1 Research Centre, Institut universitaire de gériatrie de Montréal, Québec, Canada.
2 Department of Psychology, Université de Montréal, Québec, Canada.
3 CERVO Brain Research Centre, Institut universitaire en santé mentale de Québec, Canada.
4 Department of Psychology, Université de Laval, Québec, Canada.
5 Departement of Psychology, Université du Québec à Trois-Rivières, Québec, Canada.
6 Department of Radiology, Université de Laval, Québec, Canada.
7 Research Centre, Centre de recherche sur le vieillissement de Sherbrooke, Québec, Canada.
8 Department of Psychology, Université de Sherbrooke, Québec, Canada.
9 Department of Psychology, Université du Québec à Montréal, Québec, Canada.
10 Department of Psychology, Centre for Research in Human Development (CRDH), Concordia University, Montreal, Québec, Canada.

Objective: The concepts of mild cognitive impairment (MCI) and subjective cognitive decline (SCD) have been proposed to identify individuals in the early stages of Alzheimer's disease (AD), or other neurodegenerative diseases. One approach to validate these concepts is to investigate the relationship between pathological brain markers and cognition in those individuals.

Method: We included 126 participants from the Consortium for the Early Identification of Alzheimer's disease-Quebec (CIMA-Q) cohort (67 SCD, 29 MCI, and 30 cognitively healthy controls [CH]). All participants underwent a complete cognitive assessment and structural magnetic resonance imaging. Group comparisons were done using cognitive data, and then correlated with hippocampal volumes and white matter hyperintensities (WMHs).

Results: Significant differences were found between participants with MCI and CH on episodic and executive tasks, but no differences were found when comparing SCD and CH. Scores on episodic memory tests correlated with hippocampal volumes in both MCI and SCD, whereas performance on executive tests correlated with WMH in all of our groups.

Discussion: As expected, the SCD group was shown to be cognitively healthy on tasks where MCI participants showed impairment. However, SCD's hippocampal volume related to episodic memory performances, and WMH to executive functions. Thus, SCD represents a valid research concept and should be used, alongside MCI, to better understand the preclinical/prodromal phase of AD.