Number 293 (Story #1), October 30, 1996 by Phillip F. Schewe and Ben Stein SIGNAL TRANSMISSION THROUGH A MAMMALIAN NERVE-CELL NETWORK can be enhanced with the help of electrical noise, a new experiment has shown. First proposed to explain the periodicity of ancient ice ages (in which the random "noise" of climate variations may have augmented the effects of predictable Earth-Sun distance variations from year to year) and first experimentally demonstrated in lasers (in which the direction of laser light traveling around a loop was switched from clockwise to counterclockwise by adding acoustical noise to the crystal from which the light emerged), the phenomenon of "stochastic resonance" (SR) describes how introducing a certain amount of noise into a system can actually enhance the transmission or detection of a weak signal so as to maximize the ratio of signal to noise. In the first demonstration of SR in mammalian tissue, researchers (Mark Spano, Naval Surface Warfare Center, 301-227-4466) apply a weak electric signal (containing both signal and noise) to a slice of rat hippocampus, a brain region essential for memory and other tasks. With the slice parallel to the plane in which nerve cells convert incoming signals into electrical nerve impulses, the researchers could transmit a weak signal to all nerve cells in the network. At an optimal noise intensity a maximum in the signal-to-noise ratio was reached--a hallmark of SR. This experiment offers the intriguing possibility that SR may potentially be exploited to aid transmission, detection and processing of signals in neuronal networks. (B.J. Gluckman et al., Physical Review Letters, 4 November 1996.)