210 Functional Interrelations of the Brain Stem 



still further released -when the cerebral cortex is removed. Connor has not yet 

 had opportunity to study the effects of isolated cortical ablations in relation 

 to isolated ablations of the anterior lobe; but it is clear that the postural 

 mechanisms originating in the cerebral cortex interact with those of the an- 

 terior lobe. 



Neocerebelhim.— It is less essential to dwell upon cortico-neocerebellar in- 

 terrelations since they are more commonly recognized. Phasic movements are 

 grossly disturbed following removal of the neocerebellar cortex. When large 

 lesions of the neocerebellum occur, errors of rate, range, force, and direction 

 of volitional movements commonly take place, and the discontinuities of move- 

 ment which constitute the summation of these errors is generally referred to 

 as "cerebellar tremor." 



One thing frequently lost sight of in the analysis of cerebellar syndromes is 

 that cerebellar tremor does not arise in the cerebellum, for it develops after 

 its complete removal. It is due to action in some other part of the nervous 

 system, and one can readily prove that cerebellar tremor, so-called, results 

 from activity of the cerebral cortex, since the discontinuities of movement 

 characteristic of cerebellar disease completely disappear on removal of the 

 cerebral cortex (Fulton, Liddell and Rioch"") or, in monkeys, on bilateral abla- 

 tion of areas 4 and 6. 



Hence, cerebellar tremors and striatal tremors have this in common, namely, 

 that they depend upon the integrity of the motor projections from the cerebral 

 cortex; and the similarities between the two types of tremor are greater than 

 is sometimes appreciated— or perhaps one should say, the differences are less 

 than our textbooks would lead us to suppose. Cerebellar tremors are most con- 

 spicuous at the end of a volitional movement and are sometimes referred to as 

 "terminal tremors." When a monkey with a neocerebellar lesion reaches for a 

 banana, the tremor, scarcely obvious at first, becomes grossly exaggerated just 

 as the animal reaches its objective. 



A Parkinson tremor, on the other hand, tends to be more exaggerated at the 

 beginning of movement and may be ironed out by the time the movement is 

 completed. 



I vigorously object to the distinction commonly made between striatal and 

 cerebellar tremors, namely, that one is a tremor of rest and the other a tremor 

 of action. The Parkinson tremor completely disappears during sleep and is 

 present only when the subject is attempting by voluntary effort to maintain 

 the body in a certain posture. It is in reality a tremor resulting from volitional 

 control over postural mechanisms, whereas cerebellar tremor appears as a re- 

 sult of volitional control of phasic movements. Both, basically, are tremors of 



action. 



Summary and Conclusions 



This survey of the two divisions of the extrapyramidal system leads to several 

 general conclusions, as well as to a number of practical considerations which 

 may be summarized as follows: 



