The Brain Rejects Inequality

The human brain likes balance. Not simply biological and physiological homeostasis that maintains the proper functioning of the brain, but emotional, social and psychological balance. Notably, the human brain dislikes inequality when it comes to money, and rejects it at all costs, according to new research in the journal Nature.

Behavioral and anthropological evidence show that humans dislike social inequality and unfair distribution of outcomes. But this evidence is not purely social, anymore, since researchers at the California Institute of Technology and Trinity College in Dublin, Ireland, have identified reward centers in the brain that are sensitive to inequality. The authors examined functional magnetic resonance imaging (fMRI) images of participants as they were presented with money-transfer scenarios. The volunteers participating in the study were initially randomized into 2 conditions: to receive a large monetary endowment at the beginning of the study ($50) or to start with no money. Participants were assigned to pairs — one participant from each of the monetary conditions — and the participants were offered the chance to transfer sums of money (between $0 and $50) between them.

The interesting finding was that the brains’ reward centers in the ventromedial prefrontal cortex (VMPFC) and ventral striatum responded differently to the money-transfer offers, depending on whether the participant started the experiment with money or without. Not surprisingly, the brains of the people who started the experiment with no money had strong reward-focused reactions to gaining money themselves, and basically no reaction to money going to someone else. However, the brains of people who started the experiment with money had a stronger reaction to other people gaining money than gaining money themselves.

This research is among the first to show that a dislike of fairness and inequality is more than just a social convention. On a physiological level, people are not as selfish as once believed. Similar studies preceding the current research demonstrated that the VMPFC is involved in making value-based decisions, including monetary gain, donation to charity and reciprocity. In several experiments, the brain rejected inequality and unfair offers, whether the outcome was monetarily advantageous or disadvantageous for the participant. Some researchers still claim that this behavior is based in emotions, rather than physiology. They postulate that humans reject inequality and attempt to restore fairness owing to anger or moral disgust over an unjust situation. Further, others contend that people who have money want to restore equity and balance to assuage their guilt and decrease their own discomfort over having more than other people.

While the new study demonstrates that humans are not completely focused on their own self-interests, it is unclear how the physiological evidence translates to behaviors in real-world circumstances. Humans experience physiological and emotional rewards from helping others and donating to charities, but the brain seems to stop short of wanting to redistribute wealth across the board. The association between work, reward and equality, and the brain’s mechanisms underlying all of them, remain unclear.


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Yamagishi, T., Horita, Y., Takagishi, H., Shinada, M., Tanida, S., & Cook, K. (2009). The private rejection of unfair offers and emotional commitment Proceedings of the National Academy of Sciences, 106 (28), 11520-11523 DOI: 10.1073/pnas.0900636106

Jennifer Gibson, PharmD

Jennifer Gibson, PharmD, is a practicing clinical pharmacist and medical writer/editor with experience in researching and preparing scientific publications, developing public relations materials, creating educational resources and presentations, and editing technical manuscripts. She is the owner of Excalibur Scientific, LLC.
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