Meta-analyses of the n-back working memory task: fMRI evidence of age-related changes in prefrontal cortex involvement across the adult lifespan

Working memory, a fundamental cognitive function that is highly dependent on the integrity of the prefrontal cortex, is known to show age-related decline across the typical healthy adult lifespan. Moreover, we know from work in neurophysiology that the prefrontal cortex is disproportionately susceptibly to the pathological effects of aging. The n-back task is arguably the most ubiquitous cognitive task for investigating working memory performance. Many functional magnetic resonance imaging (fMRI) studies examine brain regions engaged during performance of the n-back task in adults. The current meta-analyses are the first to examine concordance and age-related changes across the healthy adult lifespan in brain areas engaged when performing the n-back task. We compile data from eligible fMRI articles that report stereotaxic coordinates of brain activity from healthy adults in three age-groups: young (23.57 +/- 5.63 years), middle-aged (38.13 +/- 5.63 years) and older (66.86 +/- 5.70 years) adults. Findings show that the three groups share concordance in the engagement of parietal and cingulate cortices, which have been consistently identified as core areas involved in working memory; as well as the insula, claustrum, and cerebellum, which have not been highlighted as areas involved in working memory. Critically, prefrontal cortex engagement is concordant for young, to a lesser degree for middle-aged adults, and absent in older adults, suggesting a gradual linear decline in concordance of prefrontal cortex engagement. Our results provide important new knowledge for improving methodology and theories of cognition across the lifespan.