Planning is a fundamental cognitive function frequently employed in common daily activities. The Travelling Salesperson Problem (TSP), in which participants decide what order between a number of locations optimizes total travel distance, is a paradigm that allows the study of planning and strategy choice. In the TSP, subjects adopt visuo-spatial heuristics to perform the task and operate a continuous monitoring to adapt their behaviour. We present a connectionist model of the TSP that simulates bottom-up and top-down influences observed in the execution of the task. The model accounts for the continuous monitoring observed in healthy participants, and, after a simulated lesion, it also accounts for the decrease of heuristic switching observed in frontal patients and in normal subjects under repetitive transcranial magnetic stimulation (rTMS) over frontal lobe.