CENTRAL CONTROL OF EYE MOVEMENTS IIOI 



from cortical lesions in man, ijut persistence of 

 optokinetic nystagmus has been claimed in coma, 

 in the newborn and in 'extreme idiocy.' The weight 

 of evidence supports the view that the occipital cortex 

 plays an essential part in all forms of optokinetic 

 nystagmus in man. 



It was said by Ferrier & Turner that eye move- 

 ments are still possible after bilateral destruction of 

 the superior colliculi in monkeys (64). This paper 

 seems to be quoted oftener than it is read. However, 

 in order to approach the colliculi, the left occipital 

 lobe was removed in these experiments so that the 

 animals were hemianopic. The only information 

 given is that there was no ophthalmoplegia and eye 

 movements were normal. Whether adversive move- 

 ments or optokinetic movements to the left were 

 still normal is not related. In similar experiments 

 on cats by Spiegel & Scala (128), the occipital lobes 

 were pushed up out of the way. They may have been 

 damaged and their excitability was certainly lost. No 

 tests of optokinetic nystagmus were made. There is 

 no doubt that a pathway from the frontal area to the 

 nuclei of motor nerves of the eye exists which does 

 not pass through the colliculi (47). 



In man the presence of supranuclear palsies from 

 pressure on the tectum (Parinaud's syndrome) is 

 most easily explained as interference with the su- 

 perior colliculi. The representation of the upper 

 quadrants at the anterior medial parts of each col- 

 liculus would account for the frequencx' of paralysis 

 of upward movement. A nuclear ophthalmoplegia 

 could be due to pressure and distortion of the mid- 

 brain extending more deeply to tiie third nerve 

 nucleus. How such a lesion would affect fibers from 

 the frontal lobes is not clear. 



In the lower mammals the coiliculus plays a large 

 part in adversive movements; in monkeys and man 

 it is at least a distribution center for descending 

 pathways for eye movement. 



Proprioceptors 



It has been remarked by Cooper et al. (40) that 

 units stimulated by pulling on the external extra- 

 ocular muscles in the goat were to he found only in 

 the deeper layers — stratum griseum profunduni — in 

 the coiliculus (see fig. 4). One may therefore specu- 

 late that whether a particular visual stimulus in the 

 peripheral field gives rise to an eye movement, or 

 both head and eye movement, may depend on 

 proprioceptive impulses signalling the initial rela- 

 tion of the eve to the head. 



FIG. 8. Adver- 

 sise movements in 

 the unanesthetized 

 cat following stimu- 

 lation of the left 

 superior coiliculus. 

 [From Hess (80).] 



EVE MOVEMENTS .AND VISUAL CORTEX 



Stimulation of the visual cortex produces eye 

 movements in the lightly anesthetized monkey (25, 

 46). Stimulation further forward on the lateral 

 surface of the hemisphere also gives eye movements, 

 Ijut the directions of the responses are reversed. 

 Whereas stimulation of the upper part of area 1 7 

 evokes downward movement of the eyes, and vice 

 versa, stimulation of the upper part of area 1 9 causes 

 upward movement. This may agree with the sup- 

 posed homology between area 18 and 19 and the 

 second — mirror image — visual area seen in the lower 

 mammals, such as in the rabbit (134). 



Fibers from areas 18 and 19 have been traced by 

 Crosby & Henderson (46) as the occipitocollicular 

 bundle in the macaque. This crosses the pulvinar 

 and runs Ijack adjacent to the posterior commissure 

 to enter the superior coiliculus as the deep layer of 

 the stratum opticum. 



The simplest picture of the process of fixation 

 would be that impulses from the peripheral field of 

 the retina reach area 17 and from there, or from the 

 areas just anterior, give rise to impulses which run 



