Introductory Remarks

Abstract

The Concise Oxford Dictionary defines the adjective plastic as applicable for describing something which is pliant, supple or capable of being moulded. That object or entity thus has the property known as plasticity. This definition implies change in physical structure but when we apply this term to dynamic phenomena such as behaviour or nervous function we need to consider more carefully its meaning. For instance, does our ability to learn and to experience changes in mood and perception suggest that the nervous system is plastic or must we consider only recovery from a lesion as diagnostic? Alternatively, do we accept changes in the efficacy of a reflex, brought about by a conscious decision, as indicative of neural plasticity? In each case changes have occurred in the functional connectivity of the nervous system and in neither case do we necessarily have information concerning structural changes. Fortunately, there is one outstanding criterion which perhaps transcends all others — that of permanency. This aspect emerges for it carries with it the covenant that the clay, once moulded, shall never again be the same. It permits us to discount the transient modulation of connections and to focus on changes that can never be fully reversed. It facilitates definition without embroiling us unnecessarily in premature discussion of mechanisms.