Figure 2.

Oprd1^−/− mice show delayed acquisition of a place strategy in the dual-solution cross-maze task, and facilitated acquisition of a response strategy in the single-solution response task. (a) WT and mutant animals similarly acquire a dual-solution cross-maze task. Probe trials reveal, however, that mutant mice need more sessions (16 vs 11) to adopt an allocentric strategy in this task. (b) In contrast, Oprd1^−/− mice develop an egocentric strategy more rapidly in the single-solution response task. Performance in cross-maze tasks is expressed as percentage of correct choices (mean±SEM). Three open stars: p<0.001 (Pearson's χ² test). one solid star: p 0.05; two solid stars: p 0.01; Three solid stars: p<0.001 (one-way analysis of variance).