NEURAL ACTIVITY IN THE RETINA 



701 



negative a-wave now is greatly increased and maximal 

 when the off-effect has reached full size. The retina 

 seems to show no refractoriness but is immediately 

 ready to re-establish the level of negativity charac- 

 teristic of that particular state of adaptation and 

 stimulus strength. The cornea-positive PI I (6-wave) 

 behaves very differently. It fails to appear until some 

 time has passed, as can also be very clearly seen with 

 the cat retina (Z)) which is dominated by this com- 

 ponent. 



Figure 8 shows the full analysis of an experiment of 

 this kind. The dotted lines represent the effects of the 

 individual flashes of reillumination, d is the rf-wave 

 control; h, the level of the A-waves; a, that of the a- 

 waves. Assuming a and b being generated in the same 

 structures, it is difficult to understand why the former 

 response is immediately ready to be re-established 

 while the latter refuses to behave in the same fashion. 

 Part of this difference has been found to be due to 

 the b- and ^/-waves sharing generators in the sense 

 that the one leaves refractoriness for the other (82). 



In recent attempts to assign the origin of the ERG 

 to definite retinal structures, experiments of this type 

 have been neglected altogether. Yet, they seem to 

 contain essential information about the components 

 of the ERG which no discussion of these problems can 



neglect. Perhaps this is the place for pointing out that 

 the ganglion cells definitely seem to be excluded as 

 sources of the ERG. From time to time since 1933 the 

 author has stimulated antidromically the optic nerve 

 of frogs and cats while recording the ERG in order 



FIG. 7. Effect of increasing the interval between two stimuli 

 on the electroretinogram of different types of retinae: .4, frog; 

 D, cat. Uppermost curve of each series shows the uninterrupted 

 off-effect. Short vertical lines indicate the beginning of re- 

 illumination. Time marking: o.i sec. [From Granit (65).] 



U U-l 0-2 



FIG. 8. Off-effect or (/-wave given by d in the frog ERG. Reillumination by single flashes elicits 

 the potential changes (a- and i-waves) shown in dotted lines, a and b trace maxima of a- and i-waves 

 respectively. Note that curves b and a are drawn through peaks of b and a waves at different 

 times of re-illumination and thus show that the a-wave reappears at once and is increased while 

 the 4-wavc requires a long time for recovery. [From Granit c& Riddell (80).] 



