Temperature Dependence and the Role of Internal Noise in Signal Transduction Efficiency of Crayfish Mechanoreceptors

A simple phenomenon called stochastic resonance (SR), well known in nonlinear statistical physics, offers an explanation of how random fluctuations can enhance the detectability and/or the coherence of a weak signal in certain nonlinear dynamical systems. It is interesting to speculate that SR may play a role in the remarkable sensitivity exhibited by numerous biological sensory systems: systems which are themselves often inherently noisy and which, moreover, must usually operate in a noisy environment. A distinction is thus drawn between the external, or environmental, noise and the internal noise inherent in the sensory neurons themselves and distinguished by the randomness in time intervals between action potential spikes. We report the results of experiments with the internal noise, the intensity of which is varied by controlling the temperature of the preparation during the experiment. The useful range of temperatures could be extended by acclimating individual crayfish to a low or high temperature environment for many weeks prior to the experiment. Our results indicate that noise plays a significant role in signal transduction efficiency, increasing the signal-to-noise (SNR) ratio exponentially with noise intensity up to a maximum. Increasing the temperature beyond this maximum results in reduced SNRs and sharply reduced internal noise levels. The results of shifts in the data due to acclimation temperature can be removed by plotting the data versus the noise level, indicating that the noise may be a universal quantity in the dynamics of biological neurons.