Cases reported "Perceptual Disorders"

Filter by keywords:



Filtering documents. Please wait...

1/32. Visual environmental rotation: a novel disorder of visiospatial integration.

    A 70-year-old man experienced an unusual disorder of visual perception after undergoing a ventriculoperitoneal shunt for normal-pressure hydrocephalus. The disorder was characterized by transient episodes of 90 degrees rotation of the visual environment, rather than the retinotopic visual field. This phenomenon is different from standard visual allesthesia and may have been caused by disordered integration of vestibular and visual inputs to the posterior parietal cortex or perseveration of a pre-existing environmental memory trace.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

2/32. Impairment of depth perception in multiple sclerosis is improved by treatment with AC pulsed electromagnetic fields.

    multiple sclerosis (MS) is associated with postural instability and an increased risk of falling which is facilitated by a variety of factors including diminished visual acuity, diplopia, ataxia, apraxia of gait, and peripheral neuropathy. Deficient binocular depth perception may also contribute to a higher incidence of postural instability and falling in these patients who, for example, find it an extremely difficult task to walk on uneven ground, over curbs, or up and down steps. I report a 51 year old woman with secondary progressive MS who experienced difficulties with binocular depth perception resulting in frequent falls and injuries. Deficient depth perception was demonstrated also on spontaneous drawing of a cube. Following a series of transcranial treatments with AC pulsed electromagnetic fields (EMFs) of 7,5 picotesla flux density, the patient experienced a major improvement in depth perception which was evident particularly on ascending and descending stairs. These clinical changes were associated with an improvement in spatial organization and depth perception on drawing a cube. These findings suggest that in MS impairment of depth perception, which is encoded in the primary visual cortex (area 17) and visual association cortex (areas 18 and 19), may be improved by administration of AC pulsed EMFs of picotesla flux density. The primary visual cortex is densely innervated by serotonergic neurons which modulate visual information processing. Cerebral serotonin concentrations are diminished in MS patients and at least some aspects of deficient depth perception in MS may be related to dysfunction of serotonergic transmission in the primary visual cortex. It is suggested that transcranial AC pulsed applications of EMFs improve depth perception partly by augmenting serotonergic transmission in the visual cortex.
- - - - - - - - - -
ranking = 5
keywords = cortex
(Clic here for more details about this article)

3/32. Tactile morphagnosia secondary to spatial deficits.

    A 73-year old man showed visual and tactile agnosia following bilateral haemorrhagic stroke. Tactile agnosia was present in both hands, as shown by his impaired recognition of objects, geometrical shapes, letters and nonsense shapes. Basic somatosensory functions and the appreciation of substance qualities (hylognosis) were preserved. The patient's inability to identify the stimulus shape (morphagnosia) was associated with a striking impairment in detecting the orientation of a line or a rod in two- and three-dimensional space. This spatial deficit was thought to underlie morphagnosia, since in the tactile modality form recognition is built upon the integration of the successive changes of orientation in space made by the hand as it explores the stimulus. Indirect support for this hypothesis was provided by the location of the lesions, which could not account for the severe impairment of both hands. Only those located in the right hemisphere encroached upon the posterior parietal cortex, which is the region assumed to be specialised in shape recognition. The left hemisphere damage spared the corresponding area and could not, therefore, be held responsible for the right hand tactile agnosia. We submit that tactile agnosia can result from the disruption of two discrete mechanisms and has different features. It may arise from a parietal lesion damaging the high level processing of somatosensory information that culminates in the structured description of the object. In this case, tactile recognition is impaired in the hand contralateral to the side of the lesion. Alternatively, it may be caused by a profound derangement of spatial skills, particularly those involved in detecting the orientation in space of lines, segments and complex patterns. This deficit results in morphagnosia, which affects both hands to the same degree.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

4/32. A category-specific deficit of spatial representation: the case of autotopagnosia.

    Following a vascular lesion in the parietal cortex of the language dominant hemisphere (right in one case), two patients showed a striking dissociation between spared naming, recognition and use of their body parts and an inability in localising on verbal command the same body parts on themselves and on a mannequin (Autotopagnosia, AT). The patients were submitted to a modified version of Reed and Farah Test (1995), a test that taps the ability to encode changes of body position as opposed to changes of position of objects. Their performance differed from normal controls, showing a specific deficit in encoding body position.It is suggested that AT could be the consequence of a lesion in a specific neural circuit, located in the language dominant hemisphere, whose function is to encode the body position for both oneself and others.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

5/32. blindness to form from motion despite intact static form perception and motion detection.

    We studied the motion perception, including form and meaning generated by motion, in a hemianopic patient who also had visual perceptual impairments in her seeing hemifield as a result of a lesion in ventral extrastriate cortex. She was unable to recognise 2- or 3-dimensional forms, and even borders, generated by motion alone, failed to recognise mimed actions or the Johannson 'biological motion' display, and ceased to recognise people well-known to her when they moved. Her performance with static displays, although impaired, could not explain her inability to perceive shape or derive meaning from moving displays. Unlike a motion-blind patient, she can still see and describe the motion, with the exception of second-order motion, but not what it creates or represents.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

6/32. MR perfusion imaging reveals regions of hypoperfusion associated with aphasia and neglect.

    OBJECTIVE: To evaluate diffusion-weighted imaging (DWI) and MR perfusion imaging (MRPI) as tools for identifying regions of infarct and hypoperfusion associated with aphasia and neglect in hyperacute stroke. Secondary goal: to establish a functional correlate of a radiologically defined "ischemic penumbra." methods: Forty subjects underwent DWI, MRPI, and standardized tests for lexical deficits or hemispatial neglect within 24 hours of stroke onset or progression. Ten patients had repeat DWI, MRPI, and cognitive testing after 3 days (in some cases after reperfusion therapy). Pearson correlations between error rate on cognitive testing and volume of abnormality on DWI versus MRPI were determined at each time period, and regions of hypoperfusion corresponding to specific cognitive deficits were identified. RESULTS: Error rate was more strongly correlated with volume of hypoperfused tissue on MRPI (r = 0.65 to 0.93; p < 0.01 to p < 0.0003) than with volume of lesion on DWI (r = 0.54 to 0.75; p = 0.14 to p < 0.01) for dominant and nondominant hemisphere stroke, at each time point. Forty-eight percent of aphasic patients and 67% of those with hemispatial neglect had either no infarct or only small subcortical infarct on DWI, but had focal cortical hypoperfusion. patients who had successful reperfusion therapy showed resolution of the hypoperfused territory beyond the infarction on repeat MRPI and showed resolution of corresponding deficits. CONCLUSIONS: MRPI shows regions of hypoperfused cortex associated with lexical deficits or hemispatial neglect, even when DWI shows no infarct or only small subcortical infarct. MRPI-DWI mismatch indicates regions of functionally salvageable tissue.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

7/32. Altitudinal neglect in a patient with occipital infarction.

    Visual neglect has been frequently described in a horizontal direction. Altitudinal neglect, however, has rarely been described and has been associated with bilateral lesions in the parieto-occipital or temporo-occipital region. The following case report presents a patient with marked altitudinal neglect of the inferior space which was elicited using a line bisection test. The previously healthy patient had well-defined lesions solely in the occipital cortex following an embolic infarction. The present case report underlines the possibility that bioccipital lesions themselves can be responsible for altitudinal neglect.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

8/32. Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex.

    Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT /V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.
- - - - - - - - - -
ranking = 4
keywords = cortex
(Clic here for more details about this article)

9/32. Visuospatial hemi-inattention following cerebellar/brain stem bleeding.

    Neglect is a unilateral lack of responsiveness to stimuli caused by visuospatial hemi-inattention, a unilateral representation deficit and/or a unilateral hypokinesia. It results most frequently from right-hemisphere brain damage, particularly of the parietal lobe but also of the frontal cortex, the basal ganglia, the thalamus, and recently it has also been described after a cerebellar lesion. We report a patient with right-sided bleeding of the posterior inferior cerebellar artery, who developed a left-sided visual hemi-inattention. She had no visual field defects, yet she had problems detecting left-sided targets in visual extinction. Furthermore, she was impaired in detecting complex motion on the left side and targets in a fixation offset paradigm. Reactions to left-sided targets in covert shifts of attention were slowed in the invalid condition. Her text reading was impaired as she could not always find the initial word of the next line. However, she was aware of her deficit. Her visuoconstructive ability was normal and she gave no indication of tactile or acoustic extinction. As the cerebellar lesion was located in the right hemisphere and the inattention involved the left side of space, we suggest that the damage to the right brain stem led to a transient imbalance of the noradrenergic ascending activation system which may explain her hemi-inattention.
- - - - - - - - - -
ranking = 1
keywords = cortex
(Clic here for more details about this article)

10/32. 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 = 2
keywords = cortex
(Clic here for more details about this article)
| Next ->


Leave a message about 'Perceptual Disorders'


We do not evaluate or guarantee the accuracy of any content in this site. Click here for the full disclaimer.