Fig 4. Longitudinal Fixed Ratio (FR) Results for Hdh^Q111/+ animals.

FR results demonstrated a significant overall effect of reward size, with animals responding more for smaller reward sizes. Hdh^Q111/+ animals made significantly fewer responses than wild type animals when all testing conditions were considered. Hdh^Q111/+ animals made significantly fewer responses than wild type animals, which was driven by the result at the 18-month time point. Data are shown for a total of 16 mice, 7 Hdh^Q111+ and 9 wild type animals. Data are shown as the average number of responses made over 3 days of testing. Error bars represent ± standard error of the mean. Significance considers genotypic differences when all ages of testing and reward sizes are considered. ** p<0.01, *** p<0.001.