Morphology of the Models: Where is the Pacemaker?

Abstract

In formulating the behavior of the individual pacer elements of the pacemaker ensemble, several concepts were incorporated which have their origin in the behavior of high-frequency neurons. The recovery phase of the pacer, with its associated stochastic variability, is in some senses related to the idea of neuronal “refractory time”, and even more closely related to the “recovery” process which is envisioned in several formal models proposed for the behavior of spontaneously firing neurons in the high-frequency domain (cf. Figs. 4.1 and 4.2). Furthermore, the idea that excitatory discriminator input does not affect the rate of the pacer recovery process, but only alters the excitatory state associated with onset of discharge (cf. Figs. 4.4, 4.5, and 4.6) is also closely related to concepts of formal models which have been developed to describe the influence of tonic stimuli on high-frequency neurons. Now that we have explored in some detail the performance of a particular sort of hypothetical network consisting of such elements, the question naturally arises, “To what extent can these models be extrapolated back into a neurophysiological context, as guidelines for the experimentalist in his search for the biological clock? ” More explicitly, what clues do the models provide which might facilitate the identification of structures within the organism which could correspond directly to elements of the hypothetical pacemaker?