WASHINGTON, D.C.: Watching someone cry often evokes an emotional response, but according to a new study published Thursday, human tears themselves contain a chemical signal that reduces brain activity linked to aggression.
The research, conducted by the Weizmann Institute of Science in Israel and published in PLOS Biology, a US science journal, sheds light on the potential social impact of tears. While the study focused on female tears due to the availability of female donors, the authors suggest that the findings are likely applicable to both sexes.
Previous studies have shown that tears in rodents serve as social signals, emitted on demand. For example, female mouse tears reduce fighting among males, and subordinate male mole rats smear themselves in their own tears to deter attacks from dominant males.
To determine if similar effects occur in humans, a team led by PhD student Shani Agron exposed 25 male volunteers to either “emotional” tears or saline. The volunteers were unaware of which substance they were exposed to, as both were clear and odorless.
The tears used in the study were obtained from six female volunteers who watched sad films in isolation. The liquid was collected in a vial using a mirror as it trickled down their cheeks. Agron noted that women were more readily available as tear donors due to the social acceptability of crying among females.
Previous research has demonstrated that tears reduce testosterone levels in men, and since lower testosterone levels have a greater impact on male aggression, the researchers chose to focus on the effect of tears on men.
The male volunteers then participated in a computer game that had been widely used in aggression studies. The game involved accumulating money while a fictional opponent had the opportunity to steal their earnings. The men were given the option to seek revenge on the opponent by causing them to lose money, despite not benefiting from the opponent’s loss themselves.
Remarkably, the study found that revenge-seeking and aggressive behavior in the game decreased by 43.7 percent after the men sniffed the tears. This mirrored the observations made in rodents, despite humans lacking a vomeronasal organ, which is responsible for detecting odorless chemical signals and was lost during our species’ evolution.
To understand the mechanism behind this effect, the researchers applied the tears to 62 olfactory receptors in a lab dish. They discovered that four receptors were activated by tears, but not saline.
In a final step, the scientists repeated the experiments with the men’s brains connected to MRI scanners. The imaging revealed that the prefrontal cortex and anterior insula, regions associated with aggression, became more active when men were provoked during the game. However, this effect was not as strong when the men had sniffed tears beforehand.
The authors of the study note that crying often occurs in close-range interactions, to the extent that “kissing teary cheeks” is a recurring theme across cultures. They suggest that emitting chemical signals through tears to prevent aggression may be even more crucial among infants, where verbal communication is not yet possible.
These findings provide valuable insights into the role of tears as a natural aggression reducer in humans. Further research may uncover additional aspects of this chemical signaling process and its potential applications in various social contexts.
In conclusion, tears are not only a visible expression of emotion but also carry a chemical signal that can influence human behavior. Understanding the power of tears in reducing aggression may lead to new approaches in managing conflict and promoting peaceful interactions in our society.
Source: The Manila Times
