Thursday, May 7th, 2020

Time	Event
3:00p	Optogenetics with SOUL Optogenetics has revolutionized neurobiology, allowing researchers to use light to activate or deactivate neurons that are genetically modified to express a light-sensitive channel. This ability to manipulate neuron activity has allowed causal testing of the function of specific neurons, and also has therapeutic potential to reduce symptoms in brain disorders. However, activating neurons deep within a given brain, especially a large primate brain but even a small mouse brain, is challenging, and currently requires implanting fibers that could cause damage or inflammation. McGovern Investigator Guoping Feng and colleagues have now overcome this challenge, developing optogenetic tools that allow non-invasive stimulation of neurons in the deep brain. “Neuroscientists have dreamed of methods to turn neurons on and off, to understand the function of different neurons, but also to repair brain malfunctions that lead to psychiatric disorders, and optogenetics made this possible” explains Feng, the James W. (1963) and Patricia T. Poitras Professor in Brain and Cognitive Sciences. “We were trying to improve the light sensitivity of optogenetic tools to broaden applications.” Engineering with light In order to stimulate neurons with minimal invasiveness, Feng and colleagues engineered a new type of opsin. The original breakthrough optogenetics protocol used channelrhodopsin, a light-sensitive channel discovered in algae. By expressing this channel in neurons, light of the right wavelength can be used to activate the neuron in a dish or in vivo. However, in vivo application requires the implantation of optical fibers to deliver the light close to the specific brain region being stimulated, especially if the target region is in the deep brain. In addition, if the neuron being targeted is in the deep brain, it is hard for light to reach the region in the absence of invasive tools that can damage tissue and impact the behavior of the animal. This new study creates a method that can activate any mouse brain region, independent of its location, non-invasively. “Prior to our study, a few studies have contributed in various ways to the development of optogenetic stimulation methods that would be minimally invasive to the brain. However, all of these studies had various limitations in the extent of brain regions they could activate,” says co-senior study author Robert Desimone, director of the McGovern Institute and the Doris and Don Berkey Professor of Neuroscience at MIT. Probing the brain with SOUL Feng and colleagues turned instead to new opsins, in particular SOUL, a new type of opsin that is very sensitive to even low-level light. The Feng group engineered this opsin, based on SSFO, a second-generation optogenetics tool, to have increased light sensitivity, and took advantage of a second property: that SOUL is activated in multiple steps, and once activated, it stays active for longer than other commonly used opsins. This means that a burst of a few seconds of low-level light can cause neurons to stay active for 10-30 minutes. In order to put SOUL through its paces, the Feng lab expressed this channel in the lateral hypothalamus of the mouse brain. This is a deep region, challenging to reach with light, but with neurons that have clear functions that will lead to changes in behavior. Feng’s group was able to turn on this region non-invasively with light from outside the skull, and cause changes in feeding behavior. “We were really surprised that SOUL was able to activate one of the deepest areas in the mouse brain, the lateral hypothalamus, which is 6 millimeters deep,” explains Feng. But there were more surprises. When the authors activated a region of the primate brain using SOUL, they saw oscillations, waves of synchronized neuronal activity coming together like a choir. Such waves are believed to be important for many brain functions, and this result suggests that the new opsin can manipulate these brain waves, allowing scientists to study their role in the brain. The authors are planning to move the study in several directions, studying models of brain disorders to identify circuits that may be suitable targets for therapy, as well as moving the methodology so that it can be used beyond the superficial cortex in larger animals. While it is too early to discuss applying the system to humans, the research brings us one step closer to future treatment of neurological disorders. (Comment on this)
3:05p	In a suddenly remote spring, library support services carry on While the MIT Libraries’ physical spaces and tangible collections are currently inaccessible, its network of people, services, and resources has mobilized behind the scenes to ensure that Institute learning and research continue despite the disruptions of Covid-19.  Since mid-March, the MIT Libraries have provided only services and resources that can be accessed remotely. Library staff — like many across MIT — had to quickly pivot to a new reality, finding creative solutions to providing the expertise and resources the community needs now.  Expanding access to digital content Without access to physical collections, library staff have had to navigate a complex landscape of publishers, platforms, and copyright to access the materials MIT students, faculty, and researchers depend on. Once physical library locations closed, staff sprang into action to identify alternative resources to print and fulfill requests from the MIT community and beyond: Staff have loaded more than 300,000 new e-books and added 475,000 links to digital versions of materials in the catalog through the HathiTrust Digital Library. The “Covid Collections Group” created a guide to dozens of free and expanded resources for textbooks, e-books, journals, film, and music through offers from publishers during Covid-19.  1.4 million titles are available through the Internet Archive’s National Emergency Library. Staff expedited 150 purchases of materials requested by the MIT community, including technical standards related to face mask manufacturing. Article requests, which have seen a 33 percent increase during the closure, have been filled at a rate of 88 percent, with an average turnaround time of nine hours. Staff fulfilled 90 percent of lending requests despite the difficult circumstances, with less than a half-day turnaround, on average.  The rapid move to remote work has required a nimble, creative response from library staff, but the benefits of pivoting to a digital-first model could last far beyond Covid-19. “Providing comprehensive digital access to content has been a foundational part of our vision for the future of research libraries,” says Chris Bourg, director of the MIT Libraries. “But I think our current crisis, where we’ve been forced to quickly adapt to a remote environment, has really thrown into relief how important it is. Research and learning depend on more open and equitable access to knowledge, and that will be true long after this crisis passes.” Here to help, wherever you are Some library services have had to adjust to provide more flexibility: recognizing that plans change and time zones and working hours vary, the libraries increased the hours the AskUs chat service is available, and extended the length of time interlibrary borrowing requests can be downloaded. Others have adapted easily — such as providing expertise in a specific subject area, data management, or copyright — with the help of a few new tools. Daniel Sheehan, program head for GIS and Statistical Software Services, describes a recent morning’s work: “I got a couple of economics grad students — one in France — together with a political science grad student to talk over Zoom about redistricting software while getting real-time help from a colleague over Slack. An undergrad needed help accessing the mapping software Arcgis Pro remotely on one of our GIS and Data Lab computers, so I got her going with screen sharing. Then I looked at data via Dropbox from an EAPS grad student in advance of a Zoom meeting he requested. It’s not the same as being on campus in person, but the technology seems to be working well in this strange time.”  All in it together: Support across the community Beyond one-on-one help, library departments are finding ways to adapt to current needs, often requiring collaborations between teams or across the Institute. The libraries are gearing up for MIT-wide electronic thesis submission this spring. After running a successful e-thesis pilot with several departments, labs, and centers last year, library staff will take an existing tool developed for digital archives transfers and test to ensure it’s ready for widespread production to support the graduating class of 2020. Distinctive Collections, meanwhile, is working with several classes, including Debbie Douglas’s History of MIT, to find ways of incorporating documentary efforts into assignments, so students take an active role in archiving our current experience. Staff are also web-archiving MIT websites and working to collect experiences across the Institute during this unprecedented time. Finding opportunity amid the crisis, staff have found ways to streamline processes, call on diverse experts to problem-solve jointly, and employ their sophisticated understanding of the online information landscape to help MIT users. Looking to the future, they could brainstorm with faculty on new ways to bring library expertise into remote courses.   “At the libraries, our vision is for a more open, equitable, and interactive information ecosystem,” says Karrie Peterson, head of Liaison, Instruction, and Reference Services. “Librarians — online and asynchronously — are still working toward that vision, whether helping researchers with data-sharing practices or assisting student teams in exploring sustainability issues in their literature reviews. The current situation has highlighted the importance of open and equitable knowledge sharing and provides us with an extraordinary opportunity to move in that direction.” (Comment on this)
3:15p	When baby planets melt Let’s start at the beginning. Before humans, before Earth, before any of the planets existed, there were baby planets — planetesimals. Coalesced from dust exploded outward by the solar nebula, these blobs of material were just a few kilometers in diameter. Soon, they too aggregated due to gravity to form the rocky planets in the innermost part of the solar system, leaving the early details about these planetesimals to the imagination. Their mysterious identity is complicated by the fact that Mercury, Venus, Earth, and Mars are all different in chemical composition. Like a blender mixing the ingredients in a cake, Earth has undergone some rearrangement, largely due to volcanism and plate tectonics that shift elements into and out of the interior, that further obscures information about what the original ingredients might have been, and their proportions. Now, a pair of MIT scientists in the Department of Earth, Atmospheric and Planetary Sciences (EAPS) have revealed some key information about those planetesimals by recreating in a laboratory the first magmas these objects might have produced in the solar system’s infancy. And it turns out, there’s physical evidence of these magmas in meteorites, adding validation to their claims. “This formation and differentiation of these planetesimals is kind of an important step in how you make the inner terrestrial planets, and we’re really just starting to unlock that story,” says R R Schrock Professor of Geology Timothy Grove, senior author on the study, published in a trilogy of papers in the journals Geochimica et Cosmochimica Acta and Meteoritics and Planetary Science. Meteorite teasers Tiny pieces of evidence of the solar system’s planetary building blocks exist to this day in meteorites, which all fit into two major categories. Chondrites are made of original material and are the most common type. Achondrites come from parent bodies that have experienced some sort of modification — and understanding those modifications helps explain the processes that form and grow planets. Ureilites, the second most abundant group of achondrites, were the original subject of this investigation. But quickly, the researchers realized their findings could also be applied elsewhere. Thanks to a series of experiments designed to correct errors in past techniques, Grove and lead author Max Collinet PhD ’19 uncovered a new angle. “We really came from wanting to understand something about a small group of meteorites that might seem obscure to a lot of people,” says Collinet of his doctoral research. “But then when we did those experiments, we realized that the melts we were producing have a lot of implications to a lot of other planetary building blocks.” This includes the origin of the most abundant type of achondritic meteorites, called eucrites, presumed to come from Vesta, the second-largest body in the asteroid belt. This was because in 1970, an MIT researcher discovered that Vesta was made of the same type of basaltic rock. “We had all these basaltic lavas from the surface of Vesta, and basically everyone assumed that’s what happens when you melt these bodies,” explains Grove. But recently, other studies have overturned this hypothesis, leaving the question: What were the earliest melts formed in planetesimals? Making tiny planets “What we realized is that we did not really know at all what the composition was of those first magmas that were produced in any planetesimal, let alone the one that we were interested in — the parent body of ureilites,” says Collinet of the results from their new experimental methods. In past studies, by using a typical experimental “open system” setup that maintained the low oxygen levels expected inside a planetesimal, much of the highly reactive alkali elements — sodium and potassium — could escape. Grove and Collinet had to work together to carry out the experiments using a unique device at MIT that kept the system “closed” and retained all alkalis. They loaded a tiny metal capsule a few millimeters square with the same chemical elements that might be present in a planetesimal and subjected it to conditions of low oxygen, rock-melting temperatures, and pressures expected in the relatively small bodies’ interiors. Once those conditions were met, the sample’s magma was frozen — as recorded in their methods — by “whacking” the machine with a wrench to ensure their capsule popped free, dropping to room temperature quickly. Analyzing the magma, cooled into a glass, was tricky. Because they were looking for the onset of melting, the pools inside the samples were quite small. It took a few adjustments to their procedures to get all the tiny pools to combine into one larger pocket. Once they were able to measure the samples, the pair were shocked at the implications of what they found. “We had no idea that we were going to produce this stuff. It was completely unanticipated,” Grove marvels. “This stuff” was an alkali-rich granite — a light-colored, silica-rich composition like you might see on a kitchen countertop, on the opposite end of the rock-type spectrum from the alkali-poor, silica-poor basalts on Vesta — like those formed from lava in Hawaii. “Collinet and Grove show that previous ideas about the compositions of the earliest melts in our solar system, ~4.6 billion years ago, may have been incorrect because the record of early processes has been obscured by geological activity in more recent times,” says Cyrena Goodrich, a senior research scientist at the Lunar and Planetary Institute in the Universities Space Research Association, who was not involved in the research. “These results will have applications to a wide range of topics in geology and planetary sciences and will substantially influence future work.” These surprising results almost nearly matched melts measured in many natural meteorite samples. Additionally, the pair had learned something about the mysterious alkalis missing from the rocky planets and the differences between Earth, Mars, Venus and Mercury. Reimagining the beginning Previously, it was assumed dissimilarities between the terrestrial planets came about during the initial scattering of elements in the solar nebula and related to how those elements condensed from gases into solids. “Now we have another way,” says Grove. With the melts hosting a lot of the alkalis, it would only take some method of melt removal to leave the residual planetesimals depleted in potassium and sodium. The next step will be to determine just how these melts could be extracted from the planetesimals’ interiors, given that the drivers of magma movement in Earth would likely not be the same in these planetary bodies. In fact, migration of elements in early planets, such as the formation of metal cores, is a wide area of unknown that the pair of scientists are eager to continue exploring. Due to the inability to observe what actually happened in the establishment of the solar system, the surprises exposed by this study are a significant step. “We bring new clues into how the nebula created these bodies,” summarizes Collinet, who is now a postdoc in Germany, working on understanding the layers beneath Mars’ outer crust. From a tiny capsule in a lab on the MIT campus or a microscopic droplet of melt in a meteorite, it is possible to reveal insight into the birth of a vast planet. (Comment on this)
11:59p	Researchers map tiny twists in “magic-angle” graphene Made of a single layer of carbon atoms linked in a hexagonal honeycomb pattern, graphene’s structure is simple and seemingly delicate. Since its discovery in 2004, scientists have found that graphene is in fact exceptionally strong. And although graphene is not a metal, it conducts electricity at ultrahigh speeds, better than most metals. In 2018, MIT scientists led by Pablo Jarillo-Herrero and Yuan Cao discovered that when two sheets of graphene are stacked together at a slightly offset “magic” angle, the new “twisted” graphene structure can become either an insulator, completely blocking electricity from flowing through the material, or paradoxically, a superconductor, able to let electrons fly through without resistance. It was a monumental discovery that helped launch a new field known as “twistronics,” the study of electronic behavior in twisted graphene and other materials. Now the MIT team reports their latest advancements in graphene twistronics, in two papers published this week in the journal Nature. In the first study, the researchers, along with collaborators at the Weizmann Institute of Science, have imaged and mapped an entire twisted graphene structure for the first time, at a resolution fine enough that they are able to see very slight variations in local twist angle across the entire structure. The results revealed regions within the structure where the angle between the graphene layers veered slightly away from the average offset of 1.1 degrees. The team detected these variations at an ultrahigh angular resolution of 0.002 degree. That’s equivalent to being able to see the angle of an apple against the horizon from a mile away. They found that structures with a narrower range of angle variations had more pronounced exotic properties, such as insulation and superconductivity, versus structures with a wider range of twist angles. “This is the first time an entire device has been mapped out to see what is the twist angle at a given region in the device,” says Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT. “And we see that you can have a little bit of variation and still show superconductivity and other exotic physics, but it can’t be too much. We now have characterized how much twist variation you can have, and what is the degradation effect of having too much.” In the second study, the team report creating a new twisted graphene structure with not two, but four layers of graphene. They observed that the new four-layer magic-angle structure is more sensitive to certain electric and magnetic fields compared to its two-layer predecessor. This suggests that researchers may be able to more easily and controllably study the exotic properties of magic-angle graphene in four-layer systems. “These two studies are aiming to better understand the puzzling physical behavior of magic-angle twistronics devices,” says Cao, a graduate student at MIT. “Once understood, physicists believe these devices could help design and engineer a new generation of high-temperature superconductors, topological devices for quantum information processing, and low-energy technologies.” Like wrinkles in plastic wrap Since Jarillo-Herrero and his group first discovered magic-angle graphene, others have jumped at the chance to observe and measure its properties. Several groups have imaged magic-angle structures, using scanning tunneling microscopy, or STM, a technique that scans a surface at the atomic level. However, researchers have only been able to scan small patches of magic-angle graphene, spanning at most a few hundred square nanometers, using this approach. “Going over an entire micron-scale structure to look at millions of atoms is something that STM is not best suited for,” Jarillo-Herrero says. “In principle it could be done, but would take an enormous amount of time.” So the group consulted with researchers at the Weizmann Institute for Science, who had developed a scanning technique they call “scanning nano-SQUID,” where SQUID stands for Superconducting Quantum Interference Device. Conventional SQUIDs resemble a small bisected ring, the two halves of which are made of superconducting material and joined together by two junctions. Fit around the tip of a device similar to an STM, a SQUID can measure a sample’s magnetic field flowing through the ring at a microscopic scale. The Weizmann Institute researchers scaled down the SQUID design to sense magnetic fields at the nanoscale. When magic-angle graphene is placed in a small magnetic field, it generates persistent currents across the structure, due to the formation of what are known as “Landau levels.” These Landau levels, and hence the persistent currents, are very sensitive to the local twist angle, for instance, resulting in a magnetic field with a different magnitude, depending on the precise value of the local twist angle. In this way, the nano-SQUID technique can detect regions with tiny offsets from 1.1 degrees. “It turned out to be an amazing technique that can pick up miniscule angle variations of 0.002 degrees away from 1.1 degrees,” Jarillo-Herrero says. “This was very good for mapping magic-angle graphene.” The group used the technique to map two magic-angle structures: one with a narrow range of twist variations, and another with a broader range. “We placed one sheet of graphene on top of another, similar to placing plastic wrap on top of plastic wrap,” Jarillo-Herrero says. “You would expect there would be wrinkles, and regions where the two sheets would be a bit twisted, some less twisted, just as we see in graphene.” They found that the structure with a narrower range of twist variations had more pronounced properties of exotic physics, such as superconductivity, compared with the structure with more twist variations. “Now that we can directly see these local twist variations, it might be interesting to study how to engineer variations in twist angles to achieve different quantum phases in a device,” Cao says. Tunable physics Over the past two years, researchers have experimented with different configurations of graphene and other materials to see whether twisting them at certain angles would bring out exotic physical behavior. Jarillo-Herrero’s group wondered whether the fascinating physics of magic-angle graphene would hold up if they expanded the structure, to offset not two, but four graphene layers. Since graphene’s discovery nearly 15 years ago, a huge amount of information has been revealed about its properties, not just as a single sheet, but also stacked and aligned in multiple layers — a configuration that is similar to what you find in graphite, or pencil lead. “Bilayer graphene — two layers at a 0-degree angle from each-other — is a system whose properties we understand well,” Jarillo-Herrero says. “Theoretical calculations have shown that in a bilayer-on-top-of-bilayer structure, the range of angles over which interesting physics would happen is larger. So this type of structure might be more forgiving in terms of making devices.” Partly inspired by this theoretical possibility, the researchers fabricated a new magic-angle structure, offsetting one graphene bilayer with another bilayer by 1.1 degrees. They then connected the new “double-layer” twisted structure to a battery, applied a voltage, and measured the current that flowed through the device as they placed the structure under various conditions, such as a magnetic field, and a perpendicular electric field. Just like magic-angle structures made from two layers of graphene, the new four-layered structure showed an exotic insulating behavior. But uniquely, the researchers were able to tune this insulating property up and down with an electric field — something that’s not possible with two-layered magic-angle graphene. “This system is highly tunable, meaning we have a lot of control, which will allow us to study things we cannot understand with monolayer magic-angle graphene,” Cao says. “It’s still very early in the field,” Jarillo-Herrero says. “For the moment, the physics community is still fascinated just by the phenomena of it. People fantasize about what type of devices we could make but realize it’s still too early and we have so much yet to learn about these systems.” This research was funded, in part, by the U.S. Department of Energy, the National Science Foundation, the Gordon and Betty Moore Foundation, and the Sagol Weizmann-MIT Bridge Program. (Comment on this)

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