Span capacity and age-related differences in prefrontal functional organization during visual discrimination

Aging alters prefrontal recruitment, often showing posterior-anterior shifts that may reflect compensatory mechanisms. Working memory capacity (WMC) is a key individual difference shaping attention and control but its role in age-related functional reorganization remains unclear. We examined 72 adults (36 younger, 36 older) who completed standardized span tasks and an fMRI visual discrimination paradigm with three manipulations: perceptual load, fine discrimination, and mapping-switch. Whole-brain analyses first tested age-group differences in span-brain associations using interaction models, and subsequent regressions related simple and complex span scores to task-evoked activation, controlling for sex and education. Behavioral results showed that WMC was associated with efficiency mainly under high-demand conditions. In younger adults, higher simple span was positively associated with posterior parietal and occipitotemporal activity, whereas higher complex span was associated with greater dorsolateral and anterior prefrontal recruitment during mapping-switch. In older adults, higher complex span was associated with relatively greater engagement of frontal pole and inferior frontal regions, consistent with compensatory recruitment. Brain-behavior associations were strongest under executive remapping, indicating that WMC shapes capacity-dependent recruitment patterns across the lifespan.