(**A**) The time needed to consume 100 reward pellets is plotted against the deprivation level (left graph) and session number (right graph). (**B**) The food consumed during the first 30 minutes of the regular food consumption test is plotted against the deprivation level (left graph) and session number (right graph). The graphs show mean plus standard error of the mean. Two-way ANOVA results are displayed above each graph, and results from *post-hoc* analysis are shown for individual data points. Significant genotype differences are indicated by (p<0.05) *, (p<0.01) **, (p<0.001) *** and (p<0.0001) ****.