1/52. Bilateral altitudinal anopia caused by infarction of the calcarine cortex.The patient reported here had a bilateral inferior altitudinal hemianopia from lesions of the calcarine (striate) cortex of the occipital lobes. The only significant pathologic findings were bilateral calcarine artery occlusive disease, with infarcts of the striate cortex on both sides. The ages of the infarcts appeared compatible with the clinical development of the respective visual field defects. The rest of the visual system was anatomically intact.- - - - - - - - - - ranking = 1keywords = cortex (Clic here for more details about this article) |
2/52. attention without awareness in blindsight.The act of attending has frequently been equated with visual awareness. We examined this relationship in 'blindsight'--a condition in which the latter is absent or diminished as a result of damage to the primary visual cortex. Spatially selective visual attention is demonstrated when information that stimuli are likely to appear at a specific location enhances the speed or accuracy of detection of stimuli subsequently presented at that location. In a blindsight subject, we showed that attention can confer an advantage in processing stimuli presented at an attended location, without those stimuli entering consciousness. attention could be directed both by symbolic cues in the subject's spared field of vision or cues presented in his blind field. cues in his blind field were even effective in directing his attention to a second location remote from that at which the cue was presented. These indirect cues were effective whether or not they themselves elicited non-visual awareness. We concluded that the spatial selection of information by an attentional mechanism and its entry into conscious experience cannot be one and the same process.- - - - - - - - - - ranking = 0.16666666666667keywords = cortex (Clic here for more details about this article) |
3/52. Non-conscious recognition of affect in the absence of striate cortex.functional neuroimaging experiments have shown that recognition of emotional expressions does not depend on awareness of visual stimuli and that unseen fear stimuli can activate the amygdala via a colliculopulvinar pathway. perception of emotional expressions in the absence of awareness in normal subjects has some similarities with the unconscious recognition of visual stimuli which is well documented in patients with striate cortex lesions (blindsight). Presumably in these patients residual vision engages alternative extra-striate routes such as the superior colliculus and pulvinar. Against this background, we conjectured that a blindsight subject (GY) might recognize facial expressions presented in his blind field. The present study now provides direct evidence for this claim.- - - - - - - - - - ranking = 0.83333333333333keywords = cortex (Clic here for more details about this article) |
4/52. Intact verbal description of letters with diminished awareness of their forms.Visual processing and its conscious awareness can be dissociated. To examine the extent of dissociation between ability to read characters or words and to be consciously aware of their forms, reading ability and conscious awareness for characters were examined using a tachistoscope in an alexic patient. A right handed woman with 14 years of education presented with incomplete right hemianopia, alexia with kanji (ideogram) agraphia, anomia, and amnesia. brain MRI disclosed cerebral infarction limited to the left lower bank of the calcarine fissure, lingual and parahippocampal gyri, and an old infarction in the right medial frontal lobe. Tachistoscopic examination disclosed that she could read characters aloud in the right lower hemifield when she was not clearly aware of their forms and only noted their presence vaguely. Although her performance in reading kanji was better in the left than the right field, she could read kana (phonogram) characters and Arabic numerals equally well in both fields. By contrast, she claimed that she saw only a flash of light in 61% of trials and noticed vague forms of stimuli in 36% of trials. She never recognised a form of a letter in the right lower field precisely. She performed judgment tasks better in the left than right lower hemifield where she had to judge whether two kana characters were the same or different. Although dissociation between performance of visual recognition tasks and conscious awareness of the visual experience was found in patients with blindsight or residual vision, reading (verbal identification) of characters without clear awareness of their forms has not been reported in clinical cases. Diminished awareness of forms in our patient may reflect incomplete input to the extrastriate cortex.- - - - - - - - - - ranking = 0.16666666666667keywords = cortex (Clic here for more details about this article) |
5/52. The representation of the horizontal meridian in the primary visual cortex.The authors report the findings of two patients that confirm the location of the horizontal meridian in the human visual cortex. The first patient had an inferior quadrant defect with a band of horizontal meridian sparing. magnetic resonance imaging showed a lesion concentrated along the medial striate cortex. The second patient had a homonymous horizontal defect that resulted from removal of an arteriovenous malformation located in the lateral striate cortex. The findings of these two patients demonstrate that the horizontal meridian is represented at the calcarine fissure base in the primary visual cortex.- - - - - - - - - - ranking = 1.3333333333333keywords = cortex (Clic here for more details about this article) |
6/52. Bilateral occipital lobe stroke with inferior altitudinal defects.BACKGROUND: Cerebrovascular disease is the most common cause of neurological disability in Western countries. patients who survive cerebrovascular accidents exclusive to the occipital lobe often have no significant neurological deficits other than visual-field loss. Visual-field defects from occipital lobe stroke typically include congruous homonymous hemianopsias or quadranopsias, with or without macular sparing. CASE REPORT: A 61-year-old white man came to us with symptoms of sudden loss of vision and difficulty reading. Visual-field testing revealed a bilateral inferior altitudinal defect with normal optic nerve and fundus appearance in both eyes. On radiological examination, he was found to have had a bioccipital lobe cerebrovascular accident secondary to complete occlusion of the left vertebral artery. An embolic event causing the artery occlusion, in combination with bilaterally compromised cerebellar and posterior cerebral arteries, presumably caused the bilateral stroke. After appropriate medical and neurological consultation, optometric management consisted of maximizing the patient's remaining vision with a prismatic spectacle correction. DISCUSSION/CONCLUSION: patients with infarction exclusive to the occipital lobe typically have no other neurological deficits except visual-field loss and are often easier to manage than patients with infarctions to other areas of the cerebral cortex or multiple infarctions. Visual-field loss from occipital lobe damage can be successfully managed with optical systems and/or visual rehabilitation. Factors related to management include location and extent of visual-field damage, functional visual needs, and both personal and health concerns of the patient. A discussion is presented on cerebrovascular disease, occipital lobe infarction, imaging techniques, and visual rehabilitation.- - - - - - - - - - ranking = 0.16666666666667keywords = cortex (Clic here for more details about this article) |
7/52. Peripheral homonymous scotomas from a cavernous angioma affecting fibers subserving the intermediate region of the striate cortex.PURPOSE: To report the case of a pure peripheral homonymous visual field defect and to delineate the representation of the visual field on the striate cortex. methods: Observational case report. Neuro-ophthalmologic and neuroimaging assessment of a patient with a cavernous angioma of the right parieto-occipital lobe. RESULTS: The patient had left homonymous scotomas located 40 degrees to 60 degrees from the vertical meridian. Neuroimaging indicated that the lesion was affecting the optic radiations at their termination in the intermediate portion of the striate cortex or the striate cortex itself. CONCLUSION: Homonymous field defects are typically located within 10 degrees of fixation. This patient had a peripheral homonymous field defect from damage to the intermediate striate cortex. Correlation of the neuroimaging findings in this case with the most commonly used maps of the representation of the visual field on the striate cortex suggests that none of the maps correctly predicts the location or extent of lesions that affect the intermediate portion of the cortex.- - - - - - - - - - ranking = 1.6666666666667keywords = cortex (Clic here for more details about this article) |
8/52. Neural correlates of conscious and unconscious vision in parietal extinction.brain areas activated by stimuli in the left visual field of a right parietal patient suffering from left visual extinction were identified using event-related functional magnetic resonance imaging. Left visual field stimuli that were extinguished from awareness still activated the ventral visual cortex, including areas in the damaged right hemisphere. An extinguished face stimulus on the left produced robust category-specific activation of the right fusiform face area. On trials where the left visual stimulus was consciously seen rather than extinguished, greater activity was found in the ventral visual cortex of the damaged hemisphere, and also in frontal and parietal areas of the intact hemisphere. These findings extend recent observations on visual extinction, suggesting distinct neural correlates for conscious and unconscious perception.- - - - - - - - - - ranking = 0.33333333333333keywords = cortex (Clic here for more details about this article) |
9/52. Neuroimaging analysis of a case with left homonymous hemianopia and left hemispatial neglect.PURPOSE: To correlate the neuro-ophthalmological observations with the magnetic resonance images (MRI) and positron emission tomographic (PET) findings in a case with left homonymous hemianopia and left hemispatial neglect. CASE: A 57-year-old woman underwent surgery for a ruptured anterior communicating artery aneurysm. After she recovered consciousness, it was found that she had left homonymous hemianopia and left hemispatial neglect. Although the hemispatial neglect slowly improved, the homonymous hemianopia persisted. MRI and measurements of cerebral glucose metabolism by 2-fluoro-2-deoxy-D-glucose(FDG)-PET were performed 1 year later. RESULTS: MRI revealed infarctions on the medial surface of the frontal lobe, on the right medial surface of the occipital lobe, and global atrophy of the right cortical hemisphere. FDG-PET disclosed severe glucose hypometabolism in the entire right hemisphere. glucose metabolism in the right occipital cortex was 61.1% of that in the homologous region on the left side, 62.8% in the right anterior cingulate gyrus, and 93.8% in the temporal-parietal-occipital junction. CONCLUSIONS: The low glucose metabolism in the right visual cortex explains the persistent left hemianopia, and that in the right anterior cingulate gyrus and the right temporal-parietal-occipital junction may be responsible for the left hemispatial neglect. The relatively mild damage in the right temporal-parietal-occipital junction explained the recovery of the neglect symptom. Measurements of regional cerebral glucose metabolism by PET are useful for determining the cause of cerebral visual dysfunction and its prognosis after a cerebral lesion.- - - - - - - - - - ranking = 0.33333333333333keywords = cortex (Clic here for more details about this article) |
10/52. Good recovery in visual scanning in a patient with persistent anosognosia.A patient with hemineglect disturbance (N.G.) due to a right hemispheric lesion was admitted to rehabilitative training which featured the use of procedures devised in a previous study (Pizzamiglio et al., 1990) both in a standard way and with the addition of optokinetic stimulation. This latter paradigm produces an automatic reaction which favors the spatial orienting of the patient toward his (left) neglected side. N.G. showed good recovery in visual scanning and, by the end of training, reached a level of recovery similar to other neglect patients. However, his recovery was particularly slow and no change was observed in his attitude toward the visual disturbance. The conclusion is reached that recovery in visual scanning also can be obtained in patients with persistent anosognosic disturbances. Stimulations such as the optokinetic condition which influence patients' behavior at an automatic level may play an important role in this recovery. CBF studies obtained before and after training showed a CBF improvement mainly in the right temporoparietal regions, behind the lesion, and in the left frontal cortex. The implications of these findings on various theoretical interpretations of the hemineglect disturbance are briefly discussed.- - - - - - - - - - ranking = 0.16666666666667keywords = cortex (Clic here for more details about this article) |
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