ENHANCEMENT OF SUBTHRESHOLD SENSORY NERVE ACTION POTENTIALS DURING MUSCLE TENSION MEDIATED NOISE

Abstract

In certain nonlinear systems, of which neurons are an example, the addition of random fluctuations, or “noise”, can enhance the detectability or transmission efficiency of a weakly applied signal. This counterintuitive statistical process, called stochastic resonance, —first advanced as a possible explanation for the observed periodic recurrences of the Earth’s ice ages [Benzi et al., 1981; Nicolis, 1993] —has by now been well established in a variety of physical systems [Wiesenfeld & Moss, 1995]. Recently it has been observed in the sensory nervous systems of two different arthropods [Douglass et al., 1994; Levin & Miller, 1996; Pei et al., preprint] and may be deeply linked to the evolution of all sensory systems. We report here the results of an experiment—the first in a human modality—designed to study the possibility of SR in the median nerve. Moreover, two additional features of this work are unique: first, our study makes use of the internal noise (as opposed to previous protocols wherein the noise was introduced externally) and second, we study the transmission of an aggregate stimulus through a bundle of individual neurons which are thought to be connected in parallel, a subject of recent theoretical [Collins et al., 1995] and experimental [Bezrukov & Vodynoy, 1995] interest. In our experiment, near subthreshold electrical stimuli were applied periodically to the median nerve, and responses were detected and signal averaged by electromyography. The internal noise intensity was mediated by muscle tension. The results are consistent with the hypothesis that internally generated electrical noise can enhance the signal transmission efficiency in this modality.