Figure 2. Individual differences in motivation for remifentanil during a within-session behavioral-economic procedure.

A) A representative example of a demand curve for remifentanil of a single animal during a single session. B) To examine individual differences in demand for remifentanil, rats were divided into low (n = 12) and high (n = 12) takers based on Q₀. C) High takers exhibited more inelastic responding than low takers as price increased. D) Preferred consumption of remifentanil at null cost (Q₀) and demand elasticity (α) correlated with each other with high takers displaying enhanced motivation for remifentanil. E) Individual differences in Q₀ were evident consistently throughout training based upon the average stable baseline sessions prior to each SB test. F) Individual differences in α between low and high takers emerged over BE training. *p < 0.05; ***p < 0.001; n.s. = not statistically different.