Drug cue enhances response conflict and reduces conflict adaptation in methamphetamine addiction

The stimulus-response learning account of cognitive control suggests that conflict between a task-relevant response and a task-irrelevant interfering response is contingent upon the stimulus-response associations, the strength of which can be reinforced by rewarding experience. Here, we employed a modified Simon task to investigate if patients with methamphetamine use disorder (MA) exhibited enhanced association between drug-related cues and task-irrelevant responses compared to healthy controls (HC). A lateral picture of a drug cue or a neutral cue was presented in either the left or right visual hemifield, which triggered an automatic response tendency at the spatially corresponding hand. Participants discriminated the color of the frame enclosing the cue, with responses either congruent or incongruent with the cue. Relative to the neutral cue, the drug cue induced a stronger response tendency at the spatially congruent hand in MA, and hence a larger interference when this response tendency was incongruent with the task-required hand (i.e., Simon effect). In contrast, the two cues induced comparable Simon effects in HC. Moreover, in MA, a conflict adaptation was observed only for the neutral cue, with smaller Simon effect after an incongruent trial than after a congruent trial, but the adaptation effect was absent for the drug cue. However, the conflict adaptation effects were equally observed for both cues in HC. These results suggest a MA-specific enhanced response tendency to the drug cue. Our findings extend the theoretical scope of cognitive control into the clinical context, and provide new evidence in understanding the dysfunctional cognitive control in drug addiction.