SDPS‐prone animals displayed exaggerated active responding and thus gained higher number of rewards. Since each reward delivery was followed by an alcohol unavailability period, SDPS‐prone rats were presented with higher chances to respond during time‐out. To control for this preexisting difference, we next examined the relationship between time‐out responses and the number of actual rewards obtained. In particular, we analyzed the ratio between nonreinforced responses and total rewards gained under this 30‐second time‐out interval (Figure 4C). This revealed significant training, repeated measures ANOVA: F RATIO(3, 96) = 6.08, P = 0.001, and group, F GROUP(2, 32) = 5.43, P = 0.009, effects, in absence of a training × group interaction (F RATIO × GROUP(6, 96) = 0.23, P = 0.966). Pairwise comparisons showed that SDPS‐prone rats exhibited an increased ratio of nonreinforced responses vs total rewards compared with both control (P = 0.003) and SDPS‐resilient (P = 0.030) animals. No difference between the two latter groups was seen (P = 0.454). Together, prolongation of the time‐out period, during which alcohol delivery is omitted, increased alcohol seeking selectively in the SDPS‐prone group.
