Cognitive flexibility increases in childhood and declines in aging.

Transient control underlying switch costs shows little change across the lifespan.

Sustained control underlying mixing costs shows more pronounced lifespan changes.

We review neural findings of sustained and transient control across the lifespan.

Connectivity and representations can elucidate lifespan changes of flexibility.

The ability to flexibly switch between task sets increases early and decreases late in life. This lifespan pattern differs between mixing costs, denoting performance decrements during task switching compared with single tasking, and switch costs, denoting performance decrements on trials after the task has switched relative to trials where the task repeats. Generally, mixing costs reach their lifespan minimum later and increase again earlier than switch costs. We propose that lifespan changes in cognitive flexibility are associated with neural processes implementing sustained and transient control processes that underlie mixing and switch costs, respectively. To better understand the lifespan development of sustained and transient control processes, future research needs to delineate longitudinal changes in functional connectivity patterns and task-set representations.

© 2024 The Authors. Published by Elsevier Ltd.