Noise to Help You ThinkNoise and thinking may seem incompatible to anyone but a teenager doing homework with rock music blaring in the background. But biophysicists now suspect that an entirely different kind of noise--variations in internal electric fields--may play an important role in organizing the activity of the mammalian brain.
Networks of neurons from rat brains have a better chance of detecting and responding to a weak, regular pulse in an electric field if the pulse is embedded in ``noisy'' random variations, according to a study in the current issue of Physical Review Letters. This counterintuitive effect, known as ``stochastic resonance,'' has been detected before in such disparate systems as global climate variations and the firing of abdominal nerve bundles of crickets. But this is the first time it has been demonstrated in mammalian nervous tissue, says Georgia Institute of Technology biophysicist William Ditto, one of the study authors. While scientists have had a hard time explaining why biological systems such as the brain are rife with electrical noise, ``It might be that noise is actually used by the system in order to increase the detectability of weak signals,'' Ditto says.
To test that possibility, Ditto, George Washington University neurosurgeon Steven Schiff, and colleagues from the Naval Surface Warfare Center in Silver Spring, Maryland, put sections from a rat's hippocampus--an area of the brain thought to help form short-term memory--in an electrical field. When the field was adjusted to send either a regular signal or pure random noise, neurons in the slices fired at random times. But when both signal and noise were sent together, the bursts became synchronized with the pulsating signal, indicating the neurons had somehow separated the signal from its background.
``The experiment is really groundbreaking,'' says Frank Moss, a physicist at the University of Missouri in St. Louis and a pioneer in stochastic resonance. ``We would all like to show that internal noise in the organs of an animal enhances information processing. The Schiff experiment goes directly to the brain and opens the door to those studies.''