2o8 Functional Interrelations o£ the Brain Stem 



lesion involving area 6 and the head of the caudate nucleus. It persisted for 

 several weeks, then abruptly diminished in intensity, but was occasionally 

 seen during a period of five or six months, whenever the animal became ex- 

 cited. We have been unable in two subsequent chimpanzees, with a similar 

 lesion, to reinduce the chorea, and we are as yet unable to state what the es- 

 sential lesion may have been. 



In the analysis of the tremors and involuntary movement of our striatal 

 animals, we have been frequently aware of certain similarities between the 

 tremors of corticostriatal origin and those of corticocerebellar origin, and now 

 I would like briefly to describe a series of recent studies on the physiology of 

 the cerebellum which have an intimate bearing upon the problem in hand. 



The Cortico-ponto-cerebellar System 



From the cerebral cortex also arises a vast system of fibers which converge on 

 the pontine nuclei, and from there pass their impulses to the cerebellum. The 

 corticospinal projections, in addition, are said to send branching fibers to the 

 pontine nuclei which directly influence cerebellar mechanisms. The cerebellar 

 hemispheres have developed in evolutionary history pari passu with the elabo- 

 ration of the cerebral cortex, and all authorities are agreed that the two organs 

 have a close functional interrelation. It is customary to speak of the cortico- 

 strio-nigral system as being primarily concerned with postural reactions, 

 whereas the cortico-ponto-cerebellar system is believed to be associated pri- 

 marily with phasic movement. Neither generalization, however, can bear too 

 close scrutiny. 



The cerebellum has three primary divisions, two arising from the ancient 

 brain— the posterior lobe and the anterior lobe, both midline structures— and 

 the third, the neocerebellum, comprising the cerebellar hemispheres, which 

 are intimately associated with the hemispheres of the cerebrum. 



Posterior Lobe.— This includes two primary divisions: (a) a spinocerebellar 

 part, consisting of pyramis and uvula, and (b) the flocculonodular lobe, which 

 is primarily vestibular in its connections. Dow^*" has shown that ablation of 

 the flocculonodular lobe causes disturbances of balance similar to those seen 

 in grosser form when the vestibular nuclei are injured, and it is obvious that 

 this ancient part of the cerebellum plays an important role in maintaining 

 the equilibrium of the body. 



Less is known concerning the pyramis and uvula, except that their ablation 

 in conjunction with that of the flocculonodular lobe considerably exaggerates 

 the disturbance of equilibrium caused by ablation of the flocculonodular lobe 

 alone. Their isolated ablation, however, does not seriously affect equilibrium. 



Anterior Lobe.— The anterior lobe, also called paleocerebellum, is separated 

 from the neocerebellum by the fissura prima and is made up of three divisions: 

 the culmen, centralis, and lingula. Stimulation of the anterior lobe, as origin- 

 ally shown by Miller and Banting," causes inhibition of decerebrate rigidity, 

 and, in a lightly anesthetized animal with cortex intact, inhibition of extensor 



