342 



BRAIN MECHANISMS AND LEARNING 



Besides thus confirming the earlier work in which synpatic function 

 was tested by monosynaptic reflexes, this investigation of synaptic 

 potentials allowed quantitative estimates to be made of the depression of 

 synaptic function and established that this depression was restricted to the 

 inactivated synapses on a motoneurone. It also revealed the time course 



Fig. 3 

 Intracellular EFSPs evoked in a flexor halliicis longus motoneurone by maxi- 

 mum Group la volleys in flexor hallucis longus nerve (A), and in flexor digi- 

 torum longus nerve (B) which had been severed 1 5 days previously. Top records 

 in A and B were taken before the conditioning tetanus 400 c/s for 10 seconds, 

 and the subsequent records at the indicated intervals after the tetanus. Same 

 time scale throughout, but different voltage scales for the two series as indicated. 

 (Eccles, Krnjevic and Miledi, 1959, with permission ofthe Jotmuil ofPliysioloi^y). 



of the onset of depressed function; it was negligible at 6 days, but by 10 

 days after the nerve section the depression was already about half 

 developed and by 1 3 days it was fully developed. 



As we have seen, the operative procedures for inducing disuse by 

 sectioning the afferent fibres have the disadvantage that a small shrinkage 

 of the dorsal root fibres occurs (Eccles and Mclntyre, 1953; Szentagothai 

 and Rajkovits, 1955). Conceivably, this shrinkage may extend right to the 



