The paper starts out with Charles Darwin, and that's always a good sign. Basically the evolutionary question is why do we cry? It builds on nicely from yesterday's post on sex. Emotions are troublesome, after all. While some (like love) are typically sweet and enjoyable, others (like grief) are just plain painful. We really don't have much choice about feeling them - if you somehow suppress anger or grief, for example, it usually pops out in other unhealthy ways, such as anxiety, substance abuse, or irritability. Take it from a psychiatrist - the best thing to do with your powerful, driving emotions is to feel them and to act on what they are telling you in a reasonable way (that would not usually include busting a beer bottle over someone's head when you are angry). For example, I'm still pretty angry about what I consider the misappropriation of medical and nutritional "science" to peddle cheap commodity grains at the expense of our health. Each time I read Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health (Vintage), it gets thrown across the room a few times. So I write a blog, and I promote the blogs of like-minded folks to the right. Not because many of them also have me on their blogrolls, but because I like how they put their minds to the real problem of nutrition, lifestyle, and health in the 21st century, and I inevitably learn something from them.
But back to the paper. These researchers started out small. They took the tears of two women, ages 30 and 31, who watched sad movies in isolation. They also took a vial of saline that had been trickled over the skin of the women and let each of 24 young men (mean age 28) have a sniff - the men couldn't tell a difference in smell between the emotional tears and the saline. Then another 24 men (mean age 27) smelled the tears of three women (mean age 30) or saline and filled out some rating scales about the experience.
Then the young men were given a pad pasted to their upper lip with 100 microliters of tears or saline dribbled onto the pad. While thus anointed, the young men were asked to rate picture's of women's faces for sadness and how sexually attractive the faces were, and men were given a standard questionnaire to assess empathy. Each subject (in double blind fashion, and on different days) did the tests both with a saline and tear-stained pad. Tears or saline didn't change the men's empathy ratings or their ratings of sadness on the women's faces, but 17 out of 24 men smelling tears found the women's faces to be less sexually attractive (p <0.02).
The researchers at this point brought in 50 men and used a sensory paradigm to generate negative emotions, all the while measuring heart rate, sweating, respiration rate, skin temperature, and self-rating of mood and arousal. Salivary levels of testosterone were also measured before, during, and after smelling the tears or trickled saline of 5 donor women. After sniffing, the subjects watched sad movies (one of the news reports mentioned Terms of Endearment). Once again, the subjective arousal of tear-sniffing men was decreased, as was the level of arousal in general measured by sweating, respiration, etc., and, more tellingly, the levels of testosterone in saliva dropped.
Then the researchers got very cute (and this last bit is likely why the paper made it into Science). They took 16 young men with saline or tear-stained nose pads and had them watch sexually arousing movies and view sexy pictures - then stuck them into fMRIs. The sexual arousal signal apparently is visible in the hypothalamus and left fusiform gyrus of the brain, and within these regions, activity was significantly lower in men who were sniffing tears.
All in all, ladies, if you are looking to dampen the mood, take him to a tear-jerker. Otherwise, maybe stick with an action film or comedy. Also, tears may be a quick way to diffuse a man's overall emotional arousal - it may be an ancient hormonal way to tell an aggressive man to back off.
Now other animals also have tears, though it is thought humans are the only ones to shed emotional tears. In any event, the lacrimal secretions of mice contain chemosignals, as do human urine and sweat. Chemosignals in mammalian studies have uncovered pheromones that increase receptive sexual behavior or decrease arousal as in this study, while other chemosignals trigger sexual maturation or provide information (such as kinship - this may be why women will tend to be most attracted to men who have the most different major histocompatibility genes).
I'll let the researchers finish up:
The findings pose many questions: What is the identity of the active compound/s in tears?...Moreover, could the emotional or hormonal state (menstrual phase, oral contraceptives) of the crier/experimenter influence the outcome? In turn, what if any are the signals in men's tears... children's tears, and what are the effects of all these within rather than across gender?
My question is - what are we doing to our behaviors by masking scents with bathing, deodorant, and perfume? Would I be a more perceptive psychiatrist if my patients stopped bathing? Hmmm.