Brain responses associated with different hierarchical effects on cues and targets during rule shifting

Numerous studies have explored the neural mechanisms related to task switching or rule shifting, but few have revealed the neural substrates related to rule shifting at different hierarchical levels. The purpose of this study is to explore the different event-related potentials (ERPs) elicited by higher and lower hierarchical levels of rule shifting in a cue-target task. In the task, participants were presented with Arabic digits (1-9, excluding 5), and performed a parity or magnitude judgment according to the preceding cues, a letter R. The rules were constructed in a hierarchical set, and the rule was either repeated or shifted between neighboring trials. Importantly, the rule shifting would be at a higher or lower hierarchical level. The results showed that, for the cues, the higher hierarchical shifting evoked increased P2, P3, late positive component (LPC), and decreased N2 relative to lower hierarchical shifting, reflecting the increased demand in selective attention, rule processing, and proactive control during the rule acquisition stage. For the targets, the hierarchical effects were reversed, and emerged later than the rule shift effect. These findings imply that, in the cue-target rule-shifting task, the brain responds differently to different hierarchical levels of rule shifting.