Visual associative agnosia and optic aphasia. A single case study and a review of the syndromes

Stroke and neurodegenerative disorders: 3. Poststroke rehabilitation

OBJECTIVE

This self-directed learning module highlights rehabilitation strategies in poststroke rehabilitation. It is part of the study guide on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. Using a case vignette format, this article specifically focuses on typical clinical presentations, recovery patterns, and traditional and innovative therapeutic interventions in poststroke rehabilitation such as constraint-induced movement therapy, treadmill training, functional electrical stimulation, robot-aided therapy, virtual reality treatment, cortical stimulation, speech therapy for aphasia, and orthotic management. The goal of this article is to influence the learner's knowledge on the delivery of poststroke rehabilitation treatment.

Task-related laterality effects in the lateral occipital complex

Using functional imaging, we investigated the effects of two different tasks on activation in the lateral occipital complex (LOC). Alternating blocks of intact and scrambled objects were presented. In one task, subjects responded when an object repeated (matching task). In a second task subjects silently named objects (naming task). Identical objects (tools, animals and letters) were presented for both tasks. A relative measure of the number of voxels activated in LOC in left and right hemispheres was calculated for each task across a range of thresholds. Also the effects of task demands on category specific areas in LOC were examined. The object matching task resulted in proportionally more activity in the right hemisphere. The object naming task resulted in proportionally more activity in the left hemisphere, most prominently in the anterior portion of LOC. Effectively, changing the task changed the lateralization of activation to intact objects in LOC. In contrast, changing the task did not change the lateralization of category-specific activations. The results suggest that there are task-related top-down influences on the activation of neural populations in LOC as a whole, but the lateralization of category-specific regions in LOC is independent of task demands and may reflect bottom-up processing.

Optic aphasia: a case study

Optic aphasia is a rare syndrome in which patients are unable to name visually presented objects but have no difficulty in naming those objects on tactile or verbal presentation. We report a 79-year-old man who exhibited anomic aphasia after a left posterior cerebral artery territory infarction. His naming ability was intact on tactile and verbal semantic presentation. The results of the systematic assessment of visual processing of objects and letters indicated that he had optic aphasia with mixed features of visual associative agnosia. Interestingly, although he had difficulty reading Hanja (an ideogram), he could point to Hanja letters on verbal description of their meaning, suggesting that the processes of recognizing objects and Hanja share a common mechanism.

DTI tractography based parcellation of white matter: application to the mid-sagittal morphology of corpus callosum

Morphology of the corpus callosum (CC) at the mid-sagittal level has been a target of extensive studies. However, the lack of internal structures and its polymorphism make it a challenging task to quantitatively analyze shape differences among subjects. In this paper, diffusion tensor Imaging (DTI) and tract tracing technique were applied to incorporate cortical connectivity information to the morphological study. The CC was parcellated into six major subdivisions based on trajectories to different cortical areas. This subdivision was performed for eight normal subjects and one stroke patient. The parcellated CCs of the normal subjects were normalized for morphological analysis. When comparing the stroke patient to the normal population, we detected significant atrophy in the motor and sensory areas of the patient CC, in line with the clinical deficits. This approach provides a new tool to investigate callosal morphology and functional relationships.

Alterações de linguagem nas fases iniciais da doença de Alzheimer

A doença de Alzheimer (DA) está associada a alterações cognitivas, de linguagem e de comportamento que se agravam durante seu curso. O objetivo deste estudo foi verificar a presença de alterações de linguagem, em pacientes com DA em fase inicial. Foram avaliados 12 pacientes com diagnóstico de provável (DA). Todos tinham pontuação no Mini Exame do Estado Mental acima de 23 pontos. Os pacientes foram submetidos à aplicação do Teste de Boston e os resultados comparados aos da população normal. Todos os pacientes apresentaram alterações de linguagem. Foram encontradas diferenças estatisticamente significantes nas tarefas de Compreensão auditiva e na tarefa de denominação. Nas demais tarefas de expressão e compreensão oral, bem como nas de leitura e escrita, os pacientes tiveram desempenho similar aos normais. Embora com um grupo pequeno,esta investigação identificou alterações bem definidas de linguagem em uma fase bastante inicial da DA.

Differences in functional magnetic resonance imaging activation by category in a visual confrontation naming task

OBJECTIVE

Cortical processing involved in seemingly similar tasks may differ in important ways. The authors mapped cortical regions engaged in a commonly performed picture naming task, seeking differences by semantic category. Functional magnetic resonance imaging was used during presentation of standardized line drawings in 18 healthy right-handed female participants, comparing living versus nonliving entities. During visual naming, across categories there was strong activation of left frontal (BA45/47), bilateral temporo-occipital junction (BA19), and inferior temporal regions (BA36/37). Activation of right inferior temporal cortex (BA19 and BA37) was greater during naming of living versus nonliving category items. No category differences in activation strength in the left temporal lobe were observed. The authors conclude that visual semantic operations may involve visual association cortex in the right temporal lobe in women.

The influence of misnaming on object recognition: a case of multimodal agnosia

We present a case of multimodal agnosia in the visual and tactile modality due to an infarction in the territory of the left posterior cerebral artery. The patient's ability to recognize objects fluctuated depending on his verbal activity. When he misnamed presented objects, he tended to use them and to draw them in keeping with the wrong name. We submit that the mechanism causing associative agnosia is more dynamic than it was hitherto considered. It originates from the rivalry between top-down central regulation and bottom-up peripheral flow.

When a rose is a rose in speech but a tulip in writing

We report the pattern of performance on language tasks by a neurologically impaired patient, RCM, who makes semantic errors in writing to dictation and in written naming, but makes very few errors at all (and no semantic errors) in spoken naming, oral reading, or spontaneous speech. RCM also shows a significant effect of concreteness on spelling accuracy and other features of so-called "deep dysgraphia." However, it is shown that, unlike previously reported patients described as deep dysgraphic, RCM has intact semantic processing but impairment in accessing lexical-orthographic representations, at least for the items tested. These results demonstrate that the collection of features labelled as "deep dysgraphia" can arise from damage to different cognitive processes. Detailed analyses of RCM's performance across lexical tasks, at two different time periods of recovery, provide evidence that lexical orthographic representations can be either directly activated by lexical semantic representations, or activated by the interaction of lexical semantic and sublexical information from phonology-to-orthography conversion mechanisms.

The more you know the less you can tell: inhibitory effects of visuo-semantic activation on modality specific visual misnaming

WH, a 77-years old right-handed psychoanalyst, displayed modality specific visual misnaming as a sequel of an embolic stroke in the left posterior cerebral artery. WH's errors in visual object naming consisted mainly of semantic paraphasias and perseverations. His verbalizations during testing sometimes manifested a conflict between correct responses and perseverations. Analysis of the stream of information from visual perception via semantics to phonology suggested incomplete access from vision to semantics as the source of errors. The disconnection did not affect verbo-visual matching, though he was unable to reject names that did not correspond to visual stimuli. Action naming was relatively spared, but naming of pictures of actions with objects was worse than naming of pictures of intransitive actions. Tactile naming worsened with simultaneous vision of objects. In visual object naming the error rate increased with increasing familiarity of objects. We propose that an interaction of excitation and inhibition within a single semantic system can explain the clinical phenomena of modality specific visual misnaming.

Optic aphasia with pure alexia: a mild form of visual associative agnosia? A case study

A single-case study is reported of a naming disorder selective to the visual modality. The patient showed intact access to structural knowledge of objects and letters, but impaired access to complete semantic knowledge of objects and alphabetical knowledge of letters from visual input. The impairment was most striking when the patient had to discriminate between semantically similar objects or within a given symbolic repertoire, i.e. letters. The co-occurrence of a partial deficit of visual recognition for objects and for letters indicated features of optic aphasia and pure alexia. This symmetric performance between object and letter processing may also constitute a mild form of visual associative agnosia.

Optic aphasia: evidence of the contribution of different neural systems to object and action naming

Visual stimulus naming was studied in a 66-year-old male patient with optic aphasia subsequent to left occipito-temporal infarction. While having difficulty in naming objects perceived visually, he was able to name objects by viewing gestures illustrating their use, and to name actions shown in pictures. These results suggest that naming performance depends on the kind of stimulus that is visually presented (object vs. action). The present findings lend support to congnitive models which postulate the existence of visual and functional semantic systems.

Cognitive and Neural Mechanisms Underlying Visual and Semantic Processing: Implications from “Optic Aphasia”

We report detailed analyses of the performance of a patient, DHY, who as a consequence of strokes in the left occipital lobe and the periventricular white matter in the region of the spleniuni, showed severely impaired naming of visual stimuli despite spared recognition of visual stimuli and spared naming in other modalities. This pattern of performance—labeled “optic aphasia”—has been previously interpreted as support for the hypothesis that there are independent semantic systems, either a visual and a verbal semantic store (Beauvois, 1982; Lhermitte & Beauvois, 1973) or a right hemisphere and a left hemisphere semantic system (Coslett & Saffran, 1989, l092), which are “disconnected” in these patients. We provide evidence that DHY shows precisely the types of performance across a variety of verbal and visual tasks that have been used to support these claims of separate semantic systems: (1) good performance in naming to definition and naming objects presented for tactile exploration (which has been interpreted as evidence of spared verbal or left hemisphere semantic processing), and (2) good performance on various “semantic” tasks that do not require naming (which has been interpreted as access to spared visual or right hemisphere semantic processing). Nevertheless, when nonverbal semantic tasks were modified such that they required access to more detailed semantic information for accurate performance, DHY was Par less accurate, indicating that she did not access complete semantic information about objects in the visual modality. We argue that these data undermine the claim that cases of optic aphasia can be explained only by proposing multiple semantic systems. We propose an alternative account for this pattern of performance, within a model of visual object naming that specifies a single, modality-independent semantic system. We show that the performance of DHY and other “optic aphasic” patients can be explained by proposing a deficit in accessing a complete, modality-independent, lexical-semantic representation from an intact stored, structural description of the object. We discuss the implications of these conclusions for claims about the neuroanatomical correlates of semantic and visual object processing.

Perseverative and Semantic Influences on Visual Object Naming Errors in Optic Aphasia: A Connectionist Account

Although perseveration—the inappropriate repetition of previous responses—is quite common among patients with neurological damage, relatively few detailed computational accounts of its various forms have been put forth. A particularly well-documented variety involves the pattern of errors made by “optic aphasic” patients, who have a selective deficit in naming visually presented objects. Based on our previous work in modeling impaired reading via meaning in deep dyslexia, we develop a connectionist simulation of visual object naming. The major extension in the present work is the incorporation of short-term correlational weights that bias the network towards reproducing patterns of activity that have occurred on recently preceding trials. Under damage, the network replicates the complex semantic and perseverative effects found in the optic aphasic error pattern. Further analysis reveals that the perseverative effects are strongest when the lesions are near or within semantics, and are relatively mild when the preceding object evokes no response. Like optic aphasics, the network produces predominantly semantic rather than visual errors because, in contrast to reading, there is some structure in the mapping from visual to semantic representations for objects. Viewed together with the dyslexia simulations, the replication of complex empirical phenomena concerning impaired visual comprehension based on a small set of general connectionist principles strongly suggests that these principles provide important insights into the nature of semantic processing of visual information and its breakdown following brain damage.