Tuesday, June 18, 2013

The Ugly Cry Face

The human body is an immensely complicated thing. Each organ and bodily fluid has at least one, if not multiple functions. From your eyelashes to your toenails, humans have evolved to thrive in their surroundings. This includes tear production and the act of crying, which has its obvious perks: protection and lubrication of the eyes, delivery of important nutrients and electrolytes to the cornea, the removal of irritants. Additionally think of the great relief a sobfest can bring at the end of a hard day. The latter refers to “emotional tears”, which act as a sign of emotional distress. For decades scientists have tried to determine why it is we cry, linking it to sadness and signals of harmlessness. Randomized trials have been conducted to determine whether tears elicit a change in mood or increases empathy. These responses make sense to us because of our own personal experience with crying. But then came Dr. Sobel at the Weizmann Institute of Science in Israel, and the world of emotional tears has never been the same.

In 2011 Dr. Sobel's research group published an article where they reported that emotional tears from women elicit a seemingly odd response in men: reduced arousal and sexual attraction. To conduct this research, the scientists had women watch sad movies and collect their tears, this way the tears would be of the emotional kind. As a control, the women were also asked to trickle saline solution down their cheeks and collect the drops like they did their own tears. Men in their mid to late twenties then were asked to smell either the tears or saline and perform different tasks. One of these tasks involved looking at pictures of women like the ones below and rating their sadness and attractiveness. 

Men who were smelling tears were not any better at rating a woman's sadness compared to the men that were smelling saline. They were, however, less attracted to the female's photo. The researchers attributed the men's inability to rate sadness to the fact the men themselves were not sad. Therefore, the researchers repeated the study but first had the men watch a sad movie. Instead of asking the men to rate a female's attractiveness they measured their arousal through both self reports and proxy measurements (heart rate, skin temperature, respiration rate, among others). Salivary concentrations of testosterone were also measured. Again, the men that smelled the tears had decreased levels of arousal - both self reported and measured - as well as a decrease in salivary testosterone concentrations. Interestingly, even after watching a sad movie the men that sniffed tears did not report any differences in mood compared to the men that smelled saline. If tears contain a chemical signal that elicits sadness or empathy, the tears should have made the men more sad than the saline, yet this result was not achieved. 

Finally, to be sure that what they were seeing was a true effect, the scientists asked the men to watch an "erotic film" while they conducted brain imaging. This last portion of the study probably made for some awkward social interactions, and conjures up the image of a mad scientist creepily studying his subjects from behind a one-way mirror. Nonetheless, areas of the brain that "lit up" while viewing an erotic film had reduced activity when the men sniffed the tears, again indicating that a woman's tears reduce sexual arousal in men. 

While this study may leave us with more questions than answers, it does give us some insight into the evolutionary reason for tears. Seeing someone cry may still very well be a visual sign of sadness, but the chemical signaling compounds in tears do not seem to change the empathetic response. Now the question turns to why it would be beneficial to reduce arousal in times of sadness, and whether we would see a similar result if we were to reverse the genders or change the age group. 

Perhaps crying was the original, ahem, excuse. As in "I have a headache..." type of excuse. You get my gist. 

S. Gelstein et al. Human Tears Contain a Chemosignal. Science (2011)