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Word Retrieval Disorders in Aphasia and Alzheimer's Disease

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Inhaltsangabe:Abstract: Language is one of the pillars of human consciousness, the main implement whereby individuals articulate thoughts and convey them to others. Impairments of the brain that affect this requisite part of the human intellect stroke, head injuries, progressive conditions or developmental disorders not only disrupt a person’s ability to carry out daily activities, but can also cause severe damage to the emotional state of a person and put a tremendous strain on caregivers. Pathologia physiologiam illustrat: For more than a century, it has been primarily by evidence from speech errors that neuroscientists have tried to understand the mechanisms of how the brain learns, stores, and processes language. Owing to the brain’s structural and functional complexity, many tasks remain unresolved. These include localizing language areas within the two hemispheres, mapping language-related functions, understanding how they relate to each other, and in what way their damage contributes to different degrees and varieties of disabilities. More specifically, the main problem remains the lack of a one-to-one correspondence between specific mental processes and cortical regions. Modern neuroscientific measurement techniques that aim at extracting quantitative information about physiological functions from image-based data may offer great insights into localized brain activity for specific cognitive tasks. For example, fMRI (functional magnetic resonance imaging) noninvasively highlights potentially significant language areas by monitoring regional changes in blood oxygenation, while PET (positron emission tomography) can measure abnormalities in the patient’s cerebral glucose metabolism. However, the results are highly variable from one study to the next, as there often is no single cause or pathologic mechanism, which particularly holds true for degenerative diseases. Hence, it is premature to think of functional imaging as a reliable tool to accurate diagnostic analysis as of yet, let alone grant it the power to pinpoint the internal structure and functions of the neural subsystems involved in normal language processing. A major advance in our understanding of the cortical organization of language at the systems level has not been achieved so far. It is still primarily by a number of traditional pen-and-paper neuropsychological tests that attention, perception, memory, and speech production are assessed and conclusions are being drawn about [...]