Dissociative semantic breakdown in Alzheimer's disease: evidence from multiple category fluency test

Background: Category-specific semantic dissociation particularly in terms of biological and non-biological dichotomy has been described in Alzheimer's disease (AD). We re-examine above finding by performing multiple superordinate category verbal fluency test in AD patients.

Method: We analyze the baseline neuropsychological assessment performance of food and animal fluency test of AD patients from a tertiary hospital that collected prospectively over 5 years period and correlation was calculated by Kappa test. The analysis is stratified according to literacy level (primary: 0-6 years education and secondary: >6 years education) and disease severity (MMSE score: mild 19-24, moderate 13-18 and severe <13).

Result: A total of 296 AD patients were analyzed and only fair to moderate agreement between food and animal category fluency test was found especially in the mild AD cases (primary: kappa 0.42; secondary: kappa 0.40). Kappa agreement level increases when disease progress especially in the secondary education group. Food category, which is a more relevant semantic knowledge to Singapore population, is generally more affected. Higher educated subjects appeared to have less semantic dissociation effect when disease progress.

Conclusion: Despite less primed in daily life, biological category of semantic knowledge appears to be affected less during AD process in highly urbanized Singapore society. Brain appears to have special protective mechanism towards living things. However, education level seems have a modulation effect towards the biological protective mechanism.