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Guess the hungry cat
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CAT owners will know the feeling. Your pet is demanding to be fed, and isn’t going to give up until it gets what it wants. What most doting owners won’t realise is that the cat is using an acoustic ruse. According to Karen McComb of the University of Sussex, UK, domestic cats hide a plaintive cry within their purrs that both irritates owners and appeals to their nurturing instincts. The team recorded the purrs of 10 different cats when they were soliciting food, and when they were purring in a different context. Fifty people who were asked to rate the purrs on how pleasant and urgent they sounded consistently rated the “solicitation purrs” as more urgent and less pleasant. Cat owners were especially good at distinguishing between the two kinds of purring. When the team examined the sound spectrum of the solicitation purrs they saw an unusual peak in the 220 to 520-hertz frequency range embedded in the much lower frequencies of the usual purr. Babies’ cries have a similar frequency range, 300 to 600 hertz, McComb says. The louder this high-frequency element, the more urgent and less pleasant the purr was rated (Current Biology, DOI: 10.1016/j.cub.2009.05. 033). Cats may be exploiting “innate tendencies in humans to respond to cry-like sounds in the context of nurturing offspring”, McComb says.
Blink and you’ll miss it – the brain’s high-speed rewiring trick OUR brains can rewire themselves in just seconds to compensate for a break in incoming data, suggesting they are even more flexible than previously thought. We already knew that the brain is constantly adapting throughout our lives, for example by generating new neurons well into adulthood. But just how quickly can it adapt – and does it always involve creating new circuits? To investigate these questions, Daniel Dilks and his colleagues at the Massachusetts Institute of Technology took advantage of
the blind spots that occur naturally in our eyes where the optic nerve exits the retina. The brain normally combines images captured by both eyes to fill in the resulting gaps in vision, but Dilks prevented this in 48 volunteers by patching one eye. After identifying where the blind spot was for each volunteer’s other eye, he then presented an image of a square right next to it. The volunteers initially saw a square, but reported that within seconds it had morphed into a rectangle, by extending its edge
into the blind spot (Journal of Neuroscience, DOI: 10.1523/ jneurosci.1557-09.2009). The change in what the volunteers saw was so fast, Dilks says, that it must be due to the brain redirecting signals through pre-existing circuits rather than forging new connections. The team concludes that the neurons which would normally fill the blind spot using data from the patched eye compensated by stealing data from neighbouring neurons that were “seeing” the square, making it appear like a rectangle. AAAS/SCIENCE
The plaintive purr we can’t resist
Stunted ribs gave turtles their shell THE mystery of the origin of the turtle’s shell is a step closer to being solved. Unlike most vertebrates, turtles have ribs that are short and wide, and do not wrap around the body. Instead they fuse with vertebrae and bony plates in the skin of its back to form a shell. The big question is whether the flattened ribs or the bony plates evolved first. Last year, a fossil was uncovered with a complete shell on its belly but an incomplete shell on its back. Its ribs were short and wide as in modern turtles, but the bony plates were absent – hinting that the ribs rather than the skin drove the evolution of the shell. Now Hiroshi Nagashima and colleagues at the RIKEN Center for Developmental Biology in Kobe, Japan, have backed up this idea. Looking at the way muscle and bone develop in turtle, mouse and chicken embryos, they found that there is initially a common pattern – also likely shared with their last common ancestor. But early in the turtle’s development, a portion of its body wall folds in on itself, forcing the ribs to fuse and thicken rather than wrapping round the body (Science, DOI: 10.1126/science.1173826).
Star twins may solve galaxy mystery SOME of the first stars may not have been born alone, but as twins. If so, it could explain a long-standing mystery about our galaxy. Computer simulations of the early universe suggest that the first stars to form were very large, about 300 times the mass of our sun. To investigate further, Matthew Turk of the Kavli Institute for Particle Astrophysics and Cosmology in Menlo Park, California, and colleagues ran five simulations of conditions 20 million years after the big bang, each with slightly different initial distributions of hydrogen and helium
gas, for long enough for star-forming cores to condense out. One of the models showed a cloud had fragmented to form two such cores, possibly because the cloud’s spin had torn it apart (Science, DOI: 10.1126/ science.1173540). Many massive first stars should have blown apart in exotic explosions. Yet the telltale chemical signatures this should have left have not been observed in the ancient stars’ early descendants that roam our galaxy. If some of the first stars were twins, each might be too small to trigger such explosions.
18 July 2009 | NewScientist | 17
DAVID GREY/REUTERS
CAT owners will know the feeling. Your pet is demanding to be fed, and isn’t going to give up until it gets what it wants. What most doting owners won’t realise is that the cat is using an acoustic ruse. According to Karen McComb of the University of Sussex, UK, domestic cats hide a plaintive cry within their purrs that both irritates owners and appeals to their nurturing instincts. The team recorded the purrs of 10 different cats when they were soliciting food, and when they were purring in a different context. Fifty people who were asked to rate the purrs on how pleasant and urgent they sounded consistently rated the “solicitation purrs” as more urgent and less pleasant. Cat owners were especially good at distinguishing between the two kinds of purring. When the team examined the sound spectrum of the solicitation purrs they saw an unusual peak in the 220 to 520-hertz frequency range embedded in the much lower frequencies of the usual purr. Babies’ cries have a similar frequency range, 300 to 600 hertz, McComb says. The louder this high-frequency element, the more urgent and less pleasant the purr was rated (Current Biology, DOI: 10.1016/j.cub.2009.05. 033). Cats may be exploiting “innate tendencies in humans to respond to cry-like sounds in the context of nurturing offspring”, McComb says.
Blink and you’ll miss it – the brain’s high-speed rewiring trick OUR brains can rewire themselves in just seconds to compensate for a break in incoming data, suggesting they are even more flexible than previously thought. We already knew that the brain is constantly adapting throughout our lives, for example by generating new neurons well into adulthood. But just how quickly can it adapt – and does it always involve creating new circuits? To investigate these questions, Daniel Dilks and his colleagues at the Massachusetts Institute of Technology took advantage of
the blind spots that occur naturally in our eyes where the optic nerve exits the retina. The brain normally combines images captured by both eyes to fill in the resulting gaps in vision, but Dilks prevented this in 48 volunteers by patching one eye. After identifying where the blind spot was for each volunteer’s other eye, he then presented an image of a square right next to it. The volunteers initially saw a square, but reported that within seconds it had morphed into a rectangle, by extending its edge
into the blind spot (Journal of Neuroscience, DOI: 10.1523/ jneurosci.1557-09.2009). The change in what the volunteers saw was so fast, Dilks says, that it must be due to the brain redirecting signals through pre-existing circuits rather than forging new connections. The team concludes that the neurons which would normally fill the blind spot using data from the patched eye compensated by stealing data from neighbouring neurons that were “seeing” the square, making it appear like a rectangle. AAAS/SCIENCE
The plaintive purr we can’t resist
Stunted ribs gave turtles their shell THE mystery of the origin of the turtle’s shell is a step closer to being solved. Unlike most vertebrates, turtles have ribs that are short and wide, and do not wrap around the body. Instead they fuse with vertebrae and bony plates in the skin of its back to form a shell. The big question is whether the flattened ribs or the bony plates evolved first. Last year, a fossil was uncovered with a complete shell on its belly but an incomplete shell on its back. Its ribs were short and wide as in modern turtles, but the bony plates were absent – hinting that the ribs rather than the skin drove the evolution of the shell. Now Hiroshi Nagashima and colleagues at the RIKEN Center for Developmental Biology in Kobe, Japan, have backed up this idea. Looking at the way muscle and bone develop in turtle, mouse and chicken embryos, they found that there is initially a common pattern – also likely shared with their last common ancestor. But early in the turtle’s development, a portion of its body wall folds in on itself, forcing the ribs to fuse and thicken rather than wrapping round the body (Science, DOI: 10.1126/science.1173826).
Star twins may solve galaxy mystery SOME of the first stars may not have been born alone, but as twins. If so, it could explain a long-standing mystery about our galaxy. Computer simulations of the early universe suggest that the first stars to form were very large, about 300 times the mass of our sun. To investigate further, Matthew Turk of the Kavli Institute for Particle Astrophysics and Cosmology in Menlo Park, California, and colleagues ran five simulations of conditions 20 million years after the big bang, each with slightly different initial distributions of hydrogen and helium
gas, for long enough for star-forming cores to condense out. One of the models showed a cloud had fragmented to form two such cores, possibly because the cloud’s spin had torn it apart (Science, DOI: 10.1126/ science.1173540). Many massive first stars should have blown apart in exotic explosions. Yet the telltale chemical signatures this should have left have not been observed in the ancient stars’ early descendants that roam our galaxy. If some of the first stars were twins, each might be too small to trigger such explosions.
18 July 2009 | NewScientist | 17