A Nose for Noise
The paddlefish is the Pinocchio of the fish world, with a proboscis that nearly doubles the length of its body. This so-called "rostrum" helps the paddlefish find plankton, its preferred meal, in the muddy waters of the Missouri River. The rostrum works like an antenna, detecting weak electric signals produced by animal plankton as they swim. Now, biologists have found that the paddlefish has a sophisticated way to enhance these signals that may someday prove useful to people struggling with sensory impairment.
The trick the fish employ, says David Russell, a neurobiologist at the University of Missouri, St. Louis, is to use the ambient noise to enhance the signal from plankton they're looking for. To anyone who's ever tried to tune a radio to a station whose signal is coming in poorly, the idea of bolstering the signal by adding static may sound ludicrous. But physicists have shown that it can work: If a signal is very weak, just below the threshold of a detector, then a little random noise can boost the signal so that it becomes detectable intermittently. Too much noise, however, drowns out the signal. Thus there is an optimal amount of noise--the "Goldilocks level," as one researcher calls it--that lets a signal come through most clearly.
Russell and two colleagues learned that paddlefish exploit this effect, called stochastic resonance, after placing two electrodes at either end of a tank holding a paddlefish and plankton. They found that the fish could find the plankton from farther away when the electrodes were broadcasting a low level of electrical noise than when there was either no noise or too much. "When we show a film of this at meetings, people are astounded by it," says Russell. "Their reaction is 'Wow, you can see it!'"
"This will overcome some skepticism" among scientists who rejected the notion that organisms can benefit from stochastic resonance, says James Collins, a biomedical engineer at Boston University. He hopes the study will boost interest in applications of stochastic resonance that he's developing for patients who, as a result of diabetes, stroke, or joint replacements, have lost part of the sensation in their limbs. A vibrator that tickles their limbs, he says, might create enough electrical noise to boost the weak signal from their impaired nerves. Collins predicts that prototype devices could be on the market for experimental use in the next few years.