The population of Long Evans male rats are skewed toward sign-trackers (STs). a, PavCA Index shown as mean ± SEM across five training sessions for WT rats (n = 57) and naive TH-Cre rats (n = 38). b, Frequency histogram represents the number of rats exhibiting a mean PavCA Index (averaged from Sessions 4 and 5) between −1.0 and 1.0 for each of the groups depicted. 84% of the population (n = 95) was skewed toward STs (≥0.5, n = 46 WT and n = 34 TH-Cre), 14% of the population were intermediate responders (0.5 ≤ −0.5; n = 10 WT and n = 3 TH-Cre), and 2% GTs (≤−0.5, n = 1 WT and n = 1 TH-Cre).