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)

Labradors and Laboratories

Each Friday morning I awake with anticipation of our weekly lab meeting. Because the research interests of our lab range from epigenetic inheritance to colon cancer and obesity, conversations at these lab meetings are pretty versatile, but usually go something like this:

Scheduled start of lab meeting: Is anyone coming to this meeting? Where is everyone?15 minutes after the scheduled start of lab meeting: Lab meeting actually begins.The next 30 minutes: Mostly professional discussion about recently published scientific paper or presentation of new data from the lab.The final 20 minutes: Transition into discussion about poop, mouse colonoscopies, checking the cervical mucous plug, how to perform the best sperm extraction, which unfortunate lab technician is going to have to collect fecal samples...

As you can tell, the end of the lab meeting is the most lively part of our discussion. In today's meeting we got to learn about this little gem of a study published back in 2011 in which dogs were trained to sniff out colon cancer. Do you have a funny image of a dog smelling someone's rectum yet? How about now?

Turns out the idea of having dogs "diagnose" cancer by smelling a patient's breath, urine or stool samples is not all that new, but somehow has gotten by me for the past decade and I'm just starting to look at the published research. In the case of the study I'm going to share with you the researchers worked with trained dogs that would smell either a breath or watery stool sample (collected during a colonoscopy to make the diagnosis of cancer or cancer-free) of a study participant. Samples of the patients' breath were used to train the dogs. The researchers explain it as follows:

Each cancer detection training session was considered complete when the dog could correctly distinguish between breath samples from a cancer patient and four controls consecutively in dozens of trials. The fundamental training method was a reward-based approach in which the correct behaviour is rewarded by simultaneous play with a tennis ball.

What I think is important to note here is that (1) I've definitely chosen the wrong subject for my thesis because it did not include playing fetch with a dog, and (2) the dogs were trained using samples from other types of cancer than colon cancer. In the end of the training period the dogs could sniff out the patients with esophageal, breast, lung, gastric, pancreatic, hepatocellular, cholangiocarcinoma (bile duct), prostate, uterine, ovarian, bladder or colorectal cancer simply using samples of the patient's breath. This means that some volatile compound (or compounds) exists in both the breath and bodily excretions of cancer patients that is missing or different in cancer-free patients. Moreover, these volatile compounds are seemingly similar between cancer types.

After putting the dogs to the test 74 times (38 watery stool tests + 36 breath tests) the dogs picked out the samples from the cancer patients with amazing accuracy. Remember how I mentioned above that each study participant underwent a colonoscopy to determine whether they had colon cancer or were cancer-free? The dog's cancer diagnosis correlated with the doctor's diagnosis 91% of the time for the breath test, and 97% of the time for the watery stool test. 97%! Maybe one day we'll see Labrador retrievers roaming the halls of cancer clinics, smelling out the patients needing assistance. Or, in a more boring, practical world, we'll discover what it is in the breath and stools of cancer patients that is being detected by the dogs and come up with a lab technique to measure it. Personally, I'm keeping my fingers crossed for doggy doctors.

Sonoda, H. et al. Colorectal cancer screening with odour material by canine scent detection. Gut (2011)