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Humans Susceptible To Hidden Feelings Of Sex And Fear

Posted on: Thursday, 4 December 2008, 13:50 CST

For anyone who has experienced a sudden unexplained rush of feelings, such as sparks upon meeting someone for the first time or impulsive fears when boarding a plane despite being totally at ease with air travel, scientists have a possible explanation.

These seemingly illogical and disparate feelings may be reactions to other people's pheromones.

Although pheromones are found across the animal world from insects to mammals, research into human pheromones has been hampered by
bungling experimental designs and dubious commercial connections.  As a result, the entire field has been clouded with a tinge of disrepute.

"It's not so much that the jury is out, but that the jury has been dismissed before the trial has begun," Mike Meredith, a neuroscientist at Florida State University neuroscientist, told New Scientist magazine.

However, this is beginning to change with new evidence emerging that pheromones work differently than previously believed.  The evidence is supported by a growing number of brain-imaging studies in humans, and is convincing some scientists that humans do indeed make and respond to pheromones.

Some now believe it's time to stop asking if human pheromones exist and start investigating precisely how they affect our behavior.
The term pheromone was first used in 1959 to describe chemicals released by insects that triggered hard-wired behaviors in other members of the same species.  The standard example is female moths releasing sex pheromones to attract a mate.   However, when pheromones were discovered in mammals, their more sophisticated behavior required an expansion of this definition, something scientists have been debating ever since.   One such definition says that pheromones are chemicals that send a message that benefit both sender and receiver, in evolutionary terms.

But regardless of the precise definition, pheromones are a significant part of the animal world.  Indeed, animals use the chemicals to transmit relevant information about themselves, such as gender or sexual receptiveness, and to alter the physiology of others, for example, by stimulating ovulation.  Behavior-changing or "releaser" pheromones also used to directly affect the behavior of others, for instance, by including sexual attractants and the alarm pheromones. Many mammals, such as rats and deer, use them to put others on alert without revealing their location with an alarm call.

However, for years it was believed that humans did not produce or respond to any of these types of pheromones, due in part to a reluctance to acknowledge that humans respond in such an "animal" way.   Furthermore, there is no clear method to determine how they might act on the human brain.  In animals, pheromones are typically detected by the vomeronasal organ (VNO), a pair of receptors inside the nose that detect airborne pheromones and relay messages directly to the brain.  

While humans have something resembling a VNO, there are no neurons linking it to the brain.  Interestingly, human have the genes required for a working VNO, they just no longer code for functional pheromone receptor proteins.  The obvious explanation was that we lost this ability at some point in our evolution.

However, that hasn't stopped researchers from speculating about human pheromones. In 1971, Harvard University social psychologist Martha McClintock famously reported that women who live together gradually synchronize their menstrual cycles, and suggested this might be due to pheromones.  Her conclusion was based on evidence she and her colleague, Kathleen Stern, had gathered in 1998 that showed sweat from women in different stages of their menstrual cycle either extended or shortened the cycles of other women.  However, despite the evidence, McClintock's hypothesis remains contentious because nobody has yet isolated the actual chemicals that cause the effect.

The idea that pheromones play a role in human sexual attraction is even more contentious, due in part to some high-profile research conducted by David Berliner and Luis Monti-Bloch of the University of Utah in the mid-1990s . The scientists claimed that when they exposed people to reproductive hormones from the opposite sex, they could see an electrical response from the part of the nose where the vomeronasal organ would be.

In women, cells in this region responded most strongly to extracts containing androstadienone, a testosterone-related hormone found in male sweat.  Men reacted similarly to estratetraenol, found in female urine.

The scientists also found that releasing these compounds into the air subconsciously altered mood, inducing a calming effect on the opposite sex.   While groundbreaking, the research was viewed with skepticism because of Berliner's financial interest in a brand of pheromone-laced perfume called Realm.  And with no compelling evidence for a functional human VNO, many people the dismissed the research outright. 
Despite this questionable past, many researchers still insist that human pheromones are indeed real. Johan Lundstrom, a neuropsychologist at the Monell Chemical Senses Center in Philadelphia, has shown that women can consistently sniff out their sisters from friends, distinguishing strangers even when they are unaware of any difference in odor. A similar effect can be seen in humans’ well-known ability to select mates based on genetic signatures evident in their body odor.  This phenomenon serves as a subconscious indicator of the compatibility of their immune systems.

To Lundstrom, this provides convincing evidence that human pheromones are real, and that most researchers have a blind spot in giving proper consideration to the field. 

"If you asked scientists whether one human can convey some sort of social message to another in their body odor, 99.9 per cent of them would say yes," he told New Scientist.

"If you ask them if humans have pheromones they'll say 'that hasn't been demonstrated'. It's a semantic issue."

But that may now be changing, due to the recent discovery that some animals detect pheromones using their normal olfactory system, not the VNO.

"There are several well-established examples of pheromone communication in animals that don't require the VNO," said Meredith, who specializes in the animal VNO.

For instance, recent research found that mice detect alarm pheromones through nerve cell bundles at the tip of their nose that are hard-wired into the normal olfactory system.

Brain-imaging studies have also confirmed the idea that humans may respond to sex pheromones. In a series of recent studies, neuroscientist Ivanka Savic of the Karolinska Institute in Sweden, exposed people to androstadienone and observed the response in their anterior hypothalamus, a part of the brain believed to play a role in sexual behavior.

One study, published in 2005, showed that androstadienone activated this brain region in homosexual men and heterosexual women, but not in heterosexual men or homosexual women.   Her later work found the opposite effect with estratetraenol.

Brain-imaging studies are suggest that humans release and respond to alarm pheromones. Although these have been less examined than those involved in attraction,  a handful of psychological studies claim to show that humans can detect the "scent of fear".

In 1999, psychologist Denise Chen asked a group of volunteers to sniff sweat from people who had watched either funny or scary videos, and found that more the participants successfully distinguished the fearful sweat.

In a similar study in 2002, Kerstin Ackerl from the University of Vienna in Austria found that women appeared to be able to detect the scent of fear.   In that experiment, 60 women rated sweat from women who had watched a scary movie as stronger, less pleasant than sweat from women who had viewed a neutral movie.

However, both studies used relatively small sample sizes and failed to control for certain factors, such as how strongly different people had reacted to the scary movie.  They also had a tendency to rely on questionnaires with leading questions about whether the sweat smelled like someone who was happy, angry or frightened.

But a new study by Lilianne Mujica-Parodi at Stony Brook University in New York may have eliminated some of these problems by examining the direct effect of “fear sweat” on the brain.

In conducting the study, which is not yet published, Mujica-Parodi ‘s team taped absorbent pads to the armpits of 40 volunteers who were about to skydive for the first time. 

The scientists’ collected the sweat as the participants plummeted towards the Earth.  Back in the lab, they then transferred the sweat, in addition to samples of normal sweat, into nebulizers and asked a second group of volunteers to breathe the samples while lying in an fMRI scanner.  The volunteers were not informed of the nature of the experiment.  As expected, the volunteers showed significantly more activity in the amygdala and hypothalamus, the brain's fear centers, when inhaling the fear sweat.

It’s unclear whether or not the volunteers actually felt frightened after inhaling the “fear sweat”.  In order to not bias the results, the researchers refrained from asking this question. 

But researchers say the fact that participants’ fear circuitry lit up in response to the purported pheromone "indicates that there may be a hidden biological component to human social dynamics, in which emotional stress is, quite literally, 'contagious'".
Savic and Mujica-Parodi's work adds substantial weight to the notion that humans produce and respond to pheromones.  Nevertheless, many remain skeptical.

Lundstrom, for instance, believes the picture is not quite complete.

"To my mind, activation of brain is not enough," he told New Scientist.

"I use brain imaging in my work but I like to see that there is a behavioral response - and to see it consistently. Not just once, but every time."

To provide this evidence, any human pheromone must be identified, synthesized and, most critically, validated as to whether or not it truly triggers consistent behavioral changes.  Only then will we be able to definitively conclude the existence of pheromones.
It won’t be easy.  As Lundstrom emphasizes, human body odor contains more than 2000 unique compounds.

"Picking one is like putting a blindfold on someone, spinning them around and asking them to hit the centre of a dartboard," he said.

But if human pheromones are indeed identified, it would invite a whole new debate about their use, with some uses raising potential concerns. 

For instance, a pheromone-containing perfume to attract members of the opposite sex may be not be controversial, but the idea of synthesizing a fear-inducing substance is an entirely different matter.  The issue could become particularly contentious in light of the fact that Mujica-Parodi's research was funded by DARPA, the research arm of the U.S. military. 

Upon seeing researchers present their work at a recent conference, one blogger wondered whether the military might employ pheromones to send people "stampeding like spooked cattle".  For its part, DARPA, says it is unaware of any military plans for fear pheromones and has no plans to fund further research in the field.

Simon Wessely, a psychiatrist at the King's Centre for Military Health Research at King's College London and a consultant to the British army, also called the idea scientifically implausible.  He referenced studies conducted by Stanley Schachter at the Massachusetts Institute of Technology during the 1960s, in which participants were injected with adrenalin to induce the physical symptoms of fear.  The study found that participants only became fearful in threatening situations, suggesting that context is a critical part of how the pheromones work.

"You can generate the physical symptoms of fear but people don't necessarily get scared," Wessely told New Scientist.
Likewise, Lundstrom found that women only exhibit a reliable response to androstadienone in the presence of a man.  Furthermore, since none of the participants felt compelled to jump on the male, it is reasonable to conclude that any pheromone-induced effects are probably small and influenced by other factors.

Whether or not it's worth investing in a pheromone-laced aftershave for a big date, Lundstrom is cautious.

"Most of these companies are selling andosterone - it's a pig pheromone that 60 per cent of people can't smell and the rest think smells like urine," he says.

It’s probably better to brush up on one’s conversational skills instead, he said.

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Source: redOrbit staff

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