1a and Supplementary Fig. 2a). Lever presses were also recorded during the delay period, after pressing L5 but before receiving food. Although intra-delay presses did not result in additional food-delivery, shifting responses to L1 during this period reflected impulsive action (Supplementary Fig. 1d). While both strains displayed more intra-delay L1 presses as the delay increased (F5,145=36.73, p<0.001), this increase was more pronounced in SHRs (F5,145=10.55, p<0.001), consistent with this strain’s elevated impulsive action (Fig. 1b). Since the delay period strictly followed L5 presses, not L1, perseveration on this lever during the delay was used to distinguish compulsivity from impulsive action. Thereby, intra-delay L5 presses also increased in both strains during the testing phase (F5,145=27.13, p<0.001) and, while there was a strain × time interaction (F5,145=2.83, p=0.02), post-hoc analysis did not reveal significant differences between strains during any session (Supplementary Fig. 2b). Similar pressing patterns were observed during the fixed time-out period—during which a cue signaled the unavailability of a reward—and responses on L1 were significantly different between SHRs and WKYs (F1,29=32.79, p<0.001, Supplementary Fig. 2c).
