THE EFFECTS OF USE AND DISUSE ON 

 SYNAPTIC FUNCTION 



J. C. ECCLES 



It must be an ultimate objective of both psychology and neurology to 

 account for all the phenomena of learning and conditioning by the known 

 properties of the patterned arrangements of nerve cells that occur in the 

 central nervous system. We are still far from this goal ; but I hope to show 

 that the functional connections between nerve cells exhibit properties 

 which correspond to the 'plasticity' that has long been the basis of one 

 explanation of learning and conditioning, which may be called the trace 

 theory of memory (cf. Gomulicki, 1953). 



It is important at the outset to state that it will be assumed throughout 

 that the synaptic connections between nerve cells are the only functional 

 connections of any significance. These synapses are of two types, excita- 

 tory and inhibitory, the former type tending to make nerve cells discharge 

 impulses, the other to suppress this discharge. There is now convincing 

 evidence that in vertebrate synapses each type operates through specific 

 chemical transmitter substances that in turn change the ionic permeability 

 of the postsynaptic membrane and so bring about the excitatory or 

 inhibitory action on the postsynaptic cell (Fatt, 1954; Eccles, 1957). 



The alternative postulate is that, at least in part, interaction between 

 neurones is caused by the flow of electric currents generated by active 

 neurones. There is at present no experimental evidence that such inter- 

 action has any functional significance for the nervous system of verte- 

 brates. With the ordinary random relationships of neuronal discharges the 

 flow of electric currents between neurones is far too small to have any 

 significant effect, and this is even the case for experiments using the un- 

 physiological procedure of large synchronous volleys. For example Wall 

 (1958) found that the large electrical fields generated by the antidromic 

 activation of the motoneurones in the ventral horn caused no detectable 

 change in the excitability of the afferent fibres synapsing on those moto- 

 neurones. However, under abnormal conditions of synchronization of 

 large assemblages of nerve cells, the propagation of electrical waves 

 suggests that there is direct electrical interaction between nerve cells 

 (cf. Libet and Gerard, 194 1) and Jasper has produced further evidence 



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