Exp Brain Res (2006) DOI 10.1007/s00221-006-0457-z RESEARCH NOTE Demis Basso · Martin Lotze · Lavinia Vitale Florinda Ferreri · Patrizia Bisiacchi Marta Olivetti Belardinelli · Paolo Maria Rossini Niels Birbaumer The role of prefrontal cortex in visuo-spatial planning: a repetitive TMS study Received: 1 June 2005 / Accepted: 16 March 2006  Springer-Verlag 2006 Abstract The visuo-spatial planning process is based on an “opportunistic” combination of heuristics and strate- gies, carried out in small units during the execution of plans. In order to investigate the functional role of the pre- frontal cortex in heuristic switching, 42 healthy controls performed a labyrinth crossing task (the Maps Test). Dur- ing this computerized version of the Travelling Salesper- son Problem, subjects had to decide which order of locations optimizes total travel time and distance. This task was performed with and without 1 Hz repetitive transcranial magnetic stimulation (rTMS), which exerts an inhibitory action on the targeted area, applied during the task over bilateral frontal sites (active stimulation) and parieto-occipital site (sham stimulation). Only repetitive bilateral rTMS over F3 and F4 signiWcantly decreased the number of strategies with changes of heuristics, and increased the number of movements required to solve the task. This behaviour contrasts with the performance of healthy subjects in the planning task, but is consistent with the performance of frontal traumatic brain injury patients. The results indicate that, in a visuo-spatial problem-solv- ing task, the prefrontal cortex is involved in the switching between heuristics during the execution of a plan. Introduction Planning has been deWned as a “mental simulation, envisaging the circumstances and running through possi- ble actions, evaluating the consequences and selecting the optimal order for executing them” (Cohen 1989, pp. 13–14). It has been demonstrated that the execution is simply a process involving pure mechanics of the move- ment, but rather, it is an active process that demands constant central monitoring (Cisek 2005). Recent studies (Basso et al. 2001; Phillips et al. 2001) proved that plan- ning is largely carried out during path execution, rather than in a distinct stage in which entire plans of perfor- mance are made previously. Therefore, Hirtle and Gär- ling (1992) argued that human planning should be based on cognitive heuristics. A heuristic could be deWned as a general principle regarded as being roughly correct although not completely accurate. In cognitive psychol- ogy, heuristics are described as behavioural schemas that approximate the correct solution, while they are more Xexible and use fewer cognitive resources than algo- rithms. While planning processes are based on heuristics, a strategy is deWned as an “opportunistic” combination of heuristics (Hayes-Roth and Hayes-Roth 1979). There- fore, a strategy is the speciWc way in which one or more heuristics have been used to produce the path. Subjects do not simply apply heuristics based on pattern recogni- tion, they use continuous monitoring and change their behaviour in accordance with unexpected events, new information, or elements that were not previously con- sidered (due to limits in working memory) in a general plan constructed before the execution phase. D. Basso (&) · M. Olivetti Belardinelli ECONA, Interuniversity Center for Research on Cognitive Processing in Natural and ArtiWcial Systems, Via dei Marsi, 78, Stanza 16, 2 Piano, 00185 Rome, Italy E-mail: demis.basso@uniroma1.it Tel.: +39-06-49917609 Fax: +39-06-4462449 M. Lotze · N. Birbaumer Institut für Medizinische Psychologie und Verhaltensneurobiologie, Tübingen, Germany L. Vitale · M. Olivetti Belardinelli Department of Psychology, University of Rome “La Sapienza”, Rome, Italy F. Ferreri · P. M. Rossini Neurology, University Campus Bio-Medico, Rome, Italy P. Bisiacchi Department of General Psychology, University of Padua, Padua, Italy P. M. Rossini IRCCS Centro S. Giovanni di Dio-Fatebenefratelli, Brescia, Italy