The relationship between theory of mind and cognition in Alzheimer's disease: A systematic review

Introduction: Theory of Mind (ToM) refers to an individual's ability to attribute mental states to others. It is well established that the behavioral variant of frontotemporal dementia can undermine ToM. However, there is no consensus on how Alzheimer's disease affects ToM. The following report represents a systematic literature review of ToM in Alzheimer's disease over the past ten years. Method: We performed a survey using the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes (PRISMA) criteria. The literature search was performed using the electronic databases MEDLINE (Pubmed) and Science Citation Index (ISI). The following descriptors were used in the review process: theory of mind or mentalizing and Alzheimer disease or Alzheimer's disease or Alzheimer type dementia. This systematic review was recorded in the International Prospective Register of Systematic Reviews (PROSPERO) under the number CDR42018115152. Results: We identified 117 articles, 24 of which met our criteria. The most common assessment measure used in the evaluation of the ToM was the first and second order false belief task. Many studies reported that individuals with Alzheimer's disease were impaired on more complex tasks, such as second-order false belief tasks, but had intact performance on simpler tasks, such as first order false beliefs and affective ToM. In contrast, some studies reported that ToM deficits may also appears in simpler and affective tasks. Conclusions: The variability in methodologies, the design and complexity of the tasks applied, the heterogeneity in terms of dementia stage/severity, and the level of cognitive impairment contribute to the variability and inconsistency of the results. Future research should investigate the ToM using more ecological and standardized methods.