At each neuroimaging visit, participants performed a positive and negative performance feedback task, called the motion prediction task, previously shown to differentially activate the habenula, ACC, insula, and ventral striatum (45). The participants’ objective was to predict which of two moving balls, starting from different locations and traveling at different speeds, would be the first to reach a finish line after viewing a brief clip of the balls’ motion (Fig. 1B). Each trial began with a variable fixation interval (3500 to 4500 ms), which was followed by the appearance of the finish line (500 ms) to signify an upcoming motion event. Participants then viewed a short sequence (1400 ms) of the two balls traveling at different speeds from different starting locations on the left side of the screen toward the finish line on the right side of the screen. Still far from the finish line, the balls disappeared, and the question “Which ball?” was presented (1350 ms). Participants indicated their prediction/decision via a right-handed button press with either the index (ball 1) or middle finger (ball 2) during this response window. After a fixed delay (750 ms), performance feedback (emojis) about the correctness of the participants’ prediction was presented (1000 ms).

Performance feedback was delivered to participants in a two-factor, FEEDBACK [informative (i) versus noninformative (n)] * RESPONSE [correct (C) versus error (E)], fashion. Under informative feedback, participants always received positive feedback (i.e., a happy emoji) following a correct response (iC) and always received negative feedback (i.e., a sad emoji) following an erroneous response (iE). Under noninformative feedback, participants received no information on whether they gave a correct or erroneous response as the same feedback was presented on both nC and nE trials (i.e., an ambiguous emoji). Informative feedback was presented on 73% of trials and noninformative feedback on 27%. This feedback schedule allowed us to determine which task-related aspect more robustly influenced brain activity, namely, the type of feedback (positive versus negative) or the type of response (correct versus error). Task-related BOLD signal change was anticipated to be robustly modulated on error versus correct trials when followed by informative feedback. If participants failed to respond during the designated response window, then they received a fifth type of feedback (i.e., a confused emoji) for these no-response trials.

Task difficulty, operationalized as the time difference between the two balls’ arrival at the finish line, was dynamically manipulated on the basis of each participant’s behavior to maintain error rates at ~35% (i.e., an error rate between 0.3 and 0.4 over a sliding window). Specifically, over a 10-trial sliding window, if error rates were below 0.3, then task difficulty was increased, and if the rate was above 0.4, then task difficulty was decreased. This task feature was intended to induce participant uncertainty about trial performance until feedback delivery (i.e., to mitigate the self-detection of errors). While the dynamic difficulty manipulation was intended to consistently maintain error rates across participants and across the six neuroimaging visits, one behavioral aspect not under the control of the task’s adaptive algorithm was the number of no-response trials (errors of omission), which reflect momentary lapses of attention. For each no-response trial encountered, the adaptive algorithm reduced the targeted number of correct trials by one. Hence, the percent values of no-response and correct trials were inversely related, demonstrated more variability across participants and sessions than that for error trials, and thus provided a convenient behavioral metric to assess group- and drug-related effects on these two dependent variables, which we interpreted as gross behavioral measures of attention. Given that the percent of no-response and correct trials were “mirror images” of each other, only no-response trial results are presented. Task presentation and behavioral performance recording were controlled by E-prime software (v1.2, Psychology Software Tools). Participants completed a total of 240 trials in four 9-min runs with short rest periods between runs 1 to 2 and 3 to 4 and a longer break between runs 2 and 3 (during which a T1-weighted structural MRI was collected and participants were instructed to relax while staying as still as possible).

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