Facial expression recognition in Alzheimer's disease: A systematic review

Introduction: It is well established that behavioral variant frontotemporal dementia can impair social and emotional function. However, there is no consensus regarding how Alzheimer's disease can affect facial expression recognition. We aim to systematically review all the literature addressing this issue over the last 10 years. Method: We conducted a search based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The search for literature was undertaken on 19 September 2017, using Pubmed, SciELO, BIREME, and Thomson Reuters Web of Science electronic databases. The key terms for the search were: Alzheimer's disease, dementia, and facial expression recognition. Results: We screened 173 articles, and 22 of them were selected. The most common methodology involved showing participants photographs of people expressing the six basic emotions-fear, anger, sadness, disgust, surprise, and happiness. Results were ambiguous. Among people with mild Alzheimer's disease, happiness was easier to recognize than the other five basic emotions, with sadness and anger the most difficult to recognize. In addition, the intensity level of the emotions presented seems to be important, and facial expression recognition is related to specific cognitive capacities, including executive function and visuoperceptual abilities. Impairment in facial expression recognition does not appear to be a consistent neuropsychological finding in Alzheimer's disease. Conclusions: The lack of standardized assessment instruments and the heterogeneity of the methods and samples used across studies hamper comparisons. Future researches should investigate facial expression recognition through more ecological and standardized methods.