Involvement of Amygdala Alterations in Emotional Processing in Alzheimer’s Disease : a Review

Abstract

The amygdala, a limbic area crucial in amplifying emotional processing, is atrophied early in Alzheimer’s disease (AD). However, evidence regarding the impact of this early atrophy on cognitive and emotional processes is still lacking. The aim of this systematic review is to assess the consequences of amygdala alterations on the processing of emotional information in patients with AD and mild cognitive impairment (MCI). The Preferred Items for Systematic Reviews and Meta-Analyses (PRISMA) was used to guide searches, extraction and reporting of data in this review. We referred to the electronic databases PubMed and PsycINFO to search for articles that were published up to 9 July 2019. We included studies that assessed the correlation between structural and/or functional characteristics of the amygdala and performances in a task involving emotional stimuli in patients with AD or MCI. Risk of bias was rated using a 7-item validity scale assessing methodological rigor, selection and reporting bias. 28 studies were included that concerned emotional memory, face expression recognition, or emotional attention. Together, they suggest that amygdala alterations in AD lead to emotional memory deficit and amygdala hyperactivation to emotional stimuli with variability between studies. In the second part of this review, we discuss the fact that previous emotional protocols performed with AD patients are not sufficiently dedicated to the assessment of amygdala activity, masking some emotional decline in these patients. In this frame, we provide evidence suggesting that emotional attention is a promising way of investigation. In addition, we propose that future studies may need to take advantage of recent methods in amygdala segmentation and multimodal neuroimaging.