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Sense of justice depends on serotonin levels
Last reviewed: 01.07.2025
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The sense of fairness and the level of serotonin in our brain are interconnected: the more serotonin, the more dishonesty we are willing to forgive another person.
Our ideas about what is fair and what is not begin in early childhood. We shout our first "That's not fair!" in the children's sandbox and continue to shout it throughout our lives - for example, at a car that overtook us while we were stuck in a traffic jam on the side of the road (though in this case, a very childish cry is usually expressed in an unprintable form). We are all for the dishonest person to always be punished. But it is no secret that different people have different ideas about fairness: some can afford themselves and others more, some less. What does the "level of fairness" depend on?
Researchers from Kyoto University (Japan) conducted the following experiment. They asked several volunteers to play a well-known psychological game that allows you to determine your level of tolerance for an unfair offer. The essence of the game is that one of the players (which can be a computer) finds a certain amount of money and offers to split it. But it can split the money in different ways: equally or with an advantage in its favor. For example, out of a hundred rubles, you are offered 30, and you are free to accept the offer or refuse. At first glance, it would be more honest to split everything equally. But in reality, the other person found the money, and he is free to spend it as he wants. And yet, this consideration does not often occur to people, and therefore many regard the situation as an unfair division.
Psychologists have found that the “boundary of honesty” in this case lies somewhere in the range of 30–70, that is, few people would consider less than thirty rubles out of a hundred to be a fair and just share.
This time, the researchers decided to compare the psychological results with the positron emission scan of the brain. Using a PET scanner, the scientists analyzed the serotonin content in the central nervous system. It turned out that those who produce more serotonin have more flexible parameters of honesty. That is, the tendency to agree to a smaller share in the division coincided with an increased level of serotonin in the raphe nuclei - the area of the brain where this neurotransmitter is synthesized.
The authors emphasize that this is not related to a person's aggressiveness, but is related to trustfulness. It has been previously shown that low serotonin levels are characteristic of people who trust others excessively: perhaps such individuals develop rather strict rules of behavior as compensation, and as a result they are sensitive to even the slightest injustice.
Serotonin is truly omnipotent: it affects sleep, memory, appetite, a whole range of physiological processes depend on it, from digestion to ejaculation. But it is unlikely that such a complex cognitive construct as a sense of justice is caused by fluctuations in just one substance. Most likely, serotonin acts here together with the frontal lobes of the brain, which are responsible for higher cognitive functions. So for now we should be careful and talk only about the correlation between honesty and serotonin levels.