. There was also a large degree of secondary searching involved.

DISCUSSION

Motor neglect refers to the under-utilization of a limb opposite a brain lesion that cannot be fully explained by primary sensory and motor deficits. The paper discusses classical descriptions of motor neglect and highlights the difficulties in disentangling motor neglect from hemiparesis. The related problem of motor extinction is introduced as a useful clinical measure of neglect-related movement difficulties and a significant clinical problem in its own right.

CONCLUSION

Motor neglect is a relatively under-recognized deficit which may have a significant impact on patient performance and recovery following stroke. We conclude with a discussion of the implications of motor neglect for rehabilitation, including the relative contributions that may be made by Constraint-induced movement therapy and Bilateral movement therapy in managing patients with neglect-related movement problems.

Hyperexcitability of parietal-motor functional connections in the intact left-hemisphere of patients with neglect

Hemispatial neglect is common after unilateral brain damage, particularly to perisylvian structures in the right-hemisphere (RH). In this disabling syndrome, behaviour and awareness are biased away from the contralesional side of space towards the ipsilesional side. Theoretical accounts of this in terms of hemispheric rivalry have speculated that the intact left-hemisphere (LH) may become hyper-excitable after a RH lesion, due to release of inhibition from the damaged hemisphere. We tested this directly using a novel twin-coil transcranial magnetic stimulation (TMS) approach to measure excitability within the intact LH of neglect patients. This involved applying a conditioning TMS pulse over left posterior parietal cortex (PPC), in order to test its effect on the amplitude of motor evoked potentials (MEPs) produced by a subsequent test pulse over left motor cortex (M1). Twelve RH stroke patients with neglect, an age-matched group of eight RH stroke patients without neglect, and 10 healthy controls were examined. We found that excitability of left PPC-M1 circuits was higher in neglect patients than the other groups, and related to the degree of neglect on clinical cancellation tests. A follow-up found that 1 Hz repetitive TMS over left PPC normalized this over-excitability, and also ameliorated visual neglect on an experimental measure with chimeric objects. Our results provide 'direct' evidence for pathological over-excitability of the LH in the neglect syndrome, as quantified by left PPC influences on left M1, with implications for possible treatment.

The perceptual and functional consequences of parietal top-down modulation on the visual cortex

The posterior parietal cortex (PPC) has been proposed to play a critical role in exerting top-down influences on occipital visual areas. By inducing activity in the PPC (angular gyrus) using transcranial magnetic stimulation (TMS), and using the phosphene threshold as a measure of visual cortical excitability, we investigated the functional role of this region in modulating the activity of the visual cortex. When triple-pulses of TMS were applied over the PPC unilaterally, the intensity of stimulation required to elicit a phosphene from the visual cortex (area V1/V2) was reduced, indicating an increase in visual cortical excitability. The increased excitability that was observed with unilateral TMS was abolished when TMS was applied over the PPC bilaterally. Our results provide a demonstration of the top-down modulation exerted by the PPC on the visual cortex and show that these effects are subject to interhemispheric competition.

Interactive perceptual and attentional limits in visual extinction

We report a case-study of YE, a 54-year-old person who suffered multiple shell injuries that caused a right-parietal lesion and left hemianopia, almost 30 years ago. We conducted 4 experiments using a basic extinction paradigm in which YE had to report single stimuli presented on the left or right or two stimuli presented simultaneously in both visual fields. We show that extinction was selectively affected both by increasing the relative perceptual salience of the contralesional stimulus and by cueing attention to the contralesional side. The effects of perceptual salience and attentional cueing interacted, with cueing being more effective when the stimuli had relatively high perceptual salience. The data are consistent with attentional and perceptual factors interacting to determine the competition between left and right side stimuli that underlies extinction.

Left hand movements and right hemisphere activation in unilateral spatial neglect: a test of the interhemispheric imbalance hypothesis

The aim of the present study was to check one of the main assumptions of the interhemispheric imbalance hypothesis, namely, the prediction that the severity of neglect should be reduced by conditions activating the right hemisphere. To achieve this, a group of neglect patients was studied using a slightly modified version of the limb activation technique. The (verbal or visuo-spatial) nature of the stimuli to be processed by the patient and the (left or right) side of space where the left hand moved were considered as the critical variables to check the interhemispheric imbalance hypothesis. Three traditional and one new methods were used to measure changes induced in the severity of neglect by the material to be processed or by the side of space where the left hand moved. The traditional methods, all based on counting omissions, consisted of measuring: (a) the overall number of omissions; (b) the number of omissions made on the left half sheet; or (c) the difference between the omissions made on the left and right sides of the sheet. The new index, based on the notion of the 'attentional field' and defined as the spatial distribution of stimuli detected by the patient, was operationally measured by computing the distance between each stimulus crossed out by the patient and the right margin of the sheet. The study was conducted by rating the severity of neglect in 42 cancellation sheets which had used, respectively letters (N=21) and small geometric figures (N=21) as targets. The two sets of cancellation sheets were obtained from seven neglect patients during a limb activation task requiring the cancellation of a given target in three different conditions: (a) baseline; (b) active movements of the left hand in the left half space; (c) active movements of the left hand in the right half space. Results were at variance with the predictions based on Kinsbourne's model, since the verbal or visual spatial nature of the material to be processed did not influence the severity of unilateral spatial neglect (USN) and since left hand movements produced a significant reduction in the severity of neglect only when these movements were made on the left side of space.

Mechanisms underlying spatial representation revealed through studies of hemispatial neglect

The representations that mediate the coding of spatial position were examined by comparing the behavior of patients with left hemispatial neglect with that of nonneurological control subjects. To determine the spatial coordinate system(s) used to define "left" and "right," eye movements were measured for targets that appeared at 5 degrees, 10 degrees, and 15 degrees to the relative left or right defined with respect to the midline of the eyes, head, or midsaggital plane of the trunk. In the baseline condition, in which the various egocentric midlines were all aligned with the environmental midline, patients were disproportionately slower at initiating saccades to left than right targets, relative to the controls. When either the trunk or the head was rotated and the midline aligned with the most peripheral position while the eyes remained aligned with the midline of the environment, the results did not differ from the baseline condition. However, when the eyes were rotated and the midline aligned with the peripheral position, saccadic reaction time (SRT) differed significantly from the baseline, especially when the eyes were rotated to the right. These findings suggest that target position is coded relative to the current position of gaze (oculocentrically) and that this eye-centered coding is modulated by orbital position (eye-in-head signal). The findings dovetail well with results from existing neurophysiological studies and shed further light on the spatial representations mediated by the human parietal cortex.

Transcranial magnetic stimulation in cognitive neuroscience--virtual lesion, chronometry, and functional connectivity

Fifteen years after its introduction by Anthony Barker, transcranial magnetic stimulation (TMS) appears to be 'coming of age' in cognitive neuroscience and promises to reshape the way we investigate brain-behavior relations. Among the many methods now available for imaging the activity of the human brain, magnetic stimulation is the only technique that allows us to interfere actively with brain function. As illustrated by several experiments over the past couple of years, this property of TMS allows us to investigate the relationship between focal cortical activity and behavior, to trace the timing at which activity in a particular cortical region contributes to a given task, and to map the functional connectivity between brain regions.

Neurophysiological evaluation of tactile space perception deficits through transcranial magnetic stimulation

We describe a procedure useful to investigate the contralateral space perception deficits frequently encountered in patients with unilateral right brain damage. In particular, we focused on the phenomenon of extinction, i.e., the failure to perceive a contralesional stimulus only when a symmetrical contralateral stimulus is simultaneously applied. Fifteen right brain- and 15 left brain-damaged patients were examined. Somatosensory perception was evaluated by using a dedicated electronic device able to provide electrical stimuli of variable intensity to digits of one or both hands. The electrical stimulator was able to trigger a magnetic brain stimulator connected with a focal figure of eight coil. Threshold electrical stimuli were delivered to one or both hands of the patients, who were asked to indicate whether they perceived the stimulus (i) and to localise it (them). The electrical stimulator was connected with a magnetic stimulator with an interstimulus interval (ISI) of 40 msec (electrical stimulation preceding the transcranial one). Focal threshold transcranial magnetic stimulation (TMS) was applied to frontal and parietal scalp sites of the unaffected hemisphere. At each interpulse interval we found that TMS of the unaffected hemisphere was associated to a decrease in the level of contralesional extinction. Our method demonstrates that a basic deficit underlying neglect and extinction of contralateral space in unilaterally brain damaged patients is the interhemispheric imbalance between the two hemispheres in directing contralateral attention. A transient interference with the function of the unaffected hemisphere can improve these deficits, suggesting a possible application of TMS in the daily clinical practice for speeding up recovery from neglect.

Left frontal transcranial magnetic stimulation reduces contralesional extinction in patients with unilateral right brain damage

It has been demonstrated previously that transcranial magnetic stimulation (TMS) of the sensorimotor cortex can induce transient suppression of the perception of cutaneous near-threshold stimuli from fingers of the contralateral hand in normal individuals. One explanation accounting for deficits in the exploration of contralateral space following a unilateral hemispheric lesion refers to a loss of the normal interhemispheric balance, with a resultant hyperactivation of the unaffected hemisphere due to the release of reciprocal inhibition by the affected one. In order to verify this hypothesis, we investigated the effects of a TMS-induced transient dysfunction of the normal hemisphere upon contralateral tactile extinctions in two groups: (i) 14 right brain-damaged patients and (ii) 14 left brain-damaged control patients. Single-pulse TMS was delivered to frontal and parietal scalp sites of the unaffected hemisphere after an interval of 40 ms from an electrical unimanual or bimanual digit stimulation. In right brain-damaged patients, left frontal TMS significantly reduced the rate of contralateral extinctions compared with controls. After left parietal TMS, the number of extinctions was comparable to the baseline. This pattern of increased sensitivity to cutaneous stimulation ipsilateral to TMS was not observed in left brain-damaged control patients. In this group, right hemisphere TMS did not significantly alter the recognition of bimanual stimuli delivered to the space contralateral to the lesion. The suggestion is made that extinctions produced by right brain damage may be dependent on a breakdown in the balance of hemispheric rivalry in directing spatial attention to contralateral hemispace, so that the unaffected hemisphere generates an unopposed orienting response to the side of the lesion. The mechanisms whereby the left frontal TMS transiently ameliorates these deficits may involve stimulus-induced removal of a left frontal-right parietal transcallosal inhibitory flow, although interactions at subcortical levels cannot be excluded.

Reasons for variability in the reported rate of occurrence of unilateral spatial neglect after stroke

BACKGROUND AND PURPOSE

We sought to determine the frequency of occurrence of contralesional unilateral spatial neglect (USN) after stroke and to investigate the effect of side of lesion, nature of assessment tool used, and timing of assessment relative to stroke onset.

METHODS

We performed a systematic review of published reports, identified by a search of electronic databases (MEDLINE 1966-1997, PSYCHLIT 1974-1996, and CINAHL 1982-1997) and by searching reference lists of the reports selected. Excluded were unpublished, non-English language, and nonhuman studies.

RESULTS

Thirty published reports met the selection criteria, 17 of which directly compared right brain damage (RBD) and left brain damage (LBD). Contralesional USN appeared to occur more frequently after RBD than LBD in 16 of these. Both the assessment tool used and the time of assessment relative to stroke onset affected the reported rate of occurrence, although recovery rate data were inadequate (4 reports).

CONCLUSIONS

The clinical belief that USN occurs more frequently after RBD than LBD was apparently supported by a systematic review of published data. However, an accurate estimate of the rates of occurrence and recovery after stroke could not be derived. Four reasons for the variability among studies were discussed, including subject selection, lesion localization, and nature and timing of assessment. Different USN disorders may exist, which may require type-specific rehabilitation approaches. This may have implications for epidemiological studies and for the development of new treatments. Theoretically driven epidemiological studies are required before adequately powered randomized controlled trials of rehabilitation can be conducted.

Preserved insight in an artist with extrapersonal spatial neglect

Several reports of cases of experienced artists showing neglect after a brain lesion can be gleaned from the literature. The analysis of their drawings might provide better insight into the symptoms of neglect than that of non-artists's production. However, most of these reports are anedoctal. We describe in some detail the case of neglect of a distinguished artist, the internationally known Federico Fellini (FF), whom we followed-up for two months after his right parietal stroke. The neuropsychological profile of his neglect syndrome was characterized by left visuo-motor neglect which persisted for two months. At onset, FF also showed indications of neglect dyslexia as well as some evidence of implicit processing of the neglected parts of visual stimuli. However, there was no sign of personal and representational neglect, and FF was well aware of his motor and attentional deficits. FF's neglect was characterised by several dissociations, of which the lack of functional carryover despite intact conceptual and semantic insight is the most relevant.

Mirror agnosia

Normal people rarely confuse the mirror image of an object with a real object so long as they realize they are looking into a mirror. We report a new neurological sign, 'mirror agnosia', following right parietal lesions in which this ability is severely compromised. We studied four right hemisphere stroke patients who had left visual field 'neglect'. i.e. they were indifferent to objects in their left visual field even though they were not blind. We then placed a vertical parasagittal mirror on each patients' right so that they could clearly see the reflection of objects placed in the (neglected) visual field. When shown a candy or pen on their left, the patients kept banging their hand into the mirror or groped behind it attempting to grab the reflection; they did not reach for the real object on the left, even though they were mentally quite lucid and knew they were looking into a mirror. Remarkably, all four patients kept complaining that the object was 'in the mirror', 'outside my reach' or 'behind the mirror'. Thus, even the patients' ability to make simple logical inferences about mirrors has been selectively warped to accommodate the strange new sensory world that they now inhabit. The finding may have implications for understanding how the brain creates representations of mirror reflections.

Impairments of movement kinematics in patients with Huntington's disease: a comparison with and without a concurrent task

This study aimed to quantify the efficiency and smoothness of voluntary movement in Huntington's disease (HD) by the use of a graphics tablet that permits analysis of movements profiles. In particular, we aimed to ascertain whether a concurrent task (digit span) would affect the kinematics of goal-directed movements. Twelve patients with HD and their matched controls performed 12 vertical zig-zag movements, with both left and right hands (with and without the concurrent task), to large or small circular targets over long or short extents. The concurrent task was associated with shorter movement times and reduced right-hand superiority. Patients with HD were overall slower, especially, with long strokes, and had similar peak velocities for both small and large targets, so that controls could better accommodate differences in target size. Patients with HD spent more time decelerating, especially with small targets, whereas controls allocated more nearly equal proportions of time to the acceleration and deceleration phases of movement, especially with large targets. Short strokes were generally less force inefficient than were long strokes, especially so for either hand in either group in the absence of the concurrent task, and for the right hand is its presence. With the concurrent task, however, the left hand's behavior changed differentially for the two groups; for patients with HD, it became more force efficient with short strokes and even less efficient with long strokes, whereas for controls, it became more efficient with long strokes. Controls may be able to divert attention away from the inferior left hand, increasing its automaticity, whereas patients with HD, because of disease, may be forced to engage even further online visual control under the demands of a concurrent task. Patients with HD may perhaps become increasingly reliant on terminal visual guidance, which indicates an impairment in constructing and refining an internal representation of the movement necessary for its effective execution. Basal ganglia dysfunction may impair the ability to use internally generated cues to guide movement.

Video feedback in the rehabilitation of patients with unilateral neglect

OBJECTIVE

To compare the effects of a video procedure and a conventional verbal procedure in giving patients feedback on their neglect behavior in a practical task.

DESIGN

Subjects in group A were trained with a video feedback procedure and subjects in group B with a conventional, verbal procedure. Three hours after the procedures, the subjects were tested with four different neglect tests to evaluate the effects of training.

SUBJECTS

A consecutive series of 14 right-brain-damaged patients with moderate to severe unilateral neglect (UN): 7 patients in group A and 7 in group B.

INTERVENTIONS

Subjects in group A were given the opportunity to see their performances on video, directly after the performance of the "Baking Tray Task" (BTT). They could see their neglected left side on the right side of the TV monitor. Subjects in group B were given verbal and visual guidance to see their results in the BTT.

MAIN OUTCOME MEASURES

Line Cancellation Task, Figure Copying Task, Line Bisection, and BTT before and after procedures.

RESULTS

The video feedback group improved significantly in the BTT, as tested 3 hours after training (p < .02). Conventional training had no effect on the BTT or on the other neglect measures. In the video feedback group, no generalization effects from the videotaped BTT on other neglect tests were observed.

CONCLUSION

Video feedback seems to be a useful technique in the rehabilitation of patients with unilateral neglect.