Figure 2.

Effects of acutely administered morphine on delay discounting of food. Proportional choice of the large reinforcer is plotted as a function of delay (s) to the large reinforcer for individual monkeys; delay increased across blocks (indicated by brackets) for each session. Filled circles indicate the mean (± SEM) for 3 baseline sessions immediately prior to administration of the first dose of morphine. Open symbols indicate the effects of different doses of morphine administered s.c. 15-min prior to the session. See “Data Analyses” for further details.