Prefrontal Overrecruitment in Older Adults: Task Demand–Dependent Efficiency and Implications for Cognitive Aging

Abstract

This study examined how prefrontal overactivation in older adults relates to cognitive performance across systematically varied task demands, testing predictions from major neural compensation theories. Using a visual discrimination paradigm, we parametrically manipulated perceptual load, discrimination precision, and response rule complexity. Participants included younger (N = 36; aged 19–33) and older adults (N = 36; aged 56–82). Task performance was measured using inverse efficiency scores (IES), and functional magnetic resonance imaging assessed brain activation. Older adults demonstrated disproportionately higher IES, especially under the most complex condition, suggesting reduced efficiency with rising demand. fMRI revealed widespread frontoparietal network activation differences, with older adults showing increased recruitment of frontal regions compared with younger adults, especially at higher task demands. Critically, prefrontal overactivation in older adults correlated negatively with performance at the highest demand level, indicating capacity-limited compensation. Additionally, older adults exhibited reduced default mode network suppression and diminished dorsal attention network recruitment, both of which were associated with poorer task performance. These findings support the compensation-related utilization of neural circuits hypothesis, which predicts a transition from adaptive to inefficient recruitment as cognitive demands increase. They also align with broader frameworks such as the posterior–anterior shift in aging and the revised scaffolding theory of aging and cognition, emphasizing the role of task complexity in shaping compensatory patterns. Overall, the adaptiveness of neural overactivation in older adults appears to depend on its relationship to both task demands and behavioral performance.