Although it is clear that the prefrontal cortex is responsible for cognitive control — ensuring that our actions are appropriate not just in light of our sensory input but also for a given context or event — the organization of the prefrontal cortex is controversial. Koechlin et al. propose a new model for the functioning of the lateral prefrontal cortex (LPFC) in which different areas form a hierarchy of cognitive control, from the premotor cortex to more anterior regions.

The model is best understood by considering a well-known example of cognitive control. If a phone rings, a default response would be to answer it. However, if you are at a friend's house (a different context), you would not usually answer the phone. But this contextual control can be overridden if, for example, your friend has gone out and has asked you to take any calls.

In the model proposed by Koechlin and colleagues, there are three levels of control. The premotor cortex is responsible for 'sensory control' — answering a ringing phone. More anteriorly, the caudal LPFC carries out 'contextual control' — using cues that accompany the stimulus to tell you that it is inappropriate to answer your friend's phone. And the rostral LPFC is responsible for 'episodic control', in which earlier cues (a conversation with your friend) tell you how you should respond during a given episode. In this hierarchy, signals flow from the most anterior parts of the LPFC to the more posterior parts and the premotor cortex, conveying top–down information to control our actions.

The authors tested their model using behavioural studies and functional imaging — with rather more abstract stimuli — as well as information theory for quantifying cognitive control. Subjects were given tasks in which either sensory or contextual information could be varied, either alone or with episodic information. As predicted by the model, reaction times increased with stimulus, context and episode factors, and both stimulus and context effects were additive with the episode effect.

Functional magnetic resonance imaging (fMRI) allowed the authors to see whether different types of cognitive control were reflected in increased activity in different parts of the LPFC. Consistent with the cascading, top–down nature of the model, activity in the premotor cortex showed effects of stimulus, context and episode; caudal LPFC showed effects of context and episode, but not stimulus; and rostral LPFC only showed effects of episode. To test the prediction that the effects of context and episode in more posterior areas result from top–down control from the most anterior areas, the authors used a structural equation model to investigate the effective connectivity of the LPFC. The results also supported the three-tiered model of cognitive control.

In this model, representations are distributed in the LPFC depending on their temporal structure, rather than their content or internal complexity. It joins a number of other models of prefrontal function and is unlikely to be the last, but it can also explain the pattern of results seen in a number of other studies in which rostral and caudal LPFC showed activity that depended on whether cognitive control was contextual or episodic. The story is far from over, but this study could be an important chapter.