Analysis of repetitive transient response of lobster motor axons

Abstract

An analysis was made to determine the relation between spike timing and the intensity of a constant current evoking a repetitive discharge in the single lobster motor axon. Accurate measurements of repetition intervals during the transient phase showed that an intensity increase of about 10–3 rheobase units produces a significantly different change in spike interval timing at the 0.005 probability level. Applications of excitation theory to the latency-intensity data have produced an equation which predicts the latency to the nth spike in a repetitive sequence as a function of stimulus intensity. The equation implies that the excitation process producing the nth spike is similar to the process producing the first spike in the repetitive sequence. Influences of supernormality and refractoriness were incorporated into the analysis. Also repeated stimulation at a fixed intensity indicated an inherent variability in the timing of the repetitive response which was shown to be a function of the magnitude of the latency. To explain this result a fixed uncertainty in the level of the initiating excitatory state was postulated.