Number 121 (Story #3), March 31, 1993 by Phillip F. Schewe and Ben Stein|
NEURAL NOISE , the random fluctuations present in the electrical signals that flow through biological nervous systems, may aid rather than hinder the transmission of sensory information, new experiments suggest. At the APS March Meeting, Frank Moss and John Douglass of the University of Missouri at St. Louis presented measurements in a crayfish of a hair mechanoreceptor cell, a nerve cell that detects water motion. The external signal they applied--a weak water wave--was better picked up by the nerve cell when its internal noise levels were increased. (This was done by increasing the temperature of the crayfish's ambient water environment, which heightened the rate of random firings of the nerve cell.) Although the researchers observed an increase in the signal-to-noise ratio (SNR) with temperature, they did not isolate an expected phenomenon known as "stochastic resonance," in which a maximum in the SNR would be observed. The researchers speculated that internal effects in the crayfish, unidentified as of yet, may be obscuring or altering the phenomenon. Also at the meeting, John Milton of the University of Chicago Medical Center showed that fluctuations in human pupil size can be stabilized by noise arriving from the ascending reticular activating system, a part of the brainstem that controls consciousness.