CEREBRAL CORTEX AND VESTIBULAR NYSTAGMUS 11 



The presence of a motor cortex in rabbit, cat, and dog is well 

 recognized. Such an area has never been demonstrated in the 

 cerebrum of the frog and pigeon, while it has been alleged by 

 Johnston ('16) for the turtle, which, however, is still a mooted 

 question. So, from the standpoint of comparative anatomy and 

 physiology, the idea that the quick component of nystagmus is 

 dependent upon the integrity of a cerebral reflex arc is hardly 

 tenable. 



The increase in nystagmus in animals with lesions to the eye 

 area of the motor cortex when the slow component is directed 

 opposite to the side of the lesion is explained by the withdrawal, 

 as a result of the ablation, of the well-recognized heterolateral 

 inhibitory influence which the cerebral cortex exerts over reflexes. 

 The absence of any disturbance of nystagmus by ablation of the 

 cerebral hemispheres in those forms that have not acquired this 

 cerebral inhibitory function is evidence, I take it, in favor of 

 this idea. An attempt at an explanation of the apparent diminu- 

 tion of the nystagmus in completely hemi-decerebrate animals 

 when the slow component is directed to the side of the lesion will 

 not be made in this report (tables 2 and 3). 



Further, the observation that in the rabbit complete decerebra- 

 tion and destruction of the thalamus can be performed without 

 abolishing the quick component shows conclusively that the quick 

 component of vestibular nystagmus is dependent only upon the 

 integrity of the afferent-efferent nerves of the eye muscles and 

 their centers in the midbrain. The findings on the dog support 

 this view. 



Why depressed and comatose animals show deviation of the 

 eye on rotation and no quick component is a question which 

 cannot be answered directly. If the body temperature is sub- 

 normal, the quick component can be restored by raising the tem- 

 perature to the normal. In other conditions of depression the 

 quick component disappears, while the slow deviation persists, 

 e.g., narcosis. It should also be pointed out that, although we 

 are dealing with an entirely proprioceptive phenomenon, vestib- 

 ular nystagmus apparently involves two kinds of propriocep- 

 tion, the quick component due to a segmental proprioceptive con- 



