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Frontiers in Neurology 2017Posterior cortical atrophy (PCA) is a syndromic diagnosis. It is characterized by progressive impairment of higher (cortical) visual function with imaging evidence of... (Review)
Review
Posterior cortical atrophy (PCA) is a syndromic diagnosis. It is characterized by progressive impairment of higher (cortical) visual function with imaging evidence of degeneration affecting the occipital, parietal, and posterior temporal lobes bilaterally. Most cases will prove to have Alzheimer pathology. The aim of this review is to summarize the development of the concept of this disorder since it was first introduced. A critical discussion of the evolving diagnostic criteria is presented and the differential diagnosis with regard to the underlying pathology is reviewed. Emphasis is given to the visual dysfunction that defines the disorder, and the classical deficits, such as simultanagnosia and visual agnosia, as well as the more recently recognized visual field defects, are reviewed, along with the evidence on their neural correlates. The latest developments on the imaging of PCA are summarized, with special attention to its role on the differential diagnosis with related conditions.
PubMed: 28861031
DOI: 10.3389/fneur.2017.00389 -
Journal of Neurology Aug 2000
Topics: Aged; Aged, 80 and over; Agnosia; Brain Neoplasms; Female; Humans; Magnetic Resonance Imaging; Occipital Lobe; Visual Perception
PubMed: 11041337
DOI: 10.1007/s004150070138 -
International Journal of... Apr 2009We report a psychophysiological study of "recognition without awareness" in patient 2354, who had severe but circumscribed atrophy in the occipitoparietal region...
We report a psychophysiological study of "recognition without awareness" in patient 2354, who had severe but circumscribed atrophy in the occipitoparietal region bilaterally (caused by visual-variant Alzheimer's disease, documented by structural and functional neuroimaging) and an accompanying Balint syndrome that prevented her from recognizing the emotional valence of many highly charged negative visual scenes (e.g., a burned body). Despite this lack of overt recognition, patient 2354 nonetheless generated large amplitude skin conductance responses to highly charged negative pictures, demonstrating the same kind of recognition without awareness that has been reported previously in patients with bilateral occipitotemporal dysfunction and prosopagnosia [e.g., Tranel, D., & Damasio, A. R. (1985). Knowledge without awareness: an autonomic index of facial recognition by prosopagnosics. Science, 228, 1453-1454.]. Our case complements both previous evidence of covert, nonconscious recognition in patients with prosopagnosia, and previous behavioral studies of patients with Balint syndrome that have shown evidence of "preattentive" visual processing. The findings add to the small but important set of empirical observations regarding nonconscious visual processing in neurological patients, and indicate that recognition without awareness can occur in the setting of dorsal visual stream dysfunction and Balint syndrome. The findings in our patient suggest that she has patent pathways from higher-order visual cortices to autonomic effectors in the amygdala or hypothalamus, even though the results of such information processing are not made available to conscious awareness.
Topics: Analysis of Variance; Awareness; Emotions; Female; Fluorodeoxyglucose F18; Galvanic Skin Response; Humans; Magnetic Resonance Imaging; Middle Aged; Neuropsychological Tests; Pattern Recognition, Visual; Photic Stimulation; Positron-Emission Tomography; Prosopagnosia; Recognition, Psychology; Vision, Ocular
PubMed: 18824046
DOI: 10.1016/j.ijpsycho.2008.02.012 -
Vision Research Jul 2009Simultanagnosia is a neuropsychological disorder characterized by a restriction of visuospatial attention. In addition, patients are able to identify local elements of a... (Comparative Study)
Comparative Study
Simultanagnosia is a neuropsychological disorder characterized by a restriction of visuospatial attention. In addition, patients are able to identify local elements of a scene, but not the global whole. This may be due to a failure to scan and assemble local elements into a global whole (i.e. connect-the-dots). We monitored the eye movements of a simultanagnosic patient while she identified local and global elements of hierarchical letters. Scanning each local element was not necessary, nor sufficient, for successful global level identification. Our results argue against a connect-the-dots strategy of global identification and suggest that residual global processing may be occurring.
Topics: Agnosia; Attention; Case-Control Studies; Eye Movements; Female; Humans; Magnetic Resonance Imaging; Middle Aged; Neuropsychological Tests; Pattern Recognition, Visual; Space Perception; Visual Pathways
PubMed: 19460397
DOI: 10.1016/j.visres.2009.05.002 -
Neurocase 2016We report a patient with ventral simultanagnosia, prosopagnosia for "unfamiliar faces" (dorsal prosopagnosia), spatial agraphia, and constructional disorder,...
We report a patient with ventral simultanagnosia, prosopagnosia for "unfamiliar faces" (dorsal prosopagnosia), spatial agraphia, and constructional disorder, particularly on the left spatial side, due to a lesion in the right posterior superior and middle temporal gyri and angular gyrus. The patient showed impairment of fundamental visual and visuospatial recognition, such as in object size, configuration, and horizontal point location, which probably underlay the mechanism of simultanagnosia and prosopagnosia. This case also suggests that the coexistence of simultanagnosia and prosopagnosia results from a right hemispheric insult, and damage to the temporoparietal area interrupts the incorporation of spatial information into object recognition. This disconnection of information flow, together with impaired object recognition per se, may impair the parallel processing of multiple objects, leading to object-by-object or part-by-part recognition.
Topics: Aged; Agnosia; Brain Injuries; Face; Female; Humans; Neuropsychological Tests; Parietal Lobe; Prosopagnosia; Temporal Lobe
PubMed: 26207875
DOI: 10.1080/13554794.2015.1066827 -
Journal of Cognitive Neuroscience Mar 2012Because of our limited processing capacity, different elements of the visual scene compete for the allocation of processing resources. One of the most striking deficits...
Because of our limited processing capacity, different elements of the visual scene compete for the allocation of processing resources. One of the most striking deficits in visual selection is simultanagnosia, a rare neuropsychological condition characterized by impaired spatial awareness of more than one object at time. To decompose the neuroanatomical substrates of the syndrome and to gain insights into the structural and functional organization of visuospatial attention, we performed a systematic evaluation of lesion patterns in a group of simultanagnosic patients compared with patients with either (i) unilateral visuospatial deficits (neglect and/or extinction) or (ii) bilateral posterior lesions without visuospatial deficits, using overlap/subtraction analyses, estimation of lesion volume, and a lesion laterality index. We next used voxel-based morphometry to assess the link between different visuospatial deficits and gray matter and white matter (WM) damage. Lesion overlap/subtraction analyses, lesion laterality index, and voxel-based morphometry measures converged to indicate that bilateral parieto-occipital WM disconnections are both distinctive and necessary to create symptoms associated with simultanagnosia. We also found that bilateral gray matter damage within the middle frontal area (BA 46), cuneus, calacarine, and parieto-occipital fissure as well as right hemisphere parietal lesions within intraparietal and postcentral gyri were associated with simultanagnosia. Further analysis of the WM based on tractography revealed associations with bilateral damage to major pathways within the visuospatial attention network, including the superior longitudinal fasciculus, the inferior fronto-occipital fasciculus, and the inferior longitudinal fasciculus. We conclude that damage to the parieto-occipital regions and the intraparietal sulcus, together, with bilateral WM disconnections within the visuosptial attention network, contribute to poor visual processing of multiple objects and the loss of processing speed characteristic of simultanagnosia.
Topics: Adult; Aged; Aged, 80 and over; Attention; Brain Mapping; Diffusion Magnetic Resonance Imaging; Female; Functional Laterality; Humans; Image Processing, Computer-Assisted; Male; Middle Aged; Neuropsychological Tests; Perceptual Disorders; Severity of Illness Index; Space Perception; Young Adult
PubMed: 22066584
DOI: 10.1162/jocn_a_00159 -
Neuropsychologia 2008When confronted with two identical stimuli in a very brief period of time subjects often fail to report the second stimulus, a phenomenon termed "repetition blindness"....
When confronted with two identical stimuli in a very brief period of time subjects often fail to report the second stimulus, a phenomenon termed "repetition blindness". The "type-token" account attributes the phenomenon to a failure to individuate the exemplars. We report a subject, KE, who developed simultanagnosia (the inability to see more than one item in an array) as a consequence of bilateral parietal lobe infarctions. With presentation of two words, pictures or letters for an unlimited time, KE typically reported both stimuli on less than half of trials. Performance was significantly influenced by the semantic relationship between items in the array. He reported both items significantly more frequently if they were semantically related; in contrast, when presented either identical or visually different depictions of the same item, he reported both items on only 2-4% of trials. Performance was not influenced by the visual similarity between the stimuli; he reported visually dissimilar objects less frequently than visually similar but different objects. We suggest that KE's bilateral parietal lesions prevent the binding of preserved object representations to a representation computed by the dorsal visual system. More generally, these data are consistent with the claim that the posterior parietal cortex is crucial for individuating a stimulus by computing its unique spatio-temporal characteristics.
Topics: Agnosia; Attention; Cerebral Infarction; Form Perception; Functional Laterality; Humans; Male; Mental Recall; Middle Aged; Neuropsychological Tests; Parietal Lobe; Pattern Recognition, Visual; Photic Stimulation; Psycholinguistics; Reaction Time; Reading; Recognition, Psychology; Semantics; Space Perception; Verbal Behavior; Visual Perception
PubMed: 18514677
DOI: 10.1016/j.neuropsychologia.2007.08.024 -
Brain : a Journal of Neurology May 2012A fundamental aspect of visual cognition is our disposition to see the 'forest before the trees'. However, damage to the posterior parietal cortex, a critical brain... (Randomized Controlled Trial)
Randomized Controlled Trial
A fundamental aspect of visual cognition is our disposition to see the 'forest before the trees'. However, damage to the posterior parietal cortex, a critical brain region along the dorsal visual pathway, can produce a neurological disorder called simultanagnosia, characterized by a debilitating inability to perceive the 'forest' but not the 'trees' (i.e. impaired global processing despite intact local processing). This impairment in perceiving the global shape persists even though the ventral visual pathway, the primary recognition pathway, is intact in these patients. Here, we enabled global processing in patients with simultanagnosia using a psychophysical technique, which allowed us to bias stimuli such that they are processed predominantly by the intact ventral visual pathway. Our findings reveal that the impairment in global processing that characterizes simultanagnosia stems from a disruption in the processing of low-spatial frequencies through the dorsal pathway. These findings advance our understanding of the relationship between visuospatial attention and perception and reveal the neural mechanism mediating the disposition to see the 'forest before the trees'.
Topics: Adult; Aged; Agnosia; Bias; Brain Injuries; Brain Mapping; Contrast Sensitivity; Female; Fluorodeoxyglucose F18; Humans; Male; Parietal Lobe; Photic Stimulation; Positron-Emission Tomography; Psychophysics; Psychophysiologic Disorders; Visual Pathways; Young Adult
PubMed: 22418740
DOI: 10.1093/brain/aws066 -
Italian Journal of Neurological Sciences Apr 1986We describe a patient with a bilateral posterior lesion, who showed optic ataxia, gaze apraxia and the symptom which most authors call the inability to see more than one...
We describe a patient with a bilateral posterior lesion, who showed optic ataxia, gaze apraxia and the symptom which most authors call the inability to see more than one thing at a time. We discuss the last feature and the term simultanagnosia sometimes used to indicate it. Furthermore we stress the unusual localization of the lesion in this patient.
Topics: Aged; Agnosia; Apraxias; Cerebrovascular Disorders; Eye Movements; Humans; Male; Occipital Lobe; Parietal Lobe; Syndrome; Temporal Lobe; Visual Perception
PubMed: 3721836
DOI: 10.1007/BF02230891 -
Applied Neuropsychology 1996A case of visual agnosia is described. The patient, V C, complained of difficulties in identifying visual stimuli, after a stroke in the left occipital lobe. A...
A case of visual agnosia is described. The patient, V C, complained of difficulties in identifying visual stimuli, after a stroke in the left occipital lobe. A neuropsychological examination demonstrated a range of symptoms consistent with (ventral) simultanagnosia, and a reaching disorder--suggesting Balint's syndrome. The patient's object recognition ability improved considerably over time.
PubMed: 16318508
DOI: 10.1080/09084282.1996.9645381