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Scientists have gained new insights into how the brain’s internal compass gives us a sense of direction.
The findings shed light on how the brain orients itself in changing environments—and even the processes that can go wrong with degenerative diseases like dementia that leave people feeling lost and confused.
“Neuroscience research has witnessed a technology revolution in the last decade allowing us to ask and answer questions that could only be dreamed of just years ago,” says Mark Brandon, an associate professor of psychiatry at McGill University and researcher at the Douglas Research Centre who co-led the work with Zaki Ajabi, a former student at McGill University and now a postdoctoral research fellow at Harvard University.
To understand how visual information affects the brain’s internal compass, the researchers exposed mice to a disorienting virtual world while recording the brain’s neural activity. The team recorded the brain’s internal compass with unprecedented precision using the latest advances in neuronal recording technology.
This ability to accurately decode the animal’s internal head direction allowed the researchers to explore how the head-direction cells, which make up the brain’s internal compass, support the brain’s ability to reorient itself in changing surroundings.
Specifically, the research team identified a phenomenon they call “network gain” that allowed the brain’s internal compass to reorient after the mice were disoriented.
“It’s as if the brain has a mechanism to implement a ‘reset button’ allowing for rapid reorientation of its internal compass in confusing situations,” says Ajabi.
Although researchers exposed the animals in this study to unnatural visual experiences, the authors argue that such scenarios are already relevant to the modern human experience, especially with the rapid spread of virtual reality technology.
These findings “may eventually explain how virtual reality systems can easily take control over our sense of orientation,” adds Ajabi.
The results inspired the research team to develop new models to better understand the underlying mechanisms.
“This work is a beautiful example of how experimental and computational approaches together can advance our understanding of brain activity that drives behavior,” says coauthor Xue-Xin Wei, a computational neuroscientist and an assistant professor at the University of Texas at Austin.
The findings also have significant implications for Alzheimer’s disease. “One of the first self-reported cognitive symptoms of Alzheimer’s is that people become disoriented and lost, even in familiar settings,” Brandon says.
The researchers expect that a better understanding of how the brain’s internal compass and navigation system works will lead to earlier detection and better assessment of treatments for Alzheimer’s disease.
The study appears in the journal Nature.
The Natural Sciences and Engineering Research Council of Canada and the Canadian Institutes of Health Research funded the work.
Source: McGill University
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A new fossil discovery reveals complex ecosystems existed on Earth much earlier than previously thought.
The discovery challenges understanding of how quickly life recovered from the greatest mass extinction in Earth’s history.
About 250 million years ago, the Permian-Triassic mass extinction killed over 80% of the planet’s species. In the aftermath, scientists believe that life on Earth was dominated by simple species for up to 10 million years before more complex ecosystems could evolve.
Until now, scientists have long theorized that scorching hot ocean conditions resulting from catastrophic climate change prevented the development of complex life after the mass extinction. This idea is based on geochemical evidence of ocean conditions at the time. Now the discovery of fossils dating back 250.8 million years near the Guizhou region of China suggests that complex ecosystems were present on Earth just one million years after the Permian-Triassic mass extinction, which is much earlier than previously thought.
“The fossils of the Guizhou region reveal an ocean ecosystem with diverse species making up a complex food chain that includes plant life, boney fish, ray-finned fish, crabs, lobsters, shrimp, and mollusks. In all, our team discovered 12 classes of organisms and even found fossilized feces, revealing clues about the diets of these ancient animals,” says Morgann Perrot, a former postdoctoral researcher at McGill University, now at Université du Québec à Montréal.
Previously, it was thought that complex ecosystems would need five to 10 million years to evolve after an extinction. However, the researchers found that the specimens in the Guizhou region evolved much quicker than that by using radiometric dating to date the rocks where the fossils were discovered.
“All of this has implications for our understanding of how quickly life can respond to extreme crises. It also necessitates a re-evaluation of early Triassic ocean conditions,” says Perrot, whose research focuses on earth sciences and geochronology.
The research appears in Science.
Source: McGill University
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While changing temperatures and rainfall had little impact on crocodiles’ gene flow over the past three million years, changes to sea levels during the Ice Age had a different effect.
“The American crocodile tolerates huge variations in temperature and rainfall. But about 20,000 years ago—when much of the world’s water was frozen, forming the vast ice sheets of the last glacial maximum—sea levels dropped by more than 100 meters [about 328 feet],” says José Avila-Cervantes, a postdoctoral fellow working under the supervision of Hans Larsson, a professor of biology at the Redpath Museum of McGill University. “This created a geographical barrier that separated the gene flow of crocodiles in Panama.”
The researchers point out that the crocodiles are good swimmers, but they can’t travel long distances on land. As a result, the Caribbean and Pacific crocodile populations were isolated from each other, and consequently have undergone different genetic mutations.
For the study in the journal Evolution, the team compared the climate tolerance of living populations of American crocodiles (Crocodylus acutus) to the paleoclimate estimates for the region over the past 3 million years—the time span of extreme climate variation during the Ice Age.
“This is one of the first times Ice Age effects have been found in a tropical species. It’s exciting to discover effects of the last Ice Age glaciation still resonate in the genomes of Pacific and Caribbean American crocodiles today,” Larsson says.
“Discovering that these animals would have easily tolerated the climate swings of the Ice Age speaks to their resilience over geological time. Only humans in recent decades of hunting and land development seem to really affect crocodiles,” he says.
The findings offer new insight into how environmental drivers affect genetic evolution and where conservation efforts of particular crocodile populations in Panama should be focused.
Source: McGill University
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Astronomers have captured a radio signal from a distant galaxy at a specific wavelength known as the 21 cm line.
With the help of the Giant Metrewave Radio Telescope in India, this is the first time this type of radio signal has been detected at such a large distance.
How do stars form in distant galaxies? Astronomers have long been trying to answer this question by detecting radio signals emitted by nearby galaxies. However, these signals become weaker the further away a galaxy is from Earth, making it difficult for current radio telescopes to pick up.
“A galaxy emits different kinds of radio signals. Until now, it’s only been possible to capture this particular signal from a galaxy nearby, limiting our knowledge to those galaxies closer to Earth,” says Arnab Chakraborty, a postdoctoral researcher at McGill University under the supervision of Matt Dobbs, a professor in the physics department.
“But thanks to the help of a naturally occurring phenomenon called gravitational lensing, we can capture a faint signal from a record-breaking distance. This will help us understand the composition of galaxies at much greater distances from Earth.”
“It’s the equivalent to a look-back in time of 8.8 billion years.”
For the first time, the researchers were able to detect the signal from a distant star-forming galaxy known as SDSSJ0826+5630 and measure its gas composition. The researchers observed the atomic mass of the gas content of this particular galaxy is almost twice the mass of the stars visible to us.
The signal the team detected was emitted from this galaxy when the universe was only 4.9 billion years old, allowing the researchers to glimpse into the secrets of the early universe.
“It’s the equivalent to a look-back in time of 8.8 billion years,” says Chakraborty.
“Gravitational lensing magnifies the signal coming from a distant object to help us peer into the early universe. In this specific case, the signal is bent by the presence of another massive body, another galaxy, between the target and the observer.
“This effectively results in the magnification of the signal by a factor of 30, allowing the telescope to pick it up,” says coauthor Nirupam Roy, an associate professor in the physics department at the Indian Institute of Science.
According to the researchers, these results demonstrate the feasibility of observing faraway galaxies in similar situations with gravitational lensing. It also opens exciting new opportunities for probing the cosmic evolution of stars and galaxies with existing low-frequency radio telescopes.
The study appears in the Monthly Notices of the Royal Astronomical Society.
The Giant Metrewave Radio Telescope was built and is operated by NCRA-TIFR. The research was funded by McGill University and the Indian Institute of Science.
Source: McGill University
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