608 RADIATION BIOLOGY 



teristics. It therefore appears that some photopic events eUcit a rela- 

 tively greater response in the cortex than in the retinal action potential 

 (see Fig. 13-16). 



Further evidence for this conclusion is provided by Adrian's experi- 

 ments (1946) on the optic nerve discharges in the cat, rabbit, and guinea 

 pig. Light adaptation greatly reduces the retinal action potential but 

 does not interfere very much with optic nerve impulses. The action 

 potential shows, moreover, a duality of response in which the early com- 

 ponent is assumed to be photopic, whereas the later one (6-wave) is sco- 

 topic. No such duality appears in the records from optic nerve or cortex. 

 Adrian concludes: "It is presumably the function of the eye to furnish 



BLUE GREEN YELLOW-GREEN ORANGE" RED ORANGE-RED RED 



CORTEX 



[ I mv 



EYE 



■-^.At^ — Y — -^Yi^ —-^\^ 



[ I mv 0.1 sec 



A 



_J 1 



Fig. 13-16. Comparative responses of the cortex (striate area) and the eye (electro- 

 retinogram) of the monkey. (Adrian, 1946.) 



the brain with a coherent account of visual events, and, although it may 

 employ two kinds of receptors, it has abundant synaptic connections for 

 welding their twin messages into one." 



A notable contribution to our knowledge of visual function has been 

 made by Noell and Chinn (1950; Noell, 1951). These investigators have 

 studied the action potential, the activity of retinal fibers, and responses 

 within the optic tract, geniculate body, and cortex. They have worked 

 with man, monkey, cat, rabbit, pigeon, turtle, and frog. Some of their 

 principal findings are the following: (1) Retinal metabohsm is based upon 

 both glycolysis and respiration. Respiration predominates in lower 

 vertebrates, glycolysis in mammals. (2) Separate processes within a 

 given retina may be relatively more dependent upon respiration or upon 

 glycolysis. For example, the a-wave of the rabbit is early affected by 

 anoxia, thus indicating a dependence upon respiration, whereas the 

 fe-wave is easily abolished by the presence of sodium iodoacetate, a poison 

 that prevents glycolysis. (3) In the cat, monkey, and man the 6-wave is 

 more susceptible to anoxia than is the a-wave. However, a small 6-wave 

 is still present at the time when optic-tract potentials have dropped out 

 completely in the rabbit (see Fig. 13-17). Furthermore the human 



