What is semantic in semantic dementia? The decay of knowledge of physical entities but not of verbs, numbers and body parts

摘要

Background: Conceptual knowledge does not decay randomly in patients with cerebral damage, suggesting that dedicated neural substrates may support different categories of knowledge. Semantic dementia is an optimal natural model for studying the organization of semantic memory. Nevertheless, in a pathology primarily characterized by a semantic memory disorder categorical- and modality- specific effects are not obvious findings. In fact, there is no clear evidence of categorical effects, at least concerning two broad categories of knowledge, that is, natural items and artifacts. Furthermore, transmodal deficits do not seem to be the rule in SD. Also quite robust is the observation that some conceptual domains are relatively spared in this pathology, that is, numerical knowledge, abstract words, and action verbs. Aims: To explore category specific and modality specific deficit in SD and to support the evidence that semantic degradation in SD primarily involves knowledge of the objects in the real world, whereas categories of knowledge whose items can be less easily identified by surface attributes, such as verbs, numbers and body parts, are more preserved.