Hemispatial Neglect Syndrome Research Articles

Side bias behaviour in dogs shows parallels to the hemispatial neglect syndrome

There is a growing trend for the use of alternative translational model animals in cognitive neuroscience. The aim of the present study was to investigate side bias, a common phenomenon among family dogs and parallel it to the behavioural symptoms of hemispatial neglect syndrome. N = 29 family dogs (Canis familiaris) were recruited based on their history of side bias behaviour in previous two-way choice tests. 24 of them showed side bias in the present study as well suggesting that the phenomenon is stable across time and situations. Similarly to neglect, dogs relied on an egocentric reference frame in making their choices as demonstrated by the spatial rotation of the test setup. Contrary to our expectations there was no double dissociation to near and far places, but human literature is not conclusive in this sense either. Moreover, unlike in human neglect, there was no population-level side bias in dogs towards either side. In sum, we identified a certain subgroup of dogs that can develop strong side bias in two-way choice tasks, a neglect-like behaviour without any evidence of brain injury. We propose that investigating side biased dogs can open a new way in non-invasive translational modelling, however further empirical research is needed.

Adaptation to Laterally Asymmetrical Visuomotor Delay Has an Effect on Action But Not on Perception.

When interacting with the environment, the sensorimotor system faces temporal and spatial discrepancies between sensory inputs, such as delay in sensory information transmission, and asymmetrical visual inputs across space. These discrepancies can affect motor control and the representation of space. We recently showed that adaptation to a laterally asymmetric delay in the visual feedback induces neglect-like effects in blind drawing movements, expressed by asymmetrical elongation of circles that are drawn in different workspaces and directions; this establishes a possible connection between delayed feedback and asymmetrical spatial processing in the control of action. In the current study, we investigate whether such adaptation also influences visual perception. In addition, we examined transfer to another motor task – a line bisection task that is commonly used to detect spatial disorders, and extend these results to examine the mapping of these neglect-like effects. We performed two sets of experiments in which participants executed lateral reaching movements, and were exposed to visual feedback delay only in the left workspace. We examined transfer of adaptation to a perceptual line bisection task – answers about the perceived midline of lines that were presented in different directions and workspaces, and to a blind motor line bisection task – reaching movements toward the centers of similar lines. We found that the adaptation to the asymmetrical delay transferred to the control of lateral movements, but did not affect the perceived location of the midlines. Our results clarify the effect of asymmetrical delayed visual feedback on perception and action, and provide potential insights on the link between visuomotor delay and neurological disorders such as the hemispatial neglect syndrome.

Neglect-Like Effects on Drawing Symmetry Induced by Adaptation to a Laterally Asymmetric Visuomotor Delay.

In daily interactions, our sensorimotor system accounts for spatial and temporal discrepancies between the senses. Functional lateralization between hemispheres causes differences in attention and in the control of action across the left and right workspaces. In addition, differences in transmission delays between modalities affect movement control and internal representations. Studies on motor impairments such as hemispatial neglect syndrome suggested a link between lateral spatial biases and temporal processing. To understand this link, we computationally modeled and experimentally validated the effect of laterally asymmetric delay in visual feedback on motor learning and its transfer to the control of drawing movements without visual feedback. In the behavioral experiments, we asked healthy participants to perform lateral reaching movements while adapting to delayed visual feedback in either left, right, or both workspaces. We found that the adaptation transferred to blind drawing and caused movement elongation, which is consistent with a state representation of the delay. However, the pattern of the spatial effect varied between conditions: whereas adaptation to delay in only the left workspace or in the whole workspace caused selective leftward elongation, adaptation to delay in only the right workspace caused drawing elongation in both directions. We simulated arm movements according to different models of perceptual and motor spatial asymmetry in the representation of delay and found that the best model that accounts for our results combines both perceptual and motor asymmetry between the hemispheres. These results provide direct evidence for an asymmetrical processing of delayed visual feedback that is associated with both perceptual and motor biases that are similar to those observed in hemispatial neglect syndrome.

Corpus Callosum and Neglect Syndrome: Clinical Findings After Meningioma Removal and Anatomical Review.

Two types of neglect are described: hemispatial and motivational neglect syndromes. Neglect syndrome is a neurophysiologic condition characterized by a malfunction in one hemisphere of the brain, resulting in contralateral hemispatial neglect in the absence of sensory loss and the right parietal lobe lesion being the most common anatomical site leading to it. In motivational neglect, the less emotional input is considered from the neglected side where anterior cingulate cortex harbors the most frequent lesions. Nevertheless, there are reports of injuries in the corpus callosum (CC) causing hemispatial neglect syndrome, particularly located in the splenium. It is essential for a neurosurgeon to recognize this clinical syndrome as it can be either a primary manifestation of neurosurgical pathology (tumor, vascular lesion) or as a postoperative iatrogenic clinical finding. The authors report a postoperative hemispatial neglect syndrome after a falcotentorial meningioma removal that recovered 10 months after surgery and performs a clinical, anatomical, and histological review centered in CC as key agent in neglect syndrome.

Hemi-spatial neglect rehabilitation using non-invasive brain stimulation: Or how to modulate the disconnection syndrome?

Hemi-spatial neglect syndrome is common and sometimes long-lasting. It is characterized by a deficit in the use and awareness of one side of space, most often consecutive to a right hemisphere injury, mainly in the parietal region. Acknowledging the different types and all clinical characteristics is essential for an appropriate evaluation and adapted rehabilitation care management, especially as it constitutes a predictive factor of a poor functional prognosis. Some new approaches have been developed in the last fifteen years in the field of hemi-spatial neglect rehabilitation, where non-invasive brain stimulation (TMS and tDCS) holds an important place. Today's approaches of unilateral spatial neglect modulation via non-invasive brain stimulation are essentially based on the concept of inter-hemispheric inhibition, suggesting an over-activation of the contralesional hemisphere due to a decrease of the inhibiting influences of the injured hemisphere. Several approaches may then be used: stimulation of the injured right hemisphere, inhibition of the hyperactive left hemisphere, or a combination of both. Results are promising, but the following complementary aspects must be refined before a more systematic application: optimal stimulation protocol, individual management according to the injured region, intensity, duration and frequency of care management, delay post-stroke before the beginning of treatment, combination of different approaches, as well as prognostic and efficacy criteria. An encouraging perspective for the future is the combination of several types of approaches, which would be largely facilitated by the improvement of fundamental knowledge on neglect mechanisms, which could in the future refine the choice for the most appropriate treatment(s) for a given patient.

Influences of Long-Term Memory-Guided Attention and Stimulus-Guided Attention on Visuospatial Representations within Human Intraparietal Sulcus.

The human parietal lobe contains multiple maps of the external world that spatially guide perception, action, and cognition. Maps in each cerebral hemisphere code information from the opposite side of space, not from the same side, and the two hemispheres are symmetric. Paradoxically, damage to specific parietal regions that lack spatial maps can cause patients to ignore half of space (hemispatial neglect syndrome), but only for right (not left) hemisphere damage. Conversely, the left parietal cortex has been linked to retrieval of vivid memories regardless of space. Here, we investigate possible underlying mechanisms in healthy individuals. We demonstrate two forms of dynamic changes in parietal spatial representations: an asymmetric one for stimulus-guided attention and a symmetric one for long-term memory-guided attention.

Attention maps in the brain.

Over 20 distinct cerebral cortical areas contain spatial map representations of the visual field. These retinotopic, or visuotopic, cortical areas occur not only in the occipital lobe but also in the parietal, temporal, and frontal lobes. The cognitive influences of visuospatial attention operate via these cortical maps and can support selection of multiple objects at the same time. In early visual cortical areas, spatial attention enhances responses of selected items and diminishes the responses to distracting items. In higher order cortex, the maps support a spatial indexing role, keeping track of the items to be attended. These maps also support visual short-term memory (VSTM) representations. In each hemisphere, all the known maps respond selectively to stimuli presented within the contralateral visual field. However, a hemispheric asymmetry emerges when the attentional or VSTM demands of a task become significant. In the parietal lobe, the right hemisphere visuotopic maps switch from coding only contralateral visual targets to coding memory and attention targets across the entire visual field. This emergent asymmetry has important implications for understanding hemispatial neglect syndrome, and supports a dynamic network form of the representational model of neglect. WIREs Cogn Sci 2013, 4:327-340. doi: 10.1002/wcs.1230 This article is categorized under: Psychology > Attention Neuroscience > Cognition.

AUTOASSOCIATIVE MEMORY CELLULAR NEURAL NETWORKS

An autoassociative memory is a device which accepts an input pattern and generates an output as the stored pattern which is most closely associated with the input. In this paper, we propose an autoassociative memory cellular neural network, which consists of one-dimensional cells with spatial derivative inputs, thresholds and memories. Computer simulations show that it exhibits good performance in face recognition: The network can retrieve the whole from a part of a face image, and can reproduce a clear version of a face image from a noisy one. For human memory, research on "visual illusions" and on "brain damaged visual perception", such as the Thatcher illusion, the hemispatial neglect syndrome, the split-brain, and the hemispheric differences in recognition of faces, has fundamental importance. We simulate them in this paper using an autoassociative memory cellular neural network. Furthermore, we generate many composite face images with spurious patterns by applying genetic algorithms to this network. We also simulate a morphing between two faces using autoassociative memory.

Role of right posterior parietal cortex in maintaining attention to spatial locations over time

Recent models of human posterior parietal cortex (PPC) have variously emphasized its role in spatial perception, visuomotor control or directing attention. However, neuroimaging and lesion studies also suggest that the right PPC might play a special role in maintaining an alert state. Previously, assessments of right-hemisphere patients with hemispatial neglect have revealed significant overall deficits on vigilance tasks, but to date there has been no demonstration of a deterioration of performance over time—a vigilance decrement—considered by some to be a key index of a deficit in maintaining attention. Moreover, sustained attention deficits in neglect have not specifically been related to PPC lesions, and it remains unclear whether they interact with spatial impairments in this syndrome. Here we examined the ability of right-hemisphere patients with neglect to maintain attention, comparing them to stroke controls and healthy individuals. We found evidence of an overall deficit in sustaining attention associated with PPC lesions, even for a simple detection task with stimuli presented centrally. In a second experiment, we demonstrated a vigilance decrement in neglect patients specifically only when they were required to maintain attention to spatial locations, but not verbal material. Lesioned voxels in the right PPC spanning a region between the intraparietal sulcus and inferior parietal lobe were significantly associated with this deficit. Finally, we compared performance on a task that required attention to be maintained either to visual patterns or spatial locations, matched for task difficulty. Again, we found a vigilance decrement but only when attention had to be maintained on spatial information. We conclude that sustaining attention to spatial locations is a critical function of the human right PPC which needs to be incorporated into models of normal parietal function as well as those of the clinical syndrome of hemispatial neglect.

Immediate and delayed reaching in hemispatial neglect

Milner and Goodale (The visual brain in action, Oxford: Oxford University Press, 1995; The visual brain in action, 2nd ed., Oxford: Oxford University Press, 2006) propose a model of vision that makes a distinction between vision for perception and vision for action. One strong claim of the model is that the dorsal stream's control of action is designed for dealing with target stimuli in the ‘here and now’, yet when time is allowed to pass and a reaction has to be made on the basis of a visual memory, the ventral stream is required for successful performance.Regarding the syndrome of hemispatial neglect, Milner and Goodale further claim that the visual dorsal stream is relatively spared in these patients. In the current study we tested whether neglect patients would indeed be unimpaired in immediate pointing, yet show inaccurate pointing in a condition where a delay is interposed between the presentation of the stimulus and the response signal (in particular in left space). We tested the ability of nine neglect patients (and healthy and right hemisphere no neglect control groups) to perform reaches towards immediate and delayed targets, placed in left, central and right locations. Neglect patients showed no accuracy impairments when asked to perform an immediate action. Conversely, when pointing towards remembered leftward locations, they markedly overshoot the target or failed to initiate a reach altogether. These results confirm that patients with neglect are not specifically impaired when performing ‘here and now’ actions, but rather present deficits when the visuomotor task taps into more perceptual ‘off-line’ representations thought to depend on ventral visual stream activation.

Amantadine Treatment of Hemispatial Neglect

The resemblance of some aspects of the hemispatial neglect syndrome (hypokinesia, decreased arousal) to aspects of Parkinsonian syndromes, and the success of amantadine in treating disorders of attention, prompted a placebo-controlled, double-blind trial of amantadine, an inhibitor of the N-methyl D-aspartate (NMDA) glutamate receptor that modulates dopamine transmission, in four patients with chronic hemispatial neglect. Patients received placebo or 100 mg of amantadine twice a day in an ABA design. Dependent measures of drug effect included an extensive battery of tests assessing arousal, hemiinattention, hemihypokinesia, personal neglect, disability, anosognosia, family burden, and naturalistic action. There was no evidence of increased adverse effects with the treatment drug compared with placebo. Of the 17 measures used to assess treatment response in the four patients (68 measures total), linear regressions revealed significant positive treatment effects on very few (four) measures (uncorrected for multiple comparisons), and scattered negative responses to treatment were evident on three measures. The vast majority of measures showed no change in response to treatment. Possible reasons for failure of treatment effects in the present study are discussed. Additional study will be required to determine whether there are neglect patients who may benefit from amantadine.

Non-lateralised deficits of drawing production in hemispatial neglect

Spatially lateralised deficits that typically define the hemispatial neglect syndrome have been shown to co-occur with other non-lateralised deficits of attention, memory, and drawing. However even a simple graphic task involves multiple planning components, including the specification of drawing start position and drawing direction. In order to investigate the influence of these factors in neglect we presented patients with a circle-copying task, and specified the drawing start point. The ability to draw from the instructed location was strongly related to tests that measure constructional abilities, but not related to start point laterality. In contrast, the direction in which patients drew the circle was affected by start point laterality: patients with neglect were less likely to draw in a typical direction when the cue was on the affected side of space and this was strongly related to severity of the neglect. Patients with neglect consistently produced circles that were smaller than the model; however, the scaling was not affected by the laterality of the start point, nor was the proportion of drawings correctly started at the cue. These findings demonstrate the complex relationship between neglect and even the simplest test for the syndrome.

Effects of right-hemisphere cortical infarction and muscarinic acetylcholine receptor blockade on spatial visual attention performance in rats

The syndrome of hemispatial neglect is defined as an inability to report, respond or orient to stimuli contralateral to a cerebral lesion despite intact elementary sensory or motor function. This syndrome is typically observed after lesions of the right cerebral cortex, and has been associated with impairment of attention. We studied whether visual attention performance is impaired after right-hemisphere infarction in rats. Using a behavioural paradigm measuring spatial visual attention, we tested the effects of photothrombotic infarction to either the frontal cortex or the parietal cortex on attention performance. Since the cholinergic system is known to modulate attention performance, we additionally evaluated the role of cholinergic receptor blockade with scopolamine in our task paradigm. Our results show a transient response bias immediately after cortical infarction, with a decrease in contralesional responses and an increase in contralesional omissions after frontal infarction. Parietal infarction and systemic administration of scopolamine also resulted in a decrease in correct responses and an increase in omissions, but without a difference in side responding. In conclusion, right frontal infarction induces a transient impairment in contralesional spatial visual attention that we explain as left-sided neglect. Right parietal infarction and cholinergic blockade shows non-lateralized deficits in spatial visual attention, suggestive of global attentional impairment. We postulate that both effects of cortical infarction on attention performance may be related to cholinergic dysfunction. Our study confirms the role of frontal and parietal cortices in attention performance in rats, and corroborates the theory that attention performance is impaired in hemispatial neglect in human stroke patients.

Perceptual and Premotor Neglect: Is there an Ideal Task to Categorise Patients?

This review focuses on Edoardo Bisiach's particular input into the perceptual/premotor taxonomy within the neglect syndrome and assesses arguments and experimental designs that have been presented both for and against the dichotomy. Bisiach made most crucial contributions to this topic as well as increasing insights into the syndrome of hemispatial neglect more generally. Most importantly, he elucidated its relevance to visual neuropsychological and neuroscientific research.

Task-Dependent Modulation of Visuospatial Exploration by Transcutaneous Electrical Neural Stimulation and Cyclic Pressure Application

We investigated the effects of one somatosensory stimulation technique, the cyclic pressure application (CPA), and compared them with the effects of left transcutaneous electrical stimulation (TENS) on the expression of left visuospatial exploration deficits in 13 stroke patients, as assessed by four visuospatial exploration tasks. Four treatment conditions were given: TENS, CPA, TENS +CPA, as well as a placebo condition. For each patient, the intensity of the TENS was determined, based on his/her perception threshold of paresthesia for the electrical impulses. The results demonstrated that only TENS stimulation is a sufficient condition to reduce the expression of visuospatial exploration deficits dependent of the task. The point of time at which stimulation had an effect was also dependent of the mode of stimulation and the task. Normal visuomotor integration requires the ability to explore both sides (left and right) of the visual space with egocentric reference to the midsagittal plane of trunk. Unilateral disturbances in visuospatial exploration, often associated with the neurologic syndrome of hemispatial neglect and more frequently observed after right hemisphere damage, refers to the defective ability of patients with unilateral cerebral lesions to explore the side of space contralateral to the lesion. Many quantifiable tests have been developed to assess the expression of visuomotor exploration. These tests differ substantially in their sensitivity, but the Star Cancellation and Line Bisection tasks are cited as the most sensitive measurements of visuospatial exploration.

Ameliorating neglect with prism adaptation: visuo-manual and visuo-verbal measures

Previous studies have shown that adaptation to rightward displacing prisms improves performance of neglect patients on visuo-manual (VM) tasks such as line cancellation, figure copying, and line bisection [Nature 395 (1998) 166]. The present study further evaluated the effect of prism adaptation (PA) on neglect symptoms by investigating: (a) the range of beneficial effects on common visuo-spatial deficits as well as less frequent phenomena like neglect dyslexia; (b) the duration of improvement following a single exposure to the right optical deviation; (c) the extent to which visuo-spatial performance can be comparatively ameliorated in VM tasks and visuo-verbal (VV) tasks (i.e. involving or not the adapted arm, respectively) and (d) the presence and duration of the manual visuo-motor bias induced by the prismatic adaptation (i.e. the after-effect). We investigated these issues in a group of neglect patients with right hemispheric damage who were also affected by neglect dyslexia. Following a single, brief prismatic adaptation the results showed that (a) several visuo-spatial abilities, including accuracy in reading single words and non-words, considerably improved, (b) the amelioration was long-lasting, continuing for at least 24 h, (c) the presence, amount, and duration of neglect amelioration was not limited to VM tasks, but extended to VV tasks and (d) the presence and duration of the after-effect induced by prismatic adaptation remarkably paralleled the presence and duration of the improvement of neglect symptoms. These findings clearly demonstrate that beneficial effects induced by a single PA are very long-lasting and spread over a wide range of visuo-spatial deficits, independent of the type of response required. In addition, our results strongly suggest that the process of adaptation, as revealed by the presence of a visuo-motor after-effect, might be essential for establishing amelioration. In light of its characteristics, the prismatic adaptation technique should be a priority tool for the rehabilitation of the multifaceted hemispatial neglect syndrome.

Music draws attention to the left and speech draws attention to the right

Providing free-field music input prompts right-handers to attend to their left side in a loudness-matching task that requires no musical analysis. Conversely, speech prompts rightward attention. The processes inferred are akin to the attentional asymmetry demonstrated in the syndrome of hemispatial neglect.

The development of functional lateralization in visual hemifield attention

Based primarily on clinical‐experimental studies of adults with hemispatial neglect syndrome, a neurological model has been developed that suggests the existence of a right hemisphere mechanism for lateralized visual hemifield attention. The purpose of this study was to examine the validity of this model as it relates to important neurodevelopmental issues. Ninety subjects were grouped according to three developmental levels (15 males, 15 females per level): 9‐year‐olds, 13‐year‐olds, and 18‐year‐olds. Using a reaction time paradigm, performance ws assessed as it related to the presentation of lateral warning stimulus prior to a central visual stimulus. The results did not provide evidence for a lateralized mechanism for visual hemifield attention. However, length of foreperiod and gender were significant effects. Neurodevelopmental issues are discussed as they relate to possible neural mechanisms for visual hemifield attention.