THE brain is noisy, with billions of neurons constantly sending signals, but far from causing problems, the chattering actually boosts the brain鈥檚 processing power. 鈥淥ur brain may perform better by optimising the levels of internal noise,鈥� says neuroscientist Keiichi Kitajo. If so, it should be possible to use random noise to help our brains function better in some situations.
It isn鈥檛 easy to control or measure the noise naturally generated by neurons within the brain. So instead Kitajo, now at the University of British Columbia in Canada, and Yoshiharu Yamamoto at the University of Tokyo, showed volunteers signals on a computer screen. This enabled them to test the effect of the noise on the brain鈥檚 visual cortex, which receives its input directly from the eyes. The effect was striking, they report in a paper accepted by Physical Review Letters.
The team asked 19 people in turn to watch two grey squares on a computer screen. Each subject had wall dividing wall in front of them, so the left eye could only see the left square, and vice versa (see Graphic). One square was a constant grey while the brightness of the other oscillated steadily.
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The subject was asked to squeeze a joystick-like device in time with this varying signal. The strength of the signal was then reduced until the subject鈥檚 squeezes fell out of sync 鈥� showing that they could no longer detect the subtle shifts in greyness. But if the researchers made the square flicker randomly on top of the regular oscillations, the volunteers spotted and responded to signals that they had been unable to detect before.
The ability of noise to boost the detection of a weak signal is known as stochastic resonance, and has been measured in human receptors before. James Collins, a bioengineer at Boston University, is using the phenomenon to improve balance (快猫短视频, 2 November 2002, p 22) and has shown that individuals are more sensitive to pressure cues from their feet if they wear insoles that vibrate randomly. But it is the pressure receptors rather than the central nervous system that are responding to the added noise.
To show that in this case the effect really does occur in the brain, Kitajo changed his experiment slightly so that the subject saw the steady oscillation through one eye, and the flickering signal through the other. The flickering still enabled people to detect fainter oscillations. And because the inputs from each eye only combine when they reach the visual cortex, the effect must be within the brain itself, says Kitajo. 鈥淚t was a very nicely designed study,鈥� says Collins, adding that it is the first research to directly link stochastic resonance in the brain with behaviour.
It is a 鈥渟ignificant step鈥�, agrees Marius Usher, a psychologist at Birkbeck College, University of London. His recent work, with colleague Mario Feingold at the Ben Gurion University in Israel, has hinted that noise in the brain might also be involved in problem solving and creativity.
Kitacho鈥檚 team is already working with a company on a system to improve vision in poor light, where everything looks grey. This could be installed in cars to make driving at night safer.