A new study conducted by the Weizmann Institute of Science in Israel has revealed that tears of emotion contain a chemical signal that reduces brain activity associated with aggression. Published in the prestigious US science journal, PLOS Biology, the research provides fascinating insights into the social dynamics influenced by human tears.

While previous studies have demonstrated that tears in rodents serve as social signals, with specific effects on behavior, this study aimed to investigate whether similar effects occur in humans. To conduct the experiment, the researchers enlisted 25 male volunteers who were exposed to either "emotional" tears or saline solution. Unknown to the participants, both substances were clear and odorless to prevent any bias.

Tears used in the study were obtained from six female volunteers who watched sad films in isolation. They used a mirror to capture the liquid in a vial as it trickled down their cheeks. The authors noted that female donors were easier to find, as crying is considered more socially acceptable for women.

The research team discovered a significant decrease in revenge-seeking and aggressive behavior in the male volunteers after they sniffed the tears. Aggression in a computer game scenario, where the participants had the opportunity to harm their fictitious opponent's earnings, dropped by a remarkable 43.7 percent following exposure to tears.

While tears have been previously shown to reduce testosterone levels in men, which in turn reduces aggression, the researchers were intrigued to study the impact of tears on men specifically due to the higher likelihood of observing an effect.

Interestingly, unlike rodents, humans do not possess a structure called a vomeronasal organ in their noses, which detects odorless chemical signals. To understand the underlying mechanism behind tears' influence, the researchers conducted further experiments. They applied the tears to 62 olfactory receptors in a lab dish and found that four receptors were activated solely by tears, not saline solution.

Brain imaging during the study revealed that the prefrontal cortex and anterior insula areas, which are associated with aggression, became more active when the male participants were provoked during the game. However, this effect was noticeably weaker in participants who had sniffed tears beforehand.

The authors suggest that crying often occurs in intimate interactions, and emitting chemical signals through tears may play a vital role in preventing aggression, particularly in infants where verbal communication is not yet possible.

The findings of this study shed light on the complex nature of human tears and their potential impact on social behavior. Understanding the chemical signals present in tears could open up new avenues for research into emotional expression and interpersonal dynamics.

Further research in this field may help scientists unravel the intricate workings of our emotions and uncover ways to promote more harmonious interactions within society.

The study has been published in the journal PLOS Biology and has generated significant interest for its groundbreaking insights into the role of tears in reducing aggression.

Reference:
Agron S, de March CA, Weissgross R, Mishor E, Gorodisky L, Weiss T, et al. (2023) A chemical signal in human female tears lowers aggression in males. PLoS Biology (2023). DOI: 10.1371/journal.pbio.3002442