Figure 8. A minimum threshold for behavioral facilitation is illustrated as a trade-off function between incentive stimulus magnitude (left vertical axis) and dopamine postsynaptic receptor activation (horizontal axis). Range of effective (facilitating) incentive stimuli is illustrated on the right vertical axis as a function of level of dopamine activation. Two hypothetical individuals with low and high trait dopamine postsynaptic receptor activation (demarcated on the horizontal axis as A and B, respectively) are shown to have narrow (A) and broad (B) ranges of effective incentive stimuli, respectively. Threshold effects due to serotonin modulation and sensitization of dopamine transmission are illustrated as well.