REGULATION OF DISCHARGE RATE BY INHIBITION 67 



''n Fi Fn 



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12 I 1 M i I I I I I I I I I i I i i I I I loi i I i i i i i I i M I |,i ; ; I II I i I 13 

 Is N I ll ii i l MlilM I I I I i I I I i I ii I I 13 I i i I i I 1 i i i i i 1 1 i I I I I I I i I 1 1 III u 

 19l^ l l ll llll lN ll l il|i | ii||||||iliili| i7|l|||||ililiiiiilllllllilMlllilli;il 20 

 19l Ni i ! ;i llj il ll , i il l |i|i|i|||ii||iii 161111 ii iiiiiliili IIIMIIIIMIIIIMIm 19 



20il!lilliilllllllllll|!||||||i||||i2||||||||||||,IIIIIIIIIHIIiiili 20 



iglllMlllillMllllilllllllllllNI ulllMIMIII IIIIII lllll lllilLL 24 



1 sec 



Fig. 2. Records from three experiments showing tonic reflex discharge of single 

 fibre in ventral root to afferent stimulation at repetition rate 114/sec. Normal 

 frequency of discharge F„ 1 sec before agd after locking of antidromic shock to 

 firing spike to obtain F,. Values of F,, and Fi against the records refer to the 

 cut-out portions and not to total period of counting. The first five rows refer to 

 one experiment, the sixth and seventh to two different experiments; the seventh 

 put in to illustrate good rebound (Granit et al., 1960). 



to vary their Fn- Others can by electrical afferent stimulation (at 110/sec) 

 at different strengths be made to fire at different rates. By connecting elec- 

 tronically the tonic firing spike to the antidromic shock one can make 

 recurrent inhibition act at the average rate of motoneuron output as in 

 Fig. 2 (paper no. 2). Averaging the rate of discharge over 5 sec before and 

 5 sec after a 5 sec period of recurrent inhibition one obtains the basic fre- 

 quency of discharge Fn- The value during recurrent inhibition is the average 

 from the 5-sec period during which it acted. Plotting Ft against Fn gives 

 straight lines of the type shown in Fig. 3 (paper no. 2). Fi is proportional 

 to Fn and this relationship is reminiscent of the results of Hartline and 

 Ratliff (1956) with Hartline's (1949) lateral inhibition in the Limulus eye. 



This type of experiment also provides us with a method of measuring the 

 potency of recurrent inhibition. In the record of Fig. 4 (paper no. 2) the 

 dashed line is drawn at an angle of 45' in the Fi-Fn diagram to show the 

 theoretical case of absent recurrent inhibition or F„ = Fi. B is the result 

 actually obtained. Then concurrent tetanic stimulation of a point, low in 

 the anterior cerebellum, was began and the readings repeated. They are now 

 numbered in the order in which they were taken. The earliest ones fell on a 

 good straight line C with a slope signifying a strong increase in the efficacy 

 of recurrent inhibition. The last values fell better on line D and the eff"ect 

 was not merely visible during concurrent stimulation of the cerebellar point 

 but rose and disappeared so slowly that the numbers underlined, which 

 represent intercurrent controls without simultaneous central stimulation, did 

 not separate out from the others. We also found central inhibitory points 

 in this manner. Koizumi et al. (1959) in their work on spinal cord inter- 

 neurons described one cell which they held to be a Renshaw cell and whose 



