Development of planning abilities in normal aging: differential effects of specific cognitive demands

In line with the frontal hypothesis of aging, the ability to plan ahead undergoes substantial change during normal aging. Although impairments on the Tower of London planning task were reported earlier, associations between age-related declines and specific cognitive demands on planning have not been studied. Here we investigated the impact of search depth and goal ambiguity on planning, which impose demands on the depth and breadth of look-ahead processes, respectively. Besides an overall age-related decline in planning accuracy of 106 healthy older adults, differential search depth effects were found: Whereas planning accuracy of subjects in the early 60s was not affected by variations in search depth, between the ages of 65 and 76 years, accuracy was significantly decreased for high versus low levels of search depth. For subjects older than 76, different search depth levels did not further impact on accuracy, which was lowest overall. This nonlinear pattern may reflect differential impairments in fluid abilities and working memory capacity across various stages of older age. As no age-related effects of goal ambiguity were found, normal aging seems to be specifically sensitive to planning demands on the depth but not the breadth of anticipatory search processes. Hence, cognitive functions subserved by the prefrontal cortex experience differential development over the course of normal aging.