Learning: A Model System for Physiological Studies

Abstract

For progress to occur in the understanding of the physiological basis of associative learning, a reliable experimental system and a union of theory with experimental findings are necessary. A relatively simple animal like the gastropod Pleurobranchaea californica may provide model experimental material for studying learning in terms of the function and structure of visually reidentifiable nerve cells. Control procedures, which have been at the crux of controversies over the nature of learning, provide important information about the kinds of associations the experimental animals may be making; it is this information that offers the necessary direction for designing cellular studies. Using a broad spectrum of control criteria, we have shown that the food aversion behavior of Pleurobranchaea is attributable to associative learning which may be accounted for on the basis of a definable nerve network, one composed possibly of as few as 3 neurons. To answer this question, an experimental system must have the following properties: rapid and obvious behavior changes so that the quantity of the underlying processes will be maximized at any given time; a conditioned motor switch, rather than the cessation or appearance of a response, so that there will be available continuously in the output of the nervous system some active indication of learning; the use of parameters to measure the stimulus efficiencies and motor responses in ways that can be interpreted directly in neuronal activities; and reproducibility, in order to have a ready supply of animals for neurophysiological studies and for the continued development of the behavioral foundation.