The role of the left and right DLPFC in proactive and reactive cognitive control: A HF-rTMS study

Introduction: The Dual Mechanisms of Control framework proposes that cognitive control operates via two distinct operating modes, namely proactive control, and reactive control. Proactive control occurs before the onset of a stimulus, and it comprises anticipatory and sustained maintenance of task-relevant information that enhances coping with conflict when it is presented. Reactive control, instead, is a corrective mechanism that involves recruiting processing resources to resolve conflict when it occurs. Although the dorsolateral prefrontal cortex (DLPFC) is considered to play a critical role in proactive and reactive control, the exact role of this region and the lateralization of the process remains under debate. Objective: The aim of this study was to investigate the role of the left and right DLPFC in proactive and reactive cognitive control. Materials & methods: We used High-Frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS) to increase left and right DLPFC activity. To assess cognitive control, we used the AX version of the Continuous Performance Task (AX-CPT), a cognitive task that permits relative examination of both proactive and reactive cognitive control. Using a single-blind, sham-controlled crossover within-subjects design, 25 young healthy females performed the AX-CPT after receiving sham versus active HF-rTMS to increase left and right DLPFC activity. RTs and pupillometry were used to assess patterns of proactive and reactive cognitive control and task-related resource allocation respectively. Results: We observed that, compared to sham, HF-rTMS over the left DLPFC increased proactive control. After right DLPFC HF-rTMS, participants showed slower RTs on AX trials, suggesting more reactive control. However, this latter result was not supported by RTs on BX trials (i.e., the trial that specifically assess reactive control). Pupil measures showed a sustained increase in resource allocation after both active left and right HF-rTMS. Conclusions: Our results demonstrate that the left DLPFC participates in proactive cognitive control processes. Moreover, our findings suggest that the right DLPFC may be implicated in reactive control. Furthermore, this study shows that an increase in left and right DLPFC activity provokes an increase in the allocation of cognitive resources during cognitive control processes. This study provides experimental evidence on the role of the DLPFC in proactive and reactive cognitive control processes.