A burst of tears reduces male aggression, study finds

Watching someone cry often evokes an emotional response, but according to a new study released Thursday, human tears themselves contain a chemical signal that reduces brain activity linked to aggression.

The research was carried out by the Weizmann Institute of Science, Israel, and appeared in Biology PLOS, an American scientific journal. Although these are female tears, because women made themselves available as donors, it is probably not a sex-dependent effect, the authors say.

Numerous studies have shown that rodent tears contain chemicals that serve as social signals that they emit on demand: female mice’s tears, for example, reduce fighting between males; and subordinate male mole rats coat themselves in their own tears so that dominant males attack them less.

To find out if similar effects occurred in humans, a team led by Ph.D. student Shani Agron first exposed 25 male volunteers to either “emotional” tears or a saline solution. The volunteers couldn’t tell what they were sniffing because both substances are clear and odorless.

The tears were obtained from six female volunteers who watched sad films in isolation and used a mirror to capture the liquid in a vial as it flowed down their cheeks.

“When we looked for volunteers who could donate tears, we found mainly women, because for them it is much more socially acceptable to cry,” Agron said in a statement.

She added that since previous research had shown that tears reduced testosterone levels in men and that decreasing testosterone levels had a greater effect on aggression in men than in women, “we started by studying the impact of tears on men because that gave us a greater chance of seeing an effect.”

They asked volunteers to play a computer game well established in previous studies of aggression that involves accumulating money while a fictional opponent could steal their winnings.

If given the opportunity, men could take revenge on the other player by making him lose money, although in their own case they would not gain from the opponent’s loss.

These aggressive and revenge-seeking behaviors in the game dropped 43.7 percent after the men sniffed back their tears.

This seems to mirror what has been observed in rodents, but unlike rodents, humans do not have a structure in their noses called the vomeronasal organ, which was lost during the evolution of our species and which detects signals odorless chemicals.

To find out what was happening, the researchers applied the tears to 62 olfactory receptors in a laboratory dish and found that four receptors were activated by the tears, but not by the saline solution.

Finally, the scientists repeated the experiments with the men’s brains connected to MRI scanners.

Imaging revealed that the prefrontal cortex and anterior insula, linked to aggression, became more active when the men were provoked during play, but the effect was not as strong if they had sniffed tears .

“We note that crying often occurs during very close interactions, so much so that ‘kissing tearful cheeks’ is a recurring theme across cultures,” the authors wrote, adding that the emission of chemical signals to Preventing aggression was probably even more important in infants. , where verbal communication is not possible.

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