Scientists discover an organizing principle for our sense of smell

Scientists discover an organizing principle for our sense of smell

  12:13:00 AM    Science Lover

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The fact that certain smells cause us pleasure or disgust would seem to be a matter of personal taste. But new research at the Weizmann Institute shows that odors can be rated on a scale of pleasantness, and this turns out to be an organizing principle for the way we experience smell. The findings, which appeared today in Nature Neuroscience, reveal a correlation between the response of certain nerves to particular scents and the pleasantness of those scents. Based on this correlation, the researchers could tell by measuring the nerve responses whether a subject found a smell pleasant or unpleasant.

Our various sensory organs are have evolved patterns of organization that reflect the type of input they receive. Thus the receptors in the retina, in the back of the eye, are arranged spatially for efficiently mapping out visual coordinates. The structure of the inner ear, on the other hand, is set up according to a tonal scale. But the organizational principle for our sense of smell has remained a mystery: Scientists have not even been sure if there is a scale that determines the organization of our smell organ, much less how the arrangement of smell receptors on the membranes in our nasal passages might reflect such a scale.

A team headed by Prof. Noam Sobel of the Weizmann Institute's Neurobiology Department set out to search for the principle of organization for smell. Hints that the answer could be tied to pleasantness had been seen in research labs around the world, including that of Sobel, who had previously found a connection between the chemical structure of an odor molecule and its place on a pleasantness scale. Sobel and his team thought that smell receptors in the nose – of which there are some 400 subtypes – could be arranged on the nasal membrane according to this scale. This hypothesis goes against the conventional view, which claims that the various smell receptors are mixed -- distributed evenly, but randomly, around the membrane.



In the experiment, the researchers inserted electrodes into the nasal passages of volunteers and measured the nerves' responses to different smells in various sites. Each measurement actually captured the response of thousands of smell receptors, as these are densely packed on the membrane. The scientists found that the strength of the nerve signal varies from place to place on the membrane. It appeared that the receptors are not evenly distributed, but rather, that they are grouped into distinct sites, each engaging most strongly with a particular type of scent. Further investigation showed that the intensity of a reaction was linked to the odor's place on the pleasantness scale. A site where the nerves reacted strongly to a certain agreeable scent also showed strong reactions to other pleasing smells and vice versa: The nerves in an area with a high response to an unpleasant odor reacted similarly to other disagreeable smells. The implication is that a pleasantness scale is, indeed, an organizing principle for our smell organ.

But does our sense of smell really work according to this simple principle? Natural odors are composed of a large number of molecules – roses, for instance, release 172 different odor molecules. Nonetheless, says Sobel, the most dominant of those determine which sites on the membrane will react the most strongly, while the other substances make secondary contributions to the scent.

'We uncovered a clear correlation between the pattern of nerve reaction to various smells and the pleasantness of those smells. As in sight and hearing, the receptors for our sense of smell are spatially organized in a way that reflects the nature of the sensory experience,' says Sobel. In addition, the findings confirm the idea that our experience of smells as nice or nasty is hardwired into our physiology, and not purely the result of individual preference. Sobel doesn't discount the idea that individuals may experience smells differently. He theorizes that cultural context and personal experience may cause a certain amount of reorganization in smell perception over a person's lifetime.

More information: DOI: 10.1038/nn.2926

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Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

  10:10:00 AM    Science Lover

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What do a herd of gazelles and a fluffy mass of clouds have in common? A mathematical formula that describes the population dynamics of such prey animals as gazelles and their predators has been used to model the relationship between cloud systems, rain and tiny floating particles called aerosols. This model may help climate scientists understand, among other things, how human-produced aerosols affect rainfall patterns. The research recently appeared in the Proceedings of the National Academy of Sciences (PNAS).

A new mathematical model may help climate scientists 
understand, among other things, how human-produced 
aerosols affect rainfall patterns. (Credit: © Brian 
Jackson / Fotolia)

Clouds are major contributors to the climate system. In particular the shallow marine stratocumulus clouds that form huge cloud decks over the subtropical oceans cool the atmosphere by reflecting part of the incoming solar energy back to space. Drs. Ilan Koren of the Weizmann Institute's Environmental Sciences and Energy Research Department (Faculty of Chemistry) and Graham Feingold of the NOAA Earth System Research Laboratory, Colorado, found that equations for modeling prey-predator cycles in the animal world were a handy analogy for cloud-rain cycles: Just as respective predator and prey populations expand and contract at the expense of one another, so too rain depletes clouds, which grow again once the rain runs out. And just as the availability of grass affects herd size, the relative abundance of aerosols -- which "feed" the clouds as droplets condense around them -- affects the shapes of those clouds. A larger supply of airborne particles gives rise to more droplets, but these droplets are smaller and thus remain high up in the cloud rather than falling as rain.

In previous research, Feingold and Koren had "zoomed in" to discover oscillations in convective cells in marine stratocumulus. Now they returned to their data, but from a "top down" angle to see if a generalized formula could reveal something about these systems. Using just three simple equations, they developed a model showing that cloud-rain dynamics mimic three known predator-prey modes. Like gazelles and lions, the two can oscillate in tandem, the "predator" rain cycle following a step behind peak cloud formation. Or the two can reach a sort of steady state in which the clouds are replenished at the same rate as they are diminished (as in a light, steady drizzle). The third option is chaos -- the crash that occurs when predator populations get out of hand or a strong rain destroys the cloud system.



The model shows that as the amounts of aerosols change, the system can abruptly shift from one state to another. It also reveals a bifurcation -- two scenarios at different ends of the aerosol scale that lend themselves to stable patterns. In the first, relatively low aerosol levels lead to clouds in which development depends heavily on aerosol concentrations. In the second, high levels produce saturation; these clouds depend solely on the initial environmental conditions.

Using this so-called systems approach, says Koren, "can open new windows to view and understand the emergent behavior of the complex relationships between clouds, rain and aerosols, giving us a more useful view of the big picture and helping us to understand how shifting aerosol levels can lead to different climate patterns."

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How Social Pressure Can Affect What We Remember: Scientists Track Brain Activity as False Memories Are Formed

How Social Pressure Can Affect What We Remember: Scientists Track Brain Activity as False Memories Are Formed

  10:02:00 AM    Science Lover

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How easy is it to falsify memory? New research at the Weizmann Institute shows that a bit of social pressure may be all that is needed. The study, which appears in the journal Science, reveals a unique pattern of brain activity when false memories are formed -- one that hints at a surprising connection between our social selves and memory.

New research reveals a unique pattern of brain 
activity when false memories are formed -- one 
that hints at a surprising connection between 
our social selves and memory. (Credit: Image 
courtesy of Weizmann Institute of Science)

The experiment, conducted by Prof. Yadin Dudai and research student Micah Edelson of the Institute's Neurobiology Department with Prof. Raymond Dolan and Dr. Tali Sharot of University College London, took place in four stages. In the first, volunteers watched a documentary film in small groups. Three days later, they returned to the lab individually to take a memory test, answering questions about the film. They were also asked how confident they were in their answers.

They were later invited back to the lab to retake the test while being scanned in a functional MRI (fMRI) that revealed their brain activity. This time, the subjects were also given a "lifeline": the supposed answers of the others in their film viewing group (along with social-media-style photos). Planted among these were false answers to questions the volunteers had previously answered correctly and confidently. The participants conformed to the group on these "planted" responses, giving incorrect answers nearly 70% of the time.

But were they simply conforming to perceived social demands, or had their memory of the film actually undergone a change? To find out, the researchers invited the subjects back to the lab to take the memory test once again, telling them that the answers they had previously been fed were not those of their fellow film watchers, but random computer generations. Some of the responses reverted back to the original, correct ones, but close to half remained erroneous, implying that the subjects were relying on false memories implanted in the earlier session.

An analysis of the fMRI data showed differences in brain activity between the persistent false memories and the temporary errors of social compliance. The most outstanding feature of the false memories was a strong co-activation and connectivity between two brain areas: the hippocampus and the amygdala. The hippocampus is known to play a role in long-term memory formation, while the amygdala, sometimes known as the emotion center of the brain, plays a role in social interaction. The scientists think that the amygdala may act as a gateway connecting the social and memory processing parts of our brain; its "stamp" may be needed for some types of memories, giving them approval to be uploaded to the memory banks. Thus social reinforcement could act on the amygdala to persuade our brains to replace a strong memory with a false one.

Prof. Yadin Dudai's research is supported by the Norman and Helen Asher Center for Human Brain Imaging, which he heads; the Nella and Leon Benoziyo Center for Neurological Diseases; the Carl and Micaela Einhorn-Dominic Institute of Brain Research, which he heads; the Marc Besen and the Pratt Foundation, Australia; Lisa Mierins Smith, Canada; Abe and Kathryn Selsky Memorial Research Project; and Miel de Botton, UK. Prof. Dudai is the incumbent of the Sara and Michael Sela Professorial Chair of Neurobiology.

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Emotional Signals Are Chemically Encoded in Tears, Researchers Find

Emotional Signals Are Chemically Encoded in Tears, Researchers Find

  9:47:00 AM    Science Lover

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Emotional crying is a universal, uniquely human behavior. When we cry, we clearly send all sorts of emotional signals. In a paper published online January 6 in Science Express, scientists at the Weizmann Institute have demonstrated that some of these signals are chemically encoded in the tears themselves. Specifically, they found that merely sniffing a woman's tears -- even when the crying woman is not present -- reduces sexual arousal in men.

Scientists have found that certain emotional signals are chemically encoded in tears. (Credit: iStockphoto/Arpad Nagy-Bagoly)

Humans, like most animals, expel various compounds in body fluids that give off subtle messages to other members of the species. A number of studies in recent years, for instance, have found that substances in human sweat can carry a surprising range of emotional and other signals to those who smell them.

But tears are odorless. In fact, in a first experiment led by Shani Gelstein, Yaara Yeshurun and their colleagues in the lab of Prof. Noam Sobel in the Weizmann Institute's Neurobiology Department, the researchers first obtained emotional tears from female volunteers watching sad movies in a secluded room and then tested whether men could discriminate the smell of these tears from that of saline. The men could not.

In a second experiment, male volunteers sniffed either tears or a control saline solution, and then had these applied under their nostrils on a pad while they made various judgments regarding images of women's faces on a computer screen. The next day, the test was repeated -- the men who were previously exposed to tears getting saline and vice versa. The tests were double blinded, meaning neither the men nor the researchers performing the trials knew what was on the pads. The researchers found that sniffing tears did not influence the men's estimates of sadness or empathy expressed in the faces. To their surprise, however, sniffing tears negatively affected the sex appeal attributed to the faces.

To further explore the finding, male volunteers watched emotional movies after similarly sniffing tears or saline. Throughout the movies, participants were asked to provide self-ratings of mood as they were being monitored for such physiological measures of arousal as skin temperature, heart rate, etc. Self-ratings showed that the subjects' emotional responses to sad movies were no more negative when exposed to women's tears, and the men "smelling" tears showed no more empathy. They did, however, rate their sexual arousal a bit lower. The physiological measures, however, told a clearer story. These revealed a pronounced tear-induced drop in physiological measures of arousal, including a significant dip in testosterone -- a hormone related to sexual arousal.

Finally, in a fourth trial, Sobel and his team repeated the previous experiment within an fMRI machine that allowed them to measure brain activity. The scans revealed a significant reduction in activity levels in brain areas associated with sexual arousal after the subjects had sniffed tears.

Sobel said, "This study raises many interesting questions. What is the chemical involved? Do different kinds of emotional situations send different tear-encoded signals? Are women's tears different from, say, men's tears? Children's tears? This study reinforces the idea that human chemical signals -- even ones we're not conscious of -- affect the behavior of others."

Human emotional crying was especially puzzling to Charles Darwin, who identified functional antecedents to most emotional displays -- for example, the tightening of the mouth in disgust, which he thought originated as a response to tasting spoiled food. But the original purpose of emotional tears eluded him. The current study has offered an answer to this riddle: Tears may serve as a chemosignal. Sobel points out that some rodent tears are known to contain such chemical signals. "The uniquely human behavior of emotional tearing may not be so uniquely human after all," he says.

The work was authored by Shani Gelstein, Yaara Yeshurun, Liron Rozenkrantz, Sagit Shushan, Idan Frumin, Yehudah Roth and Noam Sobel, was conducted in collaboration with the Edith Wolfson Medical Center, Holon.

Prof. Noam Sobel's research is supported by the James S. McDonnell Foundation 21st Century Science Scholar in Understanding Human Cognition Program; the Minerva Foundation; the European Research Council; and Regina Wachter, NY.

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Invention Enables People With Disabilities Communicate and Steer a Wheelchair by Sniffing

Invention Enables People With Disabilities Communicate and Steer a Wheelchair by Sniffing

  9:21:00 AM    Science Lover

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A unique device based on sniffing -- inhaling and exhaling through the nose -- might enable numerous disabled people to navigate wheelchairs or communicate with their loved ones. Sniffing technology might even be used in the future to create a sort of 'third hand,' to assist healthy surgeons or pilots.

Brain scans. Ten patients, all quadriplegics, succeeded 
in operating a computer and writing messages through 
sniffing. (Credit: Image courtesy of Weizmann 
Institute of Science)

Developed by Prof. Noam Sobel, electronics engineers Dr. Anton Plotkin and Aharon Weissbrod and research student Lee Sela in the Weizmann Institute's Neurobiology Department, the new system identifies changes in air pressure inside the nostrils and translates these into electrical signals. The device was tested on healthy volunteers as well as quadriplegics, and the results showed that the method is easily mastered. Users were able to navigate a wheelchair around a complex path or play a computer game with nearly the speed and accuracy of a mouse or joystick.

Sobel explains: "The most stirring tests were those we did with locked-in syndrome patients. These are people with unimpaired cognitive function who are completely paralyzed -- 'locked into' their bodies. With the new system, they were able to communicate with family members, and even initiate communication with the outside. Some wrote poignant messages to their loved ones, sharing with them, for the first time in a very long time, their thoughts and feelings." Four of those who participated in the experiments are already using the new writing system, and Yeda Research and Development Company, Ltd. -- the technology transfer arm of the Weizmann Institute -- is investigating the possibilities for developing and distributing the technology.

Sniffing is a precise motor skill that is controlled, in part, by the soft palate -- the flexible divider that moves to direct air in or out through the mouth or nose. The soft palate is controlled by several nerves that connect to it directly through the braincase. This close link led Sobel and his scientific team to theorize that the ability to sniff -- that is, to control soft palate movement -- might be preserved even in the most acute cases of paralysis. Functional magnetic resonance imaging (fMRI) lent support to the idea, showing that a number of brain areas contribute to soft palate control. This imaging revealed a significant overlap between soft palate control and the language areas of the brain, hinting to the scientists that the use of sniffing to communicate might be learned intuitively.

To test their theory, the researchers created a device with a sensor that fits on the nostril's opening and measures changes in air pressure. For patients on respirators, they developed a passive version of the device, which diverts airflow to the patient's nostrils. About 75% of the subjects on respirators were able to control their soft palate movement to operate the device. Initial tests, carried out with healthy volunteers, showed that the device compared favorably with a mouse or joystick for playing computer games. In the next stage, carried out in collaboration with Prof. Nachum Soroker of Loewenstein Hospital Rehabilitation Center in Raanana, quadriplegics and locked-in patients tested the device.

One patient who had been locked in for seven months following a stroke learned to use the device over a period of several days, writing her first message to her family. Another, who had been locked in since a traffic accident 18 years earlier wrote that the new device was much easier to use than one based on blinking. Another ten patients, all quadriplegics, succeeded in operating a computer and writing messages through sniffing.

In addition to communication, the device can function as a sort of steering mechanism for wheelchairs: Two successive sniffs in tell it to go forward, two out mean reverse, out and then in turn it left, and in and out turn it right. After fifteen minutes of practice, a subject who is paralyzed from the neck down managed to navigate a wheelchair through a complex route -- sharp turns and all -- as well as a non-disabled volunteer.

Sniffs can be in or out, strong or shallow, long or short; and this gives the device's developers the opportunity to create a complex 'language' with multiple signals. The new system is relatively inexpensive to produce, and simple and quick to learn to operate in comparison with other brain-machine interfaces. Sobel believes that this invention may not only bring new hope to severely disabled people, but it could be useful in other areas, for instance as a control for a 'third arm' for surgeons and pilots.

Prof. Noam Sobel's research is supported by the Nella and Leon Benoziyo Center for Neurosciences; the J&R Foundation; and Regina Wachter, NY.

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