THE CEREBELLUM 



1269 



neglected techniques for the detection and analysis 

 of postural and reflex asymmetries. 



In the macaque, atonia and muscular weakness 

 have been observed by many {29, 123, 182, 188-190) 

 investigators. The results of unilateral cerebellar and 

 peduncular lesions in a number of primate species 

 (29-31) were reviewed by Fulton & Dow (126) who 

 were struck by the increased intensity and persistence 

 of the atonia and weakness in the chimpanzee as com- 

 pared to the lower members of the series. 



DISORDERS OF PHASIC CONTRACTIONS. The disorders 

 of phasic contractions following unilateral cerebellar 

 ablations were essentially like those following total 

 ablation with the exception that they were confined 

 to the ipsilateral side of the body (36, 1 1 1, 113, 114, 

 182, 183, 188-190, 277, 290, 335). The coarse tremor 

 and oscillations of the head and neck were obvious 

 and dramatic. These movements were best under- 

 stood as the result of inaccurate control of timing 

 and strength of muscular contraction and inaccurate 

 compensatory movements. Signs of ataxia also were 

 evident in the manner of control of limb position and 

 placement during locomotion. Similar signs appeared 

 in primates subjected to unilateral lesions (29, 123, 

 182, 188-190). In this form the astasia was more 

 prominent in the limbs than it was in the quadruped, 

 perhaps because the greater range and complexity 

 of movements of the primate limb made the defects 

 more obvious. 



Localized Ablations oj Portions of Cerebellum 



As information about the anatomical relations of 

 the cerebellum grew in amount and reliability, and 

 as the results of stimulation experiments became 

 known, numerous attempts were made to discover 

 some form of localization of function within the 

 cerebellum. Earlier experiments of this type were 

 influenced by Bolk's (27) coinparative anatomical 

 studies and consisted of attempts to test his hy- 

 potheses concerning somatotopic organization of 

 efferent pathways. Later experiments have been di- 

 rected more toward testing the anatomical sub- 

 division of the cerebellum into vestibular, spinal and 

 cerebral components as suggested by Ingvar (157, 

 164, 165, 180). With the growth of information from 

 electrophysiological studies demonstrating somato- 

 topic organization in the spinocerebellar relation- 

 ships, the ablation experiments have been designed 

 to test these findings as well. The following discussion 



will consider the results of localized ablations from 

 the point of view of the three major anatomical and 

 functional subdivisions, with attention to somato- 

 topic localization where this has been the major 

 objective of the experiment. 



FLoccULONODULAR LOBE. The many studies of the 

 results of partial cerebellar ablations which were done 

 before anatomical relations were well understood did 

 not add particularly to our knowledge of cerebellar 

 function inasmuch as they involved lesions which 

 overlapped extensively into nonvestibular portions 

 of the cerebellum. More modern attempts to destroy 

 this portion of the cerebellum are by its anatomical 

 inaccessibility also limited to a relatively few studies. 



For a few days following unilateral ablations of the 

 nodulus (X) in guinea pigs, the animals exhibited 

 marked dynamic signs consisting of forced circling, 

 rolling, nystagmus, and abnormal head and trunk 

 postures (79, 199). Disturbance of otolithic eye re- 

 flexes persisted for a few weeks longer, but eventually 

 compensation was complete. In the same species, 

 lesions confined to the flocculus (H X) failed to 

 produce the dynamic signs but did abolish the oto- 

 lithic reflex control of eye movement (199). In an 

 extended series of experiments (11) reviewed by Tyler 

 & Bard (341) and confirmed by Wang & Chinn 

 (356-358), the integrity of the nodulus of the dog 

 was found to be necessary for the development of 

 motion sickness. In cats, lesions invoKing the pyramis, 

 uvula and nodulus (\'III A, V'lII B, IX, Xj pro- 

 duced disturbances which were comparable to those 

 following destruction of the anterior lobe (67, 68). 



The vestibular type of disturbance was apparently 

 seen much more clearly in the primate. In the ma- 

 caque, baboon and chimpanzee (105) lesions involving 

 the nodulus and lower uvula produced obvious signs 

 of disequilibration without ireinor, dysreflexia or 

 atonia. Asymmetrical lesions produced disturbances 

 opposite in laterality to those produced by unilateral 

 labyrinthine lesions. These observations have been 

 confirmed in the macaque (62). Bilateral lesions of the 

 flocculus (62) produced essentially the same signs of 

 disequilibration, but these were less intense and more 

 transient. Destruction of the supramedullary portion 

 of the juxtarestiform body in the macaque (119, 120) 

 resulted in signs which duplicated those produced by 

 flocculonodular lesions (62, 105), including the ab- 

 sence of postural and reflex disturbances. Interruption 

 of the intramedullary portion of the same structure 

 reversed the laterality of the signs, causing them to re- 

 semble the results of unilateral labyrinthectomy (i 19). 



