7 January 2011
Male sex drive watered-down with tears
by Kate Melville
When we cry, we send all sorts of emotional signals. But scientists at the Weizmann Institute now say that tears carry chemical signals as well, after they observed that merely sniffing a woman's tears reduced sexual arousal in men.
Reporting their findings in Science Express, the scientists note that humans, like most animals, expel various compounds in body fluids that give off subtle messages to other members of the species. A number of studies in recent years, for instance, have found that substances in human sweat can carry a surprising range of emotional and other signals to those who smell them.
But tears are odorless. In fact, in an experiment in the Weizmann Institute's Neurobiology Department, the researchers showed that men could not discriminate between the smell of tears gathered from female volunteers watching sad movies and saline solution.
But in a second experiment, male volunteers sniffed either tears or a control saline solution, and then had these applied under their nostrils on a pad while they made various judgments regarding images of women's faces on a computer screen. The researchers found that sniffing tears did not influence the men's estimates of sadness or empathy expressed in the faces but it did negatively affect the sex appeal attributed to the faces.
To further explore the finding, male volunteers watched emotional movies after similarly sniffing tears or saline. Throughout the movies, participants were asked to provide self-ratings of mood as they were being monitored for such physiological measures of arousal as skin temperature, heart rate, etc.
Self-ratings showed that the subjects' emotional responses to sad movies were no more negative when exposed to women's tears, and the men "smelling" tears showed no more empathy. They did, however, rate their sexual arousal lower. The physiological measures, however, told a clearer story. These revealed a pronounced tear-induced drop in physiological measures of arousal, including a significant dip in testosterone - a hormone related to male sexual arousal.
Finally, the researchers repeated the previous experiment within an fMRI machine that measured brain activity. The scans revealed a significant reduction in activity levels in brain areas associated with sexual arousal after the subjects had sniffed tears.
Charles Darwin thought emotional crying to be a puzzling behavior from an evolutionary perspective. He identified functional antecedents to most emotional displays - for example, the tightening of the mouth in disgust, which he thought originated as a response to tasting spoiled food. But the purpose of emotional tears eluded him. This study perhaps offers an answer to this riddle: tears may serve as a chemosignal.
"This study raises many interesting questions," mused Weizmann researcher Noam Sobel. "What is the chemical involved? Do different kinds of emotional situations send different tear-encoded signals? Are women's tears different from, say, men's tears? This study reinforces the idea that human chemical signals - even ones we're not conscious of - affect the behavior of others."
Source: Weizmann Institute of Science