Preserved executive function in high-performing elderly is driven by large-scale recruitment of prefrontal cortical mechanisms

Abstract

High-density electrical mapping of event-related potentials was used to investigate the neural processes that permit some elderly subjects to preserve high levels of executive functioning. Two possibilities pertain: (1) high-performance in elderly subjects is underpinned by similar processing mechanisms to those seen in young adults; that is, these individuals display minimal functional decay across the lifespan, or (2) preserved function relies on successfully recruiting and amplifying control processes to compensate for normal sensory-perceptual decline with age. Fifteen young and nineteen elderly participants, the latter split into groups of high and low performers, regularly alternated between a letter and a number categorization task, switching between tasks every third trial (AAA-BBB-AAA : : : ). This allowed for interrogation of performance during switch, repeat, and preparatory pre-switch trials. Robust effects of age were observed in both frontal and parietal components of the task-switching network. Greatest differences originated over prefrontal regions, with elderly subjects generating amplified, earlier, and more differentiated patterns of activity. This prefrontal amplification was evident only in high-performing (HP) elderly, and was strongest on pre-switch trials when participants prepared for an upcoming task-switch. Analysis of the early transient and late sustained activity using topographic analyses and source localization collectively supported a unique and elaborated pattern of activity across frontal and parietal scalp in HP-elderly, wholly different to that seen in both young and low-performing elderly. On this basis, we propose that preserved executive function in HP-elderly is driven by large-scale recruitment and enhancement of prefrontal cortical mechanisms. © 2009 Wiley-Liss, Inc.