Thursday, October 6, 2016

Serotonin Modulates Behavioral Reactions to Unfairness


This research suggests that the neurotransmitter serotonin plays a critical role in regulating emotions such as aggression during social decision-making. Serotonin acts as a chemical messenger between nerve cells. It has long been associated with social behavior, though its involvement in impulsive aggression has been controversial.  

The study’s findings highlight why some people may become combative or aggressive when they have not eaten. The body requires the essential amino acid tryptophan to create serotonin, which can only be obtained through diet. The researchers reduced brain serotonin levels in volunteers for a short time by manipulating their diet and then used a situation known as the 'Ultimatum Game' to investigate how individuals with low serotonin react to what they perceive as unfair behavior.

In this game, one player proposes a way to split a sum of money with a partner. If the partner accepts, both players are paid accordingly. However, if he rejects the offer, neither player is paid. Normally, people tend to reject about half of all offers less than 20-30% of the total stake, despite the fact that this means they receive nothing - but rejection rates increased to more than 80% after serotonin reductions. Other measures showed that the volunteers with serotonin depletion were not simply depressed or hypersensitive to lost rewards.

PhD student Molly Crockett, a Gates Scholar at the University of Cambridge Behavioural and Clinical Neuroscience Institute, said their “results suggest that serotonin plays a critical role in social decision-making by normally keeping aggressive social responses in check. Changes in diet and stress cause our serotonin levels to fluctuate naturally, so it's important to understand how this might affect our everyday decision-making."


This study illustrates how an individual’s serotonin level affects their attitude toward risk – the lower the level, the higher the likelihood of an individual making a risky or aggressive decision. This could have large impacts on decisions made by people in power. Though the study focused on social decision-making, future research might be able to address the impact of serotonin levels on forecasting accuracy and important decisions made by executives and policy makers.

The study did not mention specific foods high in tryptophan, but the author found a medically reviewed article that suggests eating foods like eggs, cheese, pineapples, salmon, poultry, and chocolate can boost serotonin levels.


Crockett, M.J., Clark, L., Tabibnia, G., Lieberman, M.D., & Robbins, T.W. (2008). Serotonin modulates behavioral reactions to unfairness. Science (320) 5884, 1739. doi: 10.1126/science.1155577

7 Foods That Could Boost Your Serotonin. (2015). Retrieved from


  1. This comment has been removed by the author.

    1. Hank, I like this post. You made it easy to follow and understand. I am curious, however, as to what constitutes "social decision-making" as opposed to "decision-making" in general? What is your take on the topic?

  2. Hank this post was very interesting. It would be very interesting if they took the same study and added sleep deprivation. I know from may own experiences that when you mix both the above and sleep deprivation people become very snappy very quick. I saw a lot of just the food side with wrestling when people would cut weight usually maintaining a light diet of carbs. When it came down to hunger after weigh-ins dairy and protein were the first things targeted, some of which supplies and moderates serotonin levels.

  3. Hank, I agree that further research needs to be conducted for additional information and results. I like how you presented the study where certain individuals serotonin levels were manipulated to see how their decision making was effected.

  4. This comment has been removed by the author.

    1. Hank, I actually played a version of the "Ultimatum Game" in one of my political science classes during my undergrad. I remember people had trouble trusting each other as it was, so I can imagine adding hunger to the mix would only cause people to become more hostile towards each other.

  5. Very interesting article. It is certainly worth looking into the effects of how pleasure hormones alter cognitive abilities. Are happy analysts BETTER analysts? Sounds like an idea for next week's study..