The paradoxical relationship of difficulty and lateral frontal cortex activity

TL;DR

This study reveals a paradoxical relationship between task difficulty, measured by response time, and lateral frontal cortex activity, showing different regional scaling patterns during hierarchical cognitive control tasks.

Contribution

It demonstrates that task difficulty, as indexed by response time, does not uniformly influence frontal cortex activity, indicating multiple processes underpin cognitive control across regions.

Findings

Rostral regions show greater scaling with response time on first-order tasks.

Caudal regions show the opposite relationship.

Response time reflects multiple distinct processes in frontal cortex activity.

Abstract

Task difficulty is widely cited in current theory regarding cognitive control and fronto-parietal function. Ongoing debate surrounds the extent to which global difficulty across multiple cognitive demands is the main driver of lateral frontal activity. Here, we examine a commonly cited behavioral marker of difficulty in these accounts: time-on-task (ToT), as assessed by response time. Specifically, we investigate the task-dependent scaling of frontal BOLD responses with ToT during hierarchical cognitive control. We observe a paradoxical relationship, whereby rostral regions show greater scaling with ToT on a first-order task, despite showing greater recruitment on a second-order task; caudal regions show the converse relationships. Together, these results demonstrate that ToT does not reflect a single dimension of difficulty that uniformly drives lateral frontal activity. Rather, this discrepancy in the mean and scaling of BOLD requires that multiple, distinct processes are instantiated across these fronto-parietal regions in the service of cognitive control function.