Category: Perception

Most patients who have a reduced ability to smell or detect odors seem to attach less importance to the sense of smell in their daily lives than people with a normal olfactory function, according to a report in the April issue of Archives of Otolaryngology — Head & Neck Surgery, one of the JAMA/Archives journals.

"Disorders of the sense of smell are common," the authors provide as background information in the article. "In the general population, hyposmia [reduced ability to smell] varies from 13 percent to 18 percent and anosmia (total loss of olfactory function) from 4 percent to 6 percent. The main causes of olfactory disorders are viral infections, head trauma, sinonasal disease, and neurodegenerative diseases." Most cases of reduced or loss of the sense of smell seem to be associated with aging, according to the authors. They suggest that many patients do not seek medical help for these disorders because they either do not notice the impairment because they do not use the sense or because it develops so gradually that they find ways to cope and adjust. People with such disorders often complain about difficulties cooking, a lack of appetite and low interest in eating. However, reduced ability to detect odors also can pose an increased risk of hazardous events. "Approximately 17 percent to 30 percent of patients with olfactory disorders report a decreased quality of life, including symptoms of depression."

Ilona Croy, M.D., and colleagues from the University of Dresden Medical School, Dresden, Germany, evaluated data from 470 individuals (235 patients with a reduced or no sense of smell and 235 individuals with a normal sense of smell) to compare the importance of olfaction in daily life. The study participants completed the Individual Importance of Olfaction Questionnaire (IO) and olfactory testing using the "Sniffin' Sticks" test kit. The questionnaire included items to reflect emotions, memories and evaluations that are triggered by the sense of smell; how much a person uses his or her sense of smell in daily life; and how many people use their sense of smell for decision making. The "Sniffin' Sticks" test kit consists of pen-like odor dispensers that were placed close to the participant's nostrils for a few seconds to assess odor identification ability.

"The main result of the present study is that patients with olfactory disorders rate the importance attached to their olfactory sense to be lower in general and also in all the investigated subscales compared with healthy normosmic subjects," the authors report. "…Although they might not be aware, [they] seem to adjust to their olfactory constraints. Their sense of smell seems to be of less importance to them in daily life when it is reduced. So they report fewer olfactory-triggered emotions and memories, which seems reasonable because patients with olfactory disease experience fewer olfactory triggers. In accord, they also report to use their sense of smell less and to rely less on this sense in decision making."

"In conclusion, most patients attach less importance to their current sense of smell in daily life than do normosmic individuals and adjust to their reduced olfactory function. This behavior might be an example of regaining psychological health despite acquired and long-lasting impairments," the authors write.

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Journal Reference:

1. I. Croy, B. N. Landis, T. Meusel, H.-S. Seo, F. Krone, T. Hummel. Patient Adjustment to Reduced Olfactory Function. Archives of Otolaryngology – Head and Neck Surgery, 2011; 137 (4): 377 DOI: 10.1001/archoto.2011.32

— When you think you see a face in the clouds or in the moon, you may wonder why it never seems to be upside down.

It turns out the answer to this seemingly minor detail is that your brain has been wired not to.

Using tests of visual perception and functional magnetic resonance imaging (fMRI), Lars Strother and colleagues at The University of Western Ontario's world-renowned Centre for Brain & Mind recently measured activity in two regions of the brain well known for facial recognition and found they were highly sensitive to the orientation of people's faces.

The team had participants look at faces that had been camouflaged and either held upright or turned upside down. They found that right-side up faces were easier to see — and activated the face areas in the brain more strongly — thus demonstrating that our brains are specialized to understand this orientation.

The surprise came when they found this bias in brain activity also applies to pictures of animals.

Like faces, animals are biological visual forms that have a typical upright orientation. In the study, published in the current issue of the journal PLoS ONE, Strother and his colleagues propose that the human visual system allows us to see familiar objects — not just faces — more easily when viewed in the familiar upright orientation.

They also demonstrated this bias can be found in the neural activity of those brain areas involved with the most basic steps in visual processing, when visual inputs from the eyes first reach the brain.

In future research, the team hopes to chase down how this bias is set up in these early visual areas of the brain — and what this tells us about how brain circuits can be modified by knowledge and experience.

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Journal Reference:

1. Lars Strother, Pavagada S. Mathuranath, Adrian Aldcroft, Cheryl Lavell, Melvyn A. Goodale, Tutis Vilis. Face Inversion Reduces the Persistence of Global Form and Its Neural Correlates. PLoS ONE, 2011; 6 (4): e18705 DOI: 10.1371/journal.pone.0018705

— The hormone ghrelin, known to promote hunger and fat storage, has been found to enhance exploratory "sniffing" in both animals and humans.

The research, by University of Cincinnati (UC) scientists, suggests that ghrelin may be designed to boost detection of calories in our environment through smell and link those inputs with natural regulation of metabolism and body weight.

Led by Jenny Tong, MD, and Matthias Tschöp, MD, both of UC's endocrinology, diabetes and metabolism division, the study appears in the April 13, 2011, issue of The Journal of Neuroscience, the official journal of the Society for Neuroscience.

"Smell is an integral part of feeding and mammals frequently rely on smell to locate food and discriminate among food sources," says Tong. "Sniffing is the first stage of the smell process and can enhance odor detection and discrimination."

The research team tested both rats and humans. Rats were given ghrelin and monitored for sniff frequency using a video-based behavior analysis system set to record the movement of the nose tip. The investigators also measured the ability of the rats to detect specific odors mixed in water.

Human subjects were evaluated before and after ghrelin infusion using a sniff magnitude test (SMT) developed at the University of Cincinnati by co-investigator Robert Frank, PhD. Subjects were instructed to take a natural sniff of several odorants using the SMT canister and rate the smells in order of pleasantness. Software connected to the canister allowed researchers to measure sniff pressure to determine overall sniff magnitude.

Data for both humans and rats show ghrelin enhanced odor detection and exploratory sniffing.

"Other studies have shown that hunger can enhance odor detection and sniffing in animals," says Tschöp. "Since ghrelin is a hunger-inducing stomach hormone that is secreted when the stomach is empty, this hormone pathway may also be responsible for the hunger-induced enhancement of sniffing and odor detection."

The scientists say this study could open up new avenues connecting metabolic control, chemo-sensation and behavioral neuroscience research. Future studies will explore the exact molecular pathways through which ghrelin affects sniff behavior.

The study was supported by grants from the National Institutes of Health and the Netherlands Organization for Scientific Research.

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Journal Reference:

1. J. Tong, E. Mannea, P. Aime, P. T. Pfluger, C.-X. Yi, T. R. Castaneda, H. W. Davis, X. Ren, S. Pixley, S. Benoit, K. Julliard, S. C. Woods, T. L. Horvath, M. M. Sleeman, D. D'Alessio, S. Obici, R. Frank, M. H. Tschop. Ghrelin Enhances Olfactory Sensitivity and Exploratory Sniffing in Rodents and Humans. Journal of Neuroscience, 2011; 31 (15): 5841 DOI: 10.1523/JNEUROSCI.5680-10.2011

— Jenny Wan-chen Lee, a graduate student in Cornell University's Dyson School of Applied Economics and Management, has been fascinated with a phenomenon known as "the halo effect" for some time. Psychologists have long recognized that how we perceive a particular trait of a person can be influenced by how we perceive other traits of the same individual. In other words, the fact that a person has a positive attribute can radiate a "halo," resulting in the perception that other characteristics associated with that person are also positive. An example of this would be judging an attractive person as intelligent, just because he or she is good-looking.

A growing literature suggests that the halo effect may also apply to foods, and ultimately influence what and how much we eat. For instance, research has shown that people tend to consume more calories at fast-food restaurants claiming to serve "healthier" foods, compared to the amount they eat at a typical burger-and-fry joint. The reasoning is that when people perceive a food to be more nutritious, they tend to let their guard down when it comes to being careful about counting calories — ultimately leading them to overeat or feel entitled to indulge. This health halo effect also seems to apply to certain foods considered by many to be especially healthy, such as organic products. Specifically, some people mistakenly assume that these foods are more nutritious just because they carry an "organic" label -an area of longstanding active debate among food and nutrition scientists.

As part of her master's research, Lee asked whether the "health halo" surrounding organic foods would lead people to automatically perceive them as tastier or lower in calories. She tested this question by conducting a double-blind, controlled trial in which she asked 144 subjects at the local mall to compare what they thought were conventionally and organically produced chocolate sandwich cookies, plain yogurt, and potato chips. All of the products, however, were actually of the organic variety — they were just labeled as being "regular" or "organic." Participants were then asked to rate each food for 10 different attributes (e.g., overall taste, perception of fat content) using a scale from 1 to 9. She also asked them to estimate the number of calories in each food item and how much they would be willing to pay.

As part of the scientific program of the American Society for Nutrition annual meeting, results from this study will be presented on April 10 at the Experimental Biology 2011 meeting.

Confirming Lee's health halo hypothesis, the subjects reported preferring almost all of the taste characteristics of the organically-labeled foods, even though they were actually identical to their conventionally-labeled counterparts. The foods labeled "organic" were also perceived to be significantly lower in calories and evoked a higher price tag. In addition, foods with the "organic" label were perceived as being lower in fat and higher in fiber. Overall, organically-labeled chips and cookies were considered to be more nutritious than their "non-organic" counterparts.

So, not only is there a health halo emanating from organic foods, but it's strong and consistent- at least for cookies, chips, and yogurt. Although Lee is the first to acknowledge that her study was limited in the variety of foods tested, she is confident that this effect is real and has important implications as to what, and how much, people eat, especially those who preferentially seek out foods carrying an "organic" seal. Additional studies will be needed before we know whether these perceived taste and nutrition attributes result in greater consumption of organic versus conventional foods.

Until that time, remember not to judge a book (or a cookie) by its cover (or its organic label).

Jenny Wan-chen Lee (Cornell University), Mitsuru Shimizu (Cornell University), and Brian Wansink (Cornell University) were coauthors on this paper.

Beauty is said to be in the eye of the beholder, but a new study reveals that the reverse is also true; unattractiveness is in the eye of the beheld. Research published in Ethology finds that people with bloodshot eyes are considered sadder, unhealthier and less attractive than people whose eye whites are untinted, a cue which is uniquely human.

"Red, 'bloodshot' eyes are prominent in medical diagnoses and in folk culture," said lead author Dr. Robert R. Provine from the University of Maryland, Baltimore County. "We wanted to know if they influence the everyday behaviour and attitudes of those who view them, and if they trigger perceptions of attractiveness."

Bloodshot eyes occur when the small blood vessels of the usually transparent conjunctiva membrane on the surface of the eye become enlarged and congested with blood, giving a red tint to the underlying sclera, the "white" of the eyes. Redness of the sclera is believed to be a general but important sign of a person's emotional and biological state.

"If you met a friend with bloodshot eyes it may be unclear whether you should offer sympathy or medical assistance because red eyes may be a result of weeping, allergies or infectious diseases," said Provine. "Comments from our colleagues also suggest that red eyes prompt feelings of discomfort, ranging from increased monitoring of their own eyes to a hint of sympathetic tearing."

In the first empirical test to discover the perceptions and behavioural implications of red eyes Dr. Provine's team tested 208 volunteer students from the University of Maryland, Baltimore County. The volunteers composed of 93 males and 115 females, with an average age of 20.6 years.

The volunteers were shown 200 images of eyes, half with clear white sclera and half with sclera tinted red by digital image processing. The volunteers were asked how sad, healthy or attractive the owners of the eyes were. The results revealed that people with reddened eyes appear sadder, less healthy, and less attractive compared to those with whiter, untinted eyes.

This is the first study to demonstrate that eye redness is perceived as a cue of emotion. Humans appear to be the only species which uses eye colouration as an indicator of either health or emotion. This is because other primates lack the background of white sclera necessary to make the reddened conjunctiva visible.

Sclera colour provides even casual, untrained observers with a quick estimate of the emotional and health status of an individual and the study's ratings of attractiveness suggest that this information does influence our behaviour.

"Standards of beauty vary across cultures, however, youth and healthiness are always in fashion because they are associated with reproductive fitness," said Provine. "Traits such as long, lustrous hair and smooth or scar-free skin are cues of youth and offer the beholder a partial record of health.

Now clear eye whites join these traits as a universal standard for the perception of beauty and a cue of health and reproductive fitness. Given this discovery, eye drops that 'get the red out' can be considered beauty aids."

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Journal Reference:

1. Robert R. Provine, Marcello O. Cabrera, Nicole W. Brocato, Kurt A. Krosnowski. When the Whites of the Eyes are Red: A Uniquely Human Cue. Ethology, 2011; 117 (5): 395 DOI: 10.1111/j.1439-0310.2011.01888.x

The act of mind reading is something usually reserved for science-fiction movies but researchers in America have used a technique, usually associated with identifying epilepsy, for the first time to show that a computer can listen to our thoughts.

In a new study, scientists from Washington University demonstrated that humans can control a cursor on a computer screen using words spoken out loud and in their head, holding huge applications for patients who may have lost their speech through brain injury or disabled patients with limited movement.

By directly connecting the patient's brain to a computer, the researchers showed that the computer could be controlled with up to 90% accuracy even when no prior training was given.

Patients with a temporary surgical implant have used regions of the brain that control speech to "talk" to a computer for the first time, manipulating a cursor on a computer screen simply by saying or thinking of a particular sound.

"There are many directions we could take this, including development of technology to restore communication for patients who have lost speech due to brain injury or damage to their vocal cords or airway," says author Eric C. Leuthardt, MD, of Washington University School of Medicine in St. Louis.

Scientists have typically programmed the temporary implants, known as brain-computer interfaces, to detect activity in the brain's motor networks, which control muscle movements.

"That makes sense when you're trying to use these devices to restore lost mobility — the user can potentially engage the implant to move a robotic arm through the same brain areas he or she once used to move an arm disabled by injury," says Leuthardt, assistant professor of neurosurgery, of biomedical engineering and of neurobiology, "But that has the potential to be inefficient for restoration of a loss of communication."

Patients might be able to learn to think about moving their arms in a particular way to say hello via a computer speaker, Leuthardt explains. But it would be much easier if they could say hello by using the same brain areas they once engaged to use their own voices.

The research appears April 7 in The Journal of Neural Engineering.

The devices under study are temporarily installed directly on the surface of the brain in epilepsy patients. Surgeons like Leuthardt use them to identify the source of persistent, medication-resistant seizures and map those regions for surgical removal. Researchers hope one day to install the implants permanently to restore capabilities lost to injury and disease.

Leuthardt and his colleagues have recently revealed that the implants can be used to analyze the frequency of brain wave activity, allowing them to make finer distinctions about what the brain is doing. For the new study, Leuthardt and others applied this technique to detect when patients say or think of four sounds:

• oo, as in few
• e, as in see
• a, as in say
• a, as in hat

When scientists identified the brainwave patterns that represented these sounds and programmed the interface to recognize them, patients could quickly learn to control a computer cursor by thinking or saying the appropriate sound.

In the future, interfaces could be tuned to listen to just speech networks or both motor and speech networks, Leuthardt says. As an example, he suggests that it might one day be possible to let a disabled patient both use his or her motor regions to control a cursor on a computer screen and imagine saying "click" when he or she wants to click on the screen.

"We can distinguish both spoken sounds and the patient imagining saying a sound, so that means we are truly starting to read the language of thought," he says. "This is one of the earliest examples, to a very, very small extent, of what is called 'reading minds' — detecting what people are saying to themselves in their internal dialogue."

"We want to see if we can not just detect when you're saying dog, tree, tool or some other word, but also learn what the pure idea of that looks like in your mind," he says. "It's exciting and a little scary to think of reading minds, but it has incredible potential for people who can't communicate or are suffering from other disabilities."

The next step, which Leuthardt and his colleagues are working on, is to find ways to distinguish what they call "higher levels of conceptual information."

The study identified that speech intentions can be acquired through a site that is less than a centimetre wide which would require only a small insertion into the brain. This would greatly reduce the risk of a surgical procedure.

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Journal Reference:

1. Eric C. Leuthardt, Charles Gaona, Mohit Sharma, Nicholas Szrama, Jarod Roland, Zac Freudenberg, Jamie Solis, Jonathan Breshears, Gerwin Schalk. Using the electrocorticographic speech network to control a brain–computer interface in humans. Journal of Neural Engineering, 2011; DOI: 10.1088/1741-2560/8/3/036004

Do you need to be an expert to have a good nose? It turns out the answer is yes! Having a good nose is not something we are born with, but instead just a matter of training.

This has been demonstrated by Jane Plailly and Jean-Pierre Royet, researchers at the Laboratoire Neurosciences Sensorielles Comportement Cognition (CNRS/Université Claude Bernard Lyon 1), and Chantal Delon-Martin, researcher at the Institut des Neurosciences de Grenoble (Inserm/Université Joseph Fourier).

The brain imaging experiment that they carried out on professional and student perfumers reveals, for the first time, that similar regions are activated during the perception and imagination of odors and that this activation depends on the subject's level of expertise. This result shows that, like visual or auditory mental imagery, olfactory imagery depends on the reactivation of olfactory images within the brain, and that this capacity develops with experience. This work is published on 8 March 2011 on the website of the journal Human Brain Mapping.

We are all able to visualize our own living room, move about virtually or mentally hum a catchy tune. But can we recall the smell of toast or a fig to the point of actually smelling their odor? Olfactory mental imagery is a much more difficult exercise than visual or auditory mental imagery and most people say they do not have this capacity. However, perfumers, olfactory experts used to smelling, evaluating and creating odors, claim they are capable of smelling an odor even in its absence.

Where does the truth lie?

To answer this question, the researchers used functional Magnetic Resonance Imaging (fMRI). They compared the spatial organization of the cerebral activations of students from the Ecole de Parfumerie de Versailles (ISIPCA) to that of professional perfumers, a rare species (there are no more than 500 throughout the world, of which some 120 are in France and Switzerland). While placed in a scanner, the subjects were asked to mentally conjure up the smell of odorous substances (1), whose chemical name appeared on a screen.

The results show that in the experts of both groups, olfactory mental imagery activates the primary olfactory cortex (piriform cortex) a zone of the brain ordinarily stimulated during perception. This proves that similar areas are activated during the perception and imagination of odors. Like visual or auditory mental imagery, olfactory imagery depends on the reactivation of olfactory images via an internal cognitive process (our own brain generates this sensation) and not in response to an odor.

Another finding is that, in perfumers, intense olfactory training influences the activation level of the neuronal network involved in the mental imagery of odors. Surprisingly, the greater the level of expertise, the more the activity of the olfactory and mnesic (hippocampus) regions is reduced. Thus, when the brain is trained, "communication" at the neuronal level takes place more easily, rapidly and efficiently, and the message is more specific, resulting in reduced activation. This shows that regular training enhances olfactory mental imagery, which does not stem from an innate faculty.

In this study, the perfumers were able to imagine the odors rapidly, sometimes instantaneously, whereas the students experienced some difficulties and needed to concentrate their attention. By easily reactivating the mnesic representations of odors, perfumers can mentally compare and combine scents with the aim of creating new fragrances.

These results demonstrate the brain's extraordinary capacity to adapt to environmental demand and to reorganize itself with experience.

(1) Dihydromyrcenol, aldehyde C11, triplal, alpha-damascone… just some of the chemical names of the twenty or so odorants selected for the experiment among the 300 with which student perfumers normally work.

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Journal Reference:

1. Plailly J., Delon-Martin C., Royet J.P. Experience induces functional reorganisation in brain regions involved in odor imagery in perfumers. Human Brain Mapping, March 9, 2011 DOI: 10.1002/hbm.21207

Optical illusions have fascinated humans throughout history. Greek builders used an optical illusion to ensure that that their columns appeared straight (they built them with a bulge) and we are all intrigued by the mental flip involved in the case of the young girl/old woman faces.

New research published in BioMed Central's open access journal BMC Neuroscience demonstrates a more serious use of these illusions in understanding how the brain assesses relative size.

Researchers from University College London looked at two well known illusions: the Ebbinghaus illusion, where an object surrounded by small circles appears bigger than the same object surrounded by bigger circles, and the Ponzo illusion, where an object within converging lines (like train tracks or a corridor) is perceived to be larger than a same sized object nearer to the observer.

Their results show that the Ponzo illusion holds true regardless of which eye is used or whether the environmental clues are presented to a different eye than the objects. This suggests that our clues about relative size at a distance are determined after the two-dimensional images seen by the eyes have been processed into a single, three-dimensional, image. In contrast the Ebbinghaus illusion does not work as well if the central object is presented to a different eye than the surrounding circles and shows that determination of an object's size relative to others in the same plane occurs before three-dimension processing.

Chen Song said, "Although our perception of size is distorted by environmental clues, this study shows that the extent of distortion and the brain mechanisms involved are dependent on the type of environmental contexts."

So while celebrity illusionists retain their ability to fool us, scientists can use these visual tricks to further our understanding of how we relate to the world around us — and have some fun at the same time.

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Journal Reference:

1. Chen Song, D. Samuel Schwarzkopf and Geraint Rees. Interocular induction of illusory size perception. BMC Neuroscience, (in press) DOI: 10.1186/1471-2202-12-27

The brain is a black box. A complex circuitry of neurons fires information through channels, much like the inner workings of a computer chip. But while computer processors are regimented with the deft economy of an assembly line, neural circuits are impenetrable masses. Think tumbleweed.

Researchers in Harvard Medical School's Department of Neurobiology have developed a technique for unraveling these masses. Through a combination of microscopy platforms, researchers can crawl through the individual connections composing a neural network, much as Google crawls Web links.

"The questions that such a technique enables us to address are too numerous even to list," said Clay Reid, HMS professor of neurobiology and senior author on a paper reporting the findings in the March 10 edition of Nature.

The cerebral cortex is arguably the most important part of the mammalian brain. It processes sensory input, reasoning and, some say, even free will. For the past century, researchers have understood the broad outline of cerebral cortex anatomy. In the past decade, imaging technologies have allowed us to see neurons at work within a cortical circuit, to watch the brain process information.

But while these platforms can show us what a circuit does, they don't show us how it operates.

For many years, Reid's lab has been studying the cerebral cortex, adapting ways to hone the detail with which we can view the brain at work. Recently they and others have succeeded in isolating the activities of individual neurons, watching them fire in response to external stimuli.

The ultimate prize, however, would be to get inside a single cortical circuit and probe the architecture of its wiring.

Just one of these circuits, however, contains between 10,000 and 100,000 neurons, each of which makes about 10,000 interconnections, totaling upwards of 1 billion connections — all within a single circuit. "This is a radically hard problem to address," Reid said.

Reid's team, which included Davi Bock, then a graduate student, and postdoctoral researcher Wei-Chung Allen Lee, embarked on a two-part study of the pinpoint-sized region of a mouse brain that is involved in processing vision. They first injected the brain with dyes that flashed whenever specific neurons fired and recorded the firings using a laser-scanning microscope. They then conducted a large anatomy experiment, using electron microscopy to see the same neurons and hundreds of others with nanometer resolution.

Using a new imaging system they developed, the team recorded more than 3 million high-resolution images. They sent them to the Pittsburgh Supercomputing Center at Carnegie Mellon University, where researchers stitched them into 3-D images. Using the resulting images, Bock, Lee and laboratory technician Hyon Suk Kim selected 10 individual neurons and painstakingly traced many of their connections, crawling through the brain's dense thicket to create a partial wiring diagram.

This model also yielded some interesting insights into how the brain functions. Reid's group found that neurons tasked with suppressing brain activity seem to be randomly wired, putting the lid on local groups of neurons all at once rather than picking and choosing. Such findings are important because many neurological conditions, such as epilepsy, are the result of neural inhibition gone awry.

"This is just the iceberg's tip," said Reid. "Within ten years I'm convinced we'll be imaging the activity of thousands of neurons in a living brain. In a visual circuit, we'll interpret the data to reconstruct what an animal actually sees. By that time, with the anatomical imaging, we'll also know how it's all wired together."

For now, Reid and his colleagues are working to scale up this platform to generate larger data sets.

"How the brain works is one of the greatest mysteries in nature," Reid added, "and this research presents a new and powerful way for us to explore that mystery."

This research was funded by the Center for Brain Science at Harvard University, Microsoft Research, and the NIH though the National Eye Institute. Researchers report no conflicts of interest.

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Journal Reference:

1. Davi D. Bock et al. Network anatomy and in vivo physiology from a group of visual cortical neurons. Nature, March 11, 2011, Volume 471 Number 7337 DOI: 10.1038/nature09802

Neurobiologists at Vienna's Research Institute of Molecular Pathology used the mating ritual of the fruit fly to study how the nervous system initiates, controls and utilizes behavior. Using newly developed thermogenetic methods, the researchers were able to initiate the courtship song of the male fly by "remote control," and study the involved neural networks.

Male fruit flies of the Drosophila melanogaster species perform a complex courtship ritual to attract the attention of female flies and make them amenable to mating. As part of the ritual, the male fly performs a "song" by extending a wing and vibrating it. The pulsating acoustic signal produced by this exercise sounds rather like static crackling or humming to the human ear. However, the female fly finds the sound irresistible. Singing is an important part of the fly's courtship; how well the male performs its song is crucial for the success of its mating.

Under natural circumstances, the sight and smell of a female fly induce courtship in the male. At the Institute of Molecular Pathology in Vienna, scientists have developed a kind of molecular "remote control" to initiate the ritual. Anne von Philipsborn, a biologist and Postdoc in the lab of IMP Director Barry Dickson, works with genetically modified fruit flies. By raising the ambient temperature, she can get an isolated male fly — in the absence of a female, and presumably not thinking at all about sex — to become aroused and initiate courtship.

This condition is achieved by the use of a method known as thermal activation. Defined sets of nerve cells (neurons) are fitted with temperature-sensitive ion channels. These channels open up when the temperature approaches 30 degrees and become permeable for certain small molecules. The flow of ions, in turn, activates the nerve cell and triggers an impulse.

By switching on and off targeted nerve cells, the neurobiologists in Vienna were able to identify two centers in the fly's nervous system that control singing. The command to sing comes from a center located in the brain. This network of cells receives input from various sources; the most important of these are sensory organs and other regions of the brain. What the fly sees, hears and smells is channeled to this circuit and, together with pre-existing information obtained from prior experience, a decision is made to court or not to court the female.

The second neural circuit is located in the chest and is connected to the muscles that move the wings. This network is a so-called pattern generator. It coordinates the movement of the muscles and produces their rhythmic pattern.

For the scientists at the IMP, the courtship song of the fruit fly serves as a model to investigate the neural mechanisms of decision-making, action selection, and motor pattern generation. In short, they want to find out how meaningful behavior is orchestrated.

Having found the key neurons that make the fly sing, the team of neurobiologists will continue to look deeper into the mechanisms that control behavior. Barry Dickson explains their future plans: "We now need to figure out exactly how this circuit works under normal conditions, when the male is naturally aroused by a virgin female. And we are also now starting to use the same method to look for neurons that trigger other components of mating behavior, such as copulation itself."

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Journal Reference:

1. Anne C. von Philipsborn, Tianxiao Liu, Jai Y. Yu, Christopher Masser, Salil S. Bidaye, Barry J. Dickson. Neuronal Control of Drosophila Courtship Song. Neuron, 2011; 69 (3): 509 DOI: 10.1016/j.neuron.2011.01.011