The Cholinergic Synapse and the Site of Memory

Abstract

The idea that learning and memory are due to some form of change of synaptic conductance is very old, having been suggested by Tanzi in 1893. It is a simple idea and in many ways an obvious one. However, the evidence that learning is due to changes at the synapse has hitherto been meager (Eccles, 1961, 1964; Spencer and Wigdor, 1965; Beswick and Conroy, 1965; Fentress and Doty, 1966). Though changes do occur at a spinal synapse as a result of stimulation, there is no evidence that the changes are those utilized in the nervous system for information storage. To use an analogy, if we pass large amounts of current across resistors in a computer, temporary increases in temperature and perhaps even permanent increases in resistance occur. However, such an experiment shows only that the computer could store information by using "post-stimulation" alterations in its resistors but not that this is the actual way in which the computer does store information. Further, Sharpless (1964) has pointed out that learning is not due to simple use of stimulation of a pathway and he therefore questions whether the phenomena studied by Eccles (1961, 1964) have anything to do with learning as observed in the intact organism. Nevertheless this does not mean that learning is not due to synaptic changes of some sort. It means only that a different experimental test of the possibility must be devised.