Mapping levels of theory of mind in Alzheimer's disease: a preliminary study

Background: Research on Theory of Mind (ToM), the ability to understand behaviour based on mental state representation, has shifted towards a life span perspective in typical and atypical conditions (dementia). Objectives: The aim of this study is to investigate the presence and the features of ToM decay in early Alzheimer's disease (AD) patients compared to healthy controls adopting a neurodevelopmental stance. Method: Sixteen AD patients and 16 healthy controls were submitted to an increasing complexity ToM battery, tapping ToM precursors, standard first- and second-order false beliefs and advanced ToM tasks (Eyes Test and strange stories). Results: The results underline a similar pattern of increasing difficulty of the tasks that explore ToM abilities in both the groups. They also confirm the presence of a strong gap in performance between the CTR and the AD groups, especially in the more complex ToM tasks, whereas there is no significant difference between the two groups in the first level of reasoning about beliefs (first-order false belief). The impairment in specific cognitive functions (i.e. memory and executive functions) seems to correlate with the decline in the most complex mentalistic abilities. Conclusion: This study identifies a specific pattern of deterioration in ToM abilities in AD patients, following backwards developmental steps typical of the acquisition of mentalizing abilities, where the most complex ToM levels are impaired, whereas the intermediate and the simplest ones are preserved.