Verbal and visuoperceptive semantic association in MCI and AD patients

Abstract

Author correspondence: Dina Di Giacomo , PhD University of L’Aquila, Italy Faculty of Medicine and Surgery Department of Internal Medicine and Public Health Phone: +390862434689 E-mail: dina.digiacomo@cc.univaq.it Introduction Alzheimer’s Dementia (AD) is diagnosed on the basis of cognitive deficits presented by the patient in the absence of other neurological, medical, or psychiatric signs. The deterioration of the semantic system is one of the most relevant neuropsychological symptoms of probable AD, together with memory, attention and language impairments (for review, see Salmon & Bondi, 2009). While semantic deficits are widely reported as one of the early cognitive deficits in AD, in our knowledge the semantic problems that may precede them in patients with mild AD have not been investigated to date. A continued controversy has been whether the deficit in semantic memory represents a loss of information due to a degraded semantic store (Martin & Fedio, 1983; Hodges et al., 1992; Binetti et al., 1995, Salmon 2000) or whether the deficit lies in AD patients’ abilities to access, retrieve and manipulate semantic information (Nebes, 1989; Bayles et al., 1991). In a recent review, Mahon & Caramazza (2009) analyzed the characteristics of concepts and categories of semantic impairments in brain damage and in dementia. Semantic deficits are typically discerned by having patients perform confrontation naming tasks (Hodges et al., 1992; Nebes, 1989; Huff et al., 1986). Another interesting research topic is the distinction between superordinate-level and basic-level concepts. In a recent study, Marques (2007) examined the role of superordinate knowledge and posited that superordinate information was applied by patients with dementia to form inferences. He suggested that studies of conceptual relations should be conducted not only with naming but also to investigate different feature knowledge within categories (e.g., visual colour, form and surface, motion function, sound, encyclopaedic, taxonomic, taste, and tactile). Marques’ results found no difference between superordinate and basic-level concepts in terms of information or feature knowledge. The patients with degraded semantic systems were able to use superordinate information to understand and draw inferences, even though they demonstrated impairment in naming. In recent our study (Di Giacomo et al., 2012), we verified that semantic deficits in the early stage of Alzheimer’s disease reflect a segregation of concepts and that the superordinate and attribute (verbal labels) relations between concepts are more damaged than function and part/whole relations, which may be related more to visuoperceptive modalities. Second, our results also suggest the possibility that in patients with mild AD (and in patients who might be considered Mild Cognitive Impairment) the semantic impairment starts with difficulties using associative relations that link concepts to each other in the semantic store. It seems possible that the patient first loses the connection between concepts before the deterioration of semantic memory begins. On this basis, we conducted a research on the loss of semantic associations in MCI and mild AD patients. Aim of our study was a) to verify the progression of the loss of associative relations in cognitive deterioration not only in the dementia but in Mild Cognitive Impairment b) to analyze the performance of MCI and mild AD patients in their cognitive deterioration in verbal and visuoperceptual tasks of associative relations.