Involution of categorical thinking processes in Alzheimer’s disease: Preliminary results

Alzheimer's disease (AD) is a degenerative brain disorder characterized by progressive losses in cognitive functions, including memory. The sequence of these losses may correspond to the inverse order of the normal sequence of ontogenetic cognitive acquisitions, a process named retrogenesis. One of the acquisitions that improve in normal development is the ability to retrieve previously acquired categorical knowledge from semantic memory in order to guide associative thinking and memory processes; consequently, children become able to associate verbal stimuli in more complex taxonomic ways and to use this knowledge to improve their recall. Objective In this study, we investigated if AD-related deterioration of semantic memory involves a decrease in categorical thinking processes with progression of the disease, according to the retrogenesis hypothesis. Methods We compared the performance of AD patients at mild and moderate stages, and of groups of 7, 10 and 14-year-old children in tasks of free association along with recall tasks of perceptually and semantically related stimuli. Results ANOVAS showed a decrease in taxonomic associations and an increase in diffuse associations between mild and moderate stages, corresponding to the inverse order shown by the child groups. At the moderate AD stage, the pattern was similar to that of 7-year-old children. Both groups of patients performed worse than child groups in recall tasks. Conclusions These results corroborate the hypothesis of an involution of the processes of categorical associative thinking in the course of the disease.