HANDBOOK OF PHVSIOLOGV 



NEUROPHYSIOLOG'i' II 



Right Lobe 



ISO 



FIG. 7. Localization of the visual field in the optic lobe of the frog. Right: Perimeter chart for 

 the left eye in which figures / to 13 represent the different positions of the stimulus light flashes 

 required for maximal response, as the recording microelectrode was moved in orderly steps of o. I 

 mm across the surface of the contralateral (right) optic lobe. The positions of insertion of the elec- 

 trode are shown in the left diagram which gives the outline of the lobe, ."^t insertion /jj, the electrode 

 was lowered through the substance of the lobe. .\s the electrode penetrated, the optimum posi- 

 tion of the stimulus light moved downwards and outwards. This is to be expected since the surface 

 of the lobe curls around underneath at the lateral edge, and apparently some of the superior retinal 

 area is represented here. [From Gaze (72).] 



all cases the upper \isual field is represented nearer 

 the niid-linc of the superior coUiculus, the lower 

 field more laterally. The horizontal meridian is 

 shown by some workers as running Isackwards and 

 medially, by others as running parallel to the mid- 

 line. This arrangement of the projection is the same 

 for animals with frontally and with laterally directed 

 eyes, l)ut animals with laterally directed eyes, such 

 as the rabbit, ha\e almost entirely contralateral rep- 

 resentation while the cat has l^ilateral representation. 

 In tfie cat the anterior pole of the coUiculus is de- 

 voted to the area centralis of the retina which seems 

 to have a larger central projection area than the rest 

 of the retina (5). 



Effects of Stiiniihition and of Lesions 



There is no doui^t that stimulation of the superior 

 collicuhis in some mammals can cause adversive eye 

 movement. This has been shown for the cat with 

 implanted electrodes in the conscious animal (fig. 8) 



(79) and by using strvchnine with \ery light anes- 

 thesia (6). No e.xperimental data are available for 

 the monkey or man. 



There is also good e\idence that pursuit movement 

 induced bv stripes on a rotating drum can be al)ol- 

 ished by destruction of the superior coUiculus in the 

 guinea pig (125) and in the cat (122, 123). How 

 much importance this "subcortical" optokinetic mech- 

 anism lias in man is quite unknown. On the basis of 

 obser\ations on the guinea pig, it seems to be as- 

 sumed by Carmichael el id. (29) to e.xist in man 

 Rademaker & Ter Braak (113) suggest that weak 

 stimuli set up a cortical optokinetic nystagmus, 

 whereas large stripes may actuate a subcortical 

 mechanism. This distinction .seems to have some 

 experimental basis. There is no douijt that the direct 

 visual connections to the superior coUiculus becoine 

 smaller and less important in man, and corticocol- 

 licular connections from area 1 9 become much more 

 important (44, 1 1 i ). Certainly no signs of sub- 

 cortical optokinetic movements are seen in blindness 



