The Rules in the Brain

Much of cognitive psychology has undergone a profound shift in emphasis during the last decade or so, moving from theoretical information processing accounts of cognition towards a more embodied view of cognition. This embodied view seeks to identify the brain regions that implement the cognitive processes studied for decades previously in cognitive science.

One cognitive process (or set of processes?) that has been particularly elusive is executive function: this "catch-all" phrase has been difficult to pin down either in information processing terms, or in terms of which brain regions implement it. Notable exceptions include some fascinating factor analyses that identify likely executive subfunctions, and a new paper by Bunge and Zelazo in a recent issue of Current Directions in Psychological Science.

In this paper, the authors argue that orbitofrontal cortex is responsible for the control of simple stimulus-reward rules, as might be required when the reward value of a stimulus undergoes rapid reversal. Accordingly, damage to oPFC results in impaired learning of reversed stimulus-reward associations.

In contrast, ventrolateral and dorsolateral PFC seem to represent "univalent conditional" rules, or rules in which each stimulus is associated with a different response (neither of which is intrinsically rewarding or unrewarding). Alternately, dlPFC may also be involved in representing bivalent rules, in which a single stimulus is associated with multiple different responses. These regions appear to be more highly activated for bivalent than univalent rules.

Finally, rostrolateral PFC seems to be involved in resolving interference between multiple different rules, and thus choosing between them. According to these authors, rlPFC thus manages hierarchical rules.

Several structural and functional imaging studies loosely support the accounts provided here, namely that oPFC develops first, with dlPFC and rlPFC following much later afterwards. Furthermore, activity in child oPFC becomes similar to that seen in adult oPFC before this happens in dlPFC and rlPFC, though this is not surprising given that the structure of these regions takes longer to reach and adultlike state.

What is truly interesting about this paper, however, is that it is an extension of earlier work by Zelazo on the development of executive function. Specifically, his perspective has always focused on the importance of rules and rule structure to success in tasks like the Dimensional Change Card Sort, or the Tower of Hanoi. This paper can be viewed as an attempt to firmly bind these abstract information processing theories to the brain regions responsible for implementing them.

However, it is not clear that rule use is the essential function of these regions. For instance, it is possible that these regions are merely responsible for maintaining information, and biasing more downstream regions. One need not posit that these areas are intrinsically specialized for rule representation, but merely that complex rule use requires that these regions be active. In this alternative account, the most important function of prefrontal activity is active maintenance. This is the critical function that subserves rule use, merely because complex rules are too quickly forgotten unless the "prefrontal machinery" is fully developed.

Related Posts:
Task Switching in Prefrontal Cortex
Under The Rug: Executive Functioning
The Transience of Memory
Models of Active Maintenance as Oscillation