Acting selflessly: What motivates kidney donors

Anyone who has an organ removed in order to donate it to an unknown person is acting in an unusual way. Brain researchers examine such special altruists – and find a connection with anxious faces.

Humans can donate one of their two kidneys. Anatomical Model.

Annick Ramp / NZZ

The Thun physiotherapist Dieter N. donated one of his kidneys ten years ago. Not a relative, not a friend, but a complete stranger. After the successful operation, he has to rest for two months to recover. When asked what prompted him to do this selflessly, the 58-year-old says: “The question should be: Why don’t you want to do something altruistic?” Everyone has different ways of doing this. Kidney donation was the natural choice for him.

Anyone who, like Dieter N., donates a kidney to a stranger seems to take his selfless donation for granted. He or she hardly perceives his own risk. At first glance, this is difficult to fathom and has prompted neuroscientist Abigail Marsh to take a closer look at these “extraordinary altruists,” as she calls them. For more than two decades, the Georgetown University researcher has been trying to figure out what goes on in their heads and how their brains differ from the rest of the population. It has been shown, for example, that exceptional altruists recognize and process emotions differently.

Altruists are better at recognizing fearful faces

Marsh found a first indication of this in altered brain activity. To examine these, she pushed her study participants into an MRI scanner and showed them images of fearful, angry, and neutral faces. She compared the reactions with those of a neutral comparison group. The amygdala, which is part of the emotion center in the brain, was significantly more responsive to fearful faces in the altruists. The amygdala did not react differently to other emotional expressions than in the comparison group.

In addition, the emotion center in the brain of the altruists was larger. The researcher determined the brain volume of her subjects using magnetic resonance imaging and compared it with that of the non-altruistic control group. The altruists had an eight percent larger right-sided amygdala. In addition, this contained more gray matter and thus more nerve cells, which partly explains the higher activity. “About 50 percent of the anatomical differences in the amygdala can be explained by genetics, but it is also shaped significantly by social interactions,” says Marsh. Whether people are altruistic because they have a large, active amygdala or vice versa cannot be determined causally.

Exceptional altruists are rare

For these studies, Marsh had recruited participants who were so-called “non-directed” kidney donors, i.e. who had given their organs not to relatives or friends but to strangers. None of the subjects had received any consideration for their donation. This was the only way the researcher could largely ensure that they were “extraordinary” or “pure” altruists who were not pursuing any financial or selfish motives. This rare group of subjects makes their studies unique.

Just as rare are people who stand out due to their particularly selfish actions and remarkably low ability to empathize. In an earlier study, Marsh had shown that the emotional center also reacted conspicuously in these test subjects: the amygdala is less active when looking at anxious faces than in the average population. If you ask these subjects to empathize with the pain of others, rtheir amygdala also reacts weaker. In addition, the amygdala of people with little empathy, i.e. with psychopathic traits, is smaller than the average of the population.

Neuroscientists therefore place psychopathy and altruism at opposite extremes on the spectrum of human caring ability, the “caring continuum”. Most of the population falls in the middle of this bell-shaped curve. Psychopathy and pure altruism, on the other hand, are rare at less than one percent each.

The number of kidney donations in Switzerland shows how few such extraordinary altruists there are. “Between 2013 and 2021 we had 110 to 120 kidney donations per year. Almost all of them went specifically to the donor’s own family or friends,” says Nathalie Krügel, the senior doctor at Swisstransplant. Only six times in the past ten years has a patient received a donor kidney from a stranger, she adds. Dieter N. was one of them.

In general, the willingness to act altruistically can be explained by the so-called “social discounting” effect: the further away a third party is from one’s own social circle, the less willing they are to donate an organ for them, and vice versa. But this is exactly where extraordinary altruists differ from the average. In an attempt At three American universities, altruistic kidney donors stated that they value the well-being of strangers almost as much as that of their relatives, even if the strangers were far outside their own social circle.

Your own fears take a back seat

For many people, the prospect of unnecessary surgery is terrifying. Why not with donors like Dieter N.? The hormone oxytocin may play a role in suppressing this fear, which can reduce one’s fear and ultimately increase altruism. However, there is still no evidence of this in the human amygdala.

But in animal models Researchers have already found evidence for this mode of action of oxytocin. Mother rats were first conditioned to freeze in fear when smelling peppermint. However, if their young animals were nearby, the conditioning had no effect: there was no fear reaction. The presence of the young caused the mother to release more oxytocin. If this release was prevented by medication, the rat mothers froze even in the presence of the young animals.

Neuroscientist Anita Tusche of Queen’s University in Ontario is familiar with this type of oxytocin research in the amygdala. “The findings enable a better understanding of the processes in the amygdala,” says the scientist. However, the effect of oxytocin in animal experiments cannot be transferred one-to-one to altruistic behavior in humans. The interaction between oxytocin and cultural and developmental psychological factors is extremely complex.

But there are also hormones that negatively influence altruism. For example, Tusche, together with a German research team, Effects of the stress hormone cortisol investigated. To do this, they stressed the test subjects with a mock interview before an MRI examination. They then checked the participants’ cortisol levels and asked them how generously they would donate. It was found that with rising cortisol levels, the willingness to donate decreased in those altruists who had a particularly high degree of empathy, while there was no effect in the control group.

So Dieter N. was probably not under stress when he decided to donate. He was relaxed about the procedure and was able to afford the time off. Today he would make the same decision, says the physiotherapist. As complex as the processes that played a psychological and neurobiological role are, his explanation for his selfless act is as simple: “It was doable for me, so I just did it. I don’t see it as an insanely big altruistic gesture.”

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