The "Not Tonight, Dear" Pheromone

An online report in Science last week demonstrates rather convincingly that women’s emotional tears contain an odorless chemical signal, or pheromone, that reduces sexual arousal in men. The press immediately dubbed it the “Not Tonight, Dear” pheromone, though that may be a bit simplistic.

Nevertheless, the evidence is clear; the men in the study rated pictures of women’s faces as less sexually attractive after sniffing tears collected from women who cried while watching sad films. They also exhibited progressive reductions in testosterone in their saliva, reductions in several psychophysiological measures of arousal, and even reductions in the activity of regions of the brain associated with sexual arousal compared to the control group. (In the control group, the same men sniffed plain saline that had been trickled down the cheeks of the women who had previously generated the tears.)

The identity of the chemical compound in women’s emotional tears is not yet known. Nor is it known whether the compound produces any other responses in men besides sexual disinterest, or whether men’s tears might also be sending some sort of signal to women.

Texting and Fatal Driving Accidents

Text messages sent per month from hand-held phones increased more than 15-fold from 2002 to 2008. Over the same years the percentage of fatalities in which distracted driving was listed as a possible contributing factor increased from about 12% to nearly 16%.

Based on these data, the authors of a recent report speculate that texting while driving may have contributed to 16,000 additional driving fatalities between 2001 and 2007. The claim was reported in the Los Angeles Times and other papers, but is it true?

There are several problems with this report. First, the authors defined a fatality as caused by driver distraction whenever a distraction was merely listed as present. Other factors such as equipment failure, alcohol, or driver age were not considered. Second, distractions are anything that takes the driver’s attention away from driving, including texting or talking on a hand-held phone, reading an on-board navigation system (also increasingly popular these days), reaching for something, eating, drinking, putting on makeup, etc. Searching for street signs or rubbernecking another accident are also distractions. None of these were factored out in this study.

All the report really shows is that text-messaging volumes (in and out of cars) and the number of fatal accidents due to all distractions are both going up. The authors call it a correlation, but so what? A correlation does not prove causation. I’m reminded of the example presented by my thesis advisor years ago of the tight correlation between the rise in the number of telephones in the U.S. and the decline in the incidence of tuberculosis. Do telephones prevent tuberculosis? Hardly.

Is texting while driving a problem? Probably yes. Does this paper convince me that texting while driving has caused 16,000 additional fatalities? Sadly, no.

Combating Motion Sickness

What causes motion sickness? The main reason is that during certain kinds of involuntary motions the brain receives conflicting neural signals from visual receptors in the eyes, positional receptors in the inner ears and in muscles and tendons, and gravity receptors in the stomach. These conflicting signals confuse the brain, and nausea ensues.

Recently, researchers learned that the severity of motion sickness caused by a slow, cyclic motion can be reduced by deliberately breathing out of sync with the motion. Breathing either faster or slower than the cyclic motion allows the diaphragm to counteract the heaving movements of the stomach, thereby minimizing the neural disconnect between stomach gravity sensors and other motion and position receptors. The worst thing you can do is to take a breath with each heaving motion, although it’s the natural thing to do.

Reference: Denise, P. et al. Effect of temporal relationship between respiration and body motion on motion sickness. Autonomic Neuroscience 151:142-146, 2009.

Quietus for Tinnitus?

Perhaps you’ve heard the ads for Quietus, an allegedly “unique homeopathic formula” containing “proven and effective ingredients” for treating tinnitus (ringing in the ears). The product’s website doesn’t list the ingredients, but I was told by a representative who answered the phone that it contains quinine sulfate, salicylates (a close relative of aspirin), and several other ingredients.

Quinine sulfate?! The FDA banned quinine sulfate in 2006 from all FDA-approved drug products except for products used in the treatment of malaria. The FDA lists a number of possible toxic effects of quinine including disorientation, cardiac arrhythmia, allergic reactions, and even death (there have been 93 deaths associated with quinine use in the past 40 years)

Why is quinine still allowed in a homeopathic remedy? Unlike pharmaceutical drugs, homeopathic remedies derived from natural products can stay on the market until they are proven to be unsafe. In other words, the makers of homeopathic remedies do not have to prove their products safe before marketing their products; they can just wait and see what happens to users. Users beware…..

Myopia is on the Rise

According to a recent report, the prevalence of myopia (nearsightedness) in persons aged 12-54 years in the U.S. has increased from 25% to 41.6% in just the past 30 years. That’s too large a change in such a short a time to be due solely to a genetic factor; there must be an environmental component. A clue is that myopia is more common in people with more than 12 years of education, suggesting that close work such as reading and computer work might be a risk factor.

The good news is that myopia is relatively easy to correct with eyeglasses, contacts, or LASIK surgery. As health problems go, myopia is not the big one. Nevertheless, scientists are curious to know what might be causing the rise in myopia so that preventive measures could be undertaken if possible. Over 40% of the population with myopia is a lot of people! If nothing else, correction of myopia represents a significant national heath care expenditure, even if it's not a big deal to any one person.

Tasting the Bubbles

It used to be assumed that the tingling sensation of carbonated beverages was due to stimulation of mechanoreceptors by bursting bubbles of CO2. In fact, researchers now know that we also have chemoreceptors for CO2, and that they are located on the same taste cells that detect sour taste. The receptor molecule is the enzyme carbonic anhydrase, which converts CO2 (plus a water molecule) into bicarbonate and a proton. Protons activate the taste cell, which in turn activates the sensory neuron that synapses with it.

Why don’t carbonated beverages taste sour, given that the carbonic anhydrase is located on the sour-detecting taste cells? No one knows for sure, but researchers speculate that the brain interprets CO2 receptor activation plus mechanoreceptor stimulation as primarily a tingling sensation.

Can You Taste Bitter Foods?

About 25% of the human population does not perceive vegetables such as broccoli, cabbage, or Brussels sprouts as bitter-tasting. The rest of us perceive these vegetables as either mildly bitter or obviously bitter. These differences are determined by a gene that has two variations, or alleles – one for “bitter taster” and one for “non-taster”. The bitter taster allele is dominant, so if you have at least one copy of it you will perceive Brussels sprouts as mildly or intensely bitter.

At what point in human evolution did the ability to taste bitter foods first appear? Recent DNA analysis of a bone of a Neanderthal (an extinct line of archaic humans) indicates that they possessed the bitter taster allele. Therefore, the ability to taste bitter foods probably evolved more than half a million years ago, before Neanderthals and modern humans diverged from a common ancestor.

Evolutionary biologists believe that the ability to perceive bitter taste may have discouraged early humans from eating bitter-tasting plants, some of which are toxic if ingested in large quantities.

Portable Music Players and Hearing Loss

In Human Biology, 5th edition we warn that portable music players are capable of sound levels that could permanently damage one’s hearing (“Do Portable Music Players Endanger Your Hearing?” p. 293). A commission of the European Union apparently agrees. In an opinion made public yesterday, the EU Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) concluded that users of portable music players who listen at high volumes for more than an hour a day risk permanent hearing loss. Their best guess is that 5-10 percent of listeners, or up to 10 million people in the EU, fall into that category. They warn that although listening at high volumes may not seem to have an immediate effect, it still may lead to hearing loss later in life.

The European Commission is planning a conference for early 2009 to discuss the committee’s findings with industry, consumers, and governments, and to consider whether there is a need for tighter controls over portable music players. I would not be surprised to see new legislation emerge that limits the maximum sound volumes attainable with portable music players.

SCENICOR’s 80-page preliminary report, released in June for public comment, is available online.

Sensing Danger in the Air

Scientists have long known that some animals can sense danger in the air, but little was known about how they did it. Now they have a clue. According to a report in Science, specialized neural cells in mice that are part of the olfactory system can detect unidentified alarm pheromones given off by other mice under stress. The scientists collected air from around stressed mice and then exposed other mice to it. Normal mice froze (a typical danger reaction in mice) when exposed to the alarm-pheromone scented air, whereas mice whose special olfactory neural cells had been destroyed did not respond to alarm-pheromone scented air at all.

It would be interesting to know whether humans also give off alarm pheromones. Could this be an explanation for why people seem to internalize the stress of others around them?

Enhancing Taste Sensations

Scientists at San Diego-based Senomyx are searching for compounds that specifically magnify just one of the taste sensations we especially prefer (sweet, salty, or savory) or that block the sensation of bitterness. After searching through tens of thousands of synthetic and natural compounds, they now have several specific “flavor modulator” compounds that appear to work.

The commercial possibilities and health implications are almost limitless. If food product manufacturers could use less sugar in their products and still satisfy our craving for that sweet taste, perhaps people would be able to diet more effectively. Caloric intake might decline, leading to a reversal of the obesity epidemic. Less salt in our food products might mean less cardiovascular disease. Block the bitter taste receptors and children would eat more vegetables. Bitter medicines would be more palatable, improving patient compliance in taking them.

Some big companies are interested, including Coca Cola, Nestle, and Cadbury. Nestle is already using a flavor modulator from Senomyx in some of its products. Read about it in this month's Scientific American (“Magnifying Taste.” Scientific American August, 2008, pp. 96-99.) You’re likely to see “flavor modulators” or “taste enhancers” listed among your favorite products’ ingredients in the near future.

Disposable Hearing Aids

Not many people like the idea of wearing a clunky external hearing aid, and surgically implanted hearing aids are expensive. But soon there may be a better way – disposable hearing aids that slip into the ear canal, out of sight. The new hearing aid, called the Lyric, can be seen at www.lyrichearing.com. The Lyric hearing aid requires replacement every couple of months and costs about $3,000 a year. A magnet is used to turn it on and off or to control the volume.

The Lyric or other products like it may well revolutionize how we correct deficits in hearing, similar to what disposable contact lenses did for eyeglass wearers.