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Query: UMLS:C0004134 (ataxia)
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Patients with posterior cortical atrophy may have dorsal visual system (occipital-parietal) dysfunction (optic ataxia, visuospatial disorientation, and simultanagnosia), ventral visual system (occipital-temporal) dysfunction (pure alexia, prosopagnosia, visual anomia, and agnosia), or both. We report a professional musician with ventral system dysfunction whose first symptom was alexia for music. Subsequently, she developed pure alexia for words but had preserved sorting of words. These observations suggest that the ventral visual system is important in music and word reading. However, sorting of words may be mediated by the dorsal visual system.
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PMID:Progressive ventral posterior cortical degeneration presenting as alexia for music and words. 952 Dec 52

We report a 73-year-old woman who presented progressive motor clumsiness, cortical sensory loss, and focal parietal lobe atrophy. She was well until one year prior to the present admission when she suffered from what appeared to be mild Fisher syndrome from which she showed excellent recovery. However, soon she noted a gradual onset of difficulty in hand movements and in the recognition of objects by hands. Neurologic examination revealed an alert and well oriented Japanese woman without dementia. Cranial nerves were unremarkable. Although, she did not have aphasia, apraxia, or agnosia, she showed marked clumsiness in skilled hand movements such as using chopsticks, hand writing, and buttoning. She had no motor weakness, ataxia, rigidity, or spasticity. Deep tendon reflexes were symmetrically diminished. Sensory examination revealed cortical sensory loss such as disturbances of two point discrimination, weight sensation, and stereotactic sensations. Her motor clumsiness appeared to be caused by her cortical sensory loss. MRI revealed marked focal atrophy in the bilateral parietal lobe, particularly in the postcentral gyrus and the adjacent association areas. Recently, neurodegenerative disorders with focal brain atrophy such as corticobasal degeneration, Pick's disease, and dementia of frontal lobe type have been reported, however, our patient does not fit to any of these known disorders nor clinical features are distinctly different from Alzheimer's disease. Our patient may be another example of progressive cerebral degeneration with emphasis on the parietal cortex.
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PMID:[A patient with focal bi-parietal atrophy presenting motor clumsiness and cortical sensory loss]. 971 Nov 23

We describe two new clinical syndromes, mirror agnosia and mirror ataxia, both characterized by the deficit of reaching for an object through a mirror in association with a lesion of either parietal lobe. Clinical investigation of 13 patients demonstrated that the impairments affected both sides of the body. In mirror agnosia, the patients always reached toward the virtual object in the mirror and they were not capable of changing their behavior even after presentation of the position of the object in real visual space. In mirror ataxia (resembling optic ataxia) although some patients initially tended to reach for the virtual object in the mirror, they soon learned to guide their arms toward the real object, all of them producing many directional errors. Both patient groups performed poorly on mental rotation, but only the patients with mirror agnosia were impaired in line orientation. Only 1 of the patients suffered from neglect and 3 from apraxia. Magnetic resonance imaging showed that in mirror agnosia the common zone of lesion overlap was scattered around the posterior angular gyrus/superior temporal gyrus and in mirror ataxia around the postcentral sulcus. We propose that both these clinical syndromes may represent different types of dissociation of retinotopic space and body scheme, or likewise, of allocentric and egocentric space normally adjusted in the parietal lobe.
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PMID:Mirror agnosia and mirror ataxia constitute different parietal lobe disorders. 1076 76

Lesion studies show a wide range of sensorimotor functions that can be selectively disturbed in patients with parietal lobe damage. This is illustrated by the selective impairment of unimodal or polymodal sensorimotor transformations in patients with apraxia. These clinically apparent deficits of goal-directed motor behavior are complimented by more subtle sensorimotor transformation disorders such as mirror agnosia and ataxia that can only be disclosed by special tests. Imaging studies further exemplify the prominent role of the parietal cortex as a sensorimotor interface and provide new information about the interrelationship between perception and action. Action observation activates premotor cortex, but parietal cortex is also recruited whenever an action involves objects. This emphasizes the significance of parietal cortex for goal-directed motor behavior. The intact comprehension of the meaning of gestures or of tool use shows the preservation of the cognitive aspects of motor behavior as long as lesions are restricted to the parietal lobe.
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PMID:The parietal lobe as a sensorimotor interface: a perspective from clinical and neuroimaging data. 1137 46

Responding correctly to a mirror image requires the creation of a rather peculiar form of dual representation. Mirror agnosia and mirror ataxia, i.e. a deficit in reaching an object reflected in a mirror, have been reported to be associated with parietal lobe lesions. This prospective study was conducted to investigate the capacity of subjects with neglect to identify the mirror image nature of visual information. Four consecutive brain-damaged patients with neglect, selected on the basis of specific criteria, and four control subjects performed grasping and object displacement tests under two response conditions (normal mirror and inverted mirror). Video recordings of the tests were analyzed to assess performance using the following criteria: (i) direction of the arm movement during the initial phase of movement, (ii) number of corrections of the hand position before grasping. The control subjects successfully grasped the objects in both experimental conditions. The patients (1) neglected the contralesional space, grasping objects correctly in the ipsilesional space (normal mirror condition) and (2) neglected the ipsilesional space, grasping correctly objects in the contralesional space (inverted mirror). Controls used real object-centered correction clues to modify the position and direction of their hand movement. The patients only produced horizontal displacements of the upper limb in the "healthy" and neglected space. These results suggest that patients with neglect do not use the same clues and do not modify their procedures as they cannot recalibrate their spatial representations. These differences concerned non-mirror-image clues and directional and positional as well as attentional vectors. Theoretical and rehabilitative implications are discussed.
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PMID:Mirror images and unilateral spatial neglect. 1158 12

The aim of this research was to identify, analyze and classify disorders in behavior which occur in the use of mirrors in patients with right cerebral damage presenting left visual spatial hemiplegia. This work was based on models of visual information processing. Seven controls and eleven patients with right cerebral damage performed a test involving grasping of an object using only specular information from a conventional mirror and then from an inverted mirror. The controls grasped up all the cubes straight away. They only experienced minor difficulty with the inverted mirror, mainly in relation to lateral displacement. The patients revealed a variety of behaviors: 1) searching for and trying to seize the object in the conventional and/or inverted mirror, 2) inversion of the paralysed side (left versus right) in the inverted mirror or the appearance of a visual spatial hemiplegia, 3) modifications in the order of grasped (from right to left, from left to right, or at random), 4) directional anomalies in the horizontal plane linked (or not) with disorders in the use of the anteroposterior space. The results of this study confirm that the patients have abnormal behavior in mirror spaces. While the characteristics of this behavior shows analogies with those described in the non-recognition of objects and/or defects in the processing of visual information for localising objects in space, they can be disassociated from them, and constitute separate syndromes. Specific terminology and taxonomy for the clinical forms of mirror agnosia and specular agnosia, of mirror paralysis and specular paralysis, and of specular ataxia are proposed.
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PMID:[Disorders of the processing of spatial information in patients with right cerebral lesions and left hemi-neglect]. 1291 75

Optic ataxia and visual agnosia have been proposed to constitute a double dissociation which provides the main argument for the assimilation of the anatomical distinction between a dorsal and a ventral visual stream to the functional distinction between perception and action. In the present review, we argue that insufficient evidence has been collected to argue for this double dissociation. Several criteria are reviewed: (1) exploration of the visuomotor behavior in central versus peripheral vision has not been matched for the two types of patients; (2) the temporal constraints of visual processes that are impaired in the two neurological conditions appear to play a crucial role in the apparent dissociation; (3) the necessary reductionism of experimental conditions used to study action has led to an overconsideration of optic ataxia as a global deficit for action. Altogether optic ataxia appears to result from a specific impairment of immediate visuomotor control rather than of visually guided action as a whole. These results are discussed in the light of recent research on optic ataxia and on motor control, and directions for future research are proposed.
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PMID:Optic ataxia revisited: visually guided action versus immediate visuomotor control. 1368 44

The scientific study of the cerebral substrate of consciousness has been marked by significant recent achievements, resulting partially from an interaction between the exploration of cognition in both brain-damaged patients and healthy subjects. Several neuropsychological syndromes contain marked dissociations that permit the identification of principles related to the neurophysiology of consciousness. The generality of these principles can then be evaluated in healthy subjects using a combination of experimental psychology paradigms, and functional brain-imaging tools. In this chapter, I review some of the recent results relevant to visual phenomenal consciousness, which is an aspect of consciousness most frequently investigated in neuroscience. Through the exploration of neuropsychological syndromes such as "blindsight," visual form agnosia, optic ataxia, visual hallucinations, and neglect, I highlight four general principles and explain how their generality has been demonstrated in healthy subjects using conditions such as visual illusions or subliminal perception. Finally, I describe the bases of a scientific model of consciousness on the basis of the concept of a "global workspace," which takes into account the data reviewed.
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PMID:Visual phenomenal consciousness: a neurological guided tour. 1618 23

Visual-spatial agnosis, praxis deficits and hallucinations can be the features of subacute sclerosing panencephalitis (SSPE) in the early period. This study describes a 15-year-old boy with SSPE presenting with visual agnosia, prosopagnosia, simultanagnosia, optic ataxia, and oculomotor apraxia which are compatible with Balint syndrome. MRI revealed heterogenous and abnormal signal changes in the bilateral parieto-occipital areas. The signals were more prominent on the left. The case discussed herein is important because he was diagnosed as Balint's syndrome by means of clinical and neuroradiological findings before the onset of known symptomatology as dementia/myoclonus of SSPE. The case is also illustrative of the need to emphasize the prompt evaluation of a patient's cortical features before clinical progression becomes apparent. This evaluation should be performed in the early period if correct diagnosis is to be reached.
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PMID:Subacute sclerosing panencephalitis presenting with Balint's syndrome. 1637 13

In everyday life our reaching behaviour has to be guided not only by the location and properties of the target object, but also by the presence of potential obstacles in the workspace. Recent evidence from neglect and optic ataxia patients has suggested that this automatic obstacle avoidance is mediated by the dorsal, rather than the ventral, stream of visual processing. We tested this idea in two studies involving patients with visual form agnosia resulting from bilateral ventral-stream damage. In the first study, we asked patient DF to reach out and pick up a target object in the presence of obstacles placed at varying distances to the left or right of the target. We found that both DF and controls shifted their trajectories away from the potential obstacles and adjusted their grip aperture in such a way as to minimize risk of collision. In a second study, we asked DF and a second patient, SB, to either reach between, or to bisect the space between, two cylinders presented at varying locations. We found that both patients adjusted their reach trajectories to account for shifts in cylinder location in the reaching task, despite showing significantly worse performance than control subjects when asked to make a bisection judgement. Taken together, these data indicate that automatic obstacle avoidance behaviour is spared in our patients with visual form agnosia. We attribute their ability to the functional intactness of the dorsal stream of visual processing, and argue that the ventral stream plays no important role in automatic obstacle avoidance.
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PMID:Intact automatic avoidance of obstacles in patients with visual form agnosia. 1668 Apr 29


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