General Model for the Molecular Events in Synapses During Learning

Any biochemical theory about the synaptic events during learning should be based on the assumption that the critical physiological phenomenon in learning is the very first activation of a previously nonfunctional synapse. Once the nonfunctional synapse has become usable, the essential event that is responsible for learning has taken place [I]. Unfortunately, most of the presented biochemical theories about learning do not propose anything about this basic physiological phenomenon in learning but are content to suggest vaguely "specific" changes in the neuronal metabolism of proteins, nucleic acids, etc. At the same time, it seems to be the opinion of many critical neurobiologists that our present state of knowledge about the neuronal metabolism is too scattered to permit the formulation of any detailed theory about the molecular events in synapses during learning. It is, however, a fact that our inability to measure directly these extremely fast chemical reactions compels us to approach the biology of learning intuitively—from a detailed theory to experiments. In this communication an effort has been made to formulate a general model for the chemical events in the activation of a previously nonfunctional synapse. The purpose of the author is not to claim this model to be ultimately the right one, but rather to show that in spite of our diversified knowledge it is possible to present a realistic detailed chemical model for this essential event in memory fixation. The present theory is a modification of a hypothesis presented previously by the author [2, 3]. The majority of the synapses in the central nervous system are probably congenitally functional [4]. This genetically determined network of neurons is the backbone of any learning, as "learning" always involves the coupling of an unconditional stimulus with a conditional stimulus [I]. Learning and memory, however, would not be possible in any form without the existence of a particular group of nonfunctional synapses which "open" only as the result of a specific unconditional stimulus from