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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



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FIG. g. Effect of a Hash, supcrimposfd on the off-discharge 

 in the frog's optic nerve, plotted as average spike frequency 

 in impulses per sec. against time in msec. Dotted line, off- 

 discharge control. Continuous line, diminution in frequency 

 (inhibition) caused by a flash, indicated by the horizontal black 

 line, delivered at the height of the off-effect. [From Granit & 

 Therman (8i).] 



to determine whether the latter could be influenced. 

 This has never been the case (76). Yet it is possible to 

 influence both the discharge of ganglion cells and 

 their level of depolarization by such means (74). 

 Further, glaucoma with optic nerve atrophy is asso- 

 ciated with a normal ERG (96, 114). 



The question of how the ERG correlates with the 

 discharge through the optic nerve can be profitably 

 attacked by studying what happens in the nerve when 

 these large a-waves are induced on top of the ofT- 

 discharge. Figure 9 shows that there is inhibition of 

 the off-discharge (81) and this was confirmed by 

 Granit & Helme (76). This experiment provided the 

 main argument for the view that PHI is concerned 

 with inhibition rather than with excitation. The cor- 

 nea-positive PII was held to signify excitation. The 

 general likeness between the cornea-positive retino- 

 gram and the variation of the discharge-frequency 

 through the optic nerve, first pointed out lay Adrian 

 & Matthews (3, 4, 5), supports the same inference 

 (fig. 10). Granit & Therman (81) could find no eff"ect 

 in the optic nerve discharge corresponding to the 

 large c-wave of the dark adapted eye. 



In this connection the effect of alcohol on the frog 

 retina is particularly interesting (19). The left record 

 in figure 1 1 shows the light adapted ERG of a frog. 

 A drop of alcohol into the opened bulb makes it 

 change as shown in the right record. The upper 

 record shows the change of the a-wave under alcohol. 

 In this final stage it looks like the ERG of the fully 

 dark adapted retina and, like the latter, has a small 

 d-wavc and responds only to slowly flickering light. 

 Even an ERG made largely negative by potassium 



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FiG. 10. Variation in impulse frequency of the eel optic 

 nerve during stimulation. [From Adrian & Matthews (3).] 



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FIG. II. Effect of alcohol on frog ERG. Top record: diminu- 

 tion of a-wave during alcohol treatment. Left: Light-adapted 

 ERG with reillumination on top of the rf-wave. Right: Same 

 experiment after alcohol. Time, 0.2 sec. Light signal above 

 time record. [From Bernhard & Skoglund (ig).] 



chloride turns positive after alcohol. The interpre- 

 tation of these changes is that alcohol diminishes PHI 

 and augments PII, which agrees with the interpreta- 

 tion of the similar changes with state of adaptation. 

 However, still more interesting from the present point 

 of view is what happens in the test with reillumination 

 in which, after alcohol, the negative a-wave will now 

 be very small or absent. The experiment showed that 

 the corresponding inhibitory pau.se in the discharge 

 also was curtailed. The authors held their result to 

 support the view that PHI (or what now may be 

 called fast PHI) was inhil)itory, i.e. as confirming 

 the view that excitation and inhibition was charac- 

 terized ijy opposite deflections of the ERG. 



In this volume the vision of invertebrates is treated 

 in Chapter XX\"I by Milne and Milne. It is neverthe- 

 less of considerable interest here to mention the recent 

 experiments of MacNichol & Benolken (105) with 

 Hartline's so-called lateral inhiljition in the plexus of 

 nerve fibers behind the Limulus ommatidia (9O. By 

 means of interconnections in this plexus, illumination 

 of one ommatidium suppresses the discharge of 

 another (91). Now, MacNichol cS: Benolken find that 

 alcohol removes this lateral inhibition re\ersil)ly. 



For a final allocation of the retinal component po- 

 tentials to definite structures (receptors or bipolar 



