Noisy messages for crayfish.

The addition of a certain level of noise -- any randomly varying sound or other signal -- can sometimes make it easier to detect a weak, information-carrying signal. Although the overall level of noise in the detector rises, the intensity of the meaningful signal goes up even more. Researchers call this effect stochastic resonance (SN: 2/23/91, p.127). First demonstrated in electronic circuits, this effect may also play an important role in biological settings (SN: 8/31/91, p.143).

Frank Moss and his colleagues at the University of Missouri at St. Louis have now shown that an optimal level of external noise can indeed enhance weak signals traveling along individual sensory neurons in a crayfish. These particular neurons convert small motions of tiny hair cells situated on the tail of the red swamp crayfish into electrical pulses. The researchers worked with intact, excised hair cells, each one mounted on a little post that could be moved back and forth through a liquid. An electronic-noise generator coupled with a source of periodic signals controlled the post's movements.

"Crayfish live in an incredibly noisy environment," Moss notes. And they to be able to sort out from this clamor of background sounds the approach of such predators as large-mouth bass, which arrive with rapidly wiggling tails. "This is the kind of thing we were trying to mimic, but in a very controlled sort of way," he says.