Neurobiological Correlates of Apathy in Alzheimer's Disease and Mild Cognitive Impairment: A Critical Review

Background: In Alzheimer's disease (AD) and mild cognitive impairment (MCI), apathy was associated with faster clinical deterioration. Studies involving neurobiological correlates such as neuroimaging and biomarkers have presented distinct results. Objective: This work aimed to analyze neurobiological correlates of apathy in AD and MCI based on evidence from the literature involving brain neuroimaging and classical AD biomarkers. Methods: This review comprised studies published from 1996 to June 2013 from the Pubmed database. The studies were divided into Part I (neuroimaging) and Part II (chemical biomarkers). The analysis included the identification of brain regions involved and assessments of apathy and cognition. We found 68 publications: 33 fulfilled the inclusion criteria; 35 were case reports or were not clear about the measurements of apathy and were excluded. From the 33 eligible studies, 26 were classified into part I, and 7 studies were included in part II. We created specific criteria to appropriately classify the quality level of each publication. Results: Prefrontal regions and the anterior cingulate were the leading brain areas associated with apathy in AD and MCI. Other regions, including cortical and subcortical structures, have also been implicated in this syndrome. Conclusions: Abnormalities in frontal regions (associated with impairments in planning and decision making) and anterior cingulate (related to emotional blunting and loss of motivation) were the crucial structures associated with apathy in AD and MCI.