Figure 6  Mice lacking functional D2Rs display an inability to withhold inappropriate responses. Response patterns during first 10 reversal trials reveal deficits in mice lacking D2Rs. When the mice encountered the inverted reinforcement contingencies during the first reversal learning session, the D2R-/- mice demonstrated an almost complete inability to inhibit responding to previously reinforced stimuli compared to D2R+/+ mice (* p < 0.001).