Electrical noise of axon membrane and its behaviour as an adaptive system

Spectral analysis of stimuli in the excitation processes has revealed interesting correlations between macroscopical events (reflected in the excitation threshold of the nerve membrane) and microscopical events (reflected in electrical noise associated to the ionic currents) accompanying the generation of the nerve impulse. According to our analysis, the threshold function of nerve excitable membrane can be modelled by satisfying; (a) the energetic condition at low frequency and (b) the condition of spectral covering. One of the most important predictions of this model concerns the behaviour of axon membrane only in hyperpolarization as filters adapted to signals commonly used as physiological stimuli (rectangular, sinusoidal, or ramp stimuli). This prediction has generated two new theoretical objectives formulated as follows: What is the functional model of a filter adapted to a signal having the shape of an action potential; what is the signal adapted to a filter with a frequency characteristic similar to that obtained when applying white noise to the membrane biased near the excitation threshold. Our most recent studies performed by computer simulation allowed us to approach these problems.