Changing Concepts Concerning Physiological Mechanisms of Animal Motor Behaviour

AT the beginning of this century, when Pavlov undertook his gigantic research work on the physiology of higher nervous activity, he selected a particular type of response called by him conditional (or in English conditioned) reflex (hereafter denoted as CR) which he considered a simple and general model of acquired animal behaviour. This type of response is formed when any stimulus is followed a number of times— is reinforced—by some particular stimulus eliciting a specific, inborn (unconditioned) effect and consists in the first stimulus starting also to elicit the same effect. The extensive research work carried out over several decades by Pavlov and his co-workers was almost exclusively devoted to the study of alimentary and acid CRs, the salivary effect being used as the main quantitative indicator. Nevertheless, Pavlov was strongly convinced that the results obtained in experiments with these reflexes were representative of all kinds of CRs, based on other reinforcing agents, and also that the properties of this type of response are repre-sentative for the whole animal acquired behaviour. Although Pavlov was fully aware that the chief part of this behaviour consists of motor activity, he deliberately rejected the idea of using motor CRs in his experimental work, judging that they could provide too strong a tempta-tion to anthropomorphic and psychological speculations, which he wished to avoid at all costs. On the basis of their experimental findings, Pavlov and his co-workers attempted to unravel the general mechanisms of the function of the brain in much the same way as, through experi-mentation on spinal reflexes, his great contemporary Sherrington