Are there specific brain regions that regulate prosocial, altruistic behaviour? Researchers at Heinrich Heine University Düsseldorf, working with colleagues in Lausanne, Utrecht, and Cape Town, investigated a rare group of patients and found that the basolateral amygdala (part of the limbic system) plays a key role. Reporting in Proceedings of the National Academy of Sciences (PNAS), they describe this region as helping to calibrate social behaviour.
Prosocial behaviour—helping others—is fundamental to human interaction. However, the neural mechanisms that shape how we behave in different social situations are still not fully understood. One central question is how generosity changes depending on how emotionally connected two people are.
Studying this objectively is challenging, but a unique opportunity arose in South Africa. Professor Tobias Kalenscher, head of the Comparative Psychology research group at HHU and lead author of the study, explained that the team was able to work with patients affected by the extremely rare Urbach-Wiethe disease.
The condition causes selective damage to the basolateral amygdala (BLA) without broadly affecting other brain regions. People with Urbach-Wiethe disease often show differences in emotional processing and social behaviour, particularly difficulty recognising the emotional meaning of facial expressions. Fewer than 150 cases are known worldwide, but a comparatively larger group lives in Namaqualand in northern South Africa.
According to Kalenscher, this made the group a kind of “natural experiment” for studying prosocial decision-making, because the affected brain region is believed to be central to compassion and social judgement.
The international research team used a well-known behavioural economics task called the “dictator game”. Participants were given sums of money and asked to decide how much to share with another person. The recipients varied in social distance: close friends, acquaintances, neighbours or strangers.
Co-author Luca M. Lüpken, a doctoral researcher at HHU, said the outcome was striking. Participants with BLA damage were just as generous to people they were close to as the healthy control group. But when the recipient was someone with whom they had little emotional connection, the same participants behaved noticeably more selfishly.
The researchers concluded that the BLA is not required for altruism in general. Instead, it appears to regulate how much generosity a person shows based on social distance. When this calibration is impaired, a default tendency to prioritise one’s own well-being becomes stronger—unless a powerful emotional bond, such as a close friendship, prompts greater giving.
In other words, the amygdala does not simply increase or decrease prosocial behaviour across the board. It helps determine when—and to what extent—people act prosocially. The authors note that these findings may also contribute to a better understanding of conditions in which social decision-making differs from typical patterns, including autism and psychopathy.
Kalenscher added that social choices are shaped not only by upbringing and culture, but also by deeply rooted brain mechanisms. In the long term, the researchers suggest that this line of work could support the development of targeted approaches to help people with social behaviour difficulties better regulate their decision-making.
