The Relationship Between Dopamine And FRN:an Ultimatum Game

The ultimatum game is a fairly common paradigm which researches on the decision making. Lots of study results indicated that the individuals would reject inequity proposal in the ultimatum, because of the violation of fair expectation. With the help of ERP, A lot of study suggested that inequity proposal will induce more Feedback-related Negativity (FRN), a component of the event-related brain potential elicited when human participants commit negativity feedback in gambling tasks.The reinforcement learning theory propose that feedback-related negativity is generated when a negative reinforcement learning signal is conveyed to the anterior cingulate cortex via the mesencephalic dopamine system and that this signal is used by the anterior cingulate cortex to modify performance on the task. When a negativity signal conveys to ACC will induce a more FRN, on the contrary, when a positive signal conveys to ACC will induce a small FRN or none. But the other theory-The Violation of Expectation Theory thought that the stimuli event which is violation of expectation will induce a more FRN, whatever a negativity signal or positive signal. And if is there a violation of expectation which has a positive signal? From the reinforcement learning theory, there will have a small FRN or none, but from the violation of expectation theory, there will have a more FRN. So there is debate between the two:on the one hand, whether FRN is sensitive to the violation of expectation, on the other hand, how is dopamine regulate to FRN. Otherwise, we know that it has been found that SBR is a good indicator which could reflect the dopamine level.So in the paper, we try to study how do the difference which is dopamine between the individuals have an effect on the violation of expectation to regulate the FRN in the ultimatum. And we expect that the difference between dopamine and the difference between whether the violation of expectation or not which is to regulate the FRN.Experiment design:2(SBR:high, low)x2(expectation:fair, unfair)×5(proposal:1,2,3,4and5). And research results suggest that low SBR have a higher rejection rate and lower reaction time relative to high SBR when is up against the inequity proposal. And we also found that they have a higher conflict when is in the face of the mid-value proposal. Low SBR are very sensitive to the violation of expectation relative.The overall results suggest that low SBR are very sensitive to the violation of expectation. So when there is a low dopamine level, there is sensitive to the violation of expectation. On the contrary, there is a high dopamine level which is not sensitivity. It suggest that the individuals which have a difference dopamine level, there will have a different attitude from the inequity proposal.