“We show experimentally for the first time the potential that direct photon measurements are sensitive to the transverse motion of gluons and that we can use such measurements to start constraining things — to reduce the huge uncertainties in our knowledge of how gluons behave,” said Alexander Bazilevsky, deputy spokesperson of the PHENIX Collaboration and a physicist at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory.

The data, published in Physical Review Letters, come from collisions between beams of polarized protons at RHIC, a DOE Office of Science user facility for nuclear physics research located at Brookhaven Lab. RHIC is the only facility in the world capable of colliding protons with their spin directions aligned in a controlled way.

“RHIC’s spin polarization is a crucial requirement for this research. It gives us a way to establish which way is up so we can measure the motions of other particles relative to that reference direction,” explained Brookhaven Lab physicist Nicole Lewis, whose work on this analysis formed the basis of her Ph.D. thesis.

As Lewis explained in an invited talk at the 2021 Fall Meeting of the American Physical Society’s Division of Nuclear Physics on October 12, understanding the origin of proton spin is also one of the main research goals.

A proton’s spin, or intrinsic angular momentum, makes it act like a tiny bar magnet with two poles. This property is used every day in magnetic resonance imaging (MRI), where a powerful external magnet changes the alignment of protons’ spins in our bodies so doctors can see features inside. But where spin comes from is still a mystery.

Studies at RHIC and elsewhere show that quark spins and gluon spins both make substantial contributions to proton spin, but not enough. The motions of these fundamental particles within protons are expected to also play a role. Using direct photons to measure how gluons’ transverse motion is correlated with overall proton spin is expected to help solve this puzzle.

In addition, studying the motion of quarks and gluons within a proton will help reveal details of the interactions between these particles. Those interactions are governed by the strong nuclear force — the strongest force in nature — which is carried by gluons and binds the quarks within the protons and neutrons of atomic nuclei. So, studying gluons and the strong force is really about understanding the “glue” that binds visible matter — everything made of atoms.

The newly analyzed data from PHENIX reveal that direct photons can be used to study gluons’ motions inside a proton.

The PHENIX measurements are 50 times more precise than the only previously published direct photon data — about 30 years ago from an experiment at DOE’s Fermi National Accelerator Laboratory.

“Our results help to validate the use of this approach for future studies at RHIC — including at an upgraded sPHENIX detector currently being installed in the location of the original PHENIX detector, which ended its experimental run in 2016. sPHENIX is expected to be operational in 2023 and will have even better capabilities to detect direct photons,” Bazilevsky said.

The direct photon data from proton-proton collisions will also provide important cross-checking for experiments using electrons to probe the inner structure of protons at the future Electron-Ion Collider (EIC).

“Proton-proton and electron-proton collisions give us different, complementary ways to ‘see’ inside a proton to construct the final picture of how things look,” Bazilevsky said.

How to peer inside a proton

Proton-proton collisions can produce a range of interactions. A quark in one proton can interact with either a quark or gluon in the other. And a gluon also can interact with a quark or gluon. So, these collisions produce a mixture of quark-quark, gluon-gluon, and quark-gluon events.

But only one of those possible interactions — quark-gluon scattering — is a major source of photons (quantized particles of light) emitted directly from the collision zone. And because photons have no electric charge or “color” charge (the type of charge carried by quarks and gluons) they don’t interact with anything on their way out. By measuring these direct photons, scientists can zero in on the gluons involved in these interactions.

To tell whether the gluons are moving, the scientists align the spins in one proton beam transversely — that is, pointing “up” relative to their forward direction of motion. Then they measure whether there are more photons emerging to the left or the right of the forward-going proton’s up point of reference.

“The up is the spin, and the left or right gives you the momentum of the gluons in the transverse direction,” Lewis explained. That helps physicists expand beyond a one-dimensional view of quarks or gluons only moving in the same direction as the proton they are in.

“From this we are able to probe a more three-dimensional picture of the proton and study internal transverse dynamics of the quarks and gluons. If we were to measure a very large left to right asymmetry, that would indicate that there are large internal dynamics going on inside the proton, which would in turn contribute to the proton’s spin.”

Picking out direct photons

Figuring out which photons come directly from a quark-gluon interaction isn’t so simple.

“There are so many other photons present in these collisions that come from the decays of other particles or radiative processes,” Lewis said. “Trying to isolate the photons that came directly from the collision, that’s the hard part.”

The scientists use a process of elimination. If a photon picked up in the detector is surrounded by other particles with similar energy, it likely came from radiative processes that happened after the collision — so those photons are not direct. Likewise, if the energy and angles of a pair of photons can be reconstructed to have originated from the decay of a parent particle — a pi zero meson, say — then those photons are also not direct photons. After all the eliminations, the photons with no other obvious source are assumed to have originated from a quark-gluon scattering event.

“PHENIX has the resolution and other characteristics that enable it to do these measurements,” Bazilevsky said.

“Another reason why this is hard is because direct photon production is a pretty rare process,” said Lewis. “It doesn’t happen frequently, and it has a large background — which makes the signal hard to detect. We need many collisions to have enough occurrences to be able to do the analysis.”

Now for the first time, Bazilevsky said, “we show that a collider like RHIC can produce enough collisions for such measurements.”

Coming into focus

But even with the detector and collider capabilities, the PHENIX results did not show an asymmetry in the number of direct photons emerging left or right of the transversely polarized proton. “We got something that was consistent with zero,” Lewis said.

But that does not mean that the gluons involved in these interactions were not moving, because the uncertainties in the measurements are still somewhat large.

“The models based on previous measurements give only a blurry picture,” Bazilevsky said. “Within the large uncertainties of these models, we show that direct photons are starting to be sensitive to gluon motions and reducing the uncertainties. So, our picture is still blurry, but we are zooming in a bit.”

“We are looking forward to the next step — building and using the sPHENIX detector, which will be able to track many more collisions and pick out direct photons emerging from wider angles around the collision zone. Then we may start to see something that’s not zero,” he said.

The study focused on two traits previously linked to the risk of dementia: neuroticism, which measures a predisposition for negative emotions, and conscientiousness, which measures the tendency to be careful, organized, goal-directed and responsible.

“We have done studies showing who’s at risk of developing dementia, but those other studies were looking at the clinical diagnosis,” said Antonio Terracciano, professor of geriatrics at the College of Medicine. “Here, we are looking at the neuropathology; that is, the lesions in the brain that tell us about the underlying pathological change. This study shows that even before clinical dementia, personality predicts the accumulation of pathology associated with dementia.”

The findings, published as an article-in-press online with Biological Psychiatry and also available through FSU’s open access research repository, combine data from the Baltimore Longitudinal Study of Aging (BLSA) and previously published work in a meta-analysis that summarized 12 studies on personality and Alzheimer’s neuropathology. The studies combined included more than 3,000 participants. Combining results across studies provides more robust estimates of the associations between personality and neuropathology than a single individual study can typically provide.

In both the BLSA and meta-analysis, the researchers found more amyloid and tau deposits (the proteins responsible for the plaques and tangles that characterize Alzheimer’s disease) in participants who scored higher in neuroticism and lower in conscientiousness.

The team also found associations to be stronger in studies of cognitively normal people compared to studies that included people with cognitive problems.

The findings suggest that personality can help protect against Alzheimer’s and other neurological diseases by delaying or preventing the emergence of neuropathology for those strong in conscientiousness and low in neuroticism.

“Such protection against neuropathology may derive from a lifetime difference in people’s emotions and behaviors,” Terracciano said. “For example, past research has shown that low neuroticism helps with managing stress and reduces the risk of common mental health disorders. Similarly, high conscientiousness is consistently related to healthy lifestyles, like physical activity. Over time, more adaptive personality traits can better support metabolic and immunological functions, and ultimately prevent or delay the neurodegeneration process.”

The BLSA is a scientific study of human aging conducted by the National Institute on Aging (NIA), part of the National Institutes of Health (NIH), that began in 1958. Personality was measured using a five-factor personality test, the most common personality assessment tool. At the time of their enrollment in the BLSA neuroimaging sub-study, all participants were free of dementia or other severe medical conditions.

Advances in brain scan technology used to assess in vivo amyloid and tau neuropathology made it possible for researchers to complete this work.

“Until recently, researchers measured amyloid and tau in the brain through autopsy — after people died,” Terracciano said. “In recent years, advances in medical imaging have made it possible to assess neuropathology when people are still alive, even before they show any symptoms.”

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This ability is key to our survival, enabling us to safely navigate our surroundings and quickly understand and respond to new situations. It is perhaps unsurprising that the brain devotes considerable space to these sensitive skin surfaces that are specialized for fine, discriminative touch and continually gather detailed information via the sensory neurons that innervate them.

But how does the connection between sensory neurons and the brain result in such exquisitely sensitive skin?

A new study led by researchers at Harvard Medical School has unveiled a mechanism that may underlie the greater sensitivity of certain skin regions.

The research, conducted in mice and published Oct. 11 in Cell, shows that the overrepresentation of sensitive skin surfaces in the brain develops in early adolescence and can be pinpointed to the brain stem. Moreover, the sensory neurons that populate the more sensitive parts of the skin and relay information to the brain stem form more connections and stronger ones than neurons in less sensitive parts of the body.

“This study provides a mechanistic understanding of why more brain real estate is devoted to surfaces of the skin with high touch acuity,” said senior author David Ginty, the Edward R. and Anne G. Lefler Professor of Neurobiology at Harvard Medical School. “Basically, it’s a mechanism that helps explain why one has greater sensory acuity in the parts of the body that require it.”

While the study was done in mice, the overrepresentation of sensitive skin regions in the brain is seen across mammals — suggesting that the mechanism may be generalizable to other species. From an evolutionary perspective, mammals have dramatically varied body forms, which translates into sensitivity in different skin surfaces. For example, humans have highly sensitive hands and lips, while pigs explore the world using highly sensitive snouts. Thus, Ginty thinks this mechanism could provide the developmental flexibility for different species to develop sensitivity in different areas.

Moreover, the findings, while fundamental, could someday help illuminate the touch abnormalities seen in certain neurodevelopmental disorders in humans.

Scientists have long known that certain body parts are overrepresented in the brain — as depicted by the brain’s sensory map, called the somatosensory homunculus, a schematic of human body parts and the corresponding areas in the brain where signals from these body parts are processed. The striking illustration includes cartoonishly oversized hands and lips. Previously, it was thought that the overrepresentation of sensitive skin regions in the brain could be attributed to a higher density of neurons innervating those skin areas. However, earlier work by the Ginty lab revealed that while sensitive skin does contain more neurons, these extra neurons are not sufficient to account for the additional brain space.

“We noticed that there was a rather meager number of neurons that were innervating the sensitive skin compared to what we’d expect,” said co-first author Brendan Lehnert, a research fellow in neurobiology, who led the study with Celine Santiago, also a research fellow in the Ginty lab.

“It just wasn’t adding up,” Ginty added.

To investigate this contradiction, the researchers conducted a series of experiments in mice that involved imaging the brain and neurons as neurons were stimulated in different ways. First, they examined how different skin regions were represented in the brain throughout development. Early in development, the sensitive, hairless skin on a mouse’s paw was represented in proportion to the density of sensory neurons. However, between adolescence and adulthood, this sensitive skin became increasingly overrepresented in the brain, even though the density of neurons remained stable — a shift that was not seen in less sensitive, hairy paw skin.

“This immediately told us that there’s something more going on than just the density of innervation of nerve cells in the skin to account for this overrepresentation in the brain,” Ginty said.

“It was really unexpected to see changes over these postnatal developmental timepoints,” Lehnert added. “This might be just one of many changes over postnatal development that are important for allowing us to represent the tactile world around us and helping us gain the ability to manipulate objects in the world through the sensory motor loop that touch is such a special part of.”

Next, the team determined that the brain stem — the region at the base of the brain that relays information from sensory neurons to more sophisticated, higher-order brain regions — is the location where the enlarged representation of sensitive skin surfaces occurs. This finding led the researchers to a realization: The overrepresentation of sensitive skin must emerge from the connections between sensory neurons and brain stem neurons.

To probe even further, the scientists compared the connections between sensory neurons and brain stem neurons for different types of paw skin. They found that these connections between neurons were stronger and more numerous for sensitive, hairless skin than for less sensitive, hairy skin. Thus, the team concluded, the strength and number of connections between neurons play a key role in driving overrepresentation of sensitive skin in the brain. Finally, even when sensory neurons in sensitive skin weren’t stimulated, mice still developed expanded representation in the brain — suggesting that skin type, rather than stimulation by touch over time, causes these brain changes.

“We think we’ve uncovered a component of this magnification that accounts for the disproportionate central representation of sensory space.” Ginty said. “This is a new way of thinking about how this magnification comes about.”

Next, the researchers want to investigate how different skin regions tell the neurons that innervate them to take on different properties, such as forming more and stronger connections when they innervate sensitive skin. “What are the signals?” Ginty asked. “That’s a big, big mechanistic question.”

And while Lehnert describes the study as purely curiosity-driven, he noted that there is a prevalent class of neurodevelopmental disorders in humans called developmental coordination disorders that affect the connection between touch receptors and the brain — and thus might benefit from elucidating further the interplay between the two.

“This is one of what I hope will be many studies that explore on a mechanistic level changes in how the body is represented over development,” Lehnert says. “Celine and I both think this might lead, at some point in the future, to a better understanding of certain neurodevelopmental disorders.”

Co-investigators included Erica L. Huey, Alan J. Emanuel, Sophia Renauld, Nusrat Africawala, Ilayda Alkislar, Yang Zheng, Ling Bai, Charalampia Koutsioumpa, Jennifer T. Hong, Alexandra R. Magee,Christopher D. Harvey of Harvard Medical School.

The research was supported by the National Institutes of Health (F32 NS095631-01, F32-NS106807, K99 NS119739, DP1 MH125776, R01 NS089521, and R01 NS97344), a William Randolph Hearst Fellowship, a Goldenson Fellowship, a Harvard Medical School Dean’s Innovation Grant in the Basic and Social Sciences, and the Edward R. and Anne G. Lefler Center for the Study of Neurodegenerative Disorders.

Researchers from the University of Nottingham have for the first time used a path of assembled molecules liquids that travelling molecules can be propelled along by light. The research ‘Light-controlled micron-scale molecular motion’ has been published today in Nature Chemistry.

Professor David Amabilino from the School of Chemistry at the University of Nottingham is one of the lead researchers, he explains: “In living organisms, molecular motors travel along specific molecular paths, it is an essential part of cell function. We have shown that a synthetic self-made molecular fibre in a liquid behaves like a path for the movement of a molecular traveller over a distance 10,000 times its length. Light acts as the fuel to encourage the motion, while a molecular switch mixed into the system apparently propels the traveller on its way.

The system emulates, for the first time, movement of the kind taking place along fibres in cells. This is a very exciting discovery as If we can find ways to make use of the light’s potential in this process then it could pave the way for use in light activated medicines, new ways to harness light energy as a source of power and to create new sustainable ways to carry out chemical tasks.”

The team used interactions between oppositely charged chemical groups and created motion to this static system by introducing a switching molecule, that flaps back and forth quite quickly, into the fibres. Shining a light onto this weakens the traveller molecules interaction with the path as they move along it, which can be at some distance. If the molecule were our size, they would move the equivalent of 10 km.

Heat is released when the switching molecules are irradiated, and that heat has a local effect that helps the traveller move, so the mechanical movement of the switch, and the heat that is released when it does, are important for making the system work.

The technique the team used to observe these effects is a special optical microscope that allowed the simultaneous exciting of the molecules — making them move — and observation of them as they give light back out (the travelling molecules are fluorescent).

Co-author on the study Mario Samperi adds: “The system we have prepared is very sensitive to the solvent in which the fibres are formed. In a liquid about the strength of strong whisky, the travelling molecules move along the fibres to another location, whereas when the liquid is the strength of weaker limoncello, rings of rearranged fibres are formed where the travellers have moved along and incorporated into the newly formed circular track.

We want to be able to transport other molecules from one place to another in a controlled way, so that the travelling molecules can carry a package from one place to another, emulating nature, but using light as energy.”

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In a recently published paper in npj: Science of Learning, researchers at Carnegie Mellon University have found a way to decode the brain activity associated with individual abstract scientific concepts pertaining to matter and energy, such as fermion or dark matter.

Robert Mason, senior research associate, Reinhard Schumacher, professor of physics and Marcel Just, the D.O. Hebb University Professor of Psychology, at CMU investigated the thought processes of their fellow CMU physics faculty concerning advanced physics concepts by recording their brain activity using functional Magnetic Resonance Imaging (fMRI).

Unlike many other neuroscience studies that use brain imaging, this one was not out to find “the place in the brain” where advanced scientific concepts reside. Instead, this study’s goal was to discover how the brain organizes highly abstract scientific concepts. An encyclopedia organizes knowledge alphabetically, a library organizes it according to something like the Dewey Decimal System, but how does the brain of a physicist do it?

The study examined whether the activation patterns evoked by the different physics concepts could be grouped in terms of concept properties. One of the most novel findings was that the physicists’ brains organized the concepts into those with measureable versus immeasurable size. Here on Earth for most of us mortals, everything physical is measureable, given the right ruler, scale or radar gun. But for a physicist, some concepts like dark matter, neutrinos or the multiverse, their magnitude is not measureable. And in the physicists’ brains, the measureable versus immeasurable concepts are organized separately.

Of course, some parts of the brain organization of the physics professors resembled the organization in physics students’ brains such as concepts that had a periodic nature. Light, radio waves and gamma rays have a periodic nature but concepts like buoyancy and the multiverse do not.

But how can this interpretation of the brain activation findings be assessed? The study team found a way to generate predictions of the activation patterns of each of the concepts. But how can the activation evoked by dark matter be predicted? The team recruited an independent group of physics faculty to rate each concept on each of the hypothesized organizing dimensions on a 1-7 scale. For example, a concept like “duality” would tend to be rated as immeasureable (i.e., low on the measureable magnitude scale). A computational model then determined the relation between the ratings and activation patterns for all of the concepts except one of them and then used that relation to predict the activation of the left-out concept. The accuracy of this model was 70% on average, well above chance at 50%. This result indicates that the underlying organization is well-understood. This procedure is demonstrated for the activation associated with the concept of dark matter in the accompanying figure.

Creativity of Thought

Near the beginning of the 20^th century, post-Newtonian physicists radically advanced the understanding of space, time, matter, energy and sub-atomic particles. The new concepts arose not from their perceptual experience, but from the generative capabilities of the human brain. How was this possible?

The neurons in the human brain have a large number of computational capabilities with various characteristics, and experience determines which of those capabilities are put to use in various possible ways in combination with other brain regions to perform particular thinking tasks. For example, every healthy brain is prepared to learn the sounds of spoken language, but an infant’s experience in a particular language environment shapes which phonemes of which language are learned.

The genius of civilization has been to use these brain capabilities to develop new skills and knowledge. What makes all of this possible is the adaptability of the human brain. We can use our ancient brains to think of new concepts, which are organized along new, underlying dimensions. An example of a “new” physics dimension significant in 20^th century, post-Newtonian physics is “immeasurability” (a property of dark matter, for example) that stands in contrast to the “measurability” of classical physics concepts, (such as torque or velocity). This new dimension is present in the brains of all university physics faculty tested. The scientific advances in physics were built with the new capabilities of human brains.

Another striking finding was the large degree of commonality across physicists in how their brains represented the concepts. Even though the physicists were trained in different universities, languages and cultures, there was a similarity in brain representations. This commonality in conceptual representations arises because the brain system that automatically comes into play for processing a given type of information is the one that is inherently best suited to that processing. As an analogy, consider that the parts of one’s body that come into play to perform a given task are the best suited ones: to catch a tennis ball, a closing hand automatically comes into play, rather than a pair or knees or a mouth or an armpit. Similarly, when physicists are processing information about oscillation, the brain system that comes into play is the one that would normally process rhythmic events, such as dance movements or ripples in a pond. And that is the source of the commonality across people. It is the same brain regions in everyone that are recruited to process a given concept.

So the secret of teaching ancient brains new tricks, as the advance of civilization has repeatedly done, is to empower creative thinkers to develop new understandings and inventions, by building on or repurposing the inherent information processing capabilities of the human brain. By communicating these newly developed concepts to others, they will root themselves in the same information processing capabilities of the recipients’ brains as the original developers used. Mass communication and education can propogate the advances to entire populations. Thus the march of science, technology and civilization continue to be driven by the most powerful entity on Earth, the human brain.

The project was funded by the Office of Naval Research and the National Science Foundation.