# Serotonin and reactions to unfairness

![](/files/-MP5E5Qx_ZrRUEelLw7D)

### Neurotransmission has a significant relationship to human behaviour.

It is also a major focus for psychologists taking a biological approach. For example, the neurotransmitter serotonin has been investigated to determine its involvement in a wide range of emotions, behaviours, and psychological disorders. These include but are not limited to:

* Happiness and wellbeing
* Trust
* Depression
* Problems with anger control
* Suicide
* Insomnia
* Obsessive-Compulsive Disorder and other emotional disorders

[Crockett et al.](https://science.sciencemag.org/content/320/5884/1739) (2008) conducted a study to determine the role played by serotonin and reactions to unfairness:

**Study aim:** Determine the role of serotonin in individual reactions to unfairness.

**Type of study:** Double-blind experiment.

**Participants:** 20 volunteers.

**Procedures:** Participants played an ultimatum game that involved a player (the proposer) proposing a way to split a sum of money with another player (the responder). If the offer was accepted both players would be paid accordingly. For example, the proposal to split the money 45% to the responder would see the proposer pocket 65% of the money while the responder would receive 45% if accepted. If the responder were to reject the offer, no one would get paid.

Responders tended to reject offers less than 20 to 30% of the total stake, even through they would miss out on any reward. In other words, when the offer is perceived as unfair it is rejected despite the personal cost involved.

Acute tryptophan depletion (ATD) procedures were used to temporarily lower serotonin levels of the participants playing the role of responder during several one-shot ultimatum games. Offers fell into one of three fairness categories: 45% of stake (fair), 30% of stake (unfair), or 20% of stake (most unfair). The size of the stake was also manipulated.

**Results:** The participants who underwent ATD rejected significantly more unfair offers than participants who received the placebo. The size of the reward had no effect.

**Conclusion:** Serotonin plays a role in altering how individuals react to unfairness. Lower levels of serotonin are linked to higher rates of retaliation to perceived unfairness.


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