Supplementary Figure 4: Comparison of reentry behavior in the two SST variants and in the BF electrical stimulation experiment

(a) The distributions of fixation port exit and reentry events in all reentry trials in the three task conditions (Stop Reward, Stop No Reward, and BF electrical stimulation) relative to SSRT, reproducing Fig. 6b and Fig. 8e. In all cases, fixation port exit and reentry events were most common just before and after SSRT, respectively. These distributions were normalized by the number of reentry trials in each task, so the area under each distribution summed to one. (b) The distributions from (a) were normalized by the number of stop trials (or stimulated trials) in each task. The distributions of fixation port exit times in all stop trials were shown in black, and the areas under each black trace summed to one. (c) The distributions of fixation port exit in reentry trials (blue traces in (b)) were normalized by the distributions of fixation port exit in all stop trials (black traces in (b)) in each task at each 25ms bin. Fixation port exits at or around SSRT in stop trials were most likely to become reentry trials in all three task conditions.

Results in (b) and (c) show that fixation port reentries were most frequent in the Stop Reward Task, followed by BF electrical stimulation, and least frequent in the Stop No Reward Task. The difference of reentry frequency between the two variants of SST likely reflected the modulation of task contingency, such that there was a stronger motivation to reenter when successful stopping leads to reward. Despite the lower frequency of reentry events in the Stop No Reward Task, the reversal of accelerometer signals at SSRT was similarly evident in most failure-to-stop trials in the Stop No Reward Task (Fig. 6c, 6d; 13/15 sessions from the Stop No Reward Task). The reentry behaviors and accelerometer signals together suggest that, in both SST variants, movement patterns in failure-to-stop trials began to differ from latency-matched go trials at SSRT. The difference between the two SST variants, however, was that the reversals of accelerometer signals at SSRT were converted at a lower rate to fixation port reentries in the Stop No Reward Task compared to the Stop Reward Task.