Beyond Conflict Monitoring: Dorsolateral Prefrontal Cortex Mediates Congruency Sequence Effects via Post-Congruent Suppression

Cognitive control, a key mechanism for goal-directed behavior, adaptively adjusts in complex environments. This adaptability is reflected in the congruency sequence effect (CSE). Traditional conflict monitoring theory posits that the dorsolateral prefrontal cortex (dlPFC) enhances cognitive control after a conflict (incongruent) event, driving the CSE. However, recent evidences suggest dlPFC involvement in adaptive adjustments following a non-conflict (congruent) event rather than an incongruent event. We proposed an "action selection and carry-over" hypothesis, positing that the dlPFC contributes to the CSE by suppressing interference after a congruent event. To verify this hypothesis, Thirty-four healthy participants performed a modified Wisconsin Card Sorting Task with a rule-switch preparatory phase to amplify interference processing. Transcranial direct current stimulation (tDCS) was applied to inhibit left dlPFC during the task, examining its causal role in modulating the CSE. The CSE was found to increase during the switch preparatory phase compared to control conditions. tDCS-induced dlPFC inhibition further amplified this effect. Crucially, this modulation stemmed from an altered conflict processing after a congruent event, not after an incongruent event. These findings suggest that the dlPFC supports the CSE via suppressing residual interference after a congruent event, rather than post-incongruent control adaptation, thus favor the "action selection and carry-over" hypothesis over conflict monitoring accounts. Our results offer new insights into the neuropsychological mechanism of adaptive cognitive control.