For ordinary mortals, altruism is behavior that implies some kind of assignment or personal sacrifice for the benefit of others, without expecting anything in return; something that seems to contradict the Darwinian ideas of selfishness and the selection of the strongest as engines of survival and evolution. Biologists, therefore, try to explain altruism considering that it takes place above all within families, where the sacrifice of a relative (giving up, for example, a kidney) helps the survival of another member of the same family.
Another explanation is reciprocal altruism, that is, today for you, tomorrow for me. I give you the money you need hoping that you will do the same to me when I need it. But behavior that benefits the other without reciprocity is more difficult to explain. Is there always some kind of hidden reciprocity and, in reality, true altruism, as we usually define it, does not exist?
Trying to find the answer to this question, a team of researchers from the University of Milan and other Italian research centers have carried out extensive work exploring altruistic behavior and the brain in mice, mammals like us, with results as both striking and interesting, recently published in Nature Neuroscience.
Their experimental setting consisted of two adjacent compartments separated by a transparent partition. In one of them a mouse (actor) could insert its nose into two different holes. When he did it in one of them he received a dose of food himself (selfish choice). When he did it in the other hole, both he and another mouse (recipient), which he could observe through the screen in the adjacent compartment, received a dose of food (altruistic choice). Either I order food just for me, or I order it for both of us, we could say, trying to investigate the mind and behavior of the acting mouse.
With successive trials and whenever there was a receptor mouse on the other side of the screen, the acting mice developed a strong preference for one of the two options, altruistic or egotistical. The male mice showed mostly an altruistic preference, while the female mice had a 50% altruistic or 50% selfish behavior. But all these preferences lost strength, that is, they stopped developing when there was an inanimate object on the other side of the screen instead of another mouse, or when an opaque barrier stood between the two compartments. Surprisingly, all this seemed to indicate that the preferred behavior of the actor mice, whether selfish or altruistic, was motivated by social reasons, that is, by the presence of another mouse, but not an object, in the adjacent compartment.
But that was not the only surprise, because it was also observed that the altruistic choice (food for both mice) was greater when the recipient mouse was familiar and had been in contact with the actor mouse before the experiment. Social contact, therefore, developed the altruistic behavior of the mice. In addition, males continued to engage in altruistic behavior even as the requirement (up to six forays into the hole) to obtain food increased. The females also maintained it, although somewhat less.
However, what most caught the attention of the researchers was that the altruistic choice of the mice continued when the food supplied went only to the recipient and not to the actor, which means that the food was not necessarily the motivation of the actor, since there was anything else. And if the recipient mouse was not previously deprived of food, the actor mouse’s altruistic choice also decreased, as if its goal, let me say, was to feed the hungry. A social motivation, in short.
These results also indicated that the altruistic behavior of the mice was not innate, but learned through experience, that is, by reinforced learning (operant conditioning, in the language of experimental psychology), so the researchers ended up wondering if that behavior , socially rewarded, was or was not true altruism. Actually, we humans are also socially rewarded when, for example, we give money to a poor person or give up a seat to an elderly person.
Altruism and the cerebral cortex
On the other hand, as functional magnetic resonance studies have shown that when humans make altruistic decisions, areas of our brain such as the prefrontal cortex or the amygdala can be activated, the Italian researchers also studied whether something similar could occur in the brain of mice. . Indeed, this was the case, because using modern recording techniques they observed that the altruistic choices of the mice were accompanied by an increase in the activity of the neurons of their basolateral amygdala, which was not the case when the choices were selfish. In addition, the suppression of this activity in the amygdala of mice by chemogenetic techniques reduced altruistic choices when the mice were acquiring a preference, that is, during the learning period. It seemed, in short, that the increased activity of the neurons of the amygdala could be responsible for establishing the altruistic preferences of the mice.
If so, how do those neurons achieve it? Apparently, acting on the cerebral cortex, because when the researchers inhibited the activity of the neurons that project from the amygdala to the prelimbic cerebral cortex of the mice, preferences fell and altruistic choices decreased. In contrast, the inhibition of the opposing neurons, those that go from the cerebral cortex to the amygdala, increased the number of altruistic choices in the acting mice, as if the cerebral cortex told the mouse: “Let’s be altruistic, that’s good.” .
Many of the results obtained by the Italian researchers are susceptible to diverse and alternative interpretations, but if we extrapolate them to us humans (with a mammalian brain, although more evolved than that of mice), they reveal at least two important things. . One is that all altruistic (or apparently altruistic) behavior could hide some gratification or reward of an emotional nature (when we are generous, we feel like better people) or social (when others perceive our generosity, they value us more). The other conclusion is that this type of behavior always results, as expected, from an interaction between the emotional regions (amygdala) and the rational regions (cortex) of the brain.
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