Flexible coding of task rules in frontoparietal cortex

• ¹ Macquarie University, Department of Cognitive Science and ARC Centre of Excellence in Cognition and its Disorders, Australia

Background

Humans are characterised by diverse and flexible behaviour. How does the brain achieve the flexible cognitive control that is required? Several theories implicate frontoparietal cortex, which is thought to represent the information needed for current behaviour and to bias processing towards task-relevant information elsewhere in the brain. In particular, frontoparietal cortex is thought to structure and maintain task sets or rules. For behaviour to be flexible, however, the system must rapidly reorganise as mental focus changes. We have previously demonstrated this reorganisation, or “adaptive coding”, in the visual domain, with frontoparietal cortex adjusting to code perceptual information more strongly when visual input is weak. Here, we test whether this rapid reorganisation is also seen in the conceptual domain, for task rules.

Methods

20 participants learnt 4 rules determining which of 4 buttons should be pressed in response to a blue square shown in one of 4 possible horizontal locations on a screen. Two of the rules were conceptually simple (“easy”) while the other two rules were more complex (“hard”). On each trial, the current rule was cued by the background colour of the screen. Functional magnetic resonance imaging (fMRI) data were acquired on a 3T Siemens Verio scanner while participants performed alternating blocks of easy and hard rules. We used Multivoxel Pattern Analysis (MVPA) to characterise the extent to which activity patterns in frontoparietal cortex discriminated between (“coded”) the task rules, stimulus positions, and button press responses, in easy and hard blocks separately.

Results

Participants were significantly slower and less accurate for the hard compared to easy rules. In a restricted set of frontal and parietal “multiple-demand” (MD) brain regions, chosen a priori for their common response to a range of cognitive demands, coding dynamically adjusted between easy and hard blocks. MD coding of rule increased in hard compared to easy blocks, suggesting increased focus on this task element as it became more cognitively demanding. At the same time, MD coding of responses decreased in hard blocks, suggesting a redistribution of response information as focus on task rules increased.

Discussion

The results suggest an adaptive frontoparietal system that rapidly reorganises in response to changing conceptual demands. This system may provide the neural basis for flexible control of human behaviour.