How a Tiny Brain Region Guides GenerosityNEWS | 07 October 2025The decision to help a friend or stranger—and the amount of help that one chooses to give—may be powerfully shaped by the brain’s basolateral amygdala
Imagine it’s Saturday morning. You’re sipping coffee when your best friend texts, “Any chance you could help me move today?” You sigh—there go your weekend plans—but reply, “Of course.” That afternoon you sweat as you carry boxes up a flight of stairs.
A week later a co-worker you barely know mentions that she’s moving and could really use a hand. This time you hesitate. You are not as quick to offer help even though the request is nearly identical.
Why does generosity come so naturally for those we are close to but feel more like a burden when the recipient is a stranger or mere acquaintance? Psychologists call this tendency “social discounting”: we are generally more willing to make sacrifices for people to whom we feel emotionally close, and our generosity declines as the social or emotional distance to the potential recipient of help increases.
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But what happens in the brain when we make these decisions? And why are some people more generous to socially distant individuals than others are? In recent research, my colleagues and I gained new insight into these questions by examining a rare population of individuals with selective damage to a part of the brain called the basolateral amygdala. Our findings suggest that this small but important structure may be essential for calibrating our generosity based on how close or distant others feel to us.
The amygdala, a small, almond-shaped region nestled deep in the brain’s temporal lobe, is traditionally known for its role in processing emotions, especially fear. But over the past few decades it has become clear that the amygdala, particularly its basolateral part, is a central hub in our social brain.
Across species, this region has been shown to participate in evaluating social rewards, empathic responses and decisions involving others. In rodents and monkeys, neurons in the basolateral amygdala encode the value of not just rewards for oneself but also the rewards received by others. And in humans, the structure has been linked to traits such as trust, empathy, moral decision-making and extraordinary altruism. Human amygdala volume also correlates with the size and complexity of a person’s social network. And some evidence suggests that psychopathy and aggression are associated with a smaller, less functional amygdala.
So how, exactly, does the basolateral amygdala influence our decisions about whether to help others? One hypothesis is that this brain area allows us to balance competing helpful, social motives with self-interested goals. When you decide to help your best friend move, you are probably focused more on their benefit (making the move easier) than on the cost to you in time and effort. But when the person is a stranger, that mental calculation may shift. Some neuroscientists propose that the basolateral amygdala aids us as we navigate this trade-off by assigning value not just to our own well-being but also to the well-being of others.
To test this idea, my colleagues and I turned to a remarkable group of people in South Africa who have Urbach-Wiethe disease, a very rare genetic condition that causes selective bilateral damage to the basolateral amygdala while leaving the rest of the brain intact. In our study, we invited five women with this condition and 16 women without it to take part in a social discounting task. Each participant listed eight people from her own social network, ranging from her emotionally closest person (ranked as having a social distance of 1) to someone she barely knew (50) or a complete stranger (100). We then asked them to make decisions about how to split money. In each of several rounds, they received a fixed monetary amount and decided how much to share with each of their eight listed contacts. This task thus measured our participants’ willingness to share resources depending on how emotionally close or distant they felt to the people in their social network.
As expected, the participants gave more to people they were close to than they gave to others who were more distant. That is, generosity declined as social distance increased. We found it interesting, however, that participants with damage to the basolateral amygdala were less generous overall than others, and their generosity decreased more sharply as social distance increased. They showed what we call steeper social discounting: they were still willing to help those they were emotionally closest to, but their willingness to give dropped off markedly for more distant individuals.
One participant with basolateral amygdala damage was an exception—she was ungenerous across the board, even toward her closest friend. But overall the pattern was clear: damage to the basolateral amygdala did not eliminate altruism, although it did distort the fine-tuned calibration of generosity based on social distance.
Notably, variations in personality, empathy or social network size did not explain the differences in generosity among our participants. Rather our participants with Urbach-Wiethe disease seemed unable to adjust their generosity flexibly to the social context.
At first glance our findings might seem to contradict earlier studies that found those with Urbach-Wiethe disease are actually more generous than others. For example, in past research people with this condition gave away more money in the trust game, a classic experiment in behavioral economics in which participants decide how much money to send to another player, the trustee. The amount sent is typically multiplied, and the trustee then decides how much to return. The initial amount sent is often seen as a measure of trust in the trustee. People with basolateral amygdala damage tend to send much more than others, even to untrustworthy trustees who fail to reciprocate.
Researchers have described this unusual pattern of trust as a form of “pathological altruism.” In a similar vein, the authors of one study had people with Urbach-Wiethe disease respond to moral dilemmas involving hypothetical life-or-death decisions about others. They consistently refused to sacrifice one person to save many, revealing a marked reluctance to be responsible for causing harm to another individual in comparison with participants without the disease.
How, then, can we reconcile these earlier findings with our own results? We argue that the basolateral amygdala does not simply promote or hinder prosociality. Rather it is part of a neural network that helps people create a model of how the social world works, which they then can use to guide decision-making. With an intact basolateral amygdala, a person considers social context, social structure, social norms and learned expectations in social interactions when deciding whether to be generous or selfish.
When that system breaks down—as when someone suffers amygdala lesions—people may struggle to balance generous and selfish motives and consequently rely on simpler, default strategies that do not depend on networks that include this brain structure. In the trust game, the default assumption might be that others are trustworthy. In moral dilemmas, it could be to follow a rigid rule like “never harm anyone.” Such ideas might have formed in childhood and, given damage to the basolateral amygdala, not been revised later in life, even in the face of contrary experiences with untrustworthy individuals. In our task, the default strategy is to maximize one’s own payoff—unless the recipient is emotionally very close, in which case helping them comes automatically.
Although our study included only a small number of participants (which was unavoidable because of the extreme rarity of the condition), the distinctive pattern of brain damage in this group—symmetrical and precisely located in both hemispheres—is quite unique in neuroscience research. Other studies involving selective brain lesions have often relied on only one or two patients. We also feel confident in our conclusions, given how our work fits into a pattern of evidence drawing from more studies and participants that suggests amygdala functionality is crucial pillar of our social life.
The idea that the basolateral amygdala helps us weigh selfish and altruistic motives might sound abstract, but this interaction plays out in real life all the time. Think back to the moving-day dilemma. A generous impulse to help your friend move may come automatically because it is rooted in deeply encoded values and social bonds. Yet deciding whether to help an acquaintance requires something more: flexible, model-based decision-making that weighs social norms, reputational concerns and empathy against effort costs, self-care and the simple desire to have a pleasurable, lazy weekend. It’s precisely in these gray areas that the basolateral amygdala seems to do its most important work.
Generosity is therefore not an all-or-nothing trait; it is a model-based social behavior shaped by the people we are interacting with and how close we feel to them. And deep in the brain, the basolateral amygdala is helping us do that calculus.
Are you a scientist who specializes in neuroscience, cognitive science or psychology? And have you read a recent peer-reviewed paper that you would like to write about for Mind Matters? Please send suggestions to Scientific American’s Mind Matters editor Daisy Yuhas dyuhas@sciam.com.Author: Madhusree Mukerjee. Tobias Kalenscher. Daisy Yuhas. Source
