Lexical-semantic knowledge about food in patients with different types of dementia

While many theories agree that the conceptual knowledge is organized in categories, there is less agreement on the underlying organizational principle (e.g. Warrington & Shallice, 1984, Caramazza & Shelton, 1998; Capitani et al., 2003). Previous neuropsychological studies on semantic categories failed to clearly characterize the status of food as a category as they did not carefully distinguish between natural food and transformed food. Exploring how natural food and transformed food items are processed in patients suffering from primary dementia can allow us to test the theories of how semantic knowledge is organized in the brain. Thirty patients and 15 healthy controls matched for age and education took part in the study . Thirteen patients received a presumptive diagnosis of fronto-temporal dementia (FTD), 3 patients of Semantic Dementia (SD), and 14 of Alzheimer Dementia (AD). All participants performed 3 tasks tapping lexical-semantic knowledge about food and non-food items: confrontation naming (Task 1), categorization (Task 2), and word-to-picture matching (Task 3). Moreover, half food items were natural (e.g., apple) and half transformed (e.g. grana cheese), while non-food items were half non edible natural items (e.g., plant) and half kitchen implements. The results showed that, overall, patients performed poorer than controls on Tasks 1 and 3, with FTD-SD patients being more impaired than AD patients. When we compared performance on food versus non-food items, we observed that patients performed better on naming food than non-food items (Task 1). Specifically, FTD-SD patients displayed a significant difference between food and non-food items, while AD patients showed no difference. On Task 3 the same pattern was obtained. In addition, we observed that, across tasks, transformed food was processed better than natural food. These findings suggest that lexical-semantic processes are more prone to degradation in patients FTD-SD than in AD patients, and that food items, particularly the transformed ones, are more resistant to the deficit. Results are interpreted in the light of current theories of conceptual knowledge (Mahon & Caramazza, 2009).