- Scientists Scan the Brains of Mice Playing Quake
- Giant Invasive Snakes Threaten U.S. Wildlife, People
- Jupiter Moon’s Ocean Could Be Rich in Oxygen
- Monkeys Fall Into ‘Uncanny Valley,’ Just Like Humans
- Galactic Hookup Spawns Celestial Offspring
- Hunting Arctic Asteroid Impact With Hovercraft
Posted: 14 Oct 2009 11:03 AM PDT
By putting sensors in the brains of mice as they ran through a Quake-derived virtual reality, scientists have found a way to study neurological activity in moving animals.
The setup allows for real-time, almost-real-motion tracking of single neurons. That feat has eluded researchers who have a fuzzy, general understanding of brain systems, but little knowledge of how individual cells actually work. They hope that cell-level details will make sense motion, cognition and other complex mental functions.
"One of the major research areas of neuroscience is the development of techniques to study the brain at cellular resolution," said Princeton University neuroscientist David Tank, co-author of the study published Wednesday in Nature. "The information of the nervous system is contained in the activity of individual neurons."
Tank's team studied hippocampal place neurons, which are activated when an animal is in a particular location in its environment. Ever since hippocampal place neurons were identified 40 years go, scientists have wondered exactly what mechanisms make them fire.
However, the fMRI machines used to study brain activity in humans only measure the average output of millions of neurons at once. Studying individual neurons has been possible in cell cultures, but brains in a dish behave different than real, living brains. Tracking individual neurons in moving animals has been impossible.
"The neurons move back and forth while you're trying to measure things," said Tank. "So we developed a way to keep the head fixed in space, but still have mice perform behaviors that are usually studied in mice running through a maze."
Tank's team designed an apparatus in which a mouse, its head firmly held in a metal helmet, walks on the surface of a styrofoam ball. The ball is kept aloft by a jet of air, so that it functions like a multi-directional treadmill. Around it are sensors taken from optical computer mice, which read the ball's movement as the mouse runs.
Those readings were the input for the researchers' virtual reality software — a modified version of the open-source Quake 2 video game engine, tweaked to project an image on a screen surrounding the mouse. Tank called it "a mini-iMax theater."
Mice in the study ran through a virtual maze designed in the open-source Quark game editor, but rather than earning points or power-ups, they were rewarded with sips of water from a head-side nozzle.
Into the hippocampus of each mouse the researchers inserted a glass capillary just one micron wide at its tip and filled with salt water. Known as a whole-cell patch recorder, it detects electrical currents as they pulse through individual cells.
"It is difficult to overstate the importance of understanding how the dynamics of electrical activity within single neurons is related to firing patterns among collections of neurons that accompany the performance of complex tasks," wrote Douglas Nitz, a University of California at San Diego cognitive scientist, in a commentary accompanying the findings.
Scientists have proposed at least a half-dozen models of individual neuron behavior to explain the general firing patterns of hippocampal place neurons, whose general behavior is determined by a creature's specific spatial location. Tank's team found that individual neurons fired in staccato bursts of varying intensity, a result that fits one of the proposed models.
Those results are likely of interest only to neuroscientists, and "to be fair, more work is needed to nail this down," said Tank.
Nitz was less reserved, calling the observations "an exciting result" that "may prove generalizable to other brain structures, in particular the cerebral cortex." But he too was especially excited by the virtual reality-harnessing methodology.
The findings are "a first payment on the promise of the technique," and "represent a powerful example of what will be learned in decades to come," wrote Nitz.
Image & Video: David Tank
Citations: "Intracellular dynamics of hippocampal place cells during virtual navigation." By Christopher D. Harvey, Forrest Collman, Daniel A. Dombeck & David W. Tank. Nature, Vol. 461 No. 7266, October 14, 2009.
"The Inside Story on Place Cells." By Douglas Nitz. Nature, Vol. 461 No. 7266, October 14, 2009.
Posted: 13 Oct 2009 03:18 PM PDT
Nine different species of exotic giant snakes, released into the wild by irresponsible pet owners, could pose a major threat to U.S. wildlife, according to a new report published today by the U.S. Geological Survey.
Although pet constrictors start out small and cute, the largest snakes can grow up to 20 feet long and weigh as much as 200 pounds. The enormous reptiles end up in the wild when they're abandoned by overwhelmed owners, or when they use their impressive musculature to escape from inadequate enclosures.
Tens of thousands of giant Burmese pythons already inhabit parts of southern Florida, and now scientists say at least eight other species of giant snakes have the potential to breed and thrive in parts of the United States, threatening already-fragile native ecosystems and putting 150 endangered species at risk.
"They will eat almost every vertebrate of the right size, but they mostly prefer birds and mammals," said USGS biologist Gordon Rodda, who co-authored the 350-page study. "We've pulled a number of endangered species out of their stomachs."
In addition, Rodda said all nine species are large enough to kill an adult human, although fatalities are rare. For example, despite the large population of captive Burmese pythons in the United States, the first unprovoked fatal attack was recorded earlier this year, when a pet python escaped from its cage and killed a 2-year-old child.
"There have been recorded fatalities from these species," Rodda said. "Personally, I don't think it's a big deal, but if I had a small child, I would be mindful of that risk if the child was in an area where there might be pythons."
Individual snakes from all nine species have been found in the United States, but so far only three species — Burmese pythons, boa constrictors and northern African pythons — have established breeding populations in the wild, all currently confined to southern Florida. Based on the snakes' preferred climate range, potential ecological impact and prevalence in trade and commerce, the report classified five species as high risk and the other four as medium risk to native ecosystems.
A preference for warm weather means most of the snakes could only survive in Florida, southern Texas, Hawaii or tropical islands like Guam and Puerto Rico. Still, Rodda said a few species could potentially spread throughout many of the southern states. "The most temperate of the species is the Burmese python," he said. "That's the one that really goes up both coasts and across the southern U.S."
The hardy animals tolerate urban and suburban environments quite well, and boa constrictors and northern African pythons have both been spotted in the Miami metropolitan area.
Unfortunately, once invasive snakes have taken hold in a particular region, the researchers say they're almost impossible to get rid of, in part because elaborate camouflage makes the snakes very hard to spot. Some progress has been made in terms of radio-tracking and trapping the snakes, but despite several years of effort, Florida's population of Burmese pythons and boa constrictors shows no sign of shrinking.
"At this time, we have no tools that would likely suffice to eradicate a big population of snakes once they had spread," said USGS biologist Robert Reed, the other co-author of the study, who presented the findings today at a congressional briefing. "Instead of looking at the pound of cure," he said, "maybe it's time to look at the pound of prevention."
The results of the study, along with more than 1,500 public comments solicited by the Department of Interior, will be used by the U.S. Fish and Wildlife Service to decide how to prevent further spread of the giant constrictors. One option would be to place them on a list of injurious species under the federal Lacey Act, which would make it illegal to import the snakes or carry them across state lines.
Of course, reptile enthusiasts don't want to curb the sale of these exotic snakes, and the researchers point out that owning a snake has educational value. "We can testify to these snakes' attraction personally, as we both have kept pet giant constrictors," the scientists wrote. "Thus the social value of protecting native ecosystems must be weighed against the social value of fostering positive attitudes about the protection of nature through giant constrictor ownership."
Regardless of whether these giant snakes are eventually classified as injurious, the Fish and Wildlife Service says they're taking steps to reduce breeding populations in Florida and prevent further snake invasion.
"It's going to take a huge public education and outreach initiative to make people understand the value of being responsible pet owners," said FWS spokesperson Ken Warren. "We don't pretend that there's any easy solution, but no action is not an option."
Image 1: Burmese python (Python molurus). Roy Wood/National Park Service.
Posted: 13 Oct 2009 11:49 AM PDT
FAJARDO, Puerto Rico — If there are any fish on Jupiter's moon Europa, they can breathe easy.
Researchers hunting for signs of life beyond Earth have long been drawn to Europa because several features of the moon's icy surface — including its bright color, networks of long fractures and crater-free terrain — suggest that the moon contains a vast ocean buried under the ice. Now one researcher has calculated that the proposed ocean may receive about 100 times more oxygen than previous models indicated — enough to support respiration by 3 million tons of fish or their Europan equivalent.
Oxygen, generated by charged particles striking water molecules on the moon's surface, would take 1 to 2 billion years to begin seeping into the ocean, calculated Richard Greenberg of the University of Arizona in Tucson. That delay would have been critical for supporting life because it would have allowed time for primitive organisms to develop the ability to use oxygen. If oxygen instead had been immediately released into the ocean, it would have destroyed fledgling life through the well-known process oxidation, commented Jonathan Lunine, also of the University of Arizona, who was not part of the study.
Greenberg reported the findings October 9 at the annual meeting of the American Astronomical Society's Division for Planetary Sciences.
Theorists had previously calculated that the charged particles striking Europa would produce oxygen within the top few centimeters of the moon's crust. Small impacts from space debris would then kick up material that would bury this oxygenated layer to a depth of a few meters. The new part of the story, said Greenberg, came when he considered Europa's youthful, nearly crater-free appearance. The paucity of craters indicates that the crust is continually resurfaced. Today's crust is only 50 million years old, even though the moon formed soon after the solar system's birth 4.56 billion years ago.
Over a period of about 50 million years, a layer of ice 300 meters thick slowly rises from below, eventually covering the moon's surface and erasing old craters, Greenberg suggested. As a result of this facelift, Europa's oxygenated layer grows increasingly thick, until after about 1 to 2 billion years the entire ice layer is oxygen-rich, Greenberg said. At that point, ice melting at the bottom of the frozen layer would begin delivering oxygen into the buried proposed ocean at a faster rate than previously estimated, resulting in about 100 times more oxygen in the ocean.
Posted: 13 Oct 2009 10:44 AM PDT
Monkeys are freaked out by almost-but-not-quite-real depictions of themselves. That tendency is well documented in humans, but has never before been seen in another species.
To test their preference, researchers showed macaque monkeys real pictures, digital caricatures and realistic reconstructions of other monkey faces. To the latter, the macaques repeatedly averted their eyes.
"The visual behavior of the monkeys falls into the uncanny valley just the same as human visual behavior," wrote Princeton University evolutionary biologists Shawn Steckinfinger and Asif Ghazanfar in a paper published Monday in the Proceedings of the National Academy of Sciences.
The "uncanny valley" was identified in 1970 by Japanese roboticist Masahito Mori, who noticed that people presented with likenesses of increasing realism respond with increasing empathy, right up to the point where the likenesses are almost real. At that point, people are repulsed. The sudden dip in graphs describing their response gave the phenomenon its name.
Many explanations have been suggested for the uncanny valley, which has also been blamed for the box-office failure of movies like Beowulf and Final Fantasy. Perhaps almost-real humans look a bit too much like corpses for our comfort; perhaps they're so real that they engage our brains' mate-recognition or disease-avoidance systems, which promptly identify poor partners or sick individuals.
The PNAS results don't favor any one of these explanations, but do suggest that the uncanny valley has evolutionary origins deep in the primate psyche.
It remains to be seen how the monkeys would react to a simian version of The Polar Express.
Citation: "Monkey visual behavior falls into the uncanny valley." By S. Steckenfinger & A Ghazanfar. Proceedings of the National Academy of Sciences, Vol 106. No. 40, October 12, 2009.
Posted: 13 Oct 2009 07:02 AM PDT
This bizarre-looking two-armed galaxy, captured by the Hubble Space Telescope,is actually two spiral galaxies in a high-speed collision 250 million light-years away.
The crash and resulting mixing of mass and gas sparked new star birth that is visible in the arms. The arm on the right also has many star clusters that are brighter than anything nearby our own galaxy.
This star merger is taking place in the constellation Cancer and is known as NGC 2623. Because it is so bright in the infrared, it belongs to a group of galaxies known as luminous infrared galaxies (LIRG) being studied in the Great Observatories All-sky LIRG Survey (GOALS) project.
Image: NASA, ESA and A. Evans (Stony Brook University, New York)
Posted: 12 Oct 2009 02:43 PM PDT
Two polar scientists hot on the trail of an arctic mystery have a new tool for exploration: a hovercraft, specially outfitted for week-long trips over the ice with scientific instruments and solar panels.
Their quarry is a nearly 22,000 square-mile patch of disturbed Arctic sea floor that could be evidence of a massive asteroid strike. John Hall, a now-retired geoscientist, discovered the anomaly during his late-'60s graduate work aboard Fletcher's Ice Island, a huge berg U.S. scientists inhabited for several decades.
Since then, no scientific vessel has been back over the area to collect more data. The massive icebreakers that have crunched through the Arctic since the 1990s can't reach the spot, said Yngve Kristofferson, a scientist and explorer at the University of Bergen in Norway.
Kristofferson became intrigued with Hall's data and in 2004, the two of them met in Bergen to talk Arctic science from eight in the morning to 10 in the evening. At the end of their time together, they came to a decision: They needed a hovercraft.
Luckily, Hall is a partial heir to the fortune his grandfather made as head of the American Chicle Company, the trust that ran the American bubble gum game early in the 20th century, so he was able to buy the vehicle with private funds. A customized Griffon Hovercraft 2000TD, it is now going through the paces, hitting the Arctic from its home at Longyearbyen for the first time in 2008, and hoping to reach its full potential next spring.
Hall delivered a speech detailing the craft's capabilities and mission at Columbia University's Lamont Doherty Earth Observatory on Oct. 6.
"The neat thing with a hovercraft is that you drive with the same ease over 10 centimeter-thick ice as you do with five meter thick ice," Kristofferson told Wired.com.
Despite their futuristic reputation, hovercraft have been commercially available for decades. The concept is actually quite simple. A big engine or turbine pumps air into a rubber skirt that allows the vehicle to tread lightly on whatever it's touching. The R/H Sabvabaa, for example, weighs six tons but exerts no more pressure on any patch of ice than a seagull standing on one leg would by standing on it. The rest of the power from the engine is devoted to propulsion, allowing the craft to skip along at speeds up to 50 miles per hour.
For the strange terrain of the Arctic, it works perfectly, Hall and Kristofferson wrote in an article in the journal The Leading Edge in August.
"The craft has proved to be useful for a variety of scientific tasks," they wrote. "It appears more efficient than any other platform for ice-thickness measurements and oceanographic work."
Their hovercraft push comes as money has flooded into Arctic research. With Arctic ice melting, the nations adjacent to the ocean are rushing to stake their claims not just on the water, but on the oil and natural gas that lie under the sea floor, leading to calls to establish a National Park to protect the area.
The most fascinating target for the hovercraft is the area of very thick ice closer to Ellesmere Island and northern Greenland. Not even nuclear-powered icebreakers have ventured into the region. It was just Hall's good fortune to have been aboard the floating ice island doing research when it passed near this apparent sea floor anomaly. The duo, along with several other colleagues, described the discovery in a 2008 paper in the Norwegian Journal of Geology.
"The upper couple hundred meters of sediment at the bottom of the Arctic Ocean is just like a carpet that is draped over the topography except for these areas where 150 meters are just blown away and the seabed is severely deformed," Kristofferson said.
To Kristofferson and Hall, the evidence suggests that a pressure wave caused by a pieces of a large asteroid crashing into the Arctic Ocean created these strange features.
"Our working hypothesis is that the spectrum and scale of the observed disturbances are best explained as the effect of a shock wave generated by the impact of an extraterrestrial object," they wrote.
But the hypothesis remains just that without more data. The hovercraft works well, but with its on-board fuel, its range is limited to around 500 miles. For that reason, the scientists imagine they'll use a larger vessel as a base of operations.
"What we really want to do is go along with an icebreaker into the Arctic. You can greatly enhance the scientific output if you have a hovercraft. If you have more of them, even better," Kristofferson said. "We can go out and do our own science and be away for many days. If the icebreaker gets stuck, we're not stuck."
Still, both Hall and Kristofferson know they face an uphill battle to get other scientists to take both the hovercraft and asteroid impact ideas seriously.
"The task is to figure out the real message in the data—the dream challenge for any scientist," Kristofferson told the Lamont Doherty alumni magazine earlier this year. "So far, we have mostly met shaking heads, which just makes it more fun."
Image: Hall and Kristofferson. 1. The hovercraft. 2. Fletcher's Ice Island Camp.
Click through for more images of the hovercraft.
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