THE last thing you need when you are struggling to hear what someone is saying at a party is an increase in the background noise. But for communication among neurons in the brain, the opposite can be true. A team of American physicists and neuroscientists has shown that increasing the electrical noise that neurons 鈥渉ear鈥� can allow them to pick out faint signals which would otherwise go undetected. The finding raises the possibility that electrical noise could be used to aid neural processing in the brain.
The researchers, from institutions in Georgia, Maryland and the District of Columbia, exposed slices of tissue from rats鈥� brains to periodically varying electrical fields, which peaked several times a second. Each tissue sample contained a network of between 500 and 1000 interconnected neurons, explains physicist William Ditto from the Georgia Institute of Technology in Atlanta.
When the electrical field peaked beyond a certain threshold, the network of neurons would respond to it by generating a series of electrical pulses in sync with the applied field. But when the field was below the threshold, the neurons could not detect the electrical signal and no pulses appeared.
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However, Ditto says, the neurons responded to a sub-threshold signal if the researchers added a bit of 鈥渘oise鈥濃�攁 randomly fluctuating electrical field鈥攖o the mix. Although it could be expected that the noise would make it even more difficult for the neurons to detect the weak signal, the result was the opposite.
This effect is known as 鈥渟tochastic resonance鈥�, says Mark Spano of the Naval Surface Warfare Center in Maryland, another member of the team. It has been found in various physical systems, such as electronic circuits, as well as in living creatures.
In March, for instance, researchers at the University of California, Berkeley, reported that crickets use stochastic resonance in their cercal systems, which sense air disturbances. And last month, scientists in Boston showed that stochastic resonance enables people to feel pressure on their fingertips that would otherwise be too faint to detect.
But until now, Spano says, no one had seen stochastic resonance at work in networks of neurons from the brain. His group鈥檚 experiment shows that electrical noise can increase the sensitivity of neurons to a weak signal by, in essence, pushing the neurons closer to their threshold. The results were published last week in Physical Review Letters.