Cognitive control permits us to make decisions about abstract actions, such as whether to e-mail versus call a friend, and to select the concrete motor programs required to produce those actions, based on our goals and knowledge. The frontal lobes are necessary for cognitive control at all levels of abstraction. Recent neuroimaging data have motivated the hypothesis that the frontal lobes are organized hierarchically, such that control is supported in progressively caudal regions as decisions are made at more concrete levels of action. We found that frontal damage impaired action decisions at a level of abstraction that was dependent on lesion location (rostral lesions affected more abstract tasks, whereas caudal lesions affected more concrete tasks), in addition to impairing tasks requiring more, but not less, abstract action control. Moreover, two adjacent regions were distinguished on the basis of the level of control, consistent with previous functional magnetic resonance imaging results. These results provide direct evidence for a rostro-caudal hierarchical organization of the frontal lobes.The function of the prefrontal cortex (PFC) is closely associated with cognitive control or the ability of humans and other primates to internally guide behavior in accordance with goals, plans and broader contextual knowledge 1-18. Consider the simple example of entering a colleague's office and finding a place to sit down. On a daily basis, in one's own office, the chair behind the desk is the appropriate seat. In another's office, however, we easily select the chair in front of the desk as being the socially appropriate choice. Overcoming a habitual tendency in order to coordinate behavior with an abstract social rule is an example of cognitive control.From one perspective, cognitive control mechanisms operate through a process of biased competition, whereby maintenance of a distributed neural representation of the task context (colleague's office) configures processing throughout the action system to bias selection of an appropriate behavior (sit in the chair in front of the desk) over a competing one (sit in the chair behind the desk) 8, 19 -21. The frontal lobes are thought to be centrally involved in coding such contextual representations to provide internal control over action14 ,22,23 . However, the functional organization of the frontal lobe remains unknown. Although it is

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