A case of carbon monoxide poisoning by explosion of coal mine presenting as visual agnosia: re-evaluation after 40 years]

We re-evaluated a case of carbon monoxide poisoning presenting as visual agnosia who had been injured by explosion of Miike-Mikawa coal mine 40 years ago. In an early stage, his main neuropsychological symptoms were visual agnosia, severe anterograde amnesia, alexia, agraphia, constructional apraxia, left hemispatial neglect and psychic paralysis of gaze, in addition to pyramidal and extra pyramidal signs. At the time of re-evaluation after 40 years, he still showed visual agnosia associated with agraphia and constructional apraxia. Concerning visual agnosia, recognition of the real object was preserved, while recognition of object photographs and picture was impaired. Thus, this case was considered to have picture agnosia as he could not recognize the object by pictorial cues on the second dimensional space. MRI examination revealed low signal intensity lesions and cortical atrophy in the bilateral parieto-occipital lobes on T1-weighted images. Therefore, the bilateral parieto-occipital lesions are likely to be responsible for his picture agnosia.     

Visual object agnosia: current conceptions

Visual agnosia for objects is a difficulty in recognizing objects presented visually. This difficulty can not be explained by a mental deterioration, a disorder of attention or a lack of familiarity with the object. Two criteria are essential but disputed: the absence of visual sensory difficulty necessary for adequate perception; possible recognition of the object by another sensory modality. An object is characterized by a triple representation: formal, semantic, lexical. The clinical, cognitive, pathophysiological analysis lead to distinguish 3 types of visual agnosia. 1) Aperceptive visual agnosia: patients see badly with morphological errors; the disorder concerns visual informations processing that is a necessary condition for identifying the formal representation of the object; the lesions are bilateral and involve the occipito-temporal cortex. 2) Associative visual agnosia: patients can copy, are not aphasic, but give erroneous verbal responses; the disorder concerns the links between formal representations and semantic, lexical representations; the lesions are unilateral and involve the left gyrus angularis connections. 3) Asemantic visual agnosia: patients have lost the meanings of objects and words; the disorder concerns semantic representations; the lesions are bilateral and involve the temporo-limbic cortex.     

Visual and tactile agnosia

A patient presented with visual and tactile agnosia due to a spontaneous left occipito-temporal hematoma. Major memory and spatial orientation disorders were also noted, but language, gestures, auditory and olfactory perception, and interior visual imagerie were unaffected. A review of the literature since 1970 found 6 cases of an association of this type among 17 patients with visual agnosia. There appears to be no relationship between the presence of tactile agnosia and the global or partial character of the visual agnosia, the severity of memory disturbances, the presence of visuoverbal disconnection or visual imagery disorders. In contrast, these cases differed in that the lesions were more extensive and extended beyond the internal occipital regions: they were widespread in 3 cases and in the left internal occipital and parietal region in 1 case. In the patient reported in this paper there was a wide lesion of the posterior white matter of the left hemisphere.     

Right sided hemispatial neglect and bilateral cerebral lesions.

This study compared the frequency with which unilateral and bilateral cerebral disease gives rise to right sided visual hemispatial inattention. A retrospective survey identified brain injured patients for whom target omissions on visual target cancellation tasks significantly exceeded control values. Subjects consisted of 40 right handed patients referred for clinical evaluation or research study of hemispatial inattention. Right sided visual hemispatial inattention occurred with greater frequency and severity in patients with bilateral lesions than in patients with unilateral left sided or right sided lesions. All eight patients with bilateral lesions manifested right sided hemispatial inattention and failed to detect more targets overall than patients in the other two groups. Of the 13 patients with left sided lesion, seven ignored more targets on the right and six ignored more targets on the left. All but one of the 19 patients with right sided lesions ignored more targets on the left. The association of severe right sided visual hemispatial inattention with bilateral cerebral disease extends previous findings and showed that, in this sample, the most common setting for right sided hemispatial neglect occurred in patients with bilateral cerebral lesions.     

Relationship between somatosensory event-related potential N140 aberrations and hemispatial agnosia in patients with stroke: a preliminary study

Purpose: The somatosensory event-related potential N140 is thought to be related to selective attention. This study aimed to compare the somatosensory event-related potential N140 in healthy subjects to that in patients with stroke to determine whether N140 and attentiveness are associated in patients with stroke with or without hemispatial agnosia.

Materials and Methods: Normal somatosensory event-related potential N140 values were determined using data from ten healthy subjects. Fifteen patients with stroke were divided into two groups based on the presence of hemispatial neglect. Somatosensory event-related potential N140 components were compared between the two groups.

Results: Stimulation of the affected limb in the hemispatial agnosia group resulted in significantly longer N140 latency at the contralateral vs. the ipsilateral electrode. This was the inverse of the relationship observed in normal subjects, with stimulation of the intact side in patients with hemispatial agnosia, and with stimulation of both the intact and affected sides in patients without agnosia. In the hemispatial agnosia group, the peak latency of N140 following stimulation of the affected side was significantly longer than it was following stimulation of the intact side and when compared to that in patients without agnosia. In addition, abnormal N140 peak latencies were observed at the Cz and ipsilateral electrodes in patients with hemispatial agnosia following stimulation of the intact side.

Conclusions: These findings suggest that somatosensory event-related potential N140 is independently generated in each hemisphere and may reflect cognitive attention.     

Pantomime agnosia.

Visual agnosia is impaired visual recognition not explained by defective visual acuity, visual fields, attention, or general mental ability. Two nonapraxic patients with lesions in the left occipital lobe could imitate pantomimes they could not recognise. Although both patients had a hemianopia, sparing of gesture imitation shows that no visual defect accounts for their inability to recognise pantomimes. Both patients were amnestic and alexic but had no general impairment of cognitive ability to account for a pantomime-recognition disorder. These patients seem to have agnosia for pantomime. From the computed tomograms from these patients, we propose that inferior visual association cortex is critical for gesture comprehension, whereas superior portions of these structures are critical for imitating or performing pantomime to an object presented visually.     

A comparison of the organization of the projections of the dorsal lateral geniculate nucleus, the inferior pulvinar and adjacent lateral pulvinar to primary visual cortex (area 17) in the macaque monkey

Both anterograde and retrograde transport tracing methods were used to study the organization of the projections of the dorsal lateral geniculate (DLG), the inferior pulvinar and subdivisions of the lateral pulvinar to primary visual cortex (striate cortex or area 17). The DLG projects only to striate cortex. These projections are retinotopically organized, and do not extend to any cortical layers above layer IVA. In contrast the inferior pulvinar (PI) and the immediately adjacent portion of the lateral pulvinar (PL alpha 48) project to both striate and prestriate cortex. The projections from these two thalamic areas to the striate cortex are also retinotopically organized and exist in parallel with those from the DLG. In contrast to the DLG, the projections from PI and PL alpha terminate above layer IVA in striate cortex, i.e. layers I, II and III. In prestriate cortex the layers of termination include layers IV, III and I. The pulvinar terminations in layers II and III of area 17 occur in segregated patches as do the geniculate terminations in layers IVC and IVA. On the other hand the pulvinar terminations in layer I which overlie those in layers II and III of area 17 appeared to be continuous. Control studies show that the remainder of the lateral pulvinar overlying PL alpha does not project to striate cortex. It is concluded that there are 3 visuotopically organized inputs from the lateral thalamus to primary visual cortex and that each of these inputs have different layers of termination. The inputs from PI and DLG can convey direct retinal inputs while those from PI and PL alpha can also be involved in intrinsic cortico-thalamocortical connection with prestriate cortex. It remains, then that it cannot be tacitly assumed that the ascending inputs which influence the response properties of the primary cortical neurons arise solely from the dorsal lateral geniculate nucleus. It is also argued that these inputs to the supragranular layers may be excitatory as those from the DLG to the IVth layer.     

Drawings by patients with unilateral visuospatial agnosia]

Drawings made by 25 patients with neurosurgical diseases causing focal lesions in the posterior areas of the right, not dominant cerebral hemisphere due to expanding changes. Experimental clinical investigations by the method of Luria demonstrated in these cases presence of left-sided visuospatial agnosia. The material was analysed from the point of view of the features of drawings characteristic for the syndrome of disturbances and the localizatory and diagnostic value of drawings. Characteristic disturbances of drawings and their placement were observed suggesting that the patients ignored the left half of the visual space due to damage to the right parieto-occipital non-dominant cerebral hemisphere. The drawing test is regarded as a valuable method for the diagnosis and localization of lesions in the neurological and neuropsychological practice.     

Explicit and implicit perception of illusory contours in unilateral spatial neglect: behavioural and anatomical correlates of preattentive grouping mechanisms

Studies of hemispatial neglect suggest that some perceptual processes still operate on contralesional stimuli independent from spatial attention or awareness. Here we examined whether preattentive processing in extrastriate areas may group unconnected elements inducing illusory contours despite neglect. While it has been debated whether illusory contours arise from preattentive grouping or higher cognitive processes, neurophysiological studies show that neurones in secondary visual cortex (V2) can code for illusory contours. Twelve patients with right hemisphere damage and left neglect were tested for implicit and explicit detection of illusory contours using, respectively: (1) a bisection task where patients were not explicitly required to attend to lateral elements and judged the midpoint of Kanizsa illusory stimuli, as well as other physically connected or unconnected stimuli of the same length; (2) a matching task where patients had to overtly attend to lateral elements and made same/different judgements on pairs of illusory stimuli with identical or different inducers on the right or left side. In some patients, bisection judgements were consistently similar on Kanizsa stimuli with illusory contours and connected stimuli with real contours but different on unconnected gap figures, regardless of their length, suggesting implicit grouping of inducing elements prior to processing stages where a spatial attentional bias arose. Their lesions centred on the inferior parietal cortex or thalamus. Other patients did not show a systematic bisection pattern and had lesions extending posteriorly in the lateral occipital cortex. However, both groups of patients failed to detect left-side inducers in explicit matching judgements, even though errors often revealed unconscious processing, and they showed similar neglect severity on other standard tests. These findings suggest that grouping by illusory contours can occur preattentively and influence bisection independently from the ability to detect contralateral inducers explicitly, severity of inattention, and other forms of unconscious processing. Implicit grouping may depend on the sparing of lateral occipital areas involved in figure-ground segmentation at early stages of visual processing.     

The neuropsychological and neuroradiological correlates of slowly progressive visual agnosia

The case of a 64-year-old woman affected by slowly progressive visual agnosia is reported aiming to describe specific cognitive-brain relationships. Longitudinal clinical and neuropsychological assessment, combined with magnetic resonance imaging (MRI), spectroscopy, and positron emission tomography (PET) were used. Sequential neuropsychological evaluations performed during a period of 9 years since disease onset showed the appearance of apperceptive and associative visual agnosia, alexia without agraphia, agraphia, finger agnosia, and prosopoagnosia, but excluded dementia. MRI showed moderate diffuse cortical atrophy, with predominant atrophy in the left posterior cortical areas (temporal, parietal, and lateral occipital cortical gyri). 18FDG-PET showed marked bilateral posterior cortical hypometabolism; proton magnetic resonance spectroscopic imaging disclosed severe focal N-acetyl-aspartate depletion in the left temporoparietal and lateral occipital cortical areas. In conclusion, selective metabolic alterations and neuronal loss in the left temporoparietooccipital cortex may determine progressive visual agnosia in the absence of dementia.     

Spatial contrast and flicker sensitivity following medial thalamic or visual cortex lesions in hooded rats

In rats, lesions of the medial thalamus that involve the intralaminar nuclei produce a number of visual impairments similar to those obtained with visual cortex ablation, suggesting that the former functionally disrupt visual cortex. This was tested by a direct comparison between the two lesions on spatial contrast and flicker sensitivity, using behavioural techniques. Both lesions depressed spatial contrast sensitivity, visual cortex damage more than thalamic lesions. Only medial thalamic lesions produced statistically significant changes in flicker sensitivity. This dissociation suggests that medial thalamic and visual cortex lesions are disrupting different mechanisms. Alternative explanations of the thalamic deficit are discussed.     

Symptoms and lesion localization in visual agnosia]

There are two cortical visual processing streams, the ventral and dorsal stream. The ventral visual stream plays the major role in constructing our perceptual representation of the visual world and the objects within it. Disturbance of visual processing at any stage of the ventral stream could result in impairment of visual recognition. Thus we need systematic investigations to diagnose visual agnosia and its type. Two types of category-selective visual agnosia, prosopagnosia and landmark agnosia, are different from others in that patients could recognize a face as a face and buildings as buildings, but could not identify an individual person or building. Neuronal bases of prosopagnosia and landmark agnosia are distinct. Importance of the right fusiform gyrus for face recognition was confirmed by both clinical and neuroimaging studies. Landmark agnosia is related to lesions in the right parahippocampal gyrus. Enlarged lesions including both the right fusiform and parahippocampal gyri can result in prosopagnosia and landmark agnosia at the same time. Category non-selective visual agnosia is related to bilateral occipito-temporal lesions, which is in agreement with the results of neuroimaging studies that revealed activation of the bilateral occipito-temporal during object recognition tasks.     

The neural basis of visuomotor deficits in hemispatial neglect

We have recently reported that patients with hemispatial neglect demonstrate increased terminal errors when performing delayed leftward reaches and that right-brain damaged patients (irrespective of neglect) take longer to complete their movements [Rossit, S., Muir, K., Reeves, I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologiaa 47, 1563-1573]. Here we conducted an initial voxel-based lesion-symptom analysis to examine the neural basis of such deficits in 21 right-brain damaged subjects with 11 patients suffering from hemispatial neglect (2 more than in Rossit et al. [Rossit S., Muir K., Reeves I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologia 47, 1563-1573] and 10 control patients without the condition. We found that the accuracy impairments in delayed leftward reaches were associated with damage to occipito-temporal areas. In contrast, the movement time slowing was related to more anterior lesions in the frontal lobe. These findings agree with the view that neglect affects actions thought to depend on the processing carried out by the ventral visual stream. In addition, we suggest that the timing impairments which are not neglect-specific maybe be driven by frontal structures.     

Agnosia for streets and defective root finding

Topographical disorientation is identified as a condition in which patients are unable to find their way in familiar surroundings, such as their home neighborhood or the admitting hospital after the onset of illness. I proposed to classify topographical disorientation into two categories: agnosia for streets (landmark agnosia) and defective root finding (heading disorientation). Patients with agnosia for streets are unable to identify familiar buildings and landscapes. They can, however, morphologically perceive them and remember their way around familiar areas. The lesions are located in the right posterior part of the parahippocampus gyrus, anterior half of the lingual gyrus and adjacent fusiform gyrus. Clinical findings and functional imaging studies suggest that these regions play a crucial role in the interaction between the visual information of streets and memories of them, which are thought to be retained in the right anterior part of the temporal lobe. In particular, the posterior part of the parahippocampus gyrus is critical for the acquisition of novel information. On the other hand, patients with defective root finding can identify familiar streets, but cannot remember their own location or positional relation between two points within a comparatively wide range not surveyable at one time. The lesions are located in the right retrosplenial cortex (Areas 29, 30), posterior cingulate cortex (Areas 23, 31) and precuneus. Clinical findings and functional imaging studies suggest that these regions are involved in the orientation function for navigating in wide spaces. In particular, the retrosplenial cortex is critical for encoding novel information.     

EEG coherence studies in the normal brain and after early-onset cortical pathologies

Visual corpus callosum (CC) preferentially interconnects neurons selective for similar stimulus orientation near the representations of the vertical meridian. These properties allow studying the CC functionality with EEG coherence analysis. Iso-oriented and orthogonally-oriented gratings were presented to the two hemifields, either close to the vertical meridian or far from it. In animals with intact CC, and in man, interhemispheric coherence (ICoh) increased only with iso-oriented gratings presented near or crossing the vertical meridian. The increase was localized to occipital electrodes and was specific for the β–γ frequency band. Visual-stimulus induced changes in ICoh were studied in patients with early pathologies of the visual areas. From a girl with abnormal vision and severe bilateral lesion of the primary visual areas at 3 weeks, after premature birth at 30 weeks, we obtained no ICoh response until 9 years. In control children visual stimulation increased occipital ICoh at 6–7 years. From a young man having suffered similar lesions when he was 9 months older than the girl, no consistent increase in ICoh could be obtained. In a 14-year-old girl with congenital visual agnosia, no visible lesions, but with a temporal-occipital epileptic focus, ICoh responses were evoked both by iso-oriented, and by orthogonally-oriented gratings. In a young man with bilateral parieto-occipital microgyria extending into the calcarine sulcus, visual stimuli increased ICoh as in normal individuals, but the response was weaker. These cases are discussed in terms of development of CC connections and point to a variety of plastic changes in the cortical connectivity of children.     

Altitudinal neglect

Previous clinical observations on patients with hemispatial neglect from unilateral hemispheric lesions suggest the brain's attentional mechanisms are organized along the horizontal dimensions of extrapersonal space. We now report a patient with Balint's syndrome caused by bilateral parieto-occipital infarctions, who demonstrated altitudinal neglect. On visual and tactile bisection of vertical rods, the patient consistently placed her mark well above the true midpoint, and this performance remained unchanged when the stimuli were simultaneously explored visually and tactually. She also showed altitudinal inattention in the visual modality by extinguishing the stimulus presented in the lower quadrants during double simultaneous stimulation across the horizontal meridian. These findings suggest that bilateral damage to the parietal lobes can lead to multimodal attentional and exploratory deficits along the vertical dimensions of extrapersonal space.     

Progressive visual agnosia

Progressive visual agnosia was discovered in the 20th century following the discovery of classical non-progressive visual agnosia. In contrast to the classical type, which is caused by cerebral vascular disease or traumatic injury, progressive visual agnosia is a symptom of neurological degeneration. The condition of progressive visual loss, including visual agnosia, and posterior cerebral atrophy was named posterior cortical atrophy (PCA) by Benson et al. (1988). Progressive visual agnosia is also observed in semantic dementia (SD) and other degenerative diseases, but there is a difference in the subtype of visual agnosia associated with these diseases. Lissauer (1890) classified visual agnosia into apperceptive and associative types, and it in most cases, PCA is associated with the apperceptive type. However, SD patients exhibit symptoms of associative visual agnosia before changing to those of semantic memory disorder. Insights into progressive visual agnosia have helped us understand the visual system and discover how we "perceive" the outer world neuronally, with regard to consciousness. Although PCA is a type of atypical dementia, its diagnosis is important to enable patients to live better lives with appropriate functional support.     

Hémianopsie latérale homonyme et atrophie corticale postérieure

Introduction

Posterior cortical atrophy (PCA) is a clinically and radiologically defined syndrome, in which predominant symptoms focus on higher visual dysfunction with progressive course and association with cortical atrophy or hypometabolism that predominates in the posterior part of the hemispheres. Homonymous hemianopia (HH) has rarely been described in this syndrome.

Methods

We report on six patients (four females, two males, aged 63 to 80) referred for visual disorder which led to demonstration of HH using perimetry testing. These patients were followed for 1 to 5 years after discovery of HH. Brain imaging with MRI or CT scan was obtained in the six cases and a SPECT scan was performed in four cases.

Results

HH was left-sided in four cases and right-sided in two cases. Associated symptoms related to higher visual dysfunction were simultagnosia, alone or as part of a full Balint's syndrome, alexia, constructional apraxia, dressing apraxia, visual form agnosia, prosopagnosia and hemispatial neglect. These symptoms were mild at onset but invariably worsened with disease progression. Dementia eventually developed in all cases. The clinical diagnosis was probable Alzheimer's disease in five cases and corticobasal degeneration in one case. Radiology showed posterior cortex atrophy in all cases as well as reduced cerebral blood flow in the same region, with an asymmetrical pattern compatible with the side of HH.

Conclusion

Elementary cortical lesions in PCA can develop mainly in the associative visual areas and even in the primary visual area, resulting in HH. HH has rarely been documented in PCA, but its prevalence would probably be higher if systematic search was conducted. Apparently isolated HH of insidious onset should suggest PCA and lead to neuropsychological testing and search for discrete atrophic changes of the posterior cortex on MRI as well as for metabolic alterations with SPECT or PET.     

Visuo-constructional disorders and alexia-agraphia associated with posterior cortical atrophy

A 57 year-old woman developed a slowly progressive environmental agnosia and dressing apraxia without disturbances of language, memory, orientation and social activities. Two years later, alexia, agraphia, visual agnosia, constructional apraxia, simultagnosia and imitation apraxia of nonsymbolic gestures were also noted. Ophthalmic examination demonstrated a left inferior quadranopsia. Oral comprehension was normal. There was no loss of insight, and behavioral response was appropriately concerned. Computed tomography and magnetic resonance imaging revealed bilateral cortical atrophy in parieto-occipital areas, most pronounced on the right side, with enlargement of the ventricles. Positron emission tomography demonstrated low flow and metabolism values in the right parietal, temporal and occipital regions. This case is very similar to those of posterior cortical atrophy recently reported by Benson et al. (1988). It suggests a selectively degenerative dysfunction of posterior association cortex, sparing oral language and verbal memory.     

Posterior cortical atrophy

Five patients had progressive dementia heralded by disorders of higher visual function. All eventually developed alexia, agraphia, visual agnosia, and components of Balint's, Gerstmann's, and transcortical sensory aphasia syndromes. Memory, insight, and judgment were relatively preserved until late in the course. Predominant parieto-occipital atrophy was demonstrated on both computed tomography and magnetic resonance imaging in two of the patients; posterior circulation was normal by angiography in the three studied. To date, no pathologic specimen is available for study; speculations on the underlying pathologic condition include an atypical clinical variant of Alzheimer's disease, a lobar atrophy analogous to Pick's disease, or some previously unrecognized entity.