Nosepoke responses on the signaled nose task.

The two columns under each phase display mean nose pokes (SEM) in the non-reinforced (non-RF) hole (left column) and total nose pokes (right column) during the final session of Phases 1–3 (i.e., the day the animals met criterion) and the first session of Phase 4. Note that the number of sessions in Phases 1–3 varied for each animal, depending on the days to reach criterion. There were no significance differences between knockout and wild-type animals on any measure. Oprm1 +/+ HYB, n = 11; Oprm1−/− HYB, n = 10; Oprm1 +/+ BL6, n = 12; Oprm1−/− BL6, n = 11 Oprd1+/+ HYB, n = 9; Oprd1 −/− HYB, n = 8; Oprd1 +/+ BL6, n = 12; Oprd1 −/− BL6, n = 10