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17 April 2014 12:48 pm ,
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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Owlish Neurons Do Advanced Math
12 April 2001 7:00 pm
An owl knows where to aim its talons even in the dark, thanks to neurons that can pinpoint the sound of a rustling mouse. These space-specific neurons perform more sophisticated computations than expected, researchers say. While most neurons simply add incoming signals to come up with an answer, these neurons can multiply.
Space-specific neurons receive two kinds of inputs. If a mouse squeaks to an owl's right side, that ear registers a slightly louder signal, and slightly sooner, than the left ear. Earlier research by Masakazu Konishi and colleagues showed that a set of auditory neurons calculates the difference in loudness and time and sends the results to neurons that are precisely tuned to particular locations. To learn how these neurons process the signals, neuroscientists José Luis Peña and Konishi of the California Institute of Technology (Caltech) in Pasadena outfitted 14 barn owls with headphones and monitored space-specific neurons' responses to pairs of sounds.
Two properties convinced the researchers that these neurons multiply signals. First, when very faint timing and loudness signals correspond to the same spot, the neurons in the auditory map fire robustly. This happens even if the two signals, when simply added, are too faint to rile up the neurons enough to fire. Second, the lack of either a loudness or timing signal can veto a space-specific neuron's firing--just as in multiplication, 2 x 0 = 0. As the researchers report in the 13 April issue of Science, a multiplicative model predicts how the neurons respond to different stimuli with about 98% accuracy.
Archetypal neurons don't compute this way. Normally, a neuron receives a host of excitatory and inhibitory signals of various volumes along its dendrites. When the signals add up to surpass some threshold, the neuron fires. Such a neuron acts like a transistor in an electronic circuit, says neuroscientist Christof Koch, also of Caltech but not involved in this project. But a neuron with the power to multiply, he says, "is more like a little processor; computationally it's much more powerful."