Functional and structural correlates of working memory performance and stability in healthy older adults
Despite the well-described deleterious effects of aging on cognition, some individuals are able to show stability. Here, we aimed to describe the functional and structural brain characteristics of older individuals, particularly focusing on those with stable working memory (WM) performance, as measured with a verbal N-back task across a 2-year follow-up interval. Forty-seven subjects were categorized as stables or decliners based on their WM change. Stables were further subdivided into high performers (SHP) and low performers (SLP), based on their baseline scores. At both time points, magnetic resonance imaging (MRI) data were acquired, including task-based functional MRI (fMRI) and structural T1-MRI. Although there was no significant interaction between overall stables and decliners as regards fMRI patterns, decliners exhibited over-activation in the right superior parietal lobule at follow-up as compared to baseline, while SHP showed reduced the activity in this region. Further, at follow-up, decliners exhibited more activity than SHP but in left temporo-parietal cortex and posterior cingulate (i.e., non-task-related areas). Also, at the cross-sectional level, SLP showed lower activity than SHP at both time points and less activity than decliners at follow-up. Concerning brain structure, a generalized significant cortical thinning over time was identified for the whole sample. Notwithstanding, the decliners evidenced a greater rate of atrophy comprising the posterior middle and inferior temporal gyrus as compared to the stable group. Overall, fMRI data suggest unsuccessful compensation in the case of decliners, shown as increases in functional recruitment during the task in the context of a loss in WM performance and brain atrophy. On the other hand, among older individuals with WM cognitive stability, differences in baseline performance might determine dissimilar fMRI trajectories. In this vein, the findings in the SHP subgroup support the brain maintenance hypothesis, suggesting that stable and high WM performance in aging is sustained by functional efficiency and maintained brain structure rather than compensatory changes.
KeywordsAging Brain stability Cortical thickness (CTh) Functional magnetic resonance imaging (fMRI) Working memory
Stables high performers
Stables low performers
Working memory factor
We are indebted to the Magnetic Resonance Imaging Core Facility of the IDIBAPS for the technical help.
This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) through grants to D.B.-F. [Grant number PSI2015-64227-R] and L.V.-A. [Grant number BES-2016-077620]. Partially funded by EU Horizon 2020 project ‘Healthy minds 0–100 years: Optimising the use of European brain imaging cohorts (“Lifebrain”)’, [Grant agreement number: 732592. Call: Societal challenges: Health, demographic change and well-being]; and by the Walnuts and Healthy Aging (WAHA) study (https://www.clinicaltrials.gov), [Grant number NCT01634841] funded by the California Walnut Commission, Sacramento, California, USA.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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