THE SYNAPTIC MECHANISM EOR POSTSYNAPTIC INHIBITION 75 



QDOOOO O 



Fig. 4. Biceps-semitendinosus motoneuron with double-barrelled K2SO4 

 electrode, the resting membrane potential being 70 mV. I.p.s.p.'s are set 

 up by quadriceps group la afferent volleys, and the e.p.s.p.'s by biceps-semi- 

 tendinosus afferent volleys, b-k show interaction of i.p.s.p. and e.p.s.p. at 

 various intervals, the control responses being given in a and l respectively. 

 All records were formed by the superposition of about forty faint traces, but 

 the quadriceps afferent volley was only turned on for about half the traces, so that 

 the control e.p.s.p. was superimposed on all records from b to k. Lower traces 

 show the record from the L7 dorsal root, the quadriceps afferent volley con- 

 sequently giving a very small spike potential. Same time and potential scales for 

 A-L. M shows tracings of the control e.p.s.p. and i.p.s.p. while n shows an analysis 

 of records like those of a-l. It is assumed that the e.p.s.p. is unaltered by the 

 superimposed i.p.s.p.'s which are themselves greatly potentiated as shown. The 

 peak potentials of the i.p.s.p.'s so determined are plotted in o against the interval 

 between their onset and the onset of the interacting e.p.s.p., part of the series 

 being shown in n. Note that same time scale obtains for m, n and o, zero time 

 being placed at the origin of the e.p.s.p. (Curtis and Eccles, 1959.) Reproduced by 

 permission from the Journal of Physiology. 



will be potentiation of an i.p.s.p. set up during the depolarization of an 

 e.p.s.p. This is illustrated in Fig. 4, where in the superimposed records of 

 A-L, the i.p.s.p. is increased from its control value of —3 mV to as much as 

 — 5-5mV when the inhibitory currents flow during the maximum of the 



