Altered white matter limits the brain’s conscious access to information, potentially contributing to delusions and other psychotic symptoms of mental health disorders, according to new research published in JNeurosci.
Your brain is always active, but you are not always aware of it. Accepted theory holds you do not become consciously aware of something until non-conscious brain activity in sensory areas spreads to a larger network of neurons all over the brain via long-distance white matter tracts. Dysfunction in these tracts may explain the delusions characteristic of psychiatric disorders like bipolar disorder and schizophrenia.
Berkovitch et al. used MRI to compare the white matter structure and consciousness threshold of healthy adults, bipolar disorder patients with and without psychotic symptoms, and schizophrenia patients. The consciousness threshold corresponds to how long a visual stimulus must be presented on a screen to be broadcasted across the brain and become conscious – the shorter it is, the better the conscious access. Thresholds were significantly increased in patients with psychosis compared to those without. Across all participants, lower thresholds correlated with greater white matter connectivity in long distance tracts. These results mean altered white matter connectivity does not induce psychosis directly, but may through its effect on the consciousness threshold.
These results mean altered white matter connectivity does not induce psychosis directly, but may through its effect on the consciousness threshold.
A superconductor that can operate at room temperature would be a dream material able to efficiently power the cities of tomorrow and magnetically levitate cars.
The search for a superconductor that can work under less extreme conditions than hundreds of degrees below zero or at pressures like those near the center of the Earth is a quest for a revolutionary new power — one that’s needed for magnetically levitating cars and ultra-efficient power grids of the future.
But developing this kind of “room temperature” superconductor is a feat science has yet to achieve.
A University of Central Florida researcher, however, is working to move this goal closer to realization, with some of his latest research published recently in the journal Communications Physics – Nature.
In the study, Yasuyuki Nakajima, an assistant professor in UCF’s Department of Physics, and co-authors showed they could get a closer look at what is happening in “strange” metals.
These “strange” metals are special materials that show unusual temperature behavior in electrical resistance. The “strange” metallic behavior is found in many high-temperature superconductors when they are not in a superconducting state, which makes them useful to scientists studying how certain metals become high-temperature superconductors.
This work is important because insight into the quantum behavior of electrons in the “strange” metallic phase could allow researchers to understand a mechanism for superconductivity at higher temperatures.
“If we know the theory to describe these behaviors, we may be able to design high-temperature superconductors,” Nakajima says.
Superconductors get their name because they are the ultimate conductors of electricity. Unlike a conductor, they have zero resistance, which, like an electronic “friction,” causes electricity to lose power as it flows through a conductor like copper or gold wire.
This makes superconductors a dream material for supplying power to cities as the energy saved by using resistance-free wire would be huge.
Powerful superconductors also can levitate heavy magnets, paving the way for practical and affordable magnetically levitating cars, trains and more.
To turn a conductor into a superconductor, the metal material must be cooled to an extremely low temperature to lose all electrical resistance, an abrupt process that physics has yet to develop a fully comprehensive theory to explain.
These critical temperatures at which the switch is made are often in the range of -220 to -480 degrees Fahrenheit and typically involve an expensive and cumbersome cooling system using liquid nitrogen or helium.
Some researchers have achieved superconductors that work at about 59 degrees Fahrenheit, but it was also at a pressure of more than 2 million times of that at the Earth’s surface.
In the study, Nakajima and the researchers were able to measure and characterize electron behavior in a “strange” metallic state of non-superconducting material, an iron pnictide alloy, near a quantum critical point at which electrons switch from having predictable, individual behavior to moving collectively in quantum-mechanical fluctuations that are challenging for scientists to describe theoretically.
The researchers were able to measure and describe the electron behavior by using a unique metal mix in which nickel and cobalt were substituted for iron in a process called doping, thus creating an iron pnictide alloy that didn’t superconduct down to -459.63 degrees Fahrenheit, far below the point at which a conductor would typically become a superconductor.
“We used an alloy, a relative compound of high temperature iron-based superconductor, in which the ratio of the constituents, iron, cobalt and nickel in this case, is fine-tuned so that there’s no superconductivity even near absolute zero,” Nakajima says. “This allows us to access the critical point at which quantum fluctuations govern the behavior of the electrons and study how they behave in the compound.”
They found the behavior of the electrons was not described by any known theoretical predictions, but that the scattering rate at which the electrons were transported across the material can be associated with what’s known as the Planckian dissipation, the quantum speed limit on how fast matter can transport energy.
“The quantum critical behavior we observed is quite unusual and completely differs from the theories and experiments for known quantum critical materials,” Nakajima says. “The next step is to map the doping-phase diagram in this iron pnictide alloy system.”
“The ultimate goal is to design higher temperature superconductors,” he says. “If we can do that, we can use them for magnetic resonance imaging scans, magnetic levitation, power grids, and more, with low costs.”
Unlocking ways to predict the resistance behavior of “strange” metals would not only improve superconductor development but also inform theories behind other quantum-level phenomena, Nakajima says.
“Recent theoretical developments show surprising connections between black holes, gravity and quantum information theory through the Planckian dissipation,” he says. “Hence, the research of ‘strange’ metallic behavior has also become a hot topic in this context.”
Co-authors included researchers from the University of Maryland; the National Institute of Standards and Technology Center for Neutron Research; the National High Magnetic Field Laboratory at Florida State University; the Leibniz Institute for Solid State and Materials Research in Dresden, Germany; the Shanghai Institute of Microsystem and Information Technology at the Chinese Academy of Sciences in China; and the Canadian Institute for Advanced Research in Toronto, Canada.
The research was funded by the National Science Foundation Division of Materials Research, the Gordon and Betty Moore Foundation’s EPiQS Initiative. Some of the work was performed at the National High Magnetic Field Laboratory, which is supported by an NSF cooperative agreement with the State of Florida. Pressure measurements were supported by the National Institute of Standards and Technology.
Nakajima received his doctorate in physics from the University of Tokyo in Japan and worked as a postdoctoral research associate at the Center for Nanophysics and Advanced Materials at the University of Maryland. He joined UCF’s Department of Physics, part of UCF’s College of Sciences, in 2016.
Study shows that a tree frog endemic to a mountainous region of the Brazilian savanna is unable to disperse and find genetically closer mates when the terrain is rugged, potentially endangering survival of the species.
The savanna tree frog Bokermannohyla ibitiguara is about 4 cm long and is found only in gallery forest along streams in the Serra da Canastra mountain range in the state of Minas Gerais, Southeast Brazil. In this watery forest environment, it can grow, feed, mate, and lay eggs without needing to range very far throughout its life cycle, according to a study published in Diversity and Distributions.
According to the Brazilian and US researchers who conducted the study, topography rather than vegetation is the main factor leading to more or less dispersal of the species in the territory, and this information is even recorded in its DNA.
They analyzed genetic variation among groups of B. ibitiguara living inside and outside the Serra da Canastra National Park, a protected area in the region, discovering that the flatter the terrain, the more genetically diverse is the population.
In areas of highly variable elevation, individuals are genetically similar. In evolutionary terms, this can be harmful to the species, which becomes more susceptible to disease and climate change, for example.
“Genetic analysis and conservation studies typically take land cover into account, among other factors, but the Cerrado [Brazilian savanna] is topographically diverse, including montane regions with high plateaus [chapadões] separated by low areas. We set out to verify whether this variable terrain played a part in the genetic diversity of the species, and found that it did. The vegetation alone didn’t explain the genetic differences we identified between sites, or even within the same site. The topography did,” said Renato Christensen Nali, first author of the article and a professor at the Federal University of Juiz de Fora’s Institute of Biological Sciences (ICB-UFJF) in Minas Gerais, Brazil.
The study was one of the results of Nali’s doctoral research, conducted at São Paulo State University’s Bioscience Institute (IB-UNESP) in Rio Claro, Brazil, with a scholarship from FAPESP (São Paulo Research Foundation).
The research was part of the project “Reproductive ecology of anuran amphibians: an evolutionary perspective”, for which the principal investigator is Cynthia Peralta de Almeida Prado, a co-author of the article. She is a professor at UNESP’s School of Agrarian and Veterinary Sciences in Jaboticabal and teaches graduate students in zoology at IB-UNESP in Rio Claro.
The flatter the better
“The findings are very interesting because they bring to light a novel factor for conservation of the Cerrado, among other reasons. Ecological corridors and native forests are rightly considered important for conservation units, but more attention needs to be paid to the type of terrain. The topography should permit dispersal of the animals,” said Nali, who heads ICB-UFJF’s Amphibian Evolutionary Ecology Laboratory (Lecean).
To arrive at the results, the researchers analyzed 12 populations of B. ibitiguara, six inside Serra da Canastra National Park and six outside. Genetic diversity was much higher among the anurans living in the protected area than among those living outside the park. When the researchers correlated information on the degree of protection of the areas with the state of the vegetation, they found that these factors were less decisive for genetic diversity than the topography.
“The terrain is much more rugged outside the park, whereas inside it there’s a large, very even plateau where the anurans can disperse more, find mates in more distant areas, and increase their genetic diversity,” Nali said. “Outside the park, the rugged terrain and variable elevation appear to confine them to small areas.”
The influence of these factors was evidenced by genetic tests. The researchers used a technique known as macrosatellite marker analysis to examine specific regions of the genome and found higher allele diversity in the populations living in the park. Allele diversity is one of the determinants of genetic integrity and adaptive potential.
In addition, the populations living outside the park displayed a greater loss of heterozygosity. If this loss, which is associated with declining genetic variability, recurs across several generations, it can eventually threaten the population’s survival.
The study underscores the importance of topography as a factor to consider in conservation studies, as well as showing how the mere presence of a species in an area cannot ensure that it is not endangered.
“Molecular analysis enables us to find out if a population’s genetic status is favorable,” Nali said. “An area may have a large number of individuals, but DNA analysis may show that its genetic constitution is unfavorable, with few alleles and low heterozygosity. In practice, therefore, the population’s effective size is small.”
Although the study focused on only one species, he added, the findings can apply to others as well since the physical characteristics associated with dispersal are similar for other frogs and toads. More species need to be investigated to confirm the applicability of the findings.
The group noted that land cover nevertheless remains an important factor for conservation in the Cerrado, more than 50% of which has been converted into pasture or cropland, while less than 5% is protected by conservation units.
References: Nali, RC, Becker, CG, Zamudio, KR, Prado, CPA. Topography, more than land cover, explains genetic diversity in a Neotropical savanna tree frog. Divers Distrib. 2020; 26: 1798– 1812. https://doi.org/10.1111/ddi.13154
A feat of basic neuroscience co-led by UNC School of Medicine scientists, the discovery of a set of arousal-related neurons could help scientists develop better treatments for anxiety disorders, psychiatric illnesses.
Strong emotions such as fear and anxiety tend to be accompanied and reinforced by measurable bodily changes including increased blood pressure, heart rate and respiration, and dilation of the eyes’ pupils. These so-called “physiological arousal responses” are often abnormally high or low in psychiatric illnesses such as anxiety disorders and depression. Now scientists at the UNC School of Medicine have identified a population of brain cells whose activity appears to drive such arousal responses.
The scientists, whose study is published in Cell Reports, found that artificially forcing the activity of these brain cells in mice produced an arousal response in the form of dilated pupils and faster heart rate, and worsened anxiety-like behaviors.
The finding helps illuminate the neural roots of emotions, and point to the possibility that the human-brain counterpart of the newly identified population of arousal-related neurons might be a target of future treatments for anxiety disorders and other illnesses involving abnormal arousal responses.
“Focusing on arousal responses might offer a new way to intervene in psychiatric disorders,” said first author Jose Rodríguez-Romaguera, PhD, assistant professor in the UNC Department of Psychiatry and member of the UNC Neuroscience Center, and co-director of the Carolina Stress Initiative at the UNC School of Medicine.
Rodríguez-Romaguera and co-first author Randall Ung, PhD, an MD-PhD student and adjunct assistant professor in the Department of Psychiatry, led this study when they were members of the UNC laboratory of Garret Stuber, PhD, who is now at the University of Washington.
“This work not only identifies a new population of neurons implicated in arousal and anxiety, but also opens the door for future experiments to systematically examine how molecularly defined cell types contribute to complex emotional and physiological states,” Stuber said. “This will be critical going forward for developing new treatments for neuropsychiatric disorders.”
Anxiety disorders, depression, and other disorders featuring abnormally high or low arousal responses affect a large fraction of the human population, including tens of millions of adults in the United States alone. Treatments may alleviate symptoms, but many have adverse side effects, and the root causes of these disorders generally remain obscure.
Untangling these roots amid the complexity of the brain has been an enormous challenge, one that laboratory technology has only recently begun to surmount.
Rodríguez-Romaguera, Ung, Stuber and colleagues examined a brain region within the amygdala called the BNST (bed nucleus of the stria terminalis), which has been linked in prior research to fear and anxiety-like behaviors in mice.
Increasingly, scientists view this region as a promising target for future psychiatric drugs. In this case, the researchers zeroed in on a set of BNST neurons that express a neurotransmitter gene, Pnoc, known to be linked to pain sensitivity and more recently to motivation.
The team used a relatively new technique called two-photon microscopy to directly image BNST Pnoc neurons in the brains of mice while the mice were presented with noxious or appealing odors – stimuli that reliably induce fear/anxiety and reward behaviors, respectively, along with the appropriate arousal responses. In this way, the scientists found that activity in these neurons tended to be accompanied by the rapid dilation of the pupils of the mice when the animals were presented with either of these odor stimuli.
The researchers then used another advanced technique called optogenetics – using light to control genetically engineered cells – to artificially drive the activity of the BNST Pnoc neurons. They found that spurring on BNST Pnoc activity triggered a pupillary response, as well as increased heart rate. Optogenetically driving the neurons while the mice underwent an anxiety-inducing maze test (traditionally used to assess anxiety drugs) increased the animals’ signs of anxiety, while optogenetically quieting the neurons had the opposite effect.
“Essentially we found that activating these BNST Pnoc neurons drives arousal responses and worsens anxiety-like states,” Rodríguez-Romaguera said.
The discovery is mainly a feat of basic neuroscience. But it also suggests that targeting arousal-driving neurons such as BNST Pnoc neurons with future drugs might be a good way to reduce abnormally strong responses to negative stimuli in anxiety disorders, for example, and to boost abnormally weak responses to positive stimuli in depression.
The study uncovered evidence that BNST Pnoc neurons are not all the same but differ in their responses to positive or negative stimuli, and the researchers are now cataloguing these BNST Pnoc neuron sub-groups.
“Even this small part of the amygdala is a complex system with different types of neurons,” Ung said. Teasing this apart will help us understand better how this system works.”
Special activity trackers can be used to fairly accurately determine the respiratory rate of people while they sleep. This is the result of a new study conducted by researchers at Martin Luther University Halle-Wittenberg (MLU) together with Charité – Universitätsmedizin Berlin and published in the journal Scientific Reports. In the future, activity trackers could be used to detect the early stages of a disease, as a person’s respiratory rate can indicate signs of an undetected medical problem.
Breathing tells a lot about a patient’s health. Several studies have shown that deviations from a normal respiratory rate, which is about 12 to 18 times a minute, can be an indication of a serious illness. Breathing less than six times a minute is a stronger indication of a life-threatening issue than an abnormal heartbeat. Conversely, very rapid breathing can be an early sign of heart problems. “Nevertheless, the relevance of respiratory rates in the early detection of medical risks has garnered little attention,” says Dr Jan Kantelhardt, a physicist at MLU. For several years now, his research group has been investigating how physical data from measuring devices can improve patient diagnostics.
To date, a reliable measurement of respiratory rates over longer periods of time is only possible in clinics that have the right equipment. However, health studies with several hundred thousand participants, for example, require simpler devices. Up to now, a standard electrocardiogram (ECG) has often been used to measure heart rates and rhythms, thus allowing conclusions to be drawn about breathing. “We were looking for a new, inexpensive way to measure respiration,” says Kantelhardt.
Together with the research group led by Professor Thomas Penzel from the Interdisciplinary Center of Sleep Medicine at the Charité, the team from Halle wanted to examine whether special activity trackers could provide a reliable alternative to ECGs. Staff members in the sleep laboratory at the Charité placed a wristband, in addition to the usual equipment, on around 400 patients. The wristbands registered movement and also took a simple ECG measurement via an electrode attached to the skin. “They are like fitness trackers but much more precise. We can use our own software to analyse the raw data,” says Kantelhardt. This enables the researchers to detect the slightest bit of movement – even if the patient’s arm turns slightly when breathing while asleep.
A comparison of the data from the sleep laboratory showed that these minimal movements allow more precise conclusions to be drawn about the respiratory rate than the ECG recorded at the same time. “If there is too much movement, breathing can no longer be measured with the armbands. But there are always periods at night where we can very reliably observe breathing,” says Kantelhardt. According to the researcher, the armbands could be used, for example, as a diagnostic tool before a patient is sent to a sleep laboratory.
The new method will initially be used to evaluate some of the data from the so-called GNC Health Study, which began in 2014. As part of the long-term nationwide study, approximately 200,000 people regularly undergo medical examinations and interviews about their living conditions and medical histories. Some of the participants also received the same activity trackers as those in the current study. The overall aim of the project is to better understand the development of common diseases such as cancer, diabetes or cardiac arrhythmia in order to improve preventative measures, early diagnosis, and treatment in Germany.
The study was supported by the German-Israeli Foundation for Scientific Research and Development (GIF) and by the Federal Ministry of Education and Research and the Helmholtz Association as part of the GNC Health Study.
A new approach to treating cancers and other diseases that uses a mechanically interlocked molecule as a ‘magic bullet’ has been designed by researchers at the University of Birmingham.
Called rotaxanes, the molecules are tiny nanoscale structures that resemble a dumbbell with a ring trapped around the central post. Scientists have been experimenting with rotaxanes based on thin, thread-like central posts for a number of years, but this new design uses instead a much larger cylindrical-shaped supramolecular ‘helicate’ molecule – around 2nm long and 1nm wide – which have remarkable ability to bind Y-shaped junctions or forks in DNA and RNA.
These forks are created when DNA replicates and, in laboratory tests, the Birmingham researchers have shown that, when they bind to the junctions, the cylinder molecules are able to stop cancer cells, bacteria and viruses from reproducing.
To gain control over that binding, the team from the University’s Schools of Chemistry and Biosciences, collaborated with researchers in Wuhan, in China, and Marseille, in France, to solve the challenge of identifying a ring structure large enough to fit around this central cylinder molecule. They have now shown that a giant pumpkin-shaped molecule, called a cucurbituril) is able to host the cylinder. When the ring is present, the rotaxane molecule is unable to bind.
To prevent the cylinder from slipping out of the pumpkin-shaped ring, the researchers added branches to each end of the cylinder. They demonstrated that the cylinder then becomes mechanically locked inside the ring and that they can use this to control the way the supramolecular cylinder interacts with RNA and DNA.
The results, published in the Journal of the American Chemical Society, show not only how these complex molecules can be produced simply and efficiently, but also how the number of branches can be used to regulate the speed at which the cylinder can escape from the pumpkin-shaped ring – from quickly to not at all.This allows temporal control of the fork-recognition and thus the biological activity.
Lead researcher, Professor Mike Hannon, explains: “This is a really promising new approach that harnesses robust and proven chemistry in an entirely new way that has potential for targeted treatment of cancers and other diseases.
“Our approach is very different to leading cancer drugs which commonly affect all cells in the body, not just the cancer cells. The rotaxane molecule holds the promise that, by turning it on and off as required, it can specifically target and inhibit cancer cells with a high degree of accuracy.”
University of Birmingham Enterprise has a filed patent application covering the structure and design of these novel rotaxanes, and the team has already started work to explore a variety of applications for the approach.
Researchers from Kaunas University of Technology (KTU), Lithuania came up with the idea on how to measure fluctuating blood potassium levels non-invasively, through electrocardiogram.
Researchers from Kaunas University of Technology (KTU), Lithuania came up with the idea on how to measure fluctuating blood potassium levels non-invasively, through electrocardiogram. The researchers claim that their method may become a digital biomarker in the future for managing electrolyte levels. This would be a huge step towards preventing potentially life-threatening conditions among people who suffer from chronic kidney disease.
Electrolytes and especially potassium, are paramount in the conduction of the heart’s cells. When electrolytes are too low or too high, the heart cannot contract normally, leading to dangerous arrhythmias and potentially sudden cardiac death.
“Electrolyte levels are kept within the healthy range by the kidneys. However, the patients with the last stage of chronic kidney disease, who have no renal function left, rely on hemodialysis to keep their electrolyte levels regulated. This means that they are prone to electrolyte imbalance in a 2-day-long hiatus between hemodialysis sessions”, explains Ana Rodrigues, researcher at KTU Biomedical Engineering Institute, one of the authors of the invention.
According to Rodrigues, with today’s aging society, it is estimated that the number of people requiring hemodialysis will markedly increase within 10 years. As people age, so do their kidneys. Research shows that up to 50 percent of seniors over the age of 75 can have kidney disease.
Abnormal electrolyte levels disturb the heart’s natural rhythm; such abnormalities can be reflected in the electrocardiogram. However, identifying electrolyte imbalance using an electrocardiogram is difficult due to confounding factors that mask these expected changes. The task becomes particularly complicated if electrolyte levels start to fluctuate beyond normal, but not reaching levels that require immediate medical attention.
The method proposed by the team of KTU researchers, tackles the problem through mathematical models that enable to quantify subtle changes that are not visible to the naked eye at the early stages of electrolyte imbalance. The method allows to spot potassium – the most arrhythmogenic electrolyte – induced changes in a certain part of the electrocardiogram.
“The initial results are promising. Our method may become a digital biomarker in the future for the management of electrolyte levels”, says Rodrigues.
The method proposed by KTU researchers allows detecting abnormal potassium levels before the onset of life-threatening arrhythmias. Patients could then start hemodialysis sooner, decreasing the chance of hospitalization and even premature death.
Usually, in order to detect the changes in electrolyte balance, a blood sample would be drawn from a patient. However, blood samples are not routinely requested and cannot be drawn outside a clinical environment. Thus, researchers in Lithuania came up with the idea which would allow measuring electrolyte balance noninvasively at home through an electrocardiogram.
“Noninvasive monitoring of electrolyte levels is a very novel concept and is now in its infancy stages. Our paper is one of the first papers published on the topic and, to the best of our knowledge, the first to investigate potassium fluctuations in ambulatory settings between hemodialysis sessions”, says Rodrigues.
The research is the outcome of the close collaboration between KTU, Lithuanian University of Health Sciences (LSMU) and the University of Zaragoza, Spain.
At the moment, clinical studies involving 17 patients have been completed. The researchers are planning on continuing clinical trials with more patients in order to validate their findings. Their next goal is to create an algorithm that would include measuring different electrolyte levels, such as calcium.
Later on, the algorithm could be integrated into wearable wrist-worn device capable of acquiring electrocardiograms. Every once in a while, the patient would record a short electrocardiogram signal (roughly 2-min long) using their fingers, and the system would register the electrolyte levels. If electrolytes were at an alarming level, the clinic would be notified, and the patient would be instructed accordingly.
Researchers from King’s College London have identified the brain activity for the first time in a newborn baby when they are learning an association between different types of sensory experiences. Using advanced MRI scanning techniques and robotics, the researchers found that a baby’s brain activity can be changed through these associations, shedding new light on the possibility of rehabilitating babies with injured brains and promoting the development of life-long skills such as speech, language and movement.
Published recently in Cerebral Cortex, the researcher builds on the fact that learning associations is a very important part of babies’ development but the activity inside the brain that was responsible for learning these associations was unknown and unstudied.
Lead researcher, Dr Tomoki Arichi said it is the first time it has been shown that babies’ brain activity can be altered through associative learning – and in particular, brain responses become associated with particular stimuli, in this case, sound.
“We also found that when a baby is learning, it actually is activating lots of different parts of the brain, so it is starting to incorporate the ‘wider network’ inside the brain which is important for processing activity,” he said.
A total of 24 infants were studied by playing them a sound of a jingling bell for six seconds, coupled with a gentle movement induced by a custom-made 3D printed robot strapped to their right hand.
During this time, the resulting brain activity was measured using functional MRI (fMRI). After 20 minutes of learning an association between the two types of stimuli, the babies then just heard the sound on its own and the resulting brain activity was compared to that seen before the period of learning.
Dr Arichi said not only do the results provide new information about what is happening inside the normal baby brain when it is learning, but also have implications for the injured brain.
If a baby was not capable of processing movement, or movement is not associated with normal activity inside the brain (such might be the case in a baby with cerebral palsy), clinicians could then be able to induce that activity by learning an association with sound, and using the sound simulation to try and amplify and rehabilitate their movement.
“With our findings it raises the possibility of trying to do something to help with that through targeted stimulation and learning associations,” Dr Arichi said.
“It is possible to induce activity inside the part of the brain that normally processes movement, for instance, just by using a single sound. This could be used in conjunction with rehabilitation or to try and help guide brain development early in life.”
When babies are born, they have a new sensory experience around them that is completely different to what they would have been experiencing inside the womb.
They must then start to quickly understand their environment and the relationships between different things happening, which is even more important in babies that have injuries to their brain.
The researchers sought to understand how babies start to learn these key relationships between different kinds of sensory experiences and how this then contributes to the early stages of overall brain development.
“A baby’s brain is constantly learning associations and changing its activity all the time so that it can respond to the new experiences that are around it,” Dr Arichi said.
“In terms of influencing patients and interpreting it in a wider context, what it means is that we should be thinking about how we could help with disorders of brain development from a very early stage in life because we know that experience is constantly shaping the newborn brain’s activity.”
The images reveal that vibrational strong coupling can be achieved, which is a phenomenon that recently attracts wide attention for its potential use to control fundamental physical and chemical material properties. The result could lead the development of a novel platform for on-chip chemical identification of tiny amounts of molecules and for studying fundamental aspects of strong coupling phenomena on the nanometer scale. The work has been published in Nature Photonics (DOI: 10.1038/s41566-020-00725-3).
Light plays an essential role in modern science and technology, with applications ranging from fast optical communication to medical diagnosis and laser surgery. In many of these applications, the interaction of light with matter is of fundamental importance.
At infrared frequencies, light can interact with molecules via their vibrations that occur at molecule-specific frequencies. For that reason, molecular materials can be identified by measuring their infrared reflection or transmission spectra. This technique, often called infrared fingerprint spectroscopy, is widely used for the analysis of chemical, biological and medical substances.
Recently, it was found that the interaction between infrared light and molecular vibrations can be so strong that eventually the material properties are modified, such as conductivity and chemical reactivity. This effect – called vibrational strong coupling – can occur when a material is placed into a microcavity (typically formed by mirrors that are separated by micrometer-size distances) in which the light is concentrated.
The strength of the interaction between light and matter strongly depends on the amount of matter. Consequently, the interaction weakens when the number of molecules is reduced, challenging infrared spectroscopy applications and eventually preventing strong vibrational coupling to be achieved. This problem can be overcome by concentrating light in nanocavities or by compressing its wavelength, which leads to light confinement.
“A particularly strong compression of infrared light can be achieved by coupling it to lattice vibrations (phonons) of thin layers of high-quality polar crystals. This coupling leads to the formation of infrared waves – so-called phonon polaritons – that propagate along the crystal layer with a wavelength that can be more than ten times smaller than that of the corresponding light wave in free space”, says Andrei Bylinkin, first author of the work.
Now, the researchers have studied the coupling between molecule vibrations and propagating phonon polaritons. First, they placed a thin layer of hexagonal boron nitride (less than 100 nm thick) on top of organic molecules. Hexagonal boron nitride is a van der Waals crystal from which thin high-quality layers can be easily obtained by exfoliation. Next, it was necessary to generate phonon polaritons in the thin boron nitride layer. “This cannot be achieved by just shining infrared light onto the boron nitride layer, because the momentum of light is much smaller than the momentum of the phonon polaritons”, says Andrei Bylinkin.
The problem of the momentum mismatch was solved with the help of the sharp metal tip of a scanning near-field microscope, which acts as an antenna for infrared light and concentrates it to a nanoscale infrared spot at the tip apex that provides the necessary momentum to generate phonon polaritons. The microscope also plays a second important role. “It allowed us for imaging the phonon polaritons that propagate along the boron nitride while interacting with the nearby organic molecules”, says Rainer Hillenbrand who led the study. “That way we could observe in real space how the phonon polaritons couple with the molecular vibrations, thereby forming hybrid polaritons”, he added.
The set of images that were recorded at various infrared frequencies around the resonance of the molecular vibrations revealed various fundamental aspects. The hybrid polaritons are strongly attenuated at the frequency of the molecular vibration, which could be interesting for future on-chip sensing applications. The spectrally resolved images also showed that the waves propagate with negative group velocity, and most important, that the coupling between the phonon polaritons and the molecular vibrations is so strong that it falls into the regime of vibrational strong coupling.
“With the help of electromagnetic calculations we could confirm our experimental results, and further predict that strong coupling should be possible even between few atom thick layers of boron nitride and molecules”, says Alexey Nikitin.
The possibility of strong vibrational coupling on the extreme nanometer scale could be used in the future for development of ultrasensitive spectroscopy devices or to study quantum aspects of strong vibrational coupling that have been not accessible so far.
References: Andrei Bylinkin, Martin Schnell, Marta Autore, Francesco Calavalle, Peining Li, Javier Taboada-Gutièrrez, Song Liu, James H. Edgar, Fèlix Casanova Luis E. Hueso, Pablo Alonso-Gonzalez, Alexey Y. Nikitin, and Rainer Hillenbrand, “Real-space observation of vibrational strong coupling between propagating phonon polaritons and organic molecules”, Nature Photonics, 2020. DOI: 10.1038/s41566-020-00725-3