1/218. Selective horizontal dysmetropsia following prestriate lesion.We describe a patient (P.S.) who, following a right prestriate lesion, reported that objects in the left visual field appeared distorted and smaller than those on the right. Other aspects of visual processing were remarkably unaffected. We carried out a series of size comparison tests using simple or complex stimuli and requiring different types of behavioural responses. We found that P.S. significantly underestimated the size of stimuli presented in her left visual field. When comparison tasks involved stimuli placed along the vertical axis or in the right visual field, P.S. performed well. The vertical and horizontal components of size distortion were found to be differentially affected. We conclude that size processing may be dissociated from other aspects of visual processing, such as form or colour processing, and depends critically on part of the occipital, prestriate areas (Brodmann areas 18-19).- - - - - - - - - - ranking = 1keywords = visual (Clic here for more details about this article) |
2/218. Memories are made of this: the effects of time on stored visual knowledge in a case of visual agnosia.We report the effects of the passage of time on the longterm visual knowledge for objects in a patient with visual agnosia (H.J.A.). The naming of real objects was found to have improved, although this was not associated with any change in H.J.A.'s basic perceptual abilities which were stable over a 16-year period. The improvement in object naming was attributed to better use of non-contour-based visual information (such as surface detail and depth cues). In addition, we demonstrate a deterioration in H.J.A.'s long-term memory for the visual properties of objects, and argue that this has occurred as a result of his having impaired perceptual input. The deterioration was only apparent in drawing from memory and in the verbal descriptions of items; with forced-choice testing, H.J.A. operated at ceiling; we propose that current tests of visual imagery may not be sufficiently sensitive to detect subtle impairments of visual memory. Our findings can be taken to indicate that perceptual and memorial processes are not functionally independent, but are linked in an interactive manner.- - - - - - - - - - ranking = 2.8keywords = visual (Clic here for more details about this article) |
3/218. Does vestibular stimulation activate thalamocortical mechanisms that reintegrate impaired cortical regions?Caloric stimulation induced a transient reversal of multimodal hemispatial cognitive deficits in an 81-year-old woman with an acute left cerebral hemisphere stroke. The patient had unawareness of her right hand (asomatognosia), right-sided visual unawareness (hemineglect), aphasia and right-sided weakness (hemiplegia) prior to the stimulation. Transient improvements in impaired sensory, motor, linguistic and cognitive function developed within 30 s following application of the caloric stimulus and onset of horizontal nystagmus. The effect persisted for 3 min and ceased completely after 5 min. While several recent reports have described the capacity of caloric stimulation to transiently improve or reverse a wide range of attentional, cognitive and motor impairments, most examples are in right-hemisphere-damaged patients with long-standing brain injury. Typically, patients have been tested several months or years after the onset of the deficit. A possible mechanism for the temporary reintegration of multiple cognitive functions in this patient is discussed.- - - - - - - - - - ranking = 0.2keywords = visual (Clic here for more details about this article) |
4/218. Plasticity of language-related brain function during recovery from stroke.BACKGROUND AND PURPOSE: This study was undertaken to correlate functional recovery from aphasia after acute stroke with the temporal evolution of the anatomic, physiological, and functional changes as measured by MRI. methods: blood oxygenation level-dependent contrast and echo-planar MRI were used to map language comprehension in 6 normal adults and in 2 adult patients during recovery from acute stroke presenting with aphasia. perfusion, diffusion, sodium, and conventional anatomic MRI were used to follow physiological and structural changes. RESULTS: The normal activation pattern for language comprehension showed activation predominately in left-sided Wernicke's and Broca's areas, with laterality ratios of 0.8 and 0.3, respectively. Recovery of the patient confirmed as having a completed stroke affecting Broca's area occurred rapidly with a shift of activation to the homologous region in the right hemisphere within 3 days, with continued rightward lateralization over 6 months. In the second patient, in whom mapping was performed fortuitously before stroke, recovery of a Wernicke's aphasia showed a similar increasing rightward shift in activation recruitment over 9 months after the event. CONCLUSIONS: Recovery of aphasia in adults can occur rapidly and is concomitant with an activation pattern that changes from left to a homologous right hemispheric pattern. Such recovery occurs even when the stroke evolves to completion. Such plasticity must be considered when evaluating stroke interventions based on behavioral and neurological measurements.- - - - - - - - - - ranking = 0.099699971613469keywords = contrast (Clic here for more details about this article) |
5/218. The bare bones of object recognition: implications from a case of object recognition impairment.Three experiments were designed to investigate the performance of a patient (RK) who could name objects when presented in conventional views but showed catastrophic failures in identification from unconventional views. The aim of all three experiments was to assess the properties of the central representations that allow recognition of objects presented in conventional but not unconventional views. All three experiments showed that RK had problems in object identification not apparent from his naming performance. In the first experiment, RK was found to be extremely impaired at recognising the parts of objects even though he could name the whole object. In the second experiment, alterations in colour, shape and parts of objects were undetected in stimuli that he could name. In the third experiment, RK showed considerable difficulty with mirror-images and inversion tasks. The explanation for RK's impaired object recognition could not be attributed to defects to his early visual processing. We argue that RK's recognition is achieved through abstract (object-centred) representations that are global rather than local, and quite independent of their spatial framework. These abstract representations we take to be the essential bare bones for object recognition.- - - - - - - - - - ranking = 0.2keywords = visual (Clic here for more details about this article) |
6/218. Somatosensory extinction for meaningful objects in a patient with right hemispheric stroke.Implicit, high level processing of extinguished objects has often been described in the visual modality. In the tactile domain, however, research on this topic is meagre and it is still uncertain whether processing of tactually presented stimuli can be affected by the same attentional disorders as visual stimuli. In this paper we describe a patient, ENM, with visual neglect and light touch extinction who, in a naming task of objects presented in the tactile modality, simultaneously to both hands, showed extinction for left hand objects. He was, nevertheless, able to make above chance Same/Different judgements on the two stimuli. We also tested two neurologically intact subjects who performed the test wearing a ski-glove on the left hand to impair the recognition of left hand objects. In these subjects, Same/Different judgements were at chance level when recognition rate was as low as that found in patient ENM. This happened when either the objects, although sharing the same name were different in shape (conditions Same-Different) or when the two objects were different with respect to the category name but were actually physically similar (conditions Different-Similar). However, when the objects were either identical or completely different, i.e., in a condition where judgement could be based simply on the physical analysis of the object shape (condition Same Identical and Different Dissimilar), their Same/Different judgements were above chance, despite the tactual deficit. Our conclusion was that patient ENM showed implicit recognition of left hand objects, at least in the Same Different and in the Different-Similar conditions, whereas, in the same conditions, normal subjects with an artificial sensory impairment did not. Our results also show that Same/Different judgements may be, in some conditions, less demanding than naming tasks, as suggested by Farah et al. Furthermore, patient ENM performed the test both with uncrossed and crossed hands. We found that extinction always affected the hand contralateral to the brain damage, although there was a tendency for a decrement of the ipsilesional hand performance in the crossed condition. We discuss these findings with reference to the most recent theories on the existence of a body centered spatial frame of reference.- - - - - - - - - - ranking = 0.6keywords = visual (Clic here for more details about this article) |
7/218. hyperalgesia with reduced laser evoked potentials in neuropathic pain.Nociceptive evoked potentials to laser stimuli (LEPs) are able to detect lesions of pain and temperature pathways at peripheral, spinal and supraspinal levels. It is commonly accepted that LEP attenuation correlates with the loss of pain and temperature sensations, while pathological heat-pain hypersensitivity has been associated with increased LEP amplitude. Here we present two patients in whom increased pain sensation (hyperalgesia) to laser stimuli was, on the contrary, associated to delayed, desynchronized and attenuated LEPs. Both patients experienced increased unpleasantness and affective reactions to laser, associated to poor ability to localize the stimulus. In both cases the results may be explained by an overactivation of the 'medial pain system', in one patient due to deafferentation of cortical sensory areas by a capsular lesion, and in the other to imbalance between A-delta and C fiber excitation due to peripheral nerve injury. Our results suggest that LEPs, as currently recorded, reflect the activity of a 'lateral' pain system subserved by rapidly conducting fibers. They may therefore, assess the sensory and cognitive dimensions of pain, but may not index adequately the affective-emotional aspects of pain sensation conveyed by the 'medial' pain system. The dissociation between pain sensation and cortical EPs deserve to be added to the current semiology of LEPs, as the presence of abnormal pain to laser on the background of reduced LEPs substantiates the neuropathic nature of the pain.- - - - - - - - - - ranking = 0.077419975749001keywords = sensitivity (Clic here for more details about this article) |
8/218. diagnosis of MCA-occlusion and monitoring of systemic thrombolytic therapy with contrast enhanced transcranial duplex-sonography.A case of a successful systemic thrombolysis of an acute middle carotid artery occlusion is reported. The case underlines the role of contrast-enhanced transcranial color-coded duplex sonography as a noninvasive technique for rapid diagnosis of vessel occlusion in acute stroke. The diagnostic potential of transcranial color-coded duplex sonography for indication and monitoring of intravenous systemic thrombolytic therapy is demonstrated.- - - - - - - - - - ranking = 0.49849985806734keywords = contrast (Clic here for more details about this article) |
9/218. Written communication in undifferentiated jargon aphasia: a therapy study.A subject, R.M.M., with a 2-year history of jargon aphasia is described. At the beginning of this study she had minimal meaningful spoken output and showed little awareness of her speech despite having relatively well-preserved auditory comprehension. Her spoken output had proved resistant to earlier periods of therapy. In contrast, R.M.M.'s written output showed some ability to access orthographic information and monitoring of this modality was shown by an acute awareness of her errors. A 3-stage therapy programme is described. This was designed to improve R.M.M.'s writing of single words and to encourage use of writing as an alternative means of communication. The initial stage of therapy aimed to increase R.M.M.'s access to written word forms by use of picture stimuli. She showed significant improvement in writing treated items in response to pictures both immediately after therapy and at re-assessment 6 weeks later. Despite the acquisition of these skills, R.M.M. failed to use them in communicative contexts. A second stage of therapy replicated the results of the first and sought to facilitate R.M.M.'s functional use of her written vocabulary by asking her to write words to spoken questions. She again showed improved written naming of the treated items and could now produce written names appropriately in a questionnaire-type assessment. Generalization of this ability extended to items that had not been trained in this way. Functional use of writing in everyday communication remained absent, however. The final stage of therapy made explicit the potential links between items which R.M.M. could now write and functional messages which they might convey. She again showed significant changes in the acquisition of new vocabulary and, encouragingly, progress was also seen in her use of the strategy in functional communication. R.M.M.'s speech is almost entirely incomprehensible. It has remained unchanged for 2 years and has not responded to therapy. Relatively well-preserved auditory comprehension and good monitoring of written output allowed therapy to effectively target a small written vocabulary. Despite significant progress in the acquisition of new items, transfer of this skill to functional communication was initially absent. Further therapy which specifically targeted the impairment causing this failure was needed before functional use was seen. The potential for treating written output in cases of jargon aphasia which have been resistant to therapy for spoken language is discussed.- - - - - - - - - - ranking = 0.099699971613469keywords = contrast (Clic here for more details about this article) |
10/218. Residual perceptual distortion in 'recovered' hemispatial neglect.In most neglect patients, line bisection errors become smaller on repeated tests over the months following the lesion. We have tried to determine in two typical patients whether this is because of a real reduction in the perceptual distortions that appear to underlie line bisection errors in neglect, or whether it reflects a learned behavioural strategy to counteract those perceptual biases. We tested the patients on two occasions (2 and 12 months post-stroke), on line bisection and also on the 'Landmark' task. The data indicated that at the first testing session both patients showed strong 'perceptual' neglect, making large rightward errors in the standard bisection task and uniformly leftward pointing in the Landmark task. On the second occasion, as expected, both patients showed a marked recovery when tested with the line bisection task, making only very small errors. In contrast, their landmark performance was still markedly biased in the same direction as before. These findings suggest that despite their apparent recovery on the bisection task, both patients still experience some form of perceptual distortion of horizontal lines. It is suggested that the Landmark task may provide a sensitive means for identifying real recovery of the underlying perceptual deficit.- - - - - - - - - - ranking = 0.099699971613469keywords = contrast (Clic here for more details about this article) |
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