The Part of Your Brain That Makes You Stingy to Strangers but Sweet to Best Friends

Do you ever wonder what happens inside your head when you decide to hand over your hard-earned cash to a friend versus a neighbor you just met? It is a question that touches on the very essence of human connection. Researchers from Heinrich Heine University Düsseldorf along with colleagues from Lausanne, Utrecht and Cape Town decided to look for the answer. They focused on a very specific area of the brain known as the basolateral amygdala, which is part of the limbic system. According to a study published in the Proceedings of the National Academy of Sciences, this region acts as a crucial regulator for our social behavior. The authors describe how this part of the brain essentially calibrates the degree of our generosity depending on who we are interacting with.

Understanding the mechanics of prosocial behavior is no easy task. Prosocial behavior, or helping others, is a cornerstone of human interaction but the neuronal mechanisms behind it are complex. We do not yet fully understand how prosocial behavior changes depending on how much or how little decision-makers care about each other emotionally. The researchers discovered a unique opportunity to study this in South Africa. There is a larger group of individuals who suffer from the rare Urbach-Wiethe Disease living in Namaqualand in northern South Africa. This disease causes selective damage to the basolateral amygdala without affecting other areas of the brain. These individuals differ from the general population in their emotional life and social behavior. They find it difficult to recognize the emotional meaning of facial expressions. Because exactly those areas of the brain are affected in these individuals, they represent a quasi-natural experimental environment for questions about prosocial behavior.

To understand how this brain damage affects the human heart, the team conducted so-called "dictator games" with the participants. This is a special constellation from game theory where participants are asked to distribute sums of money. The participants were free to decide how much money they wanted to share with other people. They had to choose between close friends, acquaintances, neighbors or strangers. The results of the experiment were clear. Individuals with damage to the basolateral amygdala were just as generous toward people they were close to as healthy control participants. However, as soon as it came to individuals with whom they had less of an emotional connection, they were notably more selfish. This discovery suggests that the BLA is not fundamentally necessary for altruism. Instead, it helps regulate the degree of generosity depending on the social distance between individuals.