title: A Meta-Analysis of fMRI Activation Differences during Episodic Memory in Alzheimer's Disease and Mild Cognitive Impairment.
abstract: Functional MRI (fMRI) has the potential to be used as a tool to detect biomarkers related to classifying Alzheimer's disease (AD) and its prodromal stage, mild cognitive impairment (MCI). Previous meta-analyses suggest that during episodic memory tasks, MCI patients exhibit hyperactivation in the medial temporal lobe (MTL) while AD patients exhibit hypoactivation, compared to healthy older adults (HOAs). However, these previous studies have methodological weaknesses that limit the generalizability of the results. This quantitative meta-analysis re-examines the activation associated with episodic memory in AD and MCI as compared to cognitively normal populations to assess these commonly cited activation differences. A whole-brain activation likelihood estimation based meta-analysis was conducted on fMRI studies that examined episodic memory in HOA (n = 200), MCI (n = 131), and AD populations (n = 89; total n = 409). Diffuse activation was exhibited in the HOA sample, while activation was more limited in the clinical populations. Additionally, the HOA sample showed more activation in the right hippocampus compared to the AD sample. The MCI studies showed greater activation in the cerebellum compared to the HOA sample, potentially indicating a compensatory mechanism for verbal encoding. MTL hypoactivation in the AD sample is consistent with previous studies, but more evidence of MCI hyperactivation is needed before considering MTL activation as an early biomarker for the AD disease process.
authors.affiliation: Department of Psychology, University of Georgia, Athens, GA.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Terry
authors.affiliation: Department of Psychology, University of Georgia, Athens, GA.|BioImaging Research Center, Biomedical & Health Science Institute, University of Georgia, Athens, GA.
authors.forename: Dean
authors.initials: D
authors.lastname: Sabatinelli
authors.affiliation: Department of Psychology, University of Georgia, Athens, GA.
authors.forename: A Nicolas
authors.initials: AN
authors.lastname: Puente
authors.affiliation: Department of Statistics, University of Georgia, Athens, GA.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Lazar
authors.affiliation: Department of Psychology, University of Georgia, Athens, GA.|BioImaging Research Center, Biomedical & Health Science Institute, University of Georgia, Athens, GA.
authors.forename: L Stephen
authors.initials: LS
authors.lastname: Miller
mesh_terms: D000544:Alzheimer Disease / Q000503:physiopathology* / Q000523:psychology; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D060825:Cognitive Dysfunction / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D008279:Magnetic Resonance Imaging; D061212:Memory, Episodic; D009483:Neuropsychological Tests
keywords: Alzheimer's disease; MCI; Memory; episodic memory; fMRI; meta-analysis; mild cognitive impairment