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Semantic dementia (SD) is a progressive neurodegenerative language disorder characterized by fluent, empty speech and loss of word meaning. SD is one of three clinical syndromes associated with frontotemporal lobar degeneration. SD is a clinically-defined syndrome, but it is sometimes anatomically defined as the temporal variant of frontotemporal lobar degeneration (tvFTLD).
Signs and SymptomsEdit
SD patients complain of word-finding difficulties. Neuropsychology testing reveals deficits in picture naming, category fluency (e.g. "Please list as many animals as you can in one minute") and non-verbal tasks where the patient is given three photos and asked to point to a semantically related pair (known as "the pyramid and palm tree task," in which the third item is a pine tree). As the disease progresses, behavioral and personality changes are often seen similar to those seen in frontotemporal dementia.
Patients exhibit amodal deficits across semantic domains, however the regions specialised for different modalities such as colour, form, motion etc, are not damaged themselves; damage occurs in the anterior temporal lobe. This provides evidence of the 'Convergence Theory of Semantics', also known as the 'Semantic Hub' theory.
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- Kramer JH, Jurik J, Sha SJ, Rankin KP, Rosen HJ, Johnson JK, Miller BL. "Distinctive neuropsychological patterns in frontotemporal dementia, semantic dementia, and Alzheimer disease." Cogn Behav Neurol. (2003) 16(4):211-8. Available: 
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- Frontotemporal lobar degeneration
- Frontotemporal dementia
- Progressive nonfluent aphasia
- Pick's disease
- Alzheimer's disease
- Semantic memory
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