Imaging the mental components of a planning task

The Towel of London task (TOL) has been widely used to assess the ability t o plan. We used H2O15-positron emission tomography to isolate some of the c ognitive components of the task. Ten male volunteers were scanned twice in each of six conditions. In two conditions (plan) the subjects had to plan t he best solution to TOL problems. In two other conditions (plan-control) th e subjects were required to generate four moves without being constrained b y a goal. In plan and plan-control tasks the subjects either planned the mo ves and then executed them (MOVE conditions) or imagined the necessary move s (IMAGINE conditions). The plan and plan-control tasks were matched for th e working memory load and 'initial thinking time'. A visuomotor control tas k and rest served as baseline conditions. Performance on the plan tasks, in contrast to the baseline conditions, was associated with activation in the dorsal prefrontal cortex, premotor and parietal cortex, and cerebellum. Pe rformance of the plan-control tasks was associated with activation of the s ame areas. Contrasting the plan with the plan-control tasks revealed no res idual activation in the prefrontal cortex. These data show that the activit y of the dorsolateral prefrontal cortex on the TOL can be accounted for by the components of generating, selecting and/or remembering mental moves. Th e task of relating the moves to the goal involves a comparison with a repre sentation of the goal in posterior association areas. we did not find evide nce that activation of the dorsal prefrontal cortex is specifically related to the evaluation of a path towards a specified goal, a key component of p lanning. (C) 2001 Elsevier Science Ltd. All rights reserved.