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Query: UMLS:C0004134 (ataxia)
 15,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Unilateral neglect can be defined as an impairment to detect, refer, orient or respond to stimuli presented contralaterally to a cerebral lesion, without any impairments in sensory-motor elementary functions. Development. The first descriptions were those of Hughlings Jackson (1876) and Anton (1893). The most important feature of the syndrome is a lateralization bias, which is directional in nature independently of the visual fields. It can be classified in: 1. Attentional (sensory neglect). 2. Intentional (motor neglect). The lesions that may be responsible for the neglect syndromes are usually found in the inferior parietal cortex of the right cerebral hemisphere (superior parietal when optic ataxia is prominent), and the right frontal lobe. Extinction is more frequently related to subcortical lesions (right lenticular nucleus, anterior aspects of peri-ventricular white matter). Unilateral neglect comprises a set of features that may coexist or be isolated traits: 1. Attentional neglect: hemi-inattention, allesthesia, allochiria, anosognosia (with/without somato-paraphrenia or misoplegia), and anoso-diaphoria, sensory extinction. 2. Intentional neglect: hemi-akinesia, directional hypokinesia, motor impersistence, motor extinction. Different theories try to explain the patho-physiology of these phenomena: the attentional-intentional model, the neural network model, the vectorial model, the representational model, and the premotor model, among others.
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PMID:[Attention systems and unilateral neglect]. 1142 13

Unilateral neglect is a devastating condition, which manifests as a loss of a person's spatial awareness opposite the damaged side of the brain. It challenges our conception of the seat of the soul and its explanation is at the heart of the mind-body problem. A heuristic definition of the dorsal stream of a modality is here based on the categorization of parietal networks by the cerebellar component of motor efference copy. Taking this premise, the proprioceptive space of a stimulus is established as a concept in this paper. It is proposed that unilateral neglect is typically a dysfunction of proprioceptive space of a stimulus associated with lesions of the dorsal stream. Furthermore, most experimental findings of unilateral visual neglect (and by extrapolation, other sensory modalities), can be explained by two developmental mechanisms by which the proprioceptive space of a stimulus is encoded in the parietal cortex. Its right and left hemisphere representation can be dissociated from the hemifield of presentation of perceptual information, such that the left hemifield can have a left hemisphere representation through callosal connections and likewise, the right hemifield can have a right hemifield representation. The processing of a sensory stimulus in either parietal hemisphere is dynamically determined as shown by experimental modulation of performance. A theory of historical precedence will provide a developmental background to the organization of proprioceptive space and will invoke separate models according to specified terms of engagement. A model based on the expansion and contraction of the proprioceptive space of a stimulus as a gradient across both hemispheres and modulated by concurrent proprioceptive state will be differentiated from a model that is non-graduating but competitive and lacks such modulation. In other words, the dorsal representation of a sensory stimulus in the former case is shared to a varying degree by the two parietal hemispheres, whereas in the latter case the representation of left and right aspects of the same object stimulus is strictly divided between the two hemispheres. A further hypothesis of a dorsoventral gradient of the peripheral and foveal components of proprioceptive space characterizing dorsal stream networks will predict the double dissociation revealed by experimental paradigms. It will explain why some patients show neglect only in foveal while others only in peripheral vision. The paper proposes to unify neglect, extinction and optic ataxia on the one hand, and spatial and object-based neglect on the other hand, under a singularly proficient paradigmatic structure. A binding model as described is a component theory that acknowledges how the involved pathways or transitional zones in a pathway may contribute to a differential clinical picture as one progresses from posterior to anterior parietal cortex. Finally, a brief discussion is given on how autistic subjects neglect spatial cues and the inability of a spatial cognitive transformation underlies the impairments postulated for 'a theory of mind'.
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PMID:Unilateral neglect: a theory of proprioceptive space of a stimulus as determined by the cerebellar component of motor efference copy (and is autism a special case of neglect). 1707 Jun 52