Figure 4.

Cognitive deficits in GRM2/3^−/− mice cannot be explained simply by reduced appetitive motivation for the milk reward. (a) GRM2/3^−/− mice (n=14) did not differ from wild-type mice (wt; n=18) in acquisition of an appetitively motivated, non-spatial gray vs black–white stripes visual discrimination task (experiment 6). Data shown are mean percent correct responses (±SEM) for each block of 10 trials. Chance performance is indicated by the dashed line. (b) GRM2/3^−/− mice (n=13) show a reduced spatial novelty preference compared with wild-type animals (n=18; experiment 7). Data shown are mean discrimination ratios ((novel arm/(novel+other arm)) (±SEM) calculated for the number of arm entries (left) and the time spent in the arms (right) during the test phase. The discrimination ratio was significantly lower for GRM2/3^−/− mice on both measures. A discrimination ratio of 0.5 reflects chance performance. (^*p<0.05 and ^**p=0.005).