Noise-induced hearing loss restored in mice

searchers from the University of Michigan and Harvard Medical School in Boston, MA, may be well on the way to finding new therapies that restore noise-induced and age-related hearing loss in humans. In a new study, the team describes how they recovered hearing in mice partially deafened by noise.

 

The researchers, led by Gabriel Corfas, PhD, of the University of Michigan, publish their findings online in the journal eLife.

Approximately 50 million Americans have hearing loss in at least one ear, with around 26 million Americans aged 20-69 experiencing high-frequency hearing loss as a result of noise exposure. Hearing loss is also common as we age, affecting around 30% of adults aged 65-74 and 47% of adults aged 75 and over.

In their study, the researchers explain how they were able to increase production of a protein called Neurotrophin-3 (NT3) in mice, which they found plays a key role in communication between the ears and the brain.

NT3 allows sound signals to be sent from the ear to the brain. The protein is crucial in establishing a super-fast connection between the ear’s hair cells and nerve cells – a connection the researchers call the “ribbon synapse.” But this ribbon synapse can become damaged as a result of noise exposure or normal aging, which can lead to hearing loss.

Boosting NT3 production in mice

In their study, the researchers identified supporting cells in the inner ear that produce NT3. They set out to see what would happen if they increased production of NT3 through these supporting cells.

Fast facts about hearing loss

• Hearing loss is more common among men than women
• Around 60% of veterans returning from Iraq or Afghanistan have some form of hearing loss ortinnitus – ringing in the ears
• Approximately 2-3 in every 1,000 children in the US are born with detectable levels of hearing loss in one or both ears.

Learn more about hearing loss

They adopted a method called conditional gene recombination. This allows researchers to activate genes in particular cells by administering a drug that prompts the cells to “read” additional copies of a gene that have been inserted into them.

For this study, the team used the technique to activate additional NT3 genes that had been introduced to the supporting cells of the inner ear in mice that had been partially deafened by loud noise.

The drug tamoxifen was introduced to the supporting cells in the inner ear, which prompted them to produce extra NT3 protein. The researchers then tested the hearing of the mice through a test normally used in humans – the auditory brainstem response (ABR).

The researchers found the mice that had experienced boosted NT3 production regained their hearing over a 2-week period, compared with mice that had not had additional NT3 production.

According to the team, these findings indicate that NT3 production is important for making ribbon synapses, and that boosting production of this protein may restore noise-induced and age-related hearing loss.

The potential to restore hearing loss in humans

Corfas and his team say they now plan to investigate the role of NT3 in human ears and identify drugs that produce the same effect as the protein, offering the potential to restore hearing loss in humans.

The researchers note that the gene therapy technique used in this study has the potential to work in humans, but that a drug-based method would be “simpler” and a drug could be repeatedly administered for as long as it takes for hearing to be restored. Corfas says he already has some drug candidates in mind.

The researchers stress, however, that since the mice in this study were only partially deaf, it is unclear whether increased NT3 production would restore hearing in subjects that are fully deaf.

But the team believes their findings are promising. Corfas says:

“It has become apparent that hearing loss due to damaged ribbon synapses is a very common and challenging problem, whether it’s due to noise or normal aging. We began this work 15 years ago to answer very basic questions about the inner ear, and now we have been able to restore hearing after partial deafening with noise, a common problem for people. It’s very exciting.”

Their findings may even reach further than hearing loss. The researchers say they may offer new strategies to treat neurodegenerative diseases, in which nerve cell connections are impaired.

Medical News Today recently reported on a study from the University of Leicester in the UK, in which researchers reveal how loud noises damage hearing in more detail.

Written by Honor Whiteman

http://www.medicalnewstoday.com/articles/284159.php

 

 

Effectiveness of treatment to reduce blood clots in otolaryngology patients admitted for surgery examined

The effectiveness of a treatment to reduce blood clots among otolaryngology patients admitted for surgery appears to differ based on patient risk and the procedure.

Blood clots (venous thromboembolism [VTE], which includes deep vein thrombosis [DVT] and pulmonary embolism[PE]) are common complications in surgical patients. Treatment (primary thromboprophylaxis with anticoagulant medication [chemoprophylaxis]) can help reduce the incidence of VTE in surgical patients. But treatment should be considered in light of the risk of VTE and bleeding complications. The American College of Chest Physician’s guidelines for thromboprophylaxis do not specifically apply to otolaryngology. The authors sought to examine the effectiveness and safety of VTE chemoprophylaxis for otolaryngology patients admitted for surgery.

How the Study Was Conducted:

The study included 3,498 patients treated by surgeons at an academic medical center between September 2003 and June 2010. The authors analyzed the incidence of VTE and bleeding complications within 30 days after surgery.

Results:

Of the 1,482 patients who received VTE chemoprophylaxis, 18 (1.2 percent) developed a VTE compared with 27 of 2,016 patients (1.3 percent) who did not receive treatment. Patients with higher scores on a risk assessment were less likely to have a VTE with perioperative chemoprophylaxis (5.3 percent vs. 10.4 percent). Of the patients who underwent treatment, 3.5 percent developed a bleeding complication compared with 1.2 percent of patients without treatment. Among patients who underwent free tissue transfer, treatment decreased the incidence of VTE (2.1 percent vs. 7.7 percent) and increased bleeding complications (11.9 percent vs. 4.5 percent). In all other patients, treatment did not significantly influence the likelihood of VTE (1 percent vs. 0.6 percent) or bleeding (1.5 percent vs. 0.9 percent).

Discussion:

“Results from this study provide the basis for future research. … An examination of additional benefits and harms of VTE prophylaxis is warranted, including its impact on mortality due to PE. Free tissue transfer patients merit special analysis when developing recommendations for VTE prophylaxis because of the high risk of both VTE and bleeding. … Finally, further tests of the incidence of VTE by risk level and of the effectiveness and safety of chemoprophylaxis should be conducted for other otolaryngology patients, in populations large enough to produce sufficiently powered analyses.”

http://www.medicalnewstoday.com/releases/283314.php

 

Viral infection causes bacteria to colonize privileged sites like the middle ear

Influenza infection can enhance the ability of the bacterium Streptococcus pneumonia to cause ear and throat infections, according to research published ahead of print in the journal Infection and Immunity.

In the study, the investigators infected mice with either influenza alone, pneumococci alone, or both at once, and then monitored the populations of bacteria and virus over time. They also monitored the mice for development of middle ear infection.

Influenza infection enhanced the bacterium’s ability to colonize the nasopharynx, and to infect the normally sterile middle ear.

“We learned that once influenza virus is introduced, all of the “rules” regarding phase variants are out the window,” says corresponding author W. Edward Swords of Wake Forest University, Winston-Salem, NC. Phase variation refers to the fact that the colonizing bacteria have transparent cell surfaces, while those that spread within the host have opaque surfaces.

“However, in the presence of influenza, opaque variants can readily colonize the nasopharynx, and transparent variants can persist in the ear,” says Swords. “This indicates that the host environs are more permissive for infection by the entire bacterial population.”

Furthermore, recent research had shown that influenza interferes with innate immunity in a way that enables pneumococci to flourish. In this research, Swords shows that that interference manifests as increased inflammatory responses at the mucosal surface in the influenza-infected mice, such as within the middle ear, and in the nasopharynx.

“As with most pneumococcal infections, it should be appreciated that localized nonlethal infections are much more common than the rapidly lethal presentations,” says Swords. “For example, influenza is a contributing factor in otitis media (middle ear infections) in children.”

“If we can understand why and how viral infection causes bacteria to colonize privileged sites like the middle ear, we will better know what aspects of disease to focus on with preventive or therapeutic treatments,” says Swords.

http://www.medicalnewstoday.com/releases/282910.php

Picture courtesy to www.chori.org

 

 

Next-generation hearing aids emulate fly’s ability to pinpoint sound

ere is a fly that can locate a cricket from the sound it makes, despite other noises in the background. Yet the hearing mechanism that helps the fly do this spans only 1.5 mm, which is 50 times smaller than the wavelength of the cricket’s chirp. Now, engineers have found a way to mimic the fly’s super-hearing in a tiny device that does not require a bulky battery.

A paper describing the work is published in the journal Applied Physics Letters.

The engineers, from the Cockrell School of Engineering at the University of Texas at Austin, say the new device could be used in a new generation of hypersensitive hearing aids that use intelligent microphones to select only those sounds or conversations that the wearer wants to hear.

Fly’s sophisticated hearing can locate a cricket with remarkable accuracy

Neal Hall, an assistant professor in the Cockrell School’s Department of Electrical and Computer Engineering, and his team of graduate students, drew their inspiration from pioneering work by Ronald Miles at Binghamton University, NY, and Ronald Hoy at Cornell University, Ithaca, NY.

 

They were the first to describe the technological potential of emulating the super-hearing mechanism of the yellow-colored parasitoid flyOrmia ochracea, which stalks and locates male field crickets from their chirps and lays live larvae on and around them.

The fly can locate the cricket with remarkable accuracy because it has a sophisticated sound processing mechanism that determines the direction of the sound within an angle of 2 degrees.

Using the fly’s super-evolved hearing structure as a model, Prof. Hall and colleagues made a tiny pressure-sensing device out of silicon. With a span of only 2 mm, the device is nearly the same size as the fly’s hearing organ.

Unlike many insects, the reason humans and other mammals can pinpoint the source of a sound is because we have a much larger distance between our ears. The sound processing mechanism in our brains uses the time difference in the arrival of the sound at the two ears to locate the source.

But insects’ bodies are generally too small to do this – the sound waves effectively hit both sides almost at the same time.

That is, except for insects like O. ochracea – it can locate the direction of a cricket’s chirp even though its ears are less than 2 mm apart. Its highly evolved hearing mechanism can sense the 4 millisecond gap between the sound entering one ear and the other. It also amplifies this time difference using a “teeter-totter” or “see-saw” mechanism that allows it to locate the cricket with remarkable accuracy.

Engineers emulated fly’s hearing mechanism using a flexible beam

To replicate the fly’s hearing mechanism, the team made a flexible beam incorporating piezoelectric materials that allowed them to use the flexing and rotation of the beam as a way to measure sound pressure and pressure gradient at the same time.

While other teams have already tried to build hearing devices that emulate the fly’s super-hearing, Prof. Neal and colleagues are the first to use piezoelectric materials, which convert mechanical pressure into electrical signals and allow the device to work with very little power.

“Because hearing aids rely on batteries, minimizing power consumption is a critical consideration in moving hearing-aid device technology forward,” says Prof. Hall.

He sees this technology being attractive to people with hearing problems in the future. While as many as 1 in 10 Americans could benefit from a hearing aid, currently only a fifth of this number use one, he adds.

He says many believe the main reason for the gap is hearing aid wearers’ dissatisfaction with the devices:

“Turning up the volume to hear someone across from you also amplifies all of the surrounding background noise – resembling the sound of a cocktail party.”

As well as taking hearing aid technology to a new level, the device could also be useful in military and defense applications. For example, in dark environments where visual cues are absent.

Funds from the Defense Advanced Research Projects Agency (DARPA) helped finance the study.

In February 2014, Medical News Today reported how researchers have developed a new low-powered chip that offers the prospect of cochlear implants without external hardware.

Written by Catharine Paddock PhD

http://www.medicalnewstoday.com/articles/280000.php

 

 

 

Tinnitus affects processing of emotions

Patients with persistent ringing in the ears – a condition known as tinnitus – process emotions differently in the brain from those with normal hearing, researchers report in the journal Brain Research.

Tinnitus afflicts 50 million people in the United States, according to the American Tinnitus Association, and causes those with the condition to hear noises that aren’t really there. These phantom sounds are not speech, but rather whooshing noises, train whistles, cricket noises or whines. Their severity often varies day to day.

University of Illinois speech and hearing science professor Fatima Husain, who led the study, said previous studies showed that tinnitus is associated with increased stress, anxiety, irritability and depression, all of which are affiliated with the brain’s emotional processing systems.

“Obviously, when you hear annoying noises constantly that you can’t control, it may affect your emotional processing systems,” Husain said. “But when I looked at experimental work done on tinnitus and emotional processing, especially brain imaging work, there hadn’t been much research published.”

She decided to use functional magnetic resonance imaging (fMRI) brain scans to better understand how tinnitus affects the brain’s ability to process emotions. These scans show the areas of the brain that are active in response to stimulation, based upon blood flow to those areas.

Three groups of participants were used in the study: people with mild-to-moderate hearing loss and mild tinnitus; people with mild-to-moderate hearing loss without tinnitus; and a control group of age-matched people without hearing loss or tinnitus. Each person was put in an fMRI machine and listened to a standardized set of 30 pleasant, 30 unpleasant and 30 emotionally neutral sounds (for example, a baby laughing, a woman screaming and a water bottle opening). The participants pressed a button to categorize each sound as pleasant, unpleasant or neutral.

The tinnitus and normal-hearing groups responded more quickly to emotion-inducing sounds than to neutral sounds, while patients with hearing loss had a similar response time to each category of sound. Over all, the tinnitus group’s reaction times were slower than the reaction times of those with normal hearing.

Activity in the amygdala, a brain region associated with emotional processing, was lower in the tinnitus and hearing-loss patients than in people with normal hearing. Tinnitus patients also showed more activity than normal-hearing people in two other brain regions associated with emotion, the parahippocampus and the insula. The findings surprised Husain.

“We thought that because people with tinnitus constantly hear a bothersome, unpleasant stimulus, they would have an even higher amount of activity in the amygdala when hearing these sounds, but it was lesser,” she said. “Because they’ve had to adjust to the sound, some plasticity in the brain has occurred. They have had to reduce this amygdala activity and reroute it to other parts of the brain because the amygdala cannot be active all the time due to this annoying sound.”

Because of the sheer number of people who suffer from tinnitus in the United States, a group that includes many combat veterans, Husain hopes her group’s future research will be able to increase tinnitus patients’ quality of life.

“It’s a communication issue and a quality-of-life issue,” she said. “We want to know how we can get better in the clinical realm. Audiologists and clinicians are aware that tinnitus affects emotional aspects, too, and we want to make them aware that these effects are occurring so they can better help their patients.”

http://www.medicalnewstoday.com/releases/278846.php

Picture courtesy of tinnitusart.com

 

 

 

Study identifies ‘new risks’ for mouth and throat cancers

Poor oral health and irregular dental checks can increase the risk of oral cancer, a new study has found.

The International Agency for Research on Cancer report also found excessive use of mouthwash – more than three times a day – can also increase risk.

Smoking, heavy drinking and “low socio-economic status” are established risk indicators of mouth and throat cancers.

The study covered 1,962 cancer patients and a further 1,993 control subjects across nine countries in Europe.

The study was led by the Leibniz Institute for Prevention Research and Epidemiology in Bremen, Germany, (Bips) and backed by researchers from Glasgow University Dental School.

‘Really important’

Prof Wolfgang Ahrens, deputy director of Bips, described the study findings as “really important”.

“Up until now, it was not really known if these dental risk factors were independent of the well known risks for mouth and throat cancers – smoking, alcohol and low socio-economic status,” he said.

Prof Ahrens said the report findings were highly “nuanced” and there was an interconnectedness of many of the risk factors.

The definition of poor oral health included people who had complete or part dentures and people with persistently bleeding gums.

Dr David Conway, clinical senior lecturer at Glasgow University Dental School, said: “People should not assume that if they wear dentures and have none of their own teeth left, they have no need to see a dentist.

“On the contrary, even if you have got dentures, you should make sure you go for regular check-ups.”

People with poor dental care were defined as those who hardly ever or never brushed their teeth or visited the dentist.

Dr Conway said the frequency of dental visits should be determined by a dentist’s risk assessment and if people fell into the low-risk category it could be once a year or even every two years.

“It is not a case of one size fits all,” he added.

“Visits could be six-monthly, but certainly not five-yearly.”

Mouthwash ‘risk’

The research team said the possible role of mouthwash as a risk factor would require further research.

They were unable to analyse the types of mouthwash used many years ago by participants in the study.

Dr Conway added: “I would not advise routine use of mouthwash, full stop.

“There are occasions and conditions for which a dentist could prescribe a mouthwash – it could be that a patient has a low salivary flow because of a particular condition or medicine they are taking.

“But for me, all that’s necessary, in general, is good regular brushing with a fluoride toothpaste and flossing combined with regular check-ups by a dentist.”

The findings of the study have been published in Oral Oncology.

http://www.bbc.com/news/uk-scotland-glasgow-west-26875793

 

 

 

Voice-Care®: a new low-cost device developed for voice monitoring

A new device to monitor voice professionals as well as to track vocal changes that are due to chronic diseases and physical or psychological stress

Functional dysphonia is the nightmare of professional singers and even more so of amateur actors, but also of teachers and call-centre operators, to mention only a few of the workers exposed to the risk of vocal damage due to an excessive effort or misuse of the voice. This problem is much more common than people realize and the intervention of specialists, such as speech therapists or phoniatricians, often takes place when the dysphonia is already chronic and the risk of compromising the use of the voice even permanently is very high. Among the occupational categories most at risk to voice diseases, teachers is one of the most affected, followed by performers (singers and actors). In the U.S. it is estimated that up to 20% of teachers and 11% of the singers have clinical voice disorders.

Voice-Care® can be used to monitor voice professionals as well as to track vocal changes that are due to chronic diseases and physical or psychological stress. How can technology help in solve these problems? The Voice-Care® device is essentially made up of a contact microphone and a small data-processing unit. It has been developed at the Politecnico di Torino thanks to a joint project between Prof. Alessio Carullo (Department of Electronics and Telecommunications) and Prof. Arianna Astolfi (Department of Energy). Alessio Carullo is an expert in the field of electrical and electronic measurements, while Arianna Astolfi works in the field of applied acoustics.

It is a simple low-cost device with sophisticated functionalities, which is able to store a large amount of reliable data and provide an objective estimation of the stress the vocal folds are subjected to. It is a useful tool to prevent damage from dysphonia and to highlight bad acoustic conditions that are responsible for this damage. Specific tests have shown the effectiveness of the device in highlighting improvements in the use of voice by teachers after an acoustic intervention in school environments.

The Voice-Care® device is easy to wear and does not interfere with the patient’s normal activities. It gives the possibility of analysing time intervals over a range of tens of seconds to several hours, up to the whole working day. A particular feature is the traceability assurance of the obtained measurements, thanks to the implementation of suitable calibration procedures for each of the estimated parameters. Furthermore, its low cost (some hundreds of euros for an industrial production) could offer the possibility of performing extensive experimental campaigns.

A first experimental test that has involved 30 primary-school teachers has been performed. This test has allowed the bad acoustic conditions of the investigated classroom to be identified and then corrected. In some cases, the reduction of the vocal effort and vocal load of teachers has been confirmed by repeating the test after an acoustic intervention.

Another possible application of the Voice-Care® device is the diagnosis of vocal apparatus diseases. A cooperation has been set up between the present research group and the group of Ear Nose and Throat specialists of the Dept. of Surgical Sciences at the University of Turin, which is coordinated by prof. Giancarlo Pecorari. The device is available to public and private organizations for possible collaborations with the aim of conducting experimental campaigns that involve categories at risk to vocal diseases.

 

http://www.medicalnewstoday.com/releases/276633.php

 

Researchers transplant regenerated oesophagus

Tissue engineering has been used to construct natural oesophagi, which in combination with bone marrow stem cellshave been safely and effectively transplanted in rats. The study, published in Nature Communications, shows that the transplanted organs remain patent and display regeneration of nerves, muscles, epithelial cells and blood vessels.

The new method has been developed by researchers at Karolinska Institutet in Sweden, within an international collaboration lead by Professor Paolo Macchiarini. The technique to grow human tissues and organs, so called tissue engineering, has been employed so far to produce urinary bladder, trachea and blood vessels, which have also been used clinically. However, despite several attempts, it has been proven difficult to grow tissue to replace a damaged oesophagus.

In this new study, the researchers created the bioengineered organs by using oesophagi from rats and removing all the cells. With the cells gone, a scaffold remains in which the structure as well as mechanical and chemical properties of the organ are preserved. The produced scaffolds were then reseeded with cells from the bone marrow. The adhering cells have low immunogenicity which minimizes the risk of immune reaction and graft rejection and also eliminates the need for immunosuppressive drugs. The cells adhered to the biological scaffold and started to show organ-specific characteristics within three weeks.

The cultured tissues were used to replace segments of the oesophagus in rats. All rats survived and after two weeks the researchers found indications of the major components in the regenerated graft: epithelium, muscle cells, blood vessels and nerves.

“We believe that these very promising findings represent major advances towards the clinical translation of tissue engineered esophagi”, says Paolo Macchiarini, Director of Advanced center for translational regenerative medicine (ACTREM) at Karolinska Institutet.

Tissue engineered organs could improve survival and quality of life for the hundreds of thousands of patients yearly diagnosed with oesophageal disorders such as cancer, congenital anomalies or trauma. Today the patients’ own intestine or stomach is used for esophageal replacements, but satisfactory function rarely achieved. Cultured tissue might eliminate this current need and likely improve surgery-related mortality, morbidity and functional outcome.

The current study was conducted in collaboration with the Texas Heart Institute in the U.S., as well as universities in Italy, Russia, and Germany. It was supported financially by, among others, the Swedish Research Council, the Stockholm County Council through the ALF agreement, and the European Union’s Seventh Framework Programme. The equipment used in the study was developed by the company Harvard Apparatus Regenerative Technology.

Picture courtesy of www.sciencedaily.com

http://www.medicalnewstoday.com/releases/275511.php

Two breath compounds could be associated with larynx cancer

Researchers at the Rey Juan Carlos University and the Alcorcón Hospital (Madrid) have compared the volatile substances exhaled by eleven people with cancer of larynx, with those of another twenty healthy people. The results show that the concentrations of certain molecules, mainly ethanol and 2-butanone, are higher in individuals with carcinoma, therefore they act as potential markers of the disease.

Human breath contains thousands of volatile organic compounds (VOC) and some of them can be used as non-invasive biomarkers for various types of head and neck cancers as well as cancer of the larynx.

This was shown in the experiment carried out by scientists from the Rey Juan Carlos University (URJC) with 31 volunteers: 20 healthy subjects (half of which are smokers) and 11 with cancer of the larynx in various phases of the disease and who are being treated in the Alcorcón Hospital in Madrid.

The results, published in the journal Chromatographia, reveal that the air exhaled by the more seriously ill patients – in a stage called T3 – contains different concentrations of seven compounds compared with the levels of healthy people or even those with a less developed tumour (T1).

Specifically, in the graphics of individuals with advanced cancer, the peaks that represent ethanol (C2H6O) and 2-butanone (C4H8O) are particularly significant. These two compounds therefore become potential markers of laryngeal carcinoma.

“At the moment it is still a preliminary study and a wider sample has to be obtained,” Rafael García, professor of Chemical Engineering at the URJC and co-author of the study told SINC, “but it is a step in the right direction, an alternative with regard to identifying biomarkers, not only for this type of cancer but for other more prevalent and serious ones such as lung cancer, where early detection is key”.

As part of the experiment, the researchers asked the participants to breathe into tedlar bags after fasting for at least eight hours so there was no leftover food or drink on their breath.

The samples were then analysed with solid phase micro-extraction, gas chromatography and mass spectrometry techniques, which enable very small amounts of a substance to be separated and identified. The concentrations are around or slightly above the equipment’s detection limits (40 nanograms/mL), which is equivalent to 40 ppb or parts per billion.

The ultimate aim of the research is to “create an electronic nose that can be used in hospitals and health centres for the early detection of these types of diseases,” concluded Rafael García. This team, together with other Spanish and foreign research groups, is working hard to develop sensors capable of detecting diseases through breath analysis.

Head and neck cancers represent between 5% and 10% of all malignant tumours currently diagnosed in Spain. Every year nearly half a million new cases are detected worldwide, mainly attributed to tobacco and alcohol use and approximately 90% are laryngeal cancer. The study also identified four markers in the exhaled breath that are typical of smokers, such as benzene and furfural.

http://www.medicalnewstoday.com/releases/276057.php

 

Human sniff range exceeds 1 trillion odors

 

A new study published in the journal Science finds that the human sense of smell can detect more than 1 trillion odors, far exceeding the number previous studies have indicated.

Humans can discriminate several million different colors and nearly half a million sounds or tones, so by showing we can discriminate over 1 trillion odors, the study places the human sense of smell in a different league altogether.

The authors write that the study “demonstrates that the human olfactory system, with its hundreds of different olfactory receptors, far outperforms the other senses in the number of physically different stimuli it can discriminate.”

Study leader Dr. Andreas Keller, of the Laboratory of Neurogenetics and Behavior at Rockerfeller University in New York, NY, says even 1 trillion may be an underestimate:

“The message here is that we have more sensitivity in our sense of smell than for which we give ourselves credit. We just don’t pay attention to it and don’t use it in everyday life.”

Head of the Lab, Prof. Leslie Vosshall, says it was generally believed that the range of the human sense of smell was around 10,000, and adds:

“Everyone in the field had the general sense that this number was ludicrously small, but Andreas was the first to put the number to a real scientific test.”

The quality of an odor is a complex thing. The smells we come across in everyday life actually comprise many different molecules, of which we sense only a few. For example a rose scent has 275 molecules, but we only sense a small proportion of them.

Sense of smell is more complicated to study

This means studying sense of smell is not as straightforward as examining sight or hearing. It is multidimensional in comparison.

For the study, Dr. Keller and colleagues invited volunteers to sniff vials of odors that held different mixes of 128 odor molecules responsible for scents ranging from spearmint to orange to anise.

The vials contained combinations of 10, 20 and 30 of the 128 odor molecules with different proportions of them in common.

The volunteers were presented with three vials at a time. Two of them contained identical mixtures of odor molecules, and the third one was different. They were asked to pick the odd one out.

The researchers found that while some volunteers were much better at picking the odd one out than others, on average they could distinguish between mixtures that shared as much as 51% of the same components. Above this proportion, most volunteers struggled to pick the odd one out. This was the case regardless of whether the mixtures contained 10, 20 or 30 odors.

Even 1 trillion may be an underestimate

From these results, the researchers extrapolated an estimate of the total number of distinguishable mixtures, arriving at the 1 trillion figure.

However, the team believes even 1 trillion may be an underestimate, because the real world contains many more odors that can be mixed in many more different ways.

Dr. Keller suggests our ancestors made more use of their sense of smell. We now hold our noses high above the ground, and by having daily showers and storing our food in a refrigerator we have effectively cut ourselves off from many of the odor encounters much valued by our forebears.

“This could explain our attitude that smell is unimportant, compared to hearing and vision,” he adds.

In December 2013 Medical News Today reported a study that suggested we each live in a unique odor world. There, the researchers found as much as 30% of the large array of human smell receptors differs between any two individuals.

Written byCatharine Paddock PhD

http://www.medicalnewstoday.com/articles/274351.php

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