Aggressive Behavior Found To Be 43.7% Lower When Men Sniff Women's Tears, Study Finds

(Photo : Getty Images/Daniel Pockett)

A study said that aggressive behavior is found to be 43.7% lower when men sniff the tears of women.

Experts noted that rodent tears contain social chemo signals with diverse effects, including blocking male aggression. It was found that human tears also contain a chemo signal that lowers male testosterone, but its behavioral significance was unclear.

Reduced Testosterone

Because reduced testosterone is associated with reduced aggression, scientists tested the hypothesis that human tears act like rodent tears to block male aggression.

Using a standard behavioral paradigm, they found out that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%.

To probe the peripheral brain substrates of this effect, they applied tears to 62 human olfactory receptors in vitro.

They identified four receptors that responded in a dose-dependent manner to this stimulus. Finally, to probe the central brain substrates of this effect, they repeated the experiment concurrent with functional brain imaging.

They discovered that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter.

Taken together, the results have implied that like in rodents, a human tear-bound chemo signal lowers male aggression.

This mechanism likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. Researchers have suggested that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression.

In the experiment, researchers asked whether sniffing human emotional perceptually odorless tears reduces aggression in men as it does in male rodents.

First, they harvested emotional tears from human female donors (6 regular donor women, age range 22 to 25 years) using methods previously described.

Because tears that trickled down the cheek and into the collection device may have collected skin-bound signaling molecules not originating from tear fluid, as a control substance, they had trickled saline down the cheeks of the very same donors and collected it in a similar manner.

Next, they also used the point subtraction aggression paradigm (PSAP), a validated measure of aggression in response to provocation.

Aggression Provocation Ratio

It was also explained that aggression is estimated by the aggression provocation ratio (APR), namely, the ratio between the number of revenge responses to the number of provocations the participant experienced.

The study noted that a higher APR reflects higher aggression. Before the PSAP, each participant went through a stimulus exposure procedure.

Meanwhile, given that reduced male testosterone is associated with reduced male aggression, the study had set out to test the hypothesis that like in rodents, human tears contain a chemical signal that blocks aggression.

Notably, there are indeed several instances of chemical signals altering hormonal-dependent behavior in humans. Examples include maternal behavior, ingestive behavior, social behavior in general, and sociosexual behavior in particular.

In other words, a chemical signal altering human behavior is not unusual.

Moreover, particularly emotional behaviors are a prime candidate for modulation by chemical signals, possibly a reflection of their shared neural substrates in the amygdaloid complex and an extensive associated brain network spanning ventral temporal cortex, frontal cortex, anterior cingulate cortex, and insula striatum.

Tags tears, aggressive behavior